theme/

paint.rs

//! Context-free paint helpers: the process-wide appearance mirror and the
//! free functions ([`ink`], [`hairline`], [`wash`], …) that element builders
//! call without a `cx` in scope.

use std::sync::atomic::{AtomicU8, AtomicU32, Ordering};

use gpui::{BoxShadow, Hsla, hsla, point, px};

use crate::Appearance;

/// Process-wide mirror of the installed theme's appearance.
///
/// The paint helpers ([`ink`], [`hairline`], [`wash`], …) are free functions
/// called from deep inside element builders that have no `cx` in scope, so they
/// read the appearance from here instead of the gpui global. Appearance is
/// genuinely process-wide — one setting for every window — so a single mirror is
/// sound; [`Theme::install`](crate::theme::Theme::install) is the only writer
/// outside tests.
static CURRENT_APPEARANCE: AtomicU8 = AtomicU8::new(0);

/// Bumped every time a palette is installed — an appearance switch, and equally
/// a brand change, which moves every token while the appearance stands still.
///
/// Anything that caches *resolved colors* — most importantly the markdown
/// renderer's cross-frame `TextRun` cache, which bakes an `Hsla` into every run —
/// is only valid for the palette that produced it. Those caches were written when
/// the theme was a compile-time constant, so their validity keys cover content
/// only. Rather than thread the palette through every key, they compare this
/// counter and drop everything when it moves.
static THEME_GENERATION: AtomicU32 = AtomicU32::new(0);

/// The appearance the context-free paint helpers are painting for.
pub fn current_appearance() -> Appearance {
    match CURRENT_APPEARANCE.load(Ordering::Relaxed) {
        1 => Appearance::Light,
        _ => Appearance::Dark,
    }
}

/// Monotonic id of the current palette.
pub fn theme_generation() -> u32 {
    THEME_GENERATION.load(Ordering::Relaxed)
}

/// [`CURRENT_APPEARANCE`] is process-wide, so under the parallel test runner
/// any test that flips it — or asserts on the output of a helper that reads it
/// ([`ink`], [`hairline`], [`wash`], …) — must hold this lock. Crate-visible
/// because such tests exist outside this module too (see motion's tests).
/// Tests that flip the appearance restore Dark before releasing the guard.
/// Compiled unconditionally (not `cfg(test)`) so downstream crates' tests can
/// use it too; it is not part of the public API.
#[doc(hidden)]
pub fn lock_appearance() -> std::sync::MutexGuard<'static, ()> {
    static APPEARANCE_LOCK: std::sync::Mutex<()> = std::sync::Mutex::new(());
    APPEARANCE_LOCK.lock().unwrap_or_else(|e| e.into_inner())
}

/// Mark the installed palette as a new one, so anything caching resolved
/// colors drops what it has. A brand change moves every token without moving
/// the appearance, which is why this is separate from
/// [`set_current_appearance`].
pub(crate) fn bump_generation() {
    THEME_GENERATION.fetch_add(1, Ordering::Relaxed);
}

/// Point the context-free paint helpers at an appearance. Called by
/// [`Theme::install`](crate::theme::Theme::install); exposed for tests that
/// build a theme without an `App`.
pub fn set_current_appearance(appearance: Appearance) {
    let encoded = match appearance {
        Appearance::Dark => 0,
        Appearance::Light => 1,
    };
    if CURRENT_APPEARANCE.swap(encoded, Ordering::Relaxed) != encoded {
        THEME_GENERATION.fetch_add(1, Ordering::Relaxed);
    }
}

/// Light-mode alpha multiplier for **fills** (hover/active washes, chip and pill
/// backgrounds).
///
/// This was 0.5 on the theory that dark ink on a bright field reads heavier and
/// should be scaled back. That theory is right for a *large* wash and badly wrong
/// for everything else: this palette leans on very low alphas for its subtle
/// fills — the composer plate is `ink(0.03)`, key caps are `ink(0.05)` — and
/// halving those produced 1.5% black on white, which is nothing. The composer
/// lost its background entirely and selected tabs stopped reading as selected.
///
/// The established light-UI scales (Primer, Radix) land subtle ≈ 3–4%, hover ≈ 8%,
/// selected ≈ 14% black — which is where the dark palette's white alphas already
/// sit. So the honest multiplier is 1: the same number in both appearances, with
/// only the *tone* flipping. Any per-state correction belongs in that state's
/// token, not in a blanket multiplier.
pub const INK_FILL_SCALE: f32 = 1.0;

/// Light-mode alpha multiplier for **hairlines** (borders, dividers, rings).
/// Opposite of fills: a 1px edge has to hold its own against a bright surround,
/// and the dark palette's white hairlines are deliberately faint. Scaling up
/// keeps separators legible instead of dissolving into the panel.
pub const INK_HAIRLINE_SCALE: f32 = 1.35;

/// Translucent **fill** ink for interactive states and chip plates: soft-white on
/// dark, soft-black on light at [`INK_FILL_SCALE`] of the alpha.
///
/// Alphas are quoted in *dark-mode terms* at every call site — the dark theme is
/// the tuned one — and the light value is derived. Callers keep one number and
/// both appearances stay in the relationship the dark tuning established.
///
/// Fills must never rest on transparent BLACK in dark mode: fully opaque washes
/// killed the glass and flashed dark mid-fade (user reports), so hover fades rest
/// on `ink(0.0)`, which stays tonally correct at zero alpha.
pub fn ink(alpha: f32) -> Hsla {
    ink_for(current_appearance(), alpha)
}

pub(crate) fn ink_for(appearance: Appearance, alpha: f32) -> Hsla {
    match appearance {
        // Soft-white, not pure white: alphas are high enough to stay visible at
        // the brightest backdrop the 0.90 glass scrim can produce.
        Appearance::Dark => hsla(0.0, 0.0, 1.0, alpha),
        Appearance::Light => hsla(0.0, 0.0, 0.0, alpha * INK_FILL_SCALE),
    }
}

/// Translucent **hairline** ink for borders, dividers and rings: white on dark,
/// black on light at [`INK_HAIRLINE_SCALE`] of the alpha.
///
/// Separate from [`ink`] because edges and fills scale in opposite directions
/// when the field brightens — a 1px line needs *more* ink on white, a plate needs
/// less.
pub fn hairline(alpha: f32) -> Hsla {
    hairline_for(current_appearance(), alpha)
}

pub(crate) fn hairline_for(appearance: Appearance, alpha: f32) -> Hsla {
    match appearance {
        Appearance::Dark => hsla(0.0, 0.0, 1.0, alpha),
        Appearance::Light => hsla(0.0, 0.0, 0.0, (alpha * INK_HAIRLINE_SCALE).min(0.5)),
    }
}

/// Interactive-state wash: a softened [`ink`] that stops short of pure black or
/// white so hover plates read as tinted glass rather than paint.
pub fn wash(alpha: f32) -> Hsla {
    wash_for(current_appearance(), alpha)
}

pub(crate) fn wash_for(appearance: Appearance, alpha: f32) -> Hsla {
    match appearance {
        Appearance::Dark => hsla(0.0, 0.0, 0.92, alpha),
        Appearance::Light => hsla(0.0, 0.0, 0.10, alpha * INK_FILL_SCALE),
    }
}

/// Alpha of the standard modal backdrop in dark mode. Call sites that need a
/// heavier or lighter scrim pass their own dark-mode alpha to [`scrim`].
pub const SCRIM_ALPHA_DARK: f32 = 0.60;

/// Modal backdrop at `alpha_dark` (quoted, as everywhere, in dark-mode terms).
///
/// Black in both appearances — a scrim's job is to darken what is behind it, and
/// a "light scrim" of white would wash the modal out rather than seat it. What
/// changes is strength: on a bright field a dark-mode-weight scrim reads as a
/// blackout, so light mode scales to roughly half.
pub fn scrim(alpha_dark: f32) -> Hsla {
    scrim_for(current_appearance(), alpha_dark)
}

pub(crate) fn scrim_for(appearance: Appearance, alpha_dark: f32) -> Hsla {
    match appearance {
        Appearance::Dark => hsla(0.0, 0.0, 0.0, alpha_dark),
        Appearance::Light => hsla(0.0, 0.0, 0.0, 0.32 * (alpha_dark / SCRIM_ALPHA_DARK)),
    }
}

/// Recessed band behind a palette/picker header or footer strip.
///
/// A free function as well as a [`Theme`](crate::theme::Theme) field because the
/// picker chrome that paints it is built from context-free helpers; both resolve
/// to the same value.
pub fn band() -> Hsla {
    band_for(current_appearance())
}

pub(crate) fn band_for(appearance: Appearance) -> Hsla {
    match appearance {
        Appearance::Dark => hsla(0.0, 0.0, 0.0, 0.16),
        // A recessed strip on white needs far less ink than on near-black; the
        // dark 16% would read as a bruise.
        Appearance::Light => hsla(0.0, 0.0, 0.0, 0.045),
    }
}

/// Selected-state glass treatment (tabs, session rows, space rows):
/// `../desktop`'s `--color-active` — white at 12% on dark, black at 6% on
/// light, translucent enough for the vibrancy to read through (heavier flat
/// washes blocked the glass, user request).
///
/// One rung over [`Theme::element_hover`](crate::theme::Theme::element_hover),
/// carrying the ring in [`glass_selected_shadows`] on top. Selection *inside
/// floating cards* is [`card_selected_bg`].
pub fn glass_selected_bg() -> Hsla {
    match current_appearance() {
        Appearance::Dark => ink(0.12),
        Appearance::Light => ink(0.06),
    }
}

/// The user message bubble's plate: the softened [`wash`] at 8% dark, 4%
/// light. At the selection weight the bubble read too strong for settled
/// content (user report), and an opaque plate before that read as a solid slab
/// over glass.
pub fn user_bubble_bg() -> Hsla {
    match current_appearance() {
        Appearance::Dark => wash(0.08),
        Appearance::Light => wash(0.04),
    }
}

/// Selected/keyboard-active treatment for rows and chips INSIDE a floating
/// card (menu rows, the picker rail, segmented chips): `--color-active` again,
/// tone-flipped by the palette convention so a card that is already the bright
/// plane lifts with black at 6% rather than white.
pub fn card_selected_bg() -> Hsla {
    match current_appearance() {
        Appearance::Dark => ink(0.12),
        Appearance::Light => ink(0.06),
    }
}

/// The selected chip's bright outline, as an INSET shadow: gpui paints inset
/// shadows ON TOP of the background, edges only — a border with zero layout
/// cost. Drop shadows are filled rects painted BEHIND the element, and behind
/// a 5% fill they showed straight through as an opaque dark plate with a
/// greyed ring (user report) — nothing may paint behind a glass chip.
///
/// Light pins the ring at a flat 7% black rather than the scaled hairline:
/// heavier rings (the [`INK_HAIRLINE_SCALE`]d value, then 12%) outlined every
/// selected chip in a dark box (user reports) — the ring should define the
/// chip the way dark's 9% white ring does, not frame it.
///
/// There is deliberately NO drop-shadow seat under the light chip. Three
/// recipes were tried (a tight 10% layer, a 6% contact + 5% ambient pair, a
/// lone 4% whisper) and every one failed on sight: layers sum into a grey rim
/// exactly where the chip meets the frost, gpui's small-radius blur reads
/// coarse on a bright field, and the tab strip is a scroll container that
/// clips its children vertically — any shadow escaping the chip gets cut off
/// mid-fade. The near-opaque fill plus the ring carry selection, exactly as
/// dark's wash plus ring does; the two appearances share one recipe now.
pub fn glass_selected_shadows() -> Vec<BoxShadow> {
    card_selected_shadows()
}

/// The elevation shadow a floating surface casts — `shadow_lg`'s shape, which
/// is where it lived until the surface moved into the material. Painted cut to
/// outside the shape, because the same drop shadow under a translucent fill is
/// the grey plate [`card_selected_shadows`] records. `GlassSpec::shadow` says
/// which looks carry one.
pub fn surface_shadows() -> Vec<BoxShadow> {
    vec![
        BoxShadow {
            color: hsla(0.0, 0.0, 0.0, 0.1),
            offset: point(px(0.0), px(10.0)),
            blur_radius: px(15.0),
            spread_radius: px(-3.0),
            inset: false,
        },
        BoxShadow {
            color: hsla(0.0, 0.0, 0.0, 0.1),
            offset: point(px(0.0), px(4.0)),
            blur_radius: px(6.0),
            spread_radius: px(-4.0),
            inset: false,
        },
    ]
}

/// Selection outline for rows and chips INSIDE a floating card (menu rows,
/// the picker rail, segmented chips): the inset ring alone, in both
/// appearances. Card rows fill with a translucent wash
/// ([`card_selected_bg`]), and a drop shadow — a filled rect painted BEHIND
/// the element — shows straight through a translucent fill as a grey plate
/// (the same lesson [`glass_selected_shadows`] records for dark glass). The
/// card already carries the elevation shadow; selection inside it only needs
/// the edge.
pub fn card_selected_shadows() -> Vec<BoxShadow> {
    let color = match current_appearance() {
        Appearance::Dark => hairline(0.09),
        Appearance::Light => hsla(0.0, 0.0, 0.0, 0.07),
    };
    vec![BoxShadow {
        color,
        offset: point(px(0.0), px(0.0)),
        blur_radius: px(0.0),
        spread_radius: px(1.0),
        inset: true,
    }]
}