swiftui-native 0.0.1

//! Shapes.
//!
//! * Gradients

use super::*;
use crate::abi;
use crate::resolve;
use crate::mangle::{self, swift_type};

// ── Shapes ──

/// Wrap a shape value as a view. Shapes conform to `View` and fill themselves
/// with the current foreground style, so `foreground_style_color` acts as `.fill(_:)`.
pub(crate) unsafe fn shape_view(bytes: &[u8], mangled: &[u8]) -> ViewHandle {
    let meta = unsafe { abi::resolve_type_by_mangled_name(mangled) };
    assert!(!meta.is_null(), "shape metadata: {}", crate::diag::demangle_type(mangled));
    let wt = unsafe { abi::get_view_wt(meta) };
    assert!(!wt.is_null(), "{} !: View", crate::diag::demangle_type(mangled));
    unsafe { wrap_buf(bytes, meta, wt) }
}

/// `Rectangle()`
pub fn rectangle() -> ViewHandle {
    unsafe { shape_view(&[], swift_type!(SwiftUI.Rectangle).as_bytes()) }
}

/// `Circle()`
pub fn circle() -> ViewHandle {
    unsafe { shape_view(&[], swift_type!(SwiftUI.Circle).as_bytes()) }
}

/// `Ellipse()`
pub fn ellipse() -> ViewHandle {
    unsafe { shape_view(&[], swift_type!(SwiftUI.Ellipse).as_bytes()) }
}

/// `Capsule()` — `RoundedCornerStyle.circular` is case 0.
pub fn capsule() -> ViewHandle {
    unsafe { shape_view(&[0u8], swift_type!(SwiftUI.Capsule).as_bytes()) }
}

/// `RoundedRectangle(cornerRadius:style:)`.
///
/// The layout is a `CGSize` of corner radii followed by the corner style, so
/// the radius is written into both the width and height slots.
///
/// The style is not optional here the way it reads as optional in Swift. Source
/// that writes `RoundedRectangle(cornerRadius: 10)` gets `.continuous`, not
/// `.circular` — the two round the corners differently enough to disagree on a
/// couple of hundred pixels — so a binding that always wrote case 0 quietly
/// built the other shape. Callers say which one they mean.
pub fn rounded_rectangle_styled(radius: f64, continuous: bool) -> ViewHandle {
    let mut buf = [0u8; 17];
    buf[..8].copy_from_slice(&radius.to_le_bytes());
    buf[8..16].copy_from_slice(&radius.to_le_bytes());
    buf[16] = u8::from(continuous);
    unsafe { shape_view(&buf, swift_type!(SwiftUI.RoundedRectangle).as_bytes()) }
}

/// `RoundedRectangle(cornerRadius:)`, with the `.continuous` style Swift
/// source gets when it leaves the style out.
pub fn rounded_rectangle(radius: f64) -> ViewHandle {
    rounded_rectangle_styled(radius, true)
}

// ── Gradients ──

mangle::modifier_types! {
    /// `.background(_: LinearGradient)`
    /// `ModifiedContent<AnyView, _BackgroundStyleModifier<LinearGradient>>`
    pub(crate) LINEAR_GRADIENT_BG_T = ty("_BackgroundStyleModifier").of(vec![ty("LinearGradient")]);
    /// `.background(_: RadialGradient)`
    /// `ModifiedContent<AnyView, _BackgroundStyleModifier<RadialGradient>>`
    pub(crate) RADIAL_GRADIENT_BG_T = ty("_BackgroundStyleModifier").of(vec![ty("RadialGradient")]);
}


/// Build a Swift `Array<Color>` from raw `Color` references.
///
/// `Array._allocateUninitialized(_:)` hands back the array value together with a
/// pointer to its uninitialised buffer, which is the only practical way to build
/// a Swift array from outside Swift.
pub(crate) unsafe fn color_array(colors: &[u64]) -> u64 {
    let (array, buf): (u64, u64);
    unsafe {
        // `_allocateUninitializedArray<Element>(_ count:)` is what an array
        // literal compiles down to: x0 = count, x1 = Element.Type, returning
        // (Array, buffer) in x0/x1. The element metadata is a normal argument,
        // not the `self` register.
        core::arch::asm!("blr {f}", f = in(reg) resolve::array_alloc_uninit(),
            in("x0") colors.len() as u64,
            in("x1") resolve::color_meta(),
            lateout("x0") array, lateout("x1") buf,
            lateout("x2") _, lateout("x3") _, lateout("x4") _, lateout("x5") _,
            lateout("x6") _, lateout("x7") _, lateout("x8") _, lateout("x9") _,
            lateout("x10") _, lateout("x11") _, lateout("x12") _, lateout("x13") _,
            lateout("x14") _, lateout("x15") _, lateout("x16") _, lateout("x17") _,
            lateout("lr") _, lateout("x20") _, lateout("x21") _, clobber_abi("C"),
        );
        let dst = buf as *mut u64;
        for (i, c) in colors.iter().enumerate() {
            *dst.add(i) = *c;
        }
    }
    array
}

/// Build a `Gradient` from a list of colours.
pub(crate) unsafe fn gradient(colors: &[crate::Color]) -> u64 {
    let raw: Vec<u64> =
        colors.iter().map(|c| unsafe { color_value(c.r, c.g, c.b, c.a) }).collect();
    unsafe { gradient_of(&raw) }
}

/// Build a `Gradient` from `Color` values that are already built.
///
/// The components form cannot express `.yellow` or `.blue`: SwiftUI's named
/// colours are semantic and a literal triple is a visibly different colour —
/// 1371 of 1377 drawn pixels different, in the case that found this.
pub(crate) unsafe fn gradient_of(raw: &[u64]) -> u64 {
    let array = unsafe { color_array(raw) };
    let g: u64;
    unsafe {
        core::arch::asm!("blr {f}", f = in(reg) resolve::gradient_init(),
            in("x0") array,
            in("x20") resolve::gradient_meta(),
            lateout("x0") g,
            lateout("x1") _, lateout("x2") _, lateout("x3") _, lateout("x4") _,
            lateout("x5") _, lateout("x6") _, lateout("x7") _, lateout("x8") _,
            lateout("x9") _, lateout("x10") _, lateout("x11") _, lateout("x12") _,
            lateout("x13") _, lateout("x14") _, lateout("x15") _, lateout("x16") _,
            lateout("x17") _, lateout("lr") _, lateout("x21") _, clobber_abi("C"),
        );
    }
    g
}

/// `Color`'s metadata and `ShapeStyle` witness, for a call taking a style.
pub fn color_meta_for_style() -> *const c_void {
    resolve::color_meta()
}

/// See [`color_meta_for_style`].
pub fn color_shapestyle_wt_for_style() -> *const c_void {
    resolve::color_shapestyle_wt()
}

/// Which of the five hierarchical levels a style names.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Hierarchical {
    Primary,
    Secondary,
    Tertiary,
    Quaternary,
    Quinary,
}

/// `HierarchicalShapeStyle.primary` and friends, as a `ShapeStyle`.
///
/// `.primary` in a `ShapeStyle` position is *not* `Color.primary`: it is one of
/// these, four bytes wide, and the two render differently against a tinted
/// foreground. The shorthand that reaches them from `ShapeStyle` is inlinable;
/// these concrete statics are exported.
pub fn hierarchical_style(level: Hierarchical) -> (Vec<u8>, *const c_void, *const c_void) {
    unsafe {
        let getter = match level {
            Hierarchical::Primary => resolve::hierarchical_primary(),
            Hierarchical::Secondary => resolve::hierarchical_secondary(),
            Hierarchical::Tertiary => resolve::hierarchical_tertiary(),
            Hierarchical::Quaternary => resolve::hierarchical_quaternary(),
            Hierarchical::Quinary => resolve::hierarchical_quinary(),
        };
        let meta = abi::metadata0(resolve::hierarchical_ma());
        assert!(!meta.is_null(), "HierarchicalShapeStyle metadata");
        let r = abi::static_regs(getter, meta);
        let mut bytes = vec![0u8; abi::type_bytes(meta)];
        let n = bytes.len().min(8);
        bytes[..n].copy_from_slice(&r[0].to_le_bytes()[..n]);
        // Looked up rather than named: the witness table's own mangling
        // compresses `ShapeStyle` against the words in
        // `HierarchicalShapeStyle`, and guessing the substitution letters is
        // how this file has gone wrong before.
        let wt = abi::get_view_wt_for_proto(meta, resolve::shape_style_proto());
        assert!(!wt.is_null(), "HierarchicalShapeStyle !: ShapeStyle");
        (bytes, meta, wt)
    }
}

/// `.opacity(_:)` applied to a style that is already built.
///
/// `_OpacityShapeStyle<Base>` stores the base then the `Float`, so unlike the
/// `_ImplicitShapeStyle` case the base's bytes have to go in first.
pub fn opacity_of_style(
    base: &[u8],
    base_ty: mangle::Type,
    opacity: f64,
) -> (Vec<u8>, *const c_void, *const c_void) {
    unsafe {
        let ty = mangle::ty("_OpacityShapeStyle").of(vec![base_ty]).mangle();
        let meta = abi::resolve_type_by_mangled_name(ty.as_bytes());
        assert!(!meta.is_null(), "_OpacityShapeStyle metadata: {ty}");
        let wt = abi::get_view_wt_for_proto(meta, resolve::shape_style_proto());
        assert!(!wt.is_null(), "_OpacityShapeStyle !: ShapeStyle");
        let mut bytes = vec![0u8; abi::type_bytes(meta)];
        bytes[..base.len()].copy_from_slice(base);
        let at = base.len().next_multiple_of(4);
        bytes[at..at + 4].copy_from_slice(&(opacity as f32).to_le_bytes());
        (bytes, meta, wt)
    }
}

/// `ShapeStyle.opacity(_:)` — the current foreground style, faded.
///
/// `.opacity(0.5)` where a `ShapeStyle` is expected is a static on a protocol
/// extension, `@inlinable`, with no symbol. Its body builds one struct:
///
/// ```text
/// %6 = struct $_ImplicitShapeStyle ()
/// %7 = struct $_OpacityShapeStyle<_ImplicitShapeStyle> (%6, %5)
/// ```
///
/// `_ImplicitShapeStyle` has no stored properties, so the whole value is the
/// `Float` — which means it can be built here without calling anything.
pub fn implicit_opacity_style(opacity: f64) -> (Vec<u8>, *const c_void, *const c_void) {
    unsafe {
        let ty = mangle::ty("_OpacityShapeStyle")
            .of(vec![mangle::ty("_ImplicitShapeStyle")])
            .mangle();
        let meta = abi::resolve_type_by_mangled_name(ty.as_bytes());
        assert!(!meta.is_null(), "_OpacityShapeStyle<_ImplicitShapeStyle> metadata");
        let wt = abi::get_view_wt_for_proto(meta, resolve::shape_style_proto());
        assert!(!wt.is_null(), "_OpacityShapeStyle !: ShapeStyle");
        let mut bytes = vec![0u8; abi::type_bytes(meta)];
        bytes[..4].copy_from_slice(&(opacity as f32).to_le_bytes());
        (bytes, meta, wt)
    }
}

/// A `ShadowStyle` — `.drop(...)` or `.inner(...)`.
///
/// Both are exported statics: a `Color`, three `CGFloat`s and the metatype in,
/// the style out through x8. Only the *shorthand* that drops the receiver is
/// inlinable, and only the default arguments live in generator thunks — which
/// is why a search for what the SIL references reports these as missing when
/// they are not.
///
/// `color` defaults to `Color(.sRGBLinear, white: 0, opacity: _)` in Swift —
/// and the two are *not* the same default: a drop shadow gets 0.33 and an
/// inner one 0.55. Pass `None` to take whichever applies.
pub fn shadow_style(
    drop: bool,
    color: Option<u64>,
    radius: f64,
    x: f64,
    y: f64,
) -> Vec<u8> {
    unsafe {
        let meta = abi::metadata0(resolve::shadow_style_ma());
        assert!(!meta.is_null(), "ShadowStyle metadata");
        let colour = color.unwrap_or_else(|| default_shadow_colour(if drop { 0.33 } else { 0.55 }));
        let mut out = vec![0u8; abi::type_bytes(meta)];
        let f = if drop { resolve::shadow_style_drop() } else { resolve::shadow_style_inner() };
        core::arch::asm!("blr {f}", f = in(reg) f,
            in("x0") colour,
            in("d0") radius, in("d1") x, in("d2") y,
            in("x8") out.as_mut_ptr(),
            in("x20") meta,
            lateout("x1") _, lateout("x2") _, lateout("x3") _, lateout("x4") _,
            lateout("x5") _, lateout("x6") _, lateout("x7") _, lateout("x9") _,
            lateout("x10") _, lateout("x11") _, lateout("x12") _, lateout("x13") _,
            lateout("x14") _, lateout("x15") _, lateout("x16") _, lateout("x17") _,
            lateout("lr") _, lateout("x21") _, clobber_abi("C"),
        );
        out
    }
}

/// `Color(.sRGBLinear, white: 0, opacity: _)` — Swift's default shadow colour.
///
/// `RGBColorSpace` is a frozen enum passed by address; `.sRGBLinear` is case 1.
fn default_shadow_colour(opacity: f64) -> u64 {
    unsafe {
        let mut space: u8 = 1;
        let out: u64;
        core::arch::asm!("blr {f}", f = in(reg) resolve::color_white_init(),
            in("x0") &mut space as *mut u8,
            in("d0") 0.0f64, in("d1") opacity,
            in("x20") resolve::color_meta(),
            lateout("x0") out,
            lateout("x1") _, lateout("x2") _, lateout("x3") _, lateout("x4") _,
            lateout("x5") _, lateout("x6") _, lateout("x7") _, lateout("x8") _,
            lateout("x9") _, lateout("x10") _, lateout("x11") _, lateout("x12") _,
            lateout("x13") _, lateout("x14") _, lateout("x15") _, lateout("x16") _,
            lateout("x17") _, lateout("lr") _, lateout("x21") _, clobber_abi("C"),
        );
        out
    }
}

/// `.shadow(_:)` applied to the *implicit* foreground style.
///
/// `_ShadowShapeStyle<_ImplicitShapeStyle>` again stores an empty base and the
/// argument, so the whole value is the `ShadowStyle`.
pub fn implicit_shadow_style(shadow: &[u8]) -> (Vec<u8>, *const c_void, *const c_void) {
    unsafe {
        let ty = mangle::ty("_ShadowShapeStyle")
            .of(vec![mangle::ty("_ImplicitShapeStyle")])
            .mangle();
        let meta = abi::resolve_type_by_mangled_name(ty.as_bytes());
        assert!(!meta.is_null(), "_ShadowShapeStyle<_ImplicitShapeStyle> metadata");
        let wt = abi::get_view_wt_for_proto(meta, resolve::shape_style_proto());
        assert!(!wt.is_null(), "_ShadowShapeStyle !: ShapeStyle");
        let mut bytes = vec![0u8; abi::type_bytes(meta)];
        let n = shadow.len().min(bytes.len());
        bytes[..n].copy_from_slice(&shadow[..n]);
        (bytes, meta, wt)
    }
}

/// `Color.shadow(_:)` — the generic `ShapeStyle.shadow`, with `Self == Color`.
pub fn color_shadow_style(color: u64, shadow: &[u8]) -> (Vec<u8>, *const c_void, *const c_void) {
    unsafe {
        let subst = [resolve::color_meta(), resolve::color_shapestyle_wt()];
        let (meta, _, size) =
            super::opaque_result_type(resolve::shape_style_shadow_oret(), &subst);
        let wt = abi::get_view_wt_for_proto(meta, resolve::shape_style_proto());
        assert!(!wt.is_null(), "shadowed style !: ShapeStyle");

        let mut out = vec![0u8; size];
        let mut arg = shadow.to_vec();
        let mut receiver = color;
        core::arch::asm!("blr {f}", f = in(reg) resolve::shape_style_shadow_fn(),
            in("x0") arg.as_mut_ptr(),
            in("x1") subst[0], in("x2") subst[1],
            in("x8") out.as_mut_ptr(),
            in("x20") &mut receiver as *mut u64,
            lateout("x3") _, lateout("x4") _, lateout("x5") _, lateout("x6") _,
            lateout("x7") _, lateout("x9") _, lateout("x10") _, lateout("x11") _,
            lateout("x12") _, lateout("x13") _, lateout("x14") _, lateout("x15") _,
            lateout("x16") _, lateout("x17") _, lateout("lr") _, lateout("x21") _,
            clobber_abi("C"),
        );
        (out, meta, wt)
    }
}

/// `ShapeStyle.blendMode(_:)` — the current foreground style, blended.
///
/// The same shape as [`implicit_opacity_style`]: an inlinable static whose body
/// stores an empty `_ImplicitShapeStyle` and the mode into a
/// `_BlendModeShapeStyle<_ImplicitShapeStyle>`. `BlendMode` is frozen, so the
/// case number is the whole of it.
pub fn implicit_blend_mode_style(mode: u8) -> (Vec<u8>, *const c_void, *const c_void) {
    unsafe {
        let ty = mangle::ty("_BlendModeShapeStyle")
            .of(vec![mangle::ty("_ImplicitShapeStyle")])
            .mangle();
        let meta = abi::resolve_type_by_mangled_name(ty.as_bytes());
        assert!(!meta.is_null(), "_BlendModeShapeStyle<_ImplicitShapeStyle> metadata");
        let wt = abi::get_view_wt_for_proto(meta, resolve::shape_style_proto());
        assert!(!wt.is_null(), "_BlendModeShapeStyle !: ShapeStyle");
        let mut bytes = vec![0u8; abi::type_bytes(meta)];
        bytes[0] = mode;
        (bytes, meta, wt)
    }
}

swift_statics! {
    /// `SwiftUI.Gradient.ColorSpace` — which space a gradient interpolates in.
    ///
    /// `Device` walks the colour components as stored, which is what most
    /// systems do and what makes a red-to-green ramp pass through a muddy
    /// brown; `Perceptual` interpolates so that equal steps look equal, which
    /// is Swift's default wherever this is a defaulted argument.
    pub enum GradientColorSpace {
        Device = c"$s7SwiftUI8GradientV10ColorSpaceV6deviceAEvgZ",
        Perceptual = c"$s7SwiftUI8GradientV10ColorSpaceV10perceptualAEvgZ",
    }
}

/// `Gradient.colorSpace(_:)` — the gradient interpolated in another space.
///
/// Returns an `AnyGradient`, which is the `ShapeStyle` [`Shape::fill_style`]
/// wants. `Gradient.ColorSpace` is resilient, so `.perceptual` arrives through
/// x8 and is then handed over by address, with the gradient itself in x1.
pub fn gradient_color_space_perceptual(
    colors: &[u64],
) -> (Vec<u8>, *const c_void, *const c_void) {
    gradient_color_space(colors, GradientColorSpace::Perceptual)
}

/// The same, in whichever space is named.
pub fn gradient_color_space(
    colors: &[u64],
    space: GradientColorSpace,
) -> (Vec<u8>, *const c_void, *const c_void) {
    unsafe {
        let g = gradient_of(colors);
        let space_meta = abi::metadata0(resolve::gradient_color_space_ma());
        assert!(!space_meta.is_null(), "Gradient.ColorSpace metadata");
        let mut space = super::static_getter_indirect(
            space.resolved(),
            space_meta,
            abi::type_bytes(space_meta),
        );
        let out: u64;
        core::arch::asm!("blr {f}", f = in(reg) resolve::gradient_color_space_fn(),
            in("x0") space.as_mut_ptr(),
            in("x1") g,
            lateout("x0") out,
            lateout("x2") _, lateout("x3") _, lateout("x4") _, lateout("x5") _,
            lateout("x6") _, lateout("x7") _, lateout("x8") _, lateout("x9") _,
            lateout("x10") _, lateout("x11") _, lateout("x12") _, lateout("x13") _,
            lateout("x14") _, lateout("x15") _, lateout("x16") _, lateout("x17") _,
            lateout("lr") _, lateout("x20") _, lateout("x21") _, clobber_abi("C"),
        );
        (out.to_le_bytes().to_vec(), resolve::any_gradient_meta(), resolve::any_gradient_wt())
    }
}

/// Build a `LinearGradient` value, with its metadata and `ShapeStyle` witness.
///
/// What [`Shape::fill_style`] wants: `.fill(.linearGradient(...))` is the same
/// call as `.fill(Color.red)` with a different style, so the style is passed as
/// bytes rather than as one of a fixed set.
pub fn linear_gradient_style(
    colors: &[crate::Color],
    start: (f64, f64),
    end: (f64, f64),
) -> (Vec<u8>, *const c_void, *const c_void) {
    let raw: Vec<u64> = colors.iter().map(|c| super::color_value_of(*c)).collect();
    linear_gradient_style_of(&raw, start, end)
}

/// `AngularGradient(gradient:center:angle:)` — a sweep around a point.
///
/// The angle is where the sweep starts, in degrees; SwiftUI's default is zero,
/// which is what Swift's own defaulted argument passes.
pub fn angular_gradient_style(
    colors: &[crate::Color],
    center: (f64, f64),
    start_degrees: f64,
) -> (Vec<u8>, *const c_void, *const c_void) {
    let raw: Vec<u64> = colors.iter().map(|c| super::color_value_of(*c)).collect();
    unsafe {
        let g = gradient_of(&raw);
        let meta = crate::type_by_name!(swift_type!(SwiftUI.AngularGradient).as_bytes());
        assert!(!meta.is_null(), "AngularGradient metadata");
        let mut value = vec![0u8; abi::type_bytes(meta)];
        // `(sret, gradient, cx, cy, angle)` — the `Angle` is one `Double` of
        // radians, so degrees are converted here as they are for `rotate`.
        core::arch::asm!("blr {f}", f = in(reg) resolve::angular_gradient_init(),
            in("x0") g,
            in("d0") center.0, in("d1") center.1,
            in("d2") start_degrees * core::f64::consts::PI / 180.0,
            in("x8") value.as_mut_ptr(),
            in("x20") meta,
            lateout("x1") _, lateout("x2") _, lateout("x3") _, lateout("x4") _,
            lateout("x5") _, lateout("x6") _, lateout("x7") _, lateout("x9") _,
            lateout("x10") _, lateout("x11") _, lateout("x12") _, lateout("x13") _,
            lateout("x14") _, lateout("x15") _, lateout("x16") _, lateout("x17") _,
            lateout("lr") _, lateout("x21") _, clobber_abi("C"),
        );
        (value, meta, resolve::angular_gradient_wt())
    }
}

/// `EllipticalGradient(colors:center:startRadiusFraction:endRadiusFraction:)`.
///
/// Takes the colours directly rather than a built `Gradient` — a different
/// initialiser shape from the three gradients beside it, so there is no
/// `gradient_of` call here.
pub fn elliptical_gradient_style(
    colors: &[crate::Color],
    center: (f64, f64),
    start_fraction: f64,
    end_fraction: f64,
) -> (Vec<u8>, *const c_void, *const c_void) {
    let raw: Vec<u64> = colors.iter().map(|c| super::color_value_of(*c)).collect();
    unsafe {
        let array = color_array(&raw);
        let meta = crate::type_by_name!(swift_type!(SwiftUI.EllipticalGradient).as_bytes());
        assert!(!meta.is_null(), "EllipticalGradient metadata");
        let mut value = vec![0u8; abi::type_bytes(meta)];
        core::arch::asm!("blr {f}", f = in(reg) resolve::elliptical_gradient_init(),
            in("x0") array,
            in("d0") center.0, in("d1") center.1,
            in("d2") start_fraction, in("d3") end_fraction,
            in("x8") value.as_mut_ptr(),
            in("x20") meta,
            lateout("x1") _, lateout("x2") _, lateout("x3") _, lateout("x4") _,
            lateout("x5") _, lateout("x6") _, lateout("x7") _, lateout("x9") _,
            lateout("x10") _, lateout("x11") _, lateout("x12") _, lateout("x13") _,
            lateout("x14") _, lateout("x15") _, lateout("x16") _, lateout("x17") _,
            lateout("lr") _, lateout("x21") _, clobber_abi("C"),
        );
        (value, meta, resolve::elliptical_gradient_wt())
    }
}

/// As [`linear_gradient_style`], from `Color` values that are already built.
pub fn linear_gradient_style_of(
    colors: &[u64],
    start: (f64, f64),
    end: (f64, f64),
) -> (Vec<u8>, *const c_void, *const c_void) {
    unsafe {
        let g = gradient_of(colors);
        let meta = crate::type_by_name!(swift_type!(SwiftUI.LinearGradient).as_bytes());
        assert!(!meta.is_null(), "LinearGradient metadata");
        let mut value = vec![0u8; abi::type_bytes(meta)];
        core::arch::asm!("blr {f}", f = in(reg) resolve::linear_gradient_init(),
            in("x0") g,
            in("d0") start.0, in("d1") start.1, in("d2") end.0, in("d3") end.1,
            in("x8") value.as_mut_ptr(),
            in("x20") meta,
            lateout("x1") _, lateout("x2") _, lateout("x3") _, lateout("x4") _,
            lateout("x5") _, lateout("x6") _, lateout("x7") _, lateout("x9") _,
            lateout("x10") _, lateout("x11") _, lateout("x12") _, lateout("x13") _,
            lateout("x14") _, lateout("x15") _, lateout("x16") _, lateout("x17") _,
            lateout("lr") _, lateout("x21") _, clobber_abi("C"),
        );
        (value, meta, resolve::linear_gradient_wt())
    }
}

/// Apply `.background(LinearGradient(colors:startPoint:endPoint:))`.
pub fn background_linear_gradient(
    view: &ViewHandle,
    colors: &[crate::Color],
    start: (f64, f64),
    end: (f64, f64),
) -> ViewHandle {
    unsafe {
        let g = gradient(colors);
        let meta = crate::type_by_name!(swift_type!(SwiftUI.LinearGradient).as_bytes());
        assert!(!meta.is_null(), "LinearGradient metadata");
        let mut value = vec![0u8; abi::type_bytes(meta)];
        // init(gradient:startPoint:endPoint:) — x0 = Gradient, UnitPoints in d0-d3
        core::arch::asm!("blr {f}", f = in(reg) resolve::linear_gradient_init(),
            in("x0") g,
            in("d0") start.0, in("d1") start.1, in("d2") end.0, in("d3") end.1,
            in("x8") value.as_mut_ptr(),
            in("x20") meta,
            lateout("x1") _, lateout("x2") _, lateout("x3") _, lateout("x4") _,
            lateout("x5") _, lateout("x6") _, lateout("x7") _, lateout("x9") _,
            lateout("x10") _, lateout("x11") _, lateout("x12") _, lateout("x13") _,
            lateout("x14") _, lateout("x15") _, lateout("x16") _, lateout("x17") _,
            lateout("lr") _, lateout("x21") _, clobber_abi("C"),
        );
        background_style(
            view,
            value.as_mut_ptr(),
            meta,
            resolve::linear_gradient_wt(),
            &LINEAR_GRADIENT_BG_T,
        )
    }
}

/// Apply `.background(RadialGradient(colors:center:startRadius:endRadius:))`.
pub fn background_radial_gradient(
    view: &ViewHandle,
    colors: &[crate::Color],
    center: (f64, f64),
    start_radius: f64,
    end_radius: f64,
) -> ViewHandle {
    unsafe {
        let g = gradient(colors);
        let meta = crate::type_by_name!(swift_type!(SwiftUI.RadialGradient).as_bytes());
        assert!(!meta.is_null(), "RadialGradient metadata");
        let mut value = vec![0u8; abi::type_bytes(meta)];
        core::arch::asm!("blr {f}", f = in(reg) resolve::radial_gradient_init(),
            in("x0") g,
            in("d0") center.0, in("d1") center.1, in("d2") start_radius, in("d3") end_radius,
            in("x8") value.as_mut_ptr(),
            in("x20") meta,
            lateout("x1") _, lateout("x2") _, lateout("x3") _, lateout("x4") _,
            lateout("x5") _, lateout("x6") _, lateout("x7") _, lateout("x9") _,
            lateout("x10") _, lateout("x11") _, lateout("x12") _, lateout("x13") _,
            lateout("x14") _, lateout("x15") _, lateout("x16") _, lateout("x17") _,
            lateout("lr") _, lateout("x21") _, clobber_abi("C"),
        );
        background_style(
            view,
            value.as_mut_ptr(),
            meta,
            resolve::radial_gradient_wt(),
            &RADIAL_GRADIENT_BG_T,
        )
    }
}

// ── Shapes kept as shapes ───────────────────────────────────────────────────

/// A shape value, not yet erased to a view.
///
/// [`circle`] and its neighbours hand back a `ViewHandle`, because a shape
/// conforms to `View` and that is all most callers want. `Shape.fill(_:style:)`
/// and `.stroke(_:lineWidth:)` are not view modifiers, though — they are
/// extension methods on `Shape` whose receiver is `@in_guaranteed Self` with
/// `Self: Shape`, and an `AnyView` satisfies neither. So reaching them needs
/// the value, its metadata and its `Shape` witness table kept together, which
/// is what this is.
///
/// The bytes are the shape's own storage: empty for `Circle`, `Rectangle` and
/// `Ellipse`, which have no stored properties at all.
pub struct Shape {
    bytes: Vec<u8>,
    meta: *const c_void,
    wt: *const c_void,
    /// What this shape *is*, so a wrapping shape can name itself.
    ///
    /// `.offset(x:y:)` on a `Circle` gives an `OffsetShape<Circle>` — still a
    /// `Shape`, and still fillable — so each transform has to spell a type one
    /// level deeper than the last. Keeping the `mangle::Type` rather than the
    /// finished string is what makes that possible: the mangling of
    /// `OffsetShape<Circle>` is not the mangling of `Circle` with something
    /// glued on, because the substitution table depends on the whole.
    ty: mangle::Type,
}

impl Shape {
    /// A shape whose metadata and conformance are already in hand.
    ///
    /// For [`crate::views::custom_shape_value`], whose type was *minted at run
    /// time*: there is no name for it that `swift_getTypeByMangledName` can
    /// resolve, because a synthesised nominal descriptor is in no image's
    /// metadata section. The `ty` is carried anyway so the error message from a
    /// method that composes names says which shape it was — those methods cannot
    /// work for a synthesised type, and failing with its name beats failing with
    /// a null.
    ///
    /// # Safety
    /// `bytes` must hold a value of `meta`'s type, and `wt` must be that type's
    /// `Shape` conformance.
    pub(crate) unsafe fn of_metadata(
        bytes: Vec<u8>,
        meta: *const c_void,
        wt: *const c_void,
        ty: mangle::Type,
    ) -> Self {
        Self { bytes, meta, wt, ty }
    }

    unsafe fn of(bytes: Vec<u8>, ty: mangle::Type) -> Self {
        unsafe {
            let mangled = ty.mangle();
            let meta = abi::resolve_type_by_mangled_name(mangled.as_bytes());
            assert!(!meta.is_null(), "shape metadata: {}", mangle::demangle(&mangled));
            let wt = abi::get_view_wt_for_proto(meta, resolve::shape_proto());
            assert!(!wt.is_null(), "{} !: Shape", mangle::demangle(&mangled));
            Self { bytes, meta, wt, ty }
        }
    }

    /// `Circle()`
    pub fn circle() -> Self {
        unsafe { Self::empty(mangle::ty("Circle"), resolve::circle_init()) }
    }

    /// `Rectangle()`
    pub fn rectangle() -> Self {
        unsafe { Self::empty(mangle::ty("Rectangle"), resolve::rectangle_init()) }
    }

    /// `Ellipse()`
    pub fn ellipse() -> Self {
        unsafe { Self::empty(mangle::ty("Ellipse"), resolve::ellipse_init()) }
    }

    /// A shape with no stored properties, built by calling its initialiser.
    ///
    /// These three used to be an empty `Vec`, which is right for as long as
    /// they stay empty and says nothing if they stop. Calling the initialiser
    /// is what source does — the IR has one `Rectangle()` call per rectangle —
    /// and it writes whatever the type actually holds.
    ///
    /// # Safety
    /// `init` must be `ty`'s zero-argument initialiser.
    unsafe fn empty(ty: mangle::Type, init: *const c_void) -> Self {
        unsafe {
            let mut me = Self::of(Vec::new(), ty);
            let size = abi::type_bytes(me.meta);
            let mut bytes = vec![0u8; size.max(1)];
            core::arch::asm!("blr {f}", f = in(reg) init,
                in("x8") bytes.as_mut_ptr(),
                in("x20") me.meta,
                lateout("x0") _, lateout("x1") _, lateout("x2") _, lateout("x3") _,
                lateout("x4") _, lateout("x5") _, lateout("x6") _, lateout("x7") _,
                lateout("x9") _, lateout("x10") _, lateout("x11") _, lateout("x12") _,
                lateout("x13") _, lateout("x14") _, lateout("x15") _, lateout("x16") _,
                lateout("x17") _, lateout("lr") _, lateout("x21") _, clobber_abi("C"),
            );
            bytes.truncate(size);
            me.bytes = bytes;
            me
        }
    }

    /// `Capsule()` — one byte of `RoundedCornerStyle`.
    ///
    /// Case **1**, `.continuous`, which is what `Capsule()` with no argument
    /// means. This said case 0 and called it `.circular` until a listing needed
    /// a capsule's corner style to match; nothing had compared one before, and
    /// [`Self::rounded_rectangle`] next door had the numbering right all along.
    pub fn capsule() -> Self {
        unsafe { Self::of(vec![1u8], mangle::ty("Capsule")) }
    }

    /// `RoundedRectangle(cornerRadius:style:)` — a `CGSize` then the style.
    ///
    /// `style` is `RoundedCornerStyle`: `.circular` is case 0 and
    /// `.continuous` is case 1. The one-argument spelling in Swift source does
    /// *not* mean circular — the declared default is `.continuous`, and the two
    /// differ by about two hundred pixels around the corners of a 200x50 box.
    pub fn rounded_rectangle(radius: f64, continuous: bool) -> Self {
        let mut bytes = Vec::with_capacity(24);
        bytes.extend_from_slice(&radius.to_le_bytes());
        bytes.extend_from_slice(&radius.to_le_bytes());
        bytes.push(u8::from(continuous));
        unsafe { Self::of(bytes, mangle::ty("RoundedRectangle")) }
    }

    /// The shape on its own, as a view.
    /// The shape's own type, for spelling a type it appears inside.
    ///
    /// `fill_then_stroke` names its result `StrokeShapeView<Shape, Color,
    /// _ShapeView<Shape, Color>>`, which cannot be written without knowing what
    /// the shape is — and after `.inset` or `.rotation` that is no longer the
    /// shape it started as.
    pub(crate) fn ty(&self) -> &mangle::Type {
        &self.ty
    }

    pub fn view(&self) -> ViewHandle {
        unsafe {
            let wt = abi::get_view_wt(self.meta);
            ViewHandle::wrap(self.bytes.as_ptr() as _, self.meta, wt)
        }
    }

    /// A `Path`, built by the four mutating methods below.
    ///
    /// `Path` is 33 bytes — a reference plus a discriminator — so it is neither
    /// one word nor a neat multiple of one, and every method takes it as
    /// `inout` through x20 while the points travel in d0 onwards.
    pub fn path() -> PathBuilder {
        let mut bytes = vec![0u8; 40]; // stride, not size: the callee may write padding
        unsafe {
            core::arch::asm!("blr {f}", f = in(reg) resolve::path_init(),
                in("x8") bytes.as_mut_ptr(),
                lateout("x0") _, lateout("x1") _, lateout("x2") _, lateout("x3") _,
                lateout("x4") _, lateout("x5") _, lateout("x6") _, lateout("x7") _,
                lateout("x9") _, lateout("x10") _, lateout("x11") _, lateout("x12") _,
                lateout("x13") _, lateout("x14") _, lateout("x15") _, lateout("x16") _,
                lateout("x17") _, lateout("lr") _, lateout("x20") _, lateout("x21") _,
                clobber_abi("C"),
            );
        }
        PathBuilder { bytes }
    }

    /// The shape's own name, when it is a plain nominal type.
    fn base_name(&self) -> Option<&'static str> {
        match &self.ty {
            mangle::Type::Nominal { path, .. } => path.last().copied(),
            _ => None,
        }
    }

    /// `.inset(by:)` — the shape drawn inside its own bounds.
    ///
    /// `inset(by:)` is an `InsettableShape` *requirement*, so it is exported
    /// once per conforming type rather than once on the protocol: there is a
    /// `Circle.inset`, a `Rectangle.inset` and so on, and no
    /// `InsettableShape.inset` at all. The result is `some InsettableShape`,
    /// whose first conformance is `InsettableShape` — so the `Shape` witness
    /// comes from the concrete metadata, as with `stroke(lineWidth:)`.
    pub fn inset(&self, amount: f64) -> Self {
        let name = self.base_name().expect("inset needs a plain shape");
        let symbol: &core::ffi::CStr = match name {
            "Circle" => c"$s7SwiftUI6CircleV5inset2byQr12CoreGraphics7CGFloatV_tF",
            "Capsule" => c"$s7SwiftUI7CapsuleV5inset2byQr12CoreGraphics7CGFloatV_tF",
            "Ellipse" => c"$s7SwiftUI7EllipseV5inset2byQr12CoreGraphics7CGFloatV_tF",
            "Rectangle" => c"$s7SwiftUI9RectangleV5inset2byQr12CoreGraphics7CGFloatV_tF",
            "RoundedRectangle" => c"$s7SwiftUI16RoundedRectangleV5inset2byQr12CoreGraphics7CGFloatV_tF",
            other => panic!("no exported inset(by:) for {other}"),
        };
        let oret: &core::ffi::CStr = match name {
            "Circle" => c"$s7SwiftUI6CircleV5inset2byQr12CoreGraphics7CGFloatV_tFQOMQ",
            "Capsule" => c"$s7SwiftUI7CapsuleV5inset2byQr12CoreGraphics7CGFloatV_tFQOMQ",
            "Ellipse" => c"$s7SwiftUI7EllipseV5inset2byQr12CoreGraphics7CGFloatV_tFQOMQ",
            "RoundedRectangle" => c"$s7SwiftUI16RoundedRectangleV5inset2byQr12CoreGraphics7CGFloatV_tFQOMQ",
            _ => c"$s7SwiftUI9RectangleV5inset2byQr12CoreGraphics7CGFloatV_tFQOMQ",
        };
        unsafe {
            let (meta, _, size) = super::opaque_result_type(resolve::sym(oret), &[]);
            let wt = abi::get_view_wt_for_proto(meta, resolve::shape_proto());
            assert!(!wt.is_null(), "inset shape !: Shape");
            let mut bytes = vec![0u8; size.max(1)];
            let mut receiver = self.receiver();
            core::arch::asm!("blr {f}", f = in(reg) resolve::sym(symbol),
                in("d0") amount,
                in("x8") bytes.as_mut_ptr(),
                in("x20") receiver.as_mut_ptr(),
                lateout("x0") _, lateout("x1") _, lateout("x2") _, lateout("x3") _,
                lateout("x4") _, lateout("x5") _, lateout("x6") _, lateout("x7") _,
                lateout("x9") _, lateout("x10") _, lateout("x11") _, lateout("x12") _,
                lateout("x13") _, lateout("x14") _, lateout("x15") _, lateout("x16") _,
                lateout("x17") _, lateout("lr") _, lateout("x21") _, clobber_abi("C"),
            );
            // `inset(by:)` returns `some InsettableShape`, so the call site has
            // no name — but the type behind it is always `<Shape>._Inset`, and
            // keeping the shape this started as is what made `fill_then_stroke`
            // spell `StrokeShapeView<Circle, …>` for an inset circle: a type
            // that exists, is the wrong one, and is laid out differently, which
            // is what its field-offset assertion was catching.
            //
            // Spelled as a nested path rather than pasted in as a verbatim
            // name: this crate's mangler numbers its own substitutions, and a
            // full `7SwiftUI6CircleV6_InsetV` dropped into the middle shifts
            // every `AA` after it, so the composed name resolves to nothing.
            //
            // The runtime knows the real name, so the guess is checked against
            // it rather than trusted.
            let ty = mangle::Type::Nominal {
                module: "SwiftUI",
                path: vec![name, "_Inset"],
                kind: mangle::Kind::Struct,
            };
            debug_assert_eq!(
                abi::mangled_type_name(meta).as_deref(),
                Some(ty.mangle().as_bytes()),
                "{name}.inset(by:) does not return {name}._Inset",
            );
            Self { bytes, meta, wt, ty }
        }
    }

    /// `.offset(x:y:)` — an `OffsetShape` around this one.
    ///
    /// A concrete wrapper, not an opaque return, so there is no substitution
    /// list to build: the result's size comes from its own metadata and the
    /// call writes it through x8.
    pub fn offset(&self, x: f64, y: f64) -> Self {
        let ty = mangle::ty("OffsetShape").of(vec![self.ty.clone()]);
        unsafe { self.wrapped(resolve::shape_offset_fn(), ty, [x, y, 0.0, 0.0]) }
    }

    /// `.rotation(_:anchor:)` — a `RotatedShape` around this one.
    ///
    /// `Angle` stores radians, and `.center` is `UnitPoint(0.5, 0.5)`.
    pub fn rotation(&self, degrees: f64) -> Self {
        let ty = mangle::ty("RotatedShape").of(vec![self.ty.clone()]);
        let radians = degrees * std::f64::consts::PI / 180.0;
        unsafe { self.wrapped(resolve::shape_rotation_fn(), ty, [radians, 0.5, 0.5, 0.0]) }
    }

    /// Call a `Shape` extension method that returns a concrete wrapper.
    ///
    /// The floats go in d0 onwards, the receiver is `@in_guaranteed` in x20,
    /// and the two generic words — `Self` and its `Shape` witness — follow in
    /// x0 and x1 because no formal argument occupies an integer register.
    unsafe fn wrapped(&self, func: *const c_void, ty: mangle::Type, floats: [f64; 4]) -> Self {
        unsafe {
            let mangled = ty.mangle();
            let meta = abi::resolve_type_by_mangled_name(mangled.as_bytes());
            assert!(!meta.is_null(), "shape metadata: {}", mangle::demangle(&mangled));
            let wt = abi::get_view_wt_for_proto(meta, resolve::shape_proto());
            assert!(!wt.is_null(), "{} !: Shape", mangle::demangle(&mangled));

            let mut bytes = vec![0u8; abi::type_bytes(meta).max(1)];
            let mut receiver = self.receiver();
            core::arch::asm!("blr {f}", f = in(reg) func,
                in("x0") self.meta,
                in("x1") self.wt,
                in("d0") floats[0], in("d1") floats[1],
                in("d2") floats[2], in("d3") floats[3],
                in("x8") bytes.as_mut_ptr(),
                in("x20") receiver.as_mut_ptr(),
                lateout("x2") _, lateout("x3") _, lateout("x4") _, lateout("x5") _,
                lateout("x6") _, lateout("x7") _, lateout("x9") _, lateout("x10") _,
                lateout("x11") _, lateout("x12") _, lateout("x13") _, lateout("x14") _,
                lateout("x15") _, lateout("x16") _, lateout("x17") _, lateout("lr") _,
                lateout("x21") _, clobber_abi("C"),
            );
            Self { bytes, meta, wt, ty }
        }
    }

    /// `.fill(_:style:)` with any `ShapeStyle` — its value, metadata and
    /// witness table.
    /// # Safety
    /// `style` must hold an initialised value of the type `meta` describes, and
    /// `wt` must be that type's `ShapeStyle` conformance.
    pub unsafe fn fill_style(&self, style: &[u8], meta: *const c_void, wt: *const c_void) -> ViewHandle {
        unsafe { self.filled(style, meta, wt) }
    }

    /// `.fill(_:style:)`, by building the `_ShapeView` it reduces to.
    ///
    /// `Shape.fill` has two overloads — one returning `some View`, one
    /// returning `_ShapeView<Self, S>` — and source picks the second. Neither
    /// helps directly: the concrete one is `@inlinable` and not exported, and
    /// the opaque one needs its result type resolved through a descriptor.
    /// What the inlined body does is call `_ShapeView.init`, which *is*
    /// exported, so that is what this calls.
    ///
    /// The `style:` default stays a constant here. SwiftUI's own generator for
    /// it — `…FfA0_` in the IR — is emitted into the client rather than
    /// exported, so there is nothing to call: `FillStyle()` is
    /// `(eoFill: false, antialiased: true)`, two bytes, and `0x0100` is them.
    ///
    /// # Safety
    /// `style` must be a live value of `meta` conforming through `wt`.
    unsafe fn filled(
        &self,
        style: &[u8],
        style_meta: *const c_void,
        style_wt: *const c_void,
    ) -> ViewHandle {
        unsafe {
            let meta = abi::generic_metadata_from_descriptor(
                resolve::shape_view_desc(),
                &[self.meta, style_meta, self.wt, style_wt],
            );
            assert!(!meta.is_null(), "_ShapeView metadata");
            let wt = abi::get_view_wt(meta);
            assert!(!wt.is_null(), "_ShapeView !: View");

            let mut arg = style.to_vec();
            arg.resize(abi::type_bytes(style_meta).max(style.len()).max(1), 0);
            let mut receiver = self.receiver();
            let mut result = vec![0u8; abi::type_bytes(meta)];
            // `(sret, @in shape, @in style, i16 fillStyle, Self.Type, S.Type,
            //   Self: Shape WT, S: ShapeStyle WT)` — an initialiser, so the
            // shape is an ordinary argument rather than `self` in x20.
            core::arch::asm!("blr {f}", f = in(reg) resolve::shape_view_init(),
                in("x0") receiver.as_mut_ptr(),
                in("x1") arg.as_mut_ptr(),
                in("x2") FILL_STYLE_DEFAULT,
                in("x3") self.meta,
                in("x4") style_meta,
                in("x5") self.wt,
                in("x6") style_wt,
                in("x8") result.as_mut_ptr(),
                lateout("x7") _, lateout("x9") _, lateout("x10") _,
                lateout("x11") _, lateout("x12") _, lateout("x13") _, lateout("x14") _,
                lateout("x15") _, lateout("x16") _, lateout("x17") _, lateout("lr") _,
                lateout("x20") _, lateout("x21") _, clobber_abi("C"),
            );
            wrap_owned(result, meta, wt)
        }
    }

    /// `.fill(_:)`'s value as raw bytes plus its type, for composing into a
    /// larger one rather than erasing it to a view.
    ///
    /// `ShapeView.stroke(_:lineWidth:)` needs this: it is
    /// `@_alwaysEmitIntoClient`, and what it builds is a `StrokeShapeView`
    /// holding *two* filled shape views — the stroke in front, the original fill
    /// behind it as a background — so both have to survive as values.
    pub(crate) fn fill_parts(
        &self,
        style: &[u8],
        meta: *const c_void,
        wt: *const c_void,
    ) -> (Vec<u8>, *const c_void) {
        unsafe {
            let subst = [self.meta, meta, self.wt, wt];
            let (ty, _, size) = super::opaque_result_type(resolve::shape_fill_oret(), &subst);
            let mut result = vec![0u8; size];
            let mut arg = style.to_vec();
            arg.resize(abi::type_bytes(meta).max(style.len()).max(1), 0);
            let mut receiver = self.receiver();
            core::arch::asm!("blr {f}", f = in(reg) resolve::shape_fill_fn(),
                in("x0") arg.as_mut_ptr(),
                in("x1") FILL_STYLE_DEFAULT as *const c_void,
                in("x2") subst[0], in("x3") subst[1], in("x4") subst[2], in("x5") subst[3],
                in("d0") 0.0f64,
                in("x8") result.as_mut_ptr(),
                in("x20") receiver.as_mut_ptr(),
                lateout("x6") _, lateout("x7") _, lateout("x9") _, lateout("x10") _,
                lateout("x11") _, lateout("x12") _, lateout("x13") _, lateout("x14") _,
                lateout("x15") _, lateout("x16") _, lateout("x17") _, lateout("lr") _,
                lateout("x21") _, clobber_abi("C"),
            );
            (result, ty)
        }
    }

    /// `.stroke(_:lineWidth:)` with any `ShapeStyle`.
    /// # Safety
    /// `style` must hold an initialised value of the type `meta` describes, and
    /// `wt` must be that type's `ShapeStyle` conformance.
    pub unsafe fn stroke_style(
        &self,
        style: &[u8],
        meta: *const c_void,
        wt: *const c_void,
        line_width: f64,
    ) -> ViewHandle {
        unsafe {
            let inner = self.styled(
                resolve::shape_stroke_fn(),
                resolve::shape_stroke_oret(),
                style,
                meta,
                wt,
                false,
                line_width,
            );
            // Every stroke, not just the colour-taking one: Swift's
            // `.stroke(_:lineWidth:)` returns a `StrokeShapeView` whatever the
            // style is.
            self.as_stroke_shape_view(inner, meta, wt)
        }
    }

    /// `.fill(_:style:)` with a `Color`.
    pub fn fill(&self, color: u64) -> ViewHandle {
        let bytes = color.to_le_bytes();
        // SAFETY: a `Color` word with `Color`'s metadata and conformance.
        unsafe { self.fill_style(&bytes, resolve::color_meta(), resolve::color_shapestyle_wt()) }
    }

    /// `.stroke(lineWidth:)`, kept as a `Shape` rather than erased to a view.
    ///
    /// What `overlay(_:in:)` wants: its `in:` argument is a `Shape`, and a
    /// stroked shape still is one.
    pub fn stroked(&self, line_width: f64) -> Self {
        unsafe {
            let subst = [self.meta, self.wt];
            let (meta, _, size) =
                super::opaque_result_type(resolve::shape_stroke_plain_oret(), &subst);
            let wt = abi::get_view_wt_for_proto(meta, resolve::shape_proto());
            assert!(!wt.is_null(), "stroked shape !: Shape");
            let mut bytes = vec![0u8; size.max(1)];
            let mut receiver = self.receiver();
            core::arch::asm!("blr {f}", f = in(reg) resolve::shape_stroke_plain_fn(),
                in("x0") subst[0], in("x1") subst[1],
                in("d0") line_width,
                in("x8") bytes.as_mut_ptr(),
                in("x20") receiver.as_mut_ptr(),
                lateout("x2") _, lateout("x3") _, lateout("x4") _, lateout("x5") _,
                lateout("x6") _, lateout("x7") _, lateout("x9") _, lateout("x10") _,
                lateout("x11") _, lateout("x12") _, lateout("x13") _, lateout("x14") _,
                lateout("x15") _, lateout("x16") _, lateout("x17") _, lateout("lr") _,
                lateout("x21") _, clobber_abi("C"),
            );
            Self { bytes, meta, wt, ty: self.ty.clone() }
        }
    }

    /// The value, metadata and `Shape` witness, for a call that takes a shape.
    pub fn parts(&self) -> (Vec<u8>, *const c_void, *const c_void) {
        (self.bytes.clone(), self.meta, self.wt)
    }

    /// `.stroke(lineWidth:)` — no style, so it strokes with the foreground.
    ///
    /// One generic parameter rather than two, so the substitution list is just
    /// `Self` and its `Shape` witness, and the line width is the only formal
    /// argument.
    pub fn stroke_default(&self, line_width: f64) -> ViewHandle {
        unsafe {
            let subst = [self.meta, self.wt];
            // `-> some Shape`, not `-> some View`. The opaque type carries one
            // conformance and it is `Shape`, so asking for the second one hands
            // back whatever follows it in memory; the value builds, reports the
            // right type, and faults when something tries to draw it. The
            // `View` witness comes from the concrete metadata instead.
            let (meta, _, size) =
                super::opaque_result_type(resolve::shape_stroke_plain_oret(), &subst);
            let wt = abi::get_view_wt(meta);
            assert!(!wt.is_null(), "stroked shape !: View");
            let mut result = vec![0u8; size];
            let mut receiver = self.receiver();
            core::arch::asm!("blr {f}", f = in(reg) resolve::shape_stroke_plain_fn(),
                in("x0") subst[0], in("x1") subst[1],
                in("d0") line_width,
                in("x8") result.as_mut_ptr(),
                in("x20") receiver.as_mut_ptr(),
                lateout("x2") _, lateout("x3") _, lateout("x4") _, lateout("x5") _,
                lateout("x6") _, lateout("x7") _, lateout("x9") _, lateout("x10") _,
                lateout("x11") _, lateout("x12") _, lateout("x13") _, lateout("x14") _,
                lateout("x15") _, lateout("x16") _, lateout("x17") _, lateout("lr") _,
                lateout("x21") _, clobber_abi("C"),
            );
            wrap_owned(result, meta, wt)
        }
    }

    /// `.stroke(_:lineWidth:)` with a `Color`.
    pub fn stroke(&self, color: u64, line_width: f64) -> ViewHandle {
        let bytes = color.to_le_bytes();
        // SAFETY: as [`Shape::fill`].
        unsafe {
            self.stroke_style(&bytes, resolve::color_meta(), resolve::color_shapestyle_wt(), line_width)
        }
    }

    /// Present a stroked shape as the `StrokeShapeView` Swift builds.
    ///
    /// `Circle().stroke(.blue, lineWidth: 4)` in Swift is a
    /// `StrokeShapeView<Circle, Color, EmptyView>`, and dumping one shows what
    /// that is: a newtype over
    /// `ModifiedContent<_ShapeView<_StrokedShape<Circle>, Color>,
    /// _BackgroundModifier<EmptyView>>` — one stored property, so identical in
    /// layout to what it wraps. The bindings built the inner `_ShapeView` and
    /// stopped there, which rendered the same and typed differently.
    ///
    /// `.stroke` is `@inlinable`, so there is no initialiser to call and no
    /// instantiation to read a descriptor off; the descriptor itself is exported
    /// and is what this instantiates from. A wrong argument vector would build
    /// some *other* type rather than fail, so the result is checked and anything
    /// unexpected keeps the inner view, which is what this always returned.
    ///
    /// # Safety
    /// `inner` must be the `_ShapeView` this shape's stroke produced.
    unsafe fn as_stroke_shape_view(
        &self,
        inner: ViewHandle,
        style_meta: *const c_void,
        style_wt: *const c_void,
    ) -> ViewHandle {
        unsafe {
            let empty = super::empty_view();
            let bg = super::background_content(&inner, &empty, super::Alignment::Center);

            let desc = resolve::stroke_shape_view_desc();
            if desc.is_null() {
                return inner;
            }
            // Parameters first — Content, Style, Background — then their
            // conformances: Shape, ShapeStyle, View.
            let args = [
                self.meta,
                style_meta,
                resolve::emptyview_meta(),
                self.wt,
                style_wt,
                resolve::emptyview_view_wt(),
            ];
            let meta = abi::generic_metadata_from_descriptor(desc, &args);
            if meta.is_null() {
                return inner;
            }
            // `StrokeShapeView` is a newtype over the `ModifiedContent` below
            // it: one stored property at offset zero, which is what lets the
            // bytes carry over unchanged. Read that from the metadata rather
            // than inferring it from the sizes agreeing.
            if abi::struct_field_offsets(meta).as_deref() != Some(&[0][..])
                || abi::type_bytes(meta) != abi::type_bytes(bg.meta)
            {
                return inner;
            }
            if !crate::diag::type_name(meta).starts_with("SwiftUI.StrokeShapeView<") {
                return inner;
            }
            let wt = abi::get_view_wt(meta);
            if wt.is_null() {
                return inner;
            }
            // Same layout, so the bytes carry over as they are — copied through
            // the value witness so anything refcounted inside is retained.
            let vwt = &*swift_runtime_sys::SwiftABI::get_value_witness_table(bg.meta);
            let mut out = vec![0u8; abi::type_bytes(meta)];
            if vwt.size > 0 {
                (vwt.initialize_with_copy)(
                    out.as_mut_ptr() as *mut c_void,
                    bg.value_ptr() as *mut c_void,
                    bg.meta,
                );
            }
            super::wrap_owned(out, meta, wt)
        }
    }

    /// Both calls have the same shape and differ by one register.
    ///
    /// `fill(_ content: S, style: FillStyle)` puts the `FillStyle` — two
    /// `Bool`s, so loadable — in x1, which pushes the four generic words to
    /// x2. `stroke(_ content: S, lineWidth: CGFloat)` sends its second
    /// argument in d0 instead, so nothing occupies x1 and the generic words
    /// start there. Reading the style metadata out of a line width faults
    /// inside the runtime.
    #[allow(clippy::too_many_arguments)]
    unsafe fn styled(
        &self,
        func: *const c_void,
        oret: *const c_void,
        style: &[u8],
        style_meta: *const c_void,
        style_wt: *const c_void,
        filling: bool,
        line_width: f64,
    ) -> ViewHandle {
        unsafe {
            // The substitution list an opaque return wants is every generic
            // argument and then every witness table: `Self`, the style,
            // `Self: Shape`, and the style's `ShapeStyle`.
            let subst = [self.meta, style_meta, self.wt, style_wt];
            let (meta, wt, size) = super::opaque_result_type(oret, &subst);

            let mut result = vec![0u8; size];
            let mut arg = style.to_vec();
            arg.resize(abi::type_bytes(style_meta).max(style.len()).max(1), 0);
            let mut receiver = self.receiver();
            let (x1, x2, x3, x4, x5) = if filling {
                (FILL_STYLE_DEFAULT as *const c_void, subst[0], subst[1], subst[2], subst[3])
            } else {
                (subst[0], subst[1], subst[2], subst[3], core::ptr::null())
            };
            core::arch::asm!("blr {f}", f = in(reg) func,
                in("x0") arg.as_mut_ptr(),
                in("x1") x1, in("x2") x2, in("x3") x3, in("x4") x4, in("x5") x5,
                in("d0") line_width,
                in("x8") result.as_mut_ptr(),
                in("x20") receiver.as_mut_ptr(),
                lateout("x6") _, lateout("x7") _, lateout("x9") _, lateout("x10") _,
                lateout("x11") _, lateout("x12") _, lateout("x13") _, lateout("x14") _,
                lateout("x15") _, lateout("x16") _, lateout("x17") _, lateout("lr") _,
                lateout("x21") _, clobber_abi("C"),
            );
            wrap_owned(result, meta, wt)
        }
    }

    /// The shape's storage, with a byte to spare.
    ///
    /// `Circle` and `Rectangle` have no stored properties, and an empty `Vec`
    /// has a dangling pointer — fine where nothing reads it, but not worth
    /// relying on across a call whose layout is only inferred.
    fn receiver(&self) -> Vec<u8> {
        let mut v = self.bytes.clone();
        v.push(0);
        v
    }
}

/// A `Path` under construction.
///
/// Every method is `mutating` in Swift, so each takes the path through x20 and
/// writes back in place; there is no value to thread through. Finish with
/// [`PathBuilder::shape`].
pub struct PathBuilder {
    bytes: Vec<u8>,
}

impl PathBuilder {
    /// Move the `Path` into an `@out` slot and give up ownership.
    ///
    /// For a `Shape.path(in:)` witness, whose result slot SwiftUI supplies:
    /// copying and then dropping the builder would release the path's storage
    /// while SwiftUI still holds it.
    ///
    /// # Safety
    /// `out` must have room for a `Path` — the builder's own buffer is sized for
    /// one, and `bytes.len()` is that size.
    pub(crate) unsafe fn move_into(self, out: *mut u8) {
        let me = core::mem::ManuallyDrop::new(self);
        unsafe { core::ptr::copy_nonoverlapping(me.bytes.as_ptr(), out, me.bytes.len()) };
    }

    /// `move(to:)`
    pub fn move_to(&mut self, x: f64, y: f64) -> &mut Self {
        unsafe { self.point(resolve::path_move_to(), x, y, 0.0, 0.0) }
    }

    /// `addLine(to:)`
    pub fn line_to(&mut self, x: f64, y: f64) -> &mut Self {
        unsafe { self.point(resolve::path_add_line(), x, y, 0.0, 0.0) }
    }

    /// `addQuadCurve(to:control:)` — the destination in d0/d1, the control
    /// point in d2/d3.
    pub fn quad_curve_to(&mut self, x: f64, y: f64, cx: f64, cy: f64) -> &mut Self {
        unsafe { self.point(resolve::path_add_quad_curve(), x, y, cx, cy) }
    }

    /// `closeSubpath()`
    pub fn close(&mut self) -> &mut Self {
        unsafe { self.point(resolve::path_close_subpath(), 0.0, 0.0, 0.0, 0.0) }
    }

    unsafe fn point(&mut self, f: *const c_void, a: f64, b: f64, c: f64, d: f64) -> &mut Self {
        unsafe {
            core::arch::asm!("blr {f}", f = in(reg) f,
                in("d0") a, in("d1") b, in("d2") c, in("d3") d,
                in("x20") self.bytes.as_mut_ptr(),
                lateout("x0") _, lateout("x1") _, lateout("x2") _, lateout("x3") _,
                lateout("x4") _, lateout("x5") _, lateout("x6") _, lateout("x7") _,
                lateout("x8") _, lateout("x9") _, lateout("x10") _, lateout("x11") _,
                lateout("x12") _, lateout("x13") _, lateout("x14") _, lateout("x15") _,
                lateout("x16") _, lateout("x17") _, lateout("lr") _, lateout("x21") _,
                clobber_abi("C"),
            );
        }
        self
    }

    /// The finished path, as a `Shape`.
    pub fn shape(&self) -> Shape {
        unsafe { Shape::of(self.bytes.clone(), mangle::ty("Path")) }
    }
}

/// `FillStyle()` — two `Bool`s in one register: `isEOFilled` false in byte 0,
/// `isAntialiased` true in byte 1.
const FILL_STYLE_DEFAULT: u64 = 0x0100;

/// `.strokeBorder(_:lineWidth:antialiased:)` on an `InsettableShape`.
///
/// Not `.stroke`: a stroke straddles the shape's edge, a border is inset so it
/// falls entirely inside. The difference is half the line width everywhere.
///
/// Two overloads share the name. The older returns `some View` and is exported;
/// the newer returns a concrete `StrokeBorderShapeView` and is
/// `@_alwaysEmitIntoClient`, and it is the one Swift picks — so matching what a
/// reference builds means building that type's value rather than calling either.
pub fn stroke_border(
    shape: super::InsettableShape,
    color: u64,
    line_width: f64,
) -> ViewHandle {
    unsafe {
        let (ma, _insettable_wt, init) = shape.parts();
        let shape_meta = abi::metadata0(ma);
        let mut receiver = vec![0u8; abi::type_bytes(shape_meta).max(1)];
        core::arch::asm!("blr {f}", f = in(reg) init,
            in("x8") receiver.as_mut_ptr(),
            in("x20") shape_meta,
            lateout("x0") _, lateout("x1") _, lateout("x2") _, lateout("x3") _,
            lateout("x4") _, lateout("x5") _, lateout("x6") _, lateout("x7") _,
            lateout("x9") _, lateout("x10") _, lateout("x11") _, lateout("x12") _,
            lateout("x13") _, lateout("x14") _, lateout("x15") _, lateout("x16") _,
            lateout("x17") _, lateout("lr") _, lateout("x21") _, clobber_abi("C"),
        );

        let subst = [shape_meta, resolve::color_meta(), _insettable_wt, resolve::color_shapestyle_wt()];
        let (meta, wt, size) =
            super::opaque_result_type(resolve::stroke_border_oret(), &subst);
        let style = color.to_le_bytes();
        let mut result = vec![0u8; size.max(1)];
        core::arch::asm!("blr {f}", f = in(reg) resolve::stroke_border_fn(),
            in("x0") style.as_ptr(),
            in("d0") line_width,
            in("x1") 1u64,
            in("x2") subst[0], in("x3") subst[1], in("x4") subst[2], in("x5") subst[3],
            in("x8") result.as_mut_ptr(),
            in("x20") receiver.as_mut_ptr(),
            lateout("x6") _, lateout("x7") _, lateout("x9") _, lateout("x10") _,
            lateout("x11") _, lateout("x12") _, lateout("x13") _, lateout("x14") _,
            lateout("x15") _, lateout("x16") _, lateout("x17") _, lateout("lr") _,
            lateout("x21") _, clobber_abi("C"),
        );
        // The exported call produced the *inner* view. Swift's overload wraps it:
        //   StrokeBorderShapeView<Shape, Style, EmptyView> {
        //       shape, view: ModifiedContent<that, _BackgroundModifier<EmptyView>>
        //   }
        // `Circle` and `EmptyView` are both zero bytes, so the whole wrapper adds
        // only the background modifier's `Alignment` — which is `.center`.
        let outer_mangled = format!(
            "7SwiftUI21StrokeBorderShapeViewVy{}7SwiftUI5ColorV7SwiftUI9EmptyViewVG",
            shape.type_mangling()
        );
        let outer = abi::resolve_type_by_mangled_name(outer_mangled.as_bytes());
        assert!(!outer.is_null(), "{}", crate::diag::demangle_type(outer_mangled.as_bytes()));
        let outer_wt = abi::get_view_wt(outer);
        assert!(!outer_wt.is_null(), "StrokeBorderShapeView !: View");

        // `Alignment` is two `AlignmentKey`s and comes back in x0/x1, not
        // through x8 — reading it as an indirect return left both keys zero,
        // which renders the same (centre *is* what an empty background aligns
        // to) and only the value comparison saw.
        let (ah, av) = super::static_getter(resolve::alignment_center(), resolve::alignment_meta());

        let mut bytes = vec![0u8; abi::type_bytes(outer)];
        let inner = abi::type_size(meta);
        bytes[..inner].copy_from_slice(&result[..inner]);
        // Where the alignment sits is read from the metadata, by the same walk
        // [`stroke_view_offsets`] does — it is not a field of the outer type at
        // all, but of the `_BackgroundModifier` two levels in. The arithmetic
        // that used to stand in here padded the inner view to eight, and
        // writing at its unpadded 58 instead straddled the two alignment keys
        // and read back as one `AlignmentKey(bits: 0x50002)` — which still
        // rendered centred, because an empty background has nothing to
        // misalign.
        let align_at = border_view_offsets(outer)
            .map(|(_, _, _, align)| align)
            .unwrap_or_else(|| inner.next_multiple_of(8));
        bytes[align_at..align_at + 8].copy_from_slice(&ah.to_le_bytes());
        bytes[align_at + 8..align_at + 16].copy_from_slice(&av.to_le_bytes());
        let _ = wt;
        wrap_buf(&bytes, outer, outer_wt)
    }
}

/// `.fill(_:).stroke(_:lineWidth:)` — a shape filled, then outlined.
///
/// `ShapeView.stroke(_:lineWidth:antialiased:)` is `@_alwaysEmitIntoClient`, so
/// there is nothing to call. What it builds is
/// `StrokeShapeView<Content, S, Self>`, whose single field is a
/// `ModifiedContent` putting the *stroke* in front and the original *fill*
/// behind it as a `_BackgroundModifier` — so the fill is drawn as a background
/// rather than composited, and both filled shape views have to be built.
pub fn fill_then_stroke(
    shape: &Shape,
    fill: u64,
    stroke: u64,
    line_width: f64,
    result_mangled: &[u8],
) -> ViewHandle {
    unsafe {
        let color_meta = resolve::color_meta();
        let color_wt = resolve::color_shapestyle_wt();
        let (background, bg_ty) = shape.fill_parts(&fill.to_le_bytes(), color_meta, color_wt);
        let (content, content_ty) =
            shape.stroked(line_width).fill_parts(&stroke.to_le_bytes(), color_meta, color_wt);

        let meta = abi::resolve_type_by_mangled_name(result_mangled);
        assert!(!meta.is_null(), "{}", crate::diag::demangle_type(result_mangled));
        let wt = abi::get_view_wt(meta);
        assert!(!wt.is_null(), "StrokeShapeView !: View");

        let (ah, av) = super::static_getter(resolve::alignment_center(), resolve::alignment_meta());
        let content_size = abi::type_size(content_ty);
        let bg_size = abi::type_size(bg_ty);
        let (content_at, bg_at, align_at) =
            stroke_view_offsets(meta)
                .unwrap_or_else(|| {
                    // Every offset padded to eight — right for a bare shape,
                    // and an assumption rather than a fact. Only reached if one
                    // of the three nested types does not resolve.
                    let bg_at = content_size.next_multiple_of(8);
                    (0, bg_at, (bg_at + bg_size).next_multiple_of(8))
                });

        let mut bytes = vec![0u8; abi::type_bytes(meta)];
        assert!(
            align_at + 16 <= bytes.len() && bg_at + bg_size <= bytes.len(),
            "{} lays out its fields differently than expected: content at {content_at} \
             ({content_size} bytes), background at {bg_at} ({bg_size}), alignment at \
             {align_at} — but the type is only {} bytes.",
            crate::diag::type_name(meta),
            bytes.len(),
        );
        bytes[content_at..content_at + content_size].copy_from_slice(&content[..content_size]);
        bytes[bg_at..bg_at + bg_size].copy_from_slice(&background[..bg_size]);
        bytes[align_at..align_at + 8].copy_from_slice(&ah.to_le_bytes());
        bytes[align_at + 8..align_at + 16].copy_from_slice(&av.to_le_bytes());
        wrap_buf(&bytes, meta, wt)
    }
}

/// Where a `StrokeShapeView`'s three written fields actually sit.
///
/// They are not its own fields: it has exactly one, a `ModifiedContent`, whose
/// two fields are the stroked shape and a `_BackgroundModifier`, whose two are
/// the fill and the alignment. So each offset is a sum down three levels, and
/// every level is read from that level's metadata — reached with
/// [`abi::field_type_metadata`], since `_BackgroundModifier` exports no
/// accessor to ask for by name.
///
/// Returns `None` if any level does not look as expected, which leaves the
/// caller on its padded-to-eight estimate — right for a bare shape, and what
/// this replaces.
///
/// # Safety
/// `meta` must be `StrokeShapeView` metadata.
unsafe fn stroke_view_offsets(meta: *const c_void) -> Option<(usize, usize, usize)> {
    unsafe {
        let &[view_at] = abi::struct_field_offsets(meta)?.as_slice() else { return None };
        let modified = abi::field_type_metadata(meta, 0);
        if modified.is_null() {
            return None;
        }
        let &[content_at, modifier_at] = abi::struct_field_offsets(modified)?.as_slice() else {
            return None;
        };
        let background = abi::field_type_metadata(modified, 1);
        if background.is_null() {
            return None;
        }
        let &[bg_at, align_at] = abi::struct_field_offsets(background)?.as_slice() else {
            return None;
        };
        Some((
            view_at + content_at,
            view_at + modifier_at + bg_at,
            view_at + modifier_at + align_at,
        ))
    }
}

/// Where a `StrokeBorderShapeView`'s four written fields sit.
///
/// The same walk as [`stroke_view_offsets`], with the type's own `shape` field
/// in front of the `ModifiedContent`.
///
/// # Safety
/// `meta` must be `StrokeBorderShapeView` metadata.
unsafe fn border_view_offsets(meta: *const c_void) -> Option<(usize, usize, usize, usize)> {
    unsafe {
        let &[shape_at, view_at] = abi::struct_field_offsets(meta)?.as_slice() else {
            return None;
        };
        let modified = abi::field_type_metadata(meta, 1);
        if modified.is_null() {
            return None;
        }
        let &[content_at, modifier_at] = abi::struct_field_offsets(modified)?.as_slice() else {
            return None;
        };
        let background = abi::field_type_metadata(modified, 1);
        if background.is_null() {
            return None;
        }
        let &[bg_at, align_at] = abi::struct_field_offsets(background)?.as_slice() else {
            return None;
        };
        Some((
            shape_at,
            view_at + content_at,
            view_at + modifier_at + bg_at,
            view_at + modifier_at + align_at,
        ))
    }
}

/// `.fill(_:).strokeBorder(_:style:)` — a shape filled, then bordered inside its
/// own edge.
///
/// The `ShapeView` spelling of `strokeBorder`, and like the `Shape` one it is
/// `@_alwaysEmitIntoClient`. What it builds is a `StrokeBorderShapeView` whose
/// `shape` field is the original shape and whose `view` field is the same
/// stroke-over-fill `ModifiedContent` [`fill_then_stroke`] builds — except the
/// stroked shape is first `inset(by:)` half the line width, which is the whole
/// difference between a stroke and a border.
pub fn fill_then_stroke_border(
    shape: &Shape,
    fill: u64,
    border: u64,
    line_width: f64,
    result_mangled: &[u8],
) -> ViewHandle {
    unsafe {
        let color_meta = resolve::color_meta();
        let color_wt = resolve::color_shapestyle_wt();
        let (background, bg_ty) = shape.fill_parts(&fill.to_le_bytes(), color_meta, color_wt);
        let (content, content_ty) = shape
            .inset(line_width / 2.0)
            .stroked(line_width)
            .fill_parts(&border.to_le_bytes(), color_meta, color_wt);

        let meta = abi::resolve_type_by_mangled_name(result_mangled);
        assert!(!meta.is_null(), "{}", crate::diag::demangle_type(result_mangled));
        let wt = abi::get_view_wt(meta);
        assert!(!wt.is_null(), "StrokeBorderShapeView !: View");

        let (ah, av) = super::static_getter(resolve::alignment_center(), resolve::alignment_meta());
        let shape_size = abi::type_size(shape.meta);
        let content_size = abi::type_size(content_ty);
        let bg_size = abi::type_size(bg_ty);
        // `StrokeBorderShapeView` has a `shape` of its own in front of the same
        // nested `ModifiedContent` the stroke case has, so its offsets are read
        // the same way — one level further in.
        let (shape_at, content_at, bg_at, align_at) = border_view_offsets(meta)
            .unwrap_or_else(|| {
                let content_at = shape_size.next_multiple_of(8);
                let bg_at = (content_at + content_size).next_multiple_of(8);
                (0, content_at, bg_at, (bg_at + bg_size).next_multiple_of(8))
            });

        let mut bytes = vec![0u8; abi::type_bytes(meta)];
        assert!(
            align_at + 16 <= bytes.len(),
            "{} lays out its fields differently than expected",
            crate::diag::type_name(meta),
        );
        bytes[shape_at..shape_at + shape_size].copy_from_slice(&shape.bytes[..shape_size]);
        bytes[content_at..content_at + content_size].copy_from_slice(&content[..content_size]);
        bytes[bg_at..bg_at + bg_size].copy_from_slice(&background[..bg_size]);
        bytes[align_at..align_at + 8].copy_from_slice(&ah.to_le_bytes());
        bytes[align_at + 8..align_at + 16].copy_from_slice(&av.to_le_bytes());
        wrap_buf(&bytes, meta, wt)
    }
}

/// A `LinearGradient` built from explicit `Gradient.Stop`s.
///
/// Not the same as the `colors:` spelling next door: that one spaces its colours
/// evenly, this one places each at a location the caller gives. A mask built
/// from stops — which is what both of the tvOS Media Catalog's hero views use —
/// cannot be expressed as evenly-spaced colours.
pub fn linear_gradient_stops(
    stops: &[(u64, f64)],
    start: (f64, f64),
    end: (f64, f64),
) -> (Vec<u8>, *const c_void, *const c_void) {
    unsafe {
        let stop_meta = abi::metadata0(resolve::gradient_stop_ma());
        let stride = abi::type_stride(stop_meta);
        let mut bytes = vec![0u8; stride * stops.len()];
        for (i, (color, location)) in stops.iter().enumerate() {
            // Gradient.Stop.init(color:location:) — the Color in x0 and the
            // location in d0, and the result comes *back* the same way: a Stop
            // is one reference and one CGFloat, so it is returned in x0/d0
            // rather than through x8. Handing it an x8 left the buffer zeroed
            // and the array of stops full of null Colors, which faulted on the
            // first draw.
            let (word, loc): (u64, f64);
            core::arch::asm!("blr {f}", f = in(reg) resolve::gradient_stop_init(),
                inout("x0") *color => word,
                inout("d0") *location => loc,
                lateout("x1") _, lateout("x2") _, lateout("x3") _, lateout("x4") _,
                lateout("x5") _, lateout("x6") _, lateout("x7") _, lateout("x8") _,
                lateout("x9") _, lateout("x10") _, lateout("x11") _, lateout("x12") _,
                lateout("x13") _, lateout("x14") _, lateout("x15") _, lateout("x16") _,
                lateout("x17") _, lateout("lr") _, lateout("x20") _, lateout("x21") _,
                clobber_abi("C"),
            );
            bytes[i * stride..i * stride + 8].copy_from_slice(&word.to_le_bytes());
            bytes[i * stride + 8..i * stride + 16].copy_from_slice(&loc.to_le_bytes());
        }
        let array = abi::swift_array(stop_meta, stops.len(), &bytes);

        let g: u64;
        core::arch::asm!("blr {f}", f = in(reg) resolve::gradient_stops_init(),
            in("x0") array,
            in("x20") resolve::gradient_meta(),
            lateout("x0") g,
            lateout("x1") _, lateout("x2") _, lateout("x3") _, lateout("x4") _,
            lateout("x5") _, lateout("x6") _, lateout("x7") _, lateout("x8") _,
            lateout("x9") _, lateout("x10") _, lateout("x11") _, lateout("x12") _,
            lateout("x13") _, lateout("x14") _, lateout("x15") _, lateout("x16") _,
            lateout("x17") _, lateout("lr") _, lateout("x21") _, clobber_abi("C"),
        );

        let meta = crate::type_by_name!(swift_type!(SwiftUI.LinearGradient).as_bytes());
        assert!(!meta.is_null(), "LinearGradient metadata");
        let mut value = vec![0u8; abi::type_bytes(meta)];
        core::arch::asm!("blr {f}", f = in(reg) resolve::linear_gradient_init(),
            in("x0") g,
            in("d0") start.0, in("d1") start.1, in("d2") end.0, in("d3") end.1,
            in("x8") value.as_mut_ptr(),
            in("x20") meta,
            lateout("x1") _, lateout("x2") _, lateout("x3") _, lateout("x4") _,
            lateout("x5") _, lateout("x6") _, lateout("x7") _, lateout("x9") _,
            lateout("x10") _, lateout("x11") _, lateout("x12") _, lateout("x13") _,
            lateout("x14") _, lateout("x15") _, lateout("x16") _, lateout("x17") _,
            lateout("lr") _, lateout("x21") _, clobber_abi("C"),
        );
        (value, meta, resolve::linear_gradient_wt())
    }
}

/// A `LinearGradient` as a view, for `.mask { … }` and friends.
pub fn linear_gradient_stops_view(
    stops: &[(u64, f64)],
    start: (f64, f64),
    end: (f64, f64),
) -> ViewHandle {
    let (bytes, meta, _) = linear_gradient_stops(stops, start, end);
    unsafe {
        let wt = abi::get_view_wt(meta);
        assert!(!wt.is_null(), "LinearGradient !: View");
        wrap_buf(&bytes, meta, wt)
    }
}

/// `.shadow(_:)` applied to any `ShapeStyle` — `_ShadowShapeStyle<Base>`.
///
/// [`implicit_shadow_style`] is the special case where `Base` is
/// `_ImplicitShapeStyle` and so contributes no bytes. A real base — a
/// `Material`, say — sits in front of the `ShadowStyle`, which is why this takes
/// its bytes and its type rather than assuming both are empty.
pub fn shadow_over_style(
    base: &[u8],
    base_ty: &str,
    shadow: &[u8],
) -> (Vec<u8>, *const c_void, *const c_void) {
    unsafe {
        let ty = mangle::ty("_ShadowShapeStyle")
            .of(vec![mangle::Type::Verbatim(base_ty.into())])
            .mangle();
        let meta = abi::resolve_type_by_mangled_name(ty.as_bytes());
        assert!(!meta.is_null(), "{}", mangle::demangle(&ty));
        let wt = abi::get_view_wt_for_proto(meta, resolve::shape_style_proto());
        assert!(!wt.is_null(), "_ShadowShapeStyle !: ShapeStyle");
        let mut bytes = vec![0u8; abi::type_bytes(meta)];
        // Where the two fields sit comes from the metadata: `Base` is whatever
        // style this wraps, so padding the first to eight is a guess about a
        // type chosen by the caller.
        let offsets = abi::struct_field_offsets(meta).expect("two stored fields");
        let &[base_at, shadow_at] = offsets.as_slice() else {
            panic!("_ShadowShapeStyle is {} fields, not 2", offsets.len());
        };
        bytes[base_at..base_at + base.len()].copy_from_slice(base);
        let n = shadow.len().min(bytes.len() - shadow_at);
        bytes[shadow_at..shadow_at + n].copy_from_slice(&shadow[..n]);
        (bytes, meta, wt)
    }
}

/// `.opacity(_:)` applied to any `ShapeStyle` — `_OpacityShapeStyle<Base>`.
///
/// [`implicit_opacity_style`] is the case where `Base` is `_ImplicitShapeStyle`
/// and contributes nothing; a real base — `.red.gradient`, say — sits in front
/// of the `Float`.
pub fn opacity_over_style(
    base: &[u8],
    base_ty: &str,
    opacity: f64,
) -> (Vec<u8>, *const c_void, *const c_void) {
    unsafe {
        let ty = mangle::ty("_OpacityShapeStyle")
            .of(vec![mangle::Type::Verbatim(base_ty.into())])
            .mangle();
        let meta = abi::resolve_type_by_mangled_name(ty.as_bytes());
        assert!(!meta.is_null(), "{}", mangle::demangle(&ty));
        let wt = abi::get_view_wt_for_proto(meta, resolve::shape_style_proto());
        assert!(!wt.is_null(), "_OpacityShapeStyle !: ShapeStyle");
        let mut bytes = vec![0u8; abi::type_bytes(meta)];
        bytes[..base.len()].copy_from_slice(base);
        let at = base.len().next_multiple_of(4);
        bytes[at..at + 4].copy_from_slice(&(opacity as f32).to_le_bytes());
        (bytes, meta, wt)
    }
}

impl Shape {
    /// `.trim(from:to:)` — keep a fraction of the shape's path.
    ///
    /// How a progress ring is drawn: a stroked circle trimmed to the fraction
    /// complete. Without it a "ring showing 70%" is a full circle.
    ///
    /// `.trim` is `@inlinable`, so SwiftUI exports no function for it — but
    /// `_TrimmedShape<S>` is just the shape and two `CGFloat`s, its descriptor
    /// is exported, and the field offsets come from the metadata rather than
    /// being assumed.
    pub fn trim(&self, from: f64, to: f64) -> Self {
        unsafe {
            let desc = resolve::trimmed_shape_desc();
            let meta = if desc.is_null() {
                core::ptr::null()
            } else {
                abi::generic_metadata_from_descriptor(desc, &[self.meta, self.wt])
            };
            let offsets = if meta.is_null() {
                None
            } else {
                abi::struct_field_offsets(meta)
            };
            // Shape, then the two fractions — anything else is not the type
            // this was taken for, and writing into it would be a guess.
            let same = || Self {
                bytes: self.bytes.clone(),
                meta: self.meta,
                wt: self.wt,
                ty: self.ty.clone(),
            };
            let Some(offs) = offsets.filter(|o| o.len() == 3) else {
                return same();
            };
            let wt = abi::get_view_wt_for_proto(meta, resolve::shape_proto());
            if wt.is_null() {
                return same();
            }

            let mut bytes = vec![0u8; abi::type_bytes(meta)];
            let vwt = &*swift_runtime_sys::SwiftABI::get_value_witness_table(self.meta);
            if vwt.size > 0 {
                (vwt.initialize_with_copy)(
                    bytes.as_mut_ptr().add(offs[0]) as *mut c_void,
                    self.bytes.as_ptr() as *mut c_void,
                    self.meta,
                );
            }
            bytes[offs[1]..offs[1] + 8].copy_from_slice(&from.to_le_bytes());
            bytes[offs[2]..offs[2] + 8].copy_from_slice(&to.to_le_bytes());

            Self {
                bytes,
                meta,
                wt,
                ty: mangle::ty("_TrimmedShape").of(vec![self.ty.clone()]),
            }
        }
    }
}