ponko 0.0.1

//! 3D: meshes with materials, drawn from entities with a [`Transform3D`] and
//! a [`Model`], through a perspective [`Camera3D`], lit by a sun and ambient
//! light ([`Lighting`]). Behind the `3d` feature.
//!
//! The 3D pass is drawn first, with a depth buffer; 2D sprites, text and UI
//! go on top of it. Games without 3D models never run it, and builds without
//! the feature don't have it at all.
//!
//! Coordinates are right-handed with Y up (as in glTF): a camera with no
//! rotation looks down -Z.

mod animator;
mod api;
mod clip;
mod collect;
mod compute;
mod effect;
pub(crate) mod gi;
mod gltf;
mod ik;
pub(crate) mod instances;
pub use instances::{InstanceBatch, InstanceBatchOptions};
mod lod;
pub(crate) mod occlusion;
pub use gi::{GlobalIllumination, MAX_GI_PROBES, MAX_GI_PROBES_PER_FRAME};
pub use ik::{look_at_joint, two_bone_ik};
pub use lod::{LodGroup, LodLevel, LodPick, LodRenderer, LodSettings, LodShadow};
pub(crate) mod lights;
mod mesh;
pub use lights::{LIGHT_SHADOW_ATLAS_SIZE, LIGHT_SHADOW_SIZE, MAX_LIGHT_SHADOW_VIEWS, PointLight3D, SpotLight3D};
pub(crate) use lights::{MAX_LIGHT_SHADOW_RESOLUTION, MIN_LIGHT_SHADOW_RESOLUTION};
pub(crate) mod shadow_atlas;
pub(crate) use shadow_atlas::{MAX_LIGHT_SHADOW_ATLAS, MIN_LIGHT_SHADOW_ATLAS};
pub(crate) mod particles;
pub use particles::{
    ParticleBlend3D, ParticleCurve, ParticleEmitter3D, ParticleGradient, ParticleSettings3D, ParticleShape3D,
    ParticleSpace3D,
};
mod decal;
mod post;
pub(crate) mod projected;
pub use projected::{Decal3D, MAX_DECALS, MAX_DECALS_PER_CLUSTER, ReceivesDecals};
pub(crate) mod probe;
pub use probe::ReflectionProbe3D;
mod quality;
mod skin;
pub(crate) mod strips;
pub use strips::{Line3D, Trail3D};
pub(crate) mod text3d;
pub use text3d::{Text3D, TextAlign3D};
mod far_terrain;
mod sky;
mod target;
mod terrain;
pub use far_terrain::FarTerrain;
mod texture_array;

pub use animator::{
    AnimationCondition, AnimationEvent, AnimationGraph, AnimationLayer, AnimationParameter, AnimationState,
    AnimationTransition, Animator, JointMask, LayerBlend, Motion, MotionChild, RootMotion,
};
pub(crate) use api::GpuMaterialDesc;
#[cfg(feature = "window")]
pub(crate) use api::MaterialTextures;
pub use clip::{AnimationClip, AnimationTrack, Interpolation, JointAnimation, MorphAnimation};
pub(crate) mod motion;
#[cfg(feature = "window")]
pub(crate) use collect::{FADED, Instance3D, MAX_CASCADES, MAX_SHADOW_VIEWS, shadow_views};
pub(crate) use collect::{Frame3D, MAX_SHADOW_RESOLUTION, MIN_SHADOW_RESOLUTION, SHADOW_MAP_SIZE};
pub use compute::{Compute, ComputePass, GpuBuffer};
pub use effect::{Effect, ScreenEffect};
pub use mesh::{MeshData, MorphFrame, MorphTarget};
pub use post::{AmbientOcclusion, AntiAliasing, MAX_RENDER_SCALE, MIN_RENDER_SCALE, Post, Tonemap};
#[cfg(feature = "window")]
pub(crate) use post::{PostUniform, scaled_size};
pub use quality::{GraphicsQuality, QualityLevel};
#[cfg(feature = "window")]
pub(crate) use skin::blend as blend_skin;
pub use skin::{AttachToJoint, Joint, MorphWeights, Skeleton, SkinOf};
pub(crate) use skin::{MeshMorph, MeshSkin, SkinFrame};
#[cfg(all(test, feature = "window"))]
pub(crate) use skin::{SkinDraw, normalized as normalized_weights};
pub use sky::Sky;
pub(crate) use sky::SkyLight;
pub use target::TargetCamera;
pub use terrain::{Heightfield, TERRAIN_LAYERS, TERRAIN_LODS, TerrainMaterialDesc, TerrainTile, TerrainTileData};
pub use texture_array::{TextureArray, TextureKind};

use glam::{Mat3, Mat4, Quat, Vec2, Vec3, Vec4};

use crate::{Color, Texture};

/// Position, rotation and scale of a 3D entity.
///
/// ```
/// # use ponko::*;
/// let crate_box = Transform3D::at(vec3(0.0, 0.5, -3.0)).rotated(Quat::from_rotation_y(0.3));
/// # let _ = crate_box;
/// ```
#[derive(Debug, Clone, Copy, PartialEq, serde::Serialize, serde::Deserialize)]
#[serde(default)]
#[repr(C, align(16))] // shared with C/C++ (`CrabbyTransform3D`): 48 bytes everywhere
pub struct Transform3D {
    /// Which way it faces.
    pub rotation: Quat,
    /// Where it is, in world units.
    pub position: Vec3,
    /// Size along its own axes. Default `(1, 1, 1)`.
    pub scale: Vec3,
}

impl Default for Transform3D {
    fn default() -> Self {
        Self {
            position: Vec3::ZERO,
            rotation: Quat::IDENTITY,
            scale: Vec3::ONE,
        }
    }
}

impl Transform3D {
    /// At `position`, not rotated, scale 1.
    ///
    /// ```
    /// # use ponko::*;
    /// let t = Transform3D::at(vec3(1.0, 2.0, 3.0));
    /// assert_eq!(t.scale, Vec3::ONE);
    /// ```
    #[must_use]
    pub fn at(position: Vec3) -> Self {
        Self {
            position,
            ..Self::default()
        }
    }

    /// The same, rotated by `rotation`.
    ///
    /// ```
    /// # use ponko::*;
    /// let t = Transform3D::default().rotated(Quat::from_rotation_y(1.0));
    /// # let _ = t;
    /// ```
    #[must_use]
    pub fn rotated(self, rotation: Quat) -> Self {
        Self { rotation, ..self }
    }

    /// The same, scaled by `scale` on every axis.
    ///
    /// ```
    /// # use ponko::*;
    /// assert_eq!(Transform3D::default().scaled(2.0).scale, Vec3::splat(2.0));
    /// ```
    #[must_use]
    pub fn scaled(self, scale: f32) -> Self {
        Self {
            scale: Vec3::splat(scale),
            ..self
        }
    }

    /// The same, turned so its -Z axis points at `target` (with +Y as up).
    ///
    /// ```
    /// # use ponko::*;
    /// let t = Transform3D::at(vec3(0.0, 0.0, 5.0)).looking_at(Vec3::ZERO);
    /// assert!((t.forward() - vec3(0.0, 0.0, -1.0)).length() < 1e-5);
    /// ```
    #[must_use]
    pub fn looking_at(self, target: Vec3) -> Self {
        Self {
            rotation: look_rotation(target - self.position),
            ..self
        }
    }

    /// The direction it faces: its -Z axis.
    ///
    /// ```
    /// # use ponko::*;
    /// assert_eq!(Transform3D::default().forward(), vec3(0.0, 0.0, -1.0));
    /// ```
    #[must_use]
    pub fn forward(&self) -> Vec3 {
        self.rotation * Vec3::NEG_Z
    }

    /// The matrix from its local space to the world.
    ///
    /// ```
    /// # use ponko::*;
    /// let m = Transform3D::at(vec3(1.0, 0.0, 0.0)).matrix();
    /// assert_eq!(m.transform_point3(Vec3::ZERO), vec3(1.0, 0.0, 0.0));
    /// ```
    #[must_use]
    pub fn matrix(&self) -> Mat4 {
        Mat4::from_scale_rotation_translation(self.scale, self.rotation, self.position)
    }
}

/// The rotation that turns -Z towards `direction`, keeping +Y up (or +Z up
/// when looking straight up or down).
fn look_rotation(direction: Vec3) -> Quat {
    let forward = direction.try_normalize().unwrap_or(Vec3::NEG_Z);
    let up = if forward.y.abs() > 0.999 { Vec3::Z } else { Vec3::Y };
    let right = forward.cross(up).normalize();
    let up = right.cross(forward);
    Quat::from_mat3(&Mat3::from_cols(right, up, -forward))
}

/// A mesh on the GPU: triangles, split into parts that each have a
/// [`Material`]. Made with [`Ctx::create_mesh`](crate::Ctx::create_mesh) or
/// loaded with [`Ctx::load_mesh`](crate::Ctx::load_mesh); a cheap handle.
///
/// ```no_run
/// # use ponko::*;
/// # fn f(ctx: &mut Ctx) {
/// let tree: Mesh = ctx.load_mesh("tree.glb");
/// ctx.world.spawn((Transform3D::default(), Model::new(tree)));
/// # }
/// ```
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
#[repr(C)] // shared with C/C++ (`CrabbyMesh`)
pub struct Mesh {
    pub(crate) id: u32,
}

impl Mesh {
    /// No mesh: a [`Model`] showing it draws nothing and casts no shadow, at
    /// almost no cost. For models that are sometimes hidden, such as
    /// plants beyond their draw distance. Unlike a freed mesh, it never
    /// becomes another mesh, since no mesh is ever made with its id.
    ///
    /// ```
    /// # use ponko::*;
    /// Game::new("t", 1, 1).run_headless(0, |ctx| {
    ///     let material = ctx.default_material();
    ///     let bush = ctx.create_mesh(&MeshData::cube(1.0), material);
    ///     ctx.world.spawn((Transform3D::default(), Model::new(Mesh::NONE)));
    ///     assert!(!ctx.is_mesh_live(Mesh::NONE));
    ///     assert_ne!(bush, Mesh::NONE);
    /// });
    /// ```
    pub const NONE: Mesh = Mesh { id: u32::MAX };
}

/// What one mesh cost to draw in the last frame, from
/// [`Ctx::mesh_costs`](crate::Ctx::mesh_costs).
#[derive(Debug, Clone, PartialEq)]
pub struct MeshCost {
    /// The mesh.
    pub mesh: Mesh,
    /// The file it was loaded from, if it came from one (glTF meshes are
    /// `file.glb#index`-style paths as they were loaded).
    pub name: Option<String>,
    /// Models the camera drew with it.
    pub models: usize,
    /// Triangles the camera's passes drew with it.
    pub triangles: usize,
    /// Models drawn with it into the shadow maps, all cascades together.
    pub shadow_models: usize,
    /// Triangles drawn with it into the shadow maps, all cascades together.
    pub shadow_triangles: usize,
}

/// How a surface looks: its color (and texture), how rough and how metallic
/// it is, and light it gives off. Made with
/// [`Ctx::create_material`](crate::Ctx::create_material); a cheap handle.
///
/// ```no_run
/// # use ponko::*;
/// # fn f(ctx: &mut Ctx) {
/// let gold = ctx.create_material(MaterialDesc { metallic: 1.0, roughness: 0.3, ..MaterialDesc::color(Color::hex(0xFFC83D)) });
/// # }
/// ```
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
#[repr(C)] // shared with C/C++ (`CrabbyMaterial`)
pub struct Material {
    pub(crate) id: u32,
}

/// A material shader written in WGSL: made with
/// [`Ctx::load_shader`](crate::Ctx::load_shader) or
/// [`Ctx::create_shader`](crate::Ctx::create_shader); a cheap handle. See
/// the 3D chapter of the guide for what a shader can do.
///
/// ```no_run
/// # use ponko::*;
/// # fn f(ctx: &mut Ctx) {
/// let water = ctx.load_shader("shaders/water.wgsl");
/// let lake = ctx.create_material(MaterialDesc { shader: Some(water), ..Default::default() });
/// # }
/// ```
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
#[repr(C)] // shared with C/C++ (`CrabbyShader`)
pub struct Shader {
    pub(crate) id: u32,
}

impl Shader {
    /// The engine's id of this shader (for the C API).
    #[doc(hidden)]
    #[must_use]
    pub fn id(self) -> u32 {
        self.id
    }

    /// A shader handle from an id (for the C API; check it with `Ctx::has_shader`).
    #[doc(hidden)]
    #[must_use]
    pub fn from_id(id: u32) -> Self {
        Self { id }
    }
}

/// How a material covers what's behind it.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
#[repr(u32)]
pub enum Blend {
    /// Solid, whatever its alpha. The fastest: hidden pixels and shadows
    /// skip the material's shader.
    #[default]
    Opaque = 0,
    /// See-through by its alpha (glass, water). Drawn after everything
    /// solid, casts no shadow; overlapping transparent models are not
    /// sorted, so one may show over another that is in front of it.
    Transparent = 1,
    /// Solid, with pixels whose alpha is below 0.5 cut out (leaves,
    /// fences, grass cards). Their shadows have the same holes.
    Cutout = 2,
}

/// What a [`Material`] is made from.
///
/// ```
/// # use ponko::*;
/// let grass = MaterialDesc { roughness: 0.9, ..MaterialDesc::color(Color::hex(0x4C8A3A)) };
/// assert_eq!(grass.metallic, 0.0);
/// ```
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct MaterialDesc {
    /// Base color, multiplied with the texture. Default white.
    pub color: Color,
    /// An image on the surface (by the mesh's texture coordinates).
    pub texture: Option<Texture>,
    /// 0 is mirror-smooth, 1 is fully rough (matte). Default 0.6.
    pub roughness: f32,
    /// 0 for most things, 1 for bare metal. Default 0.
    pub metallic: f32,
    /// Light it gives off itself (not lighting anything else). Default black.
    pub emissive: Color,
    /// A normal map: surface detail (bumps, grooves) as tangent-space
    /// normals, OpenGL style (green up), as glTF has them.
    pub normal_map: Option<Texture>,
    /// How strong the normal map is. Default 1.
    pub normal_strength: f32,
    /// An occlusion-roughness-metallic map, as glTF has it: red is ambient
    /// occlusion, green multiplies `roughness`, blue multiplies `metallic`.
    pub orm_map: Option<Texture>,
    /// Multiplies `emissive` (which must not be black for it to show).
    pub emissive_map: Option<Texture>,
    /// How it covers what's behind it. Default [`Blend::Opaque`].
    pub blend: Blend,
    /// Draws the back of each triangle too (leaves, cloth, planes seen from
    /// below). Default false.
    pub double_sided: bool,
    /// A custom shader; `None` is the built-in one.
    pub shader: Option<Shader>,
    /// Values for a custom shader: `material.custom[0]` to `[3]` there.
    pub custom: [Vec4; 4],
    /// Textures for a custom shader: `custom_texture0` and
    /// `custom_texture1` there.
    pub custom_textures: [Option<Texture>; 2],
    /// Texture arrays for a custom shader: `custom_array0` to
    /// `custom_array2` there (`texture_2d_array<f32>`), each read as its
    /// [`TextureKind`] says.
    pub custom_arrays: [Option<TextureArray>; 3],
}

impl Default for MaterialDesc {
    fn default() -> Self {
        Self {
            color: Color::WHITE,
            texture: None,
            roughness: 0.6,
            metallic: 0.0,
            emissive: Color::rgb(0.0, 0.0, 0.0),
            normal_map: None,
            normal_strength: 1.0,
            orm_map: None,
            emissive_map: None,
            blend: Blend::Opaque,
            double_sided: false,
            shader: None,
            custom: [Vec4::ZERO; 4],
            custom_textures: [None; 2],
            custom_arrays: [None; 3],
        }
    }
}

impl MaterialDesc {
    /// A plain material of one color.
    ///
    /// ```
    /// # use ponko::*;
    /// let red = MaterialDesc::color(Color::rgb(0.8, 0.1, 0.1));
    /// # let _ = red;
    /// ```
    #[must_use]
    pub fn color(color: Color) -> Self {
        Self {
            color,
            ..Self::default()
        }
    }
}

/// Draws a [`Mesh`] where the entity's [`Transform3D`] is.
///
/// ```no_run
/// # use ponko::*;
/// # fn f(ctx: &mut Ctx) {
/// let white = ctx.default_material();
/// let cube = ctx.create_mesh(&MeshData::cube(1.0), white);
/// for i in 0..10 {
///     let tint = Color::rgb(i as f32 / 10.0, 0.5, 1.0);
///     ctx.world.spawn((Transform3D::at(vec3(i as f32 * 2.0, 0.0, 0.0)), Model::new(cube).with_color(tint)));
/// }
/// # }
/// ```
#[derive(Debug, Clone, Copy, PartialEq)]
#[repr(C)] // shared with C/C++ (`CrabbyModel`)
pub struct Model {
    /// What to draw.
    pub mesh: Mesh,
    /// Multiplied with the materials' colors, so one mesh can come in many
    /// colors without more materials. Default white (no change).
    pub color: Color,
}

/// Draws a different mesh into the shadow maps than the entity's [`Model`]
/// shows: a cheap stand-in for a detailed model's shadow (a simplified copy,
/// a billboard), or `None` for no shadow from this entity. Without it, the
/// model's own mesh casts the shadow (unless
/// [`Ctx::set_mesh_shadows`](crate::Ctx::set_mesh_shadows) turned that
/// mesh's shadows off).
///
/// Far from the camera, a shadow is a few texels of the shadow map, so a
/// mesh with a tenth of the triangles casts the same shadow for a tenth of
/// the cost. Swap it by distance, as you would the model's own detail.
///
/// An entity with a `ShadowMesh` and no [`Model`] casts only the shadow: a
/// stand-in for the shadow of several models around it that cast none. On
/// a [`TerrainTile`], `ShadowMesh(None)` turns the ground's shadow off.
///
/// In scene files it's `"ShadowMesh": { "mesh": "tree_shadow.glb" }`, or
/// `{ "mesh": null }` for no shadow.
///
/// ```no_run
/// # use ponko::*;
/// # fn f(ctx: &mut Ctx) {
/// let tree = ctx.load_mesh("tree.glb");
/// let blob = ctx.load_mesh("tree_shadow.glb"); // a few dozen triangles
/// ctx.world.spawn((Transform3D::default(), Model::new(tree), ShadowMesh(Some(blob))));
/// # }
/// ```
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct ShadowMesh(pub Option<Mesh>);

impl Model {
    /// Draws `mesh` as it is.
    ///
    /// ```no_run
    /// # use ponko::*;
    /// # fn f(ctx: &mut Ctx) {
    /// let rock = ctx.load_mesh("rock.glb");
    /// ctx.world.spawn((Transform3D::default(), Model::new(rock)));
    /// # }
    /// ```
    #[must_use]
    pub fn new(mesh: Mesh) -> Self {
        Self {
            mesh,
            color: Color::WHITE,
        }
    }

    /// The same, tinted with `color`.
    ///
    /// ```no_run
    /// # use ponko::*;
    /// # fn f(ctx: &mut Ctx, cube: Mesh) {
    /// let red_cube = Model::new(cube).with_color(Color::rgb(1.0, 0.2, 0.2));
    /// # }
    /// ```
    #[must_use]
    pub fn with_color(self, color: Color) -> Self {
        Self { color, ..self }
    }
}

/// The 3D camera: where it is, which way it looks, and how wide it sees.
/// One per game, at [`Ctx::camera3d`](crate::Ctx::camera3d).
///
/// ```no_run
/// # use ponko::*;
/// # fn f(ctx: &mut Ctx) {
/// ctx.camera3d.position = vec3(0.0, 4.0, 10.0);
/// ctx.camera3d.look_at(Vec3::ZERO);
/// # }
/// ```
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Camera3D {
    /// Where the camera is.
    pub position: Vec3,
    /// Which way it looks: it sees along its -Z axis.
    pub rotation: Quat,
    /// How tall the view is, as an angle in radians. Default 60°.
    pub fov_y: f32,
    /// Nothing closer than this is drawn. Default 0.1.
    pub near: f32,
    /// Nothing farther than this is drawn. Default 1000.
    pub far: f32,
    /// Skip models hidden behind what was drawn a frame or two before.
    /// Default off.
    ///
    /// The renderer keeps the farthest depth of small screen tiles and reads
    /// it back without waiting for the GPU; a model whose bounds lie behind
    /// it everywhere they cover isn't drawn (it still casts shadows). A model
    /// that comes out from behind something can show up a frame or two late,
    /// mostly when the camera moves fast. Needs compute shaders: on WebGL2
    /// nothing is culled.
    pub occlusion_culling: bool,
    /// Window size in pixels, kept up to date by the engine.
    viewport: Vec2,
}

impl Camera3D {
    pub(crate) fn new(viewport: Vec2) -> Self {
        Self {
            position: Vec3::new(0.0, 2.0, 8.0),
            rotation: look_rotation(Vec3::new(0.0, -2.0, -8.0)),
            fov_y: 60f32.to_radians(),
            near: 0.1,
            far: 1000.0,
            occlusion_culling: false,
            viewport,
        }
    }

    pub(crate) fn set_viewport(&mut self, viewport: Vec2) {
        self.viewport = viewport;
    }

    /// Turns the camera to look at `target`, keeping +Y up.
    ///
    /// ```no_run
    /// # use ponko::*;
    /// # fn f(ctx: &mut Ctx, player: Vec3) {
    /// ctx.camera3d.position = player + vec3(0.0, 6.0, 8.0);
    /// ctx.camera3d.look_at(player);
    /// # }
    /// ```
    pub fn look_at(&mut self, target: Vec3) {
        self.rotation = look_rotation(target - self.position);
    }

    /// The direction the camera looks.
    ///
    /// ```no_run
    /// # use ponko::*;
    /// # fn f(ctx: &mut Ctx) {
    /// let ahead = ctx.camera3d.position + ctx.camera3d.forward() * 5.0;
    /// # }
    /// ```
    #[must_use]
    pub fn forward(&self) -> Vec3 {
        self.rotation * Vec3::NEG_Z
    }

    /// World to clip space: projection times view.
    #[must_use]
    pub(crate) fn view_proj(&self) -> Mat4 {
        let aspect = (self.viewport.x / self.viewport.y.max(1.0)).max(1e-3);
        let projection = glam::camera::rh::proj::directx::perspective(self.fov_y, aspect, self.near, self.far);
        projection * self.view()
    }

    /// World to the camera's own space.
    pub(crate) fn view(&self) -> Mat4 {
        Mat4::from_rotation_translation(self.rotation, self.position).inverse()
    }

    /// The ray from the camera through window point `screen` (logical
    /// pixels, as [`Ctx::mouse_pos`](crate::Ctx::mouse_pos)): its start and
    /// unit direction. For picking things in the world with the mouse.
    ///
    /// ```no_run
    /// # use ponko::*;
    /// # fn f(ctx: &mut Ctx) {
    /// let (from, dir) = ctx.camera3d.screen_ray(ctx.mouse_pos());
    /// // Where the mouse points on the ground (y = 0):
    /// if dir.y < 0.0 {
    ///     let ground = from + dir * (-from.y / dir.y);
    /// }
    /// # }
    /// ```
    #[must_use]
    pub fn screen_ray(&self, screen: Vec2) -> (Vec3, Vec3) {
        let ndc = Vec2::new(
            screen.x / self.viewport.x.max(1.0) * 2.0 - 1.0,
            1.0 - screen.y / self.viewport.y.max(1.0) * 2.0,
        );
        let inverse = self.view_proj().inverse();
        let far = inverse * Vec4::new(ndc.x, ndc.y, 1.0, 1.0);
        let far = far.truncate() / far.w;
        (self.position, (far - self.position).normalize_or(self.forward()))
    }
}

/// The light in the 3D world: a sun far away (one direction everywhere)
/// and ambient light from all around. At [`Ctx::lighting`](crate::Ctx::lighting).
///
/// ```no_run
/// # use ponko::*;
/// # fn f(ctx: &mut Ctx) {
/// // Evening: low, orange sun.
/// ctx.lighting.sun_direction = vec3(-1.0, -0.3, -0.2);
/// ctx.lighting.sun_color = Color::hex(0xFFB066);
/// # }
/// ```
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Lighting {
    /// The way the sunlight travels (from the sun towards the ground).
    pub sun_direction: Vec3,
    /// The sun's color.
    pub sun_color: Color,
    /// How bright the sun is. Default 3.
    pub sun_intensity: f32,
    /// Light from the sky, on surfaces facing up. Used when
    /// [`Sky::atmosphere`] is off; with it, the sky's own light is used.
    pub sky_color: Color,
    /// Light bounced off the ground, on surfaces facing down. Like
    /// `sky_color`, only without an atmosphere.
    pub ground_color: Color,
    /// Light from the horizon, on surfaces facing sideways: with it, the
    /// ambient light goes from `ground_color` below through this to
    /// `sky_color` above (a three-color gradient); without it (`None`, the
    /// default), straight from ground to sky. Only without an atmosphere.
    pub equator_color: Option<Color>,
    /// How bright the sky and ground light is: 1 is as bright as the sky
    /// makes it. Default 1.
    pub ambient_intensity: f32,
    /// Whether the sun casts shadows, and point and spot lights with
    /// `shadows` set too (off turns every shadow off). Default on.
    pub shadows: bool,
    /// How far from the camera shadows reach, in world units. Default 60.
    pub shadow_distance: f32,
    /// How many shadow maps (cascades) share that distance, 1 to 4: each
    /// covers a stretch further out than the one before, so shadows stay
    /// sharp near the camera however far they reach. Fewer are cheaper.
    /// Default 4.
    pub shadow_cascades: u32,
    /// Width and height of each of the sun's shadow maps, in texels:
    /// 256 to 4096 (and no more than the GPU allows). Doubling it quadruples
    /// the memory (`4 * resolution² * cascades` bytes) and sharpens shadows.
    /// Changing it at run time makes new shadow maps. Default 2048.
    pub shadow_resolution: u32,
    /// How often the far cascades (the farther half of them) are drawn
    /// again, in frames, 1 to 8. At 1 every cascade is drawn every frame. Above
    /// 1 the far ones take turns: each is drawn into a box a little bigger
    /// than it needs and kept for up to this many frames, or until the
    /// camera leaves its box or the sun moves. Far shadows of moving things
    /// then lag by up to that many frames. Default 2: half the far
    /// cascades' drawing.
    pub shadow_refresh: u32,
    /// How soft the sun's shadow edges are, 1 to 3: how many lookups each
    /// lit pixel takes in the shadow map. 1 is one smooth lookup (2x2
    /// texels), the cheapest; 2 is four (3x3 texels); 3 is nine (4x4
    /// texels), the softest. Default 3. Each step costs about as much as the
    /// lookups it adds, on every lit pixel.
    pub shadow_filter: u32,
    /// How many shadow views point and spot lights may share, 0 to
    /// [`MAX_LIGHT_SHADOW_VIEWS`]: a shadowed spot light takes one, a
    /// shadowed point light six. 0 turns point and spot light shadows off.
    /// Default 12.
    pub light_shadow_views: u32,
    /// Width and height of the largest point or spot light shadow view, in
    /// texels: 128 to 2048, rounded down to a power of two. A light whose
    /// reach fills the view gets this; one twice as far away half of it,
    /// down to 64 (see [`PointLight3D::shadow_resolution`] to pick a
    /// light's own). Default [`LIGHT_SHADOW_SIZE`].
    pub light_shadow_resolution: u32,
    /// Width and height of the depth atlas all point and spot light shadow
    /// views are packed into, in texels: 1024 to 8192, rounded down to a
    /// power of two (and no more than the GPU allows). It takes
    /// `4 * light_shadow_atlas²` bytes once a light casts shadows; when
    /// the views don't fit, the largest shrink. Changing it at run time
    /// makes a new atlas. Default [`LIGHT_SHADOW_ATLAS_SIZE`].
    pub light_shadow_atlas: u32,
    /// Light bounced off the world's surfaces (global illumination). Off
    /// by default; see [`GlobalIllumination`].
    pub gi: GlobalIllumination,
}

impl Default for Lighting {
    fn default() -> Self {
        Self {
            sun_direction: Vec3::new(-0.4, -1.0, -0.3),
            sun_color: Color::hex(0xFFF4E0),
            sun_intensity: 3.0,
            sky_color: Color::hex(0x869BB0),
            ground_color: Color::hex(0x4D4135),
            equator_color: None,
            ambient_intensity: 1.0,
            shadows: true,
            shadow_distance: 60.0,
            shadow_cascades: 4,
            shadow_resolution: SHADOW_MAP_SIZE,
            shadow_refresh: 2,
            shadow_filter: 3,
            light_shadow_views: 12,
            light_shadow_resolution: LIGHT_SHADOW_SIZE,
            light_shadow_atlas: LIGHT_SHADOW_ATLAS_SIZE,
            gi: GlobalIllumination::default(),
        }
    }
}

impl Lighting {
    /// The sun's shadow map size, clamped to what the GPU can make (`limit`
    /// 0: no limit known).
    pub(crate) fn shadow_size(&self, limit: u32) -> u32 {
        let limit = if limit == 0 { u32::MAX } else { limit };
        self.shadow_resolution
            .clamp(MIN_SHADOW_RESOLUTION, MAX_SHADOW_RESOLUTION)
            .min(limit)
    }
    /// The point and spot lights' shadow view size, clamped likewise.
    pub(crate) fn light_shadow_size(&self, limit: u32) -> u32 {
        let limit = if limit == 0 { u32::MAX } else { limit };
        self.light_shadow_resolution
            .clamp(MIN_LIGHT_SHADOW_RESOLUTION, MAX_LIGHT_SHADOW_RESOLUTION)
            .min(limit)
    }
    /// The lights' shadow atlas size, clamped likewise.
    pub(crate) fn light_shadow_atlas_size(&self, limit: u32) -> u32 {
        let limit = if limit == 0 { u32::MAX } else { limit };
        let size = self
            .light_shadow_atlas
            .clamp(MIN_LIGHT_SHADOW_ATLAS, MAX_LIGHT_SHADOW_ATLAS)
            .min(limit);
        shadow_atlas::floor_pow2(size)
    }
    /// How many light shadow views are allowed this frame.
    pub(crate) fn light_shadow_budget(&self) -> usize {
        (self.light_shadow_views as usize).min(MAX_LIGHT_SHADOW_VIEWS)
    }
}

/// This frame's 3D scene, as the renderer gets it.
pub(crate) struct Scene3D<'a> {
    pub frame: &'a Frame3D,
    pub lighting: &'a Lighting,
    pub sky: &'a Sky,
    /// The sun and ambient light (from the sky, with an atmosphere).
    pub light: SkyLight,
    pub camera: Vec3,
    pub post: &'a Post,
    /// Seconds since the game started, and since the last frame.
    pub time: (f32, f32),
    /// Whether to make the depth grid occlusion culling reads.
    pub occlusion: bool,
}

/// What the engine keeps about each mesh and material on the CPU side: for
/// culling, and for headless runs, which have no GPU.
#[derive(Default)]
pub(crate) struct Assets3D {
    pub morph_entities: Vec<crate::Entity>,
    pub morph_bases: std::collections::HashMap<crate::Entity, (u32, MorphWeights, MorphWeights)>,
    /// Bounding sphere of each mesh, in its own space: center and radius.
    pub bounds: Vec<(Vec3, f32)>,
    /// Freed meshes' ids, for the next meshes made.
    pub free_meshes: Vec<u32>,
    pub probes: probe::ProbeAssets,
    /// How each skinned mesh binds to joints, by mesh id; shorter than
    /// `bounds` when the last ones aren't skinned.
    pub skins: Vec<Option<std::sync::Arc<MeshSkin>>>,
    /// Each mesh's morph targets, by mesh id; shorter than `bounds` when
    /// the last ones have none.
    pub morphs: Vec<Option<std::sync::Arc<MeshMorph>>>,
    /// Shared animation clips of skinned glTF files, by resolved path.
    pub loaded_clips: std::collections::HashMap<std::path::PathBuf, Vec<AnimationClip>>,
    /// The joints of skinned glTF files, by resolved path.
    pub loaded_skeletons: std::collections::HashMap<std::path::PathBuf, Skeleton>,
    /// Meshes set to cast no shadow (`Ctx::set_mesh_shadows`), by id;
    /// shorter than `bounds` when the last ones cast.
    pub shadowless: Vec<bool>,
    pub materials: u32,
    /// Texture arrays made so far, by id.
    pub arrays: Vec<TextureArray>,
    /// Whether each was made as `TextureKind::Data`, by id.
    pub array_data: Vec<bool>,
    /// The texture array decals take their images from.
    pub decal_array: Option<TextureArray>,
    /// Whether the renderer can draw projected decals (its GPU has a spare
    /// texture slot); set each frame.
    pub decals_supported: bool,
    /// Whether the renderer can draw global illumination (compute shaders
    /// and a texture slot for the probes); set each frame.
    pub gi_supported: bool,
    /// Render targets made so far.
    pub render_targets: Vec<crate::Texture>,
    /// Screen effects made so far.
    pub effects: u32,
    /// Compute passes made so far, and those loaded from files.
    pub computes: u32,
    /// GPU buffers' lengths, by id; 0 for a freed one.
    pub gpu_buffers: Vec<u32>,
    pub instance_batches: Vec<Option<instances::Batch>>,
    /// Freed GPU buffers' ids, for the next buffers made.
    pub free_gpu_buffers: Vec<u32>,
    /// Buffer-driven meshes' own bounds (before `set_mesh_gpu_bounds`
    /// grew them), by mesh id.
    pub gpu_mesh_bounds: std::collections::HashMap<u32, (Vec3, f32)>,
    pub loaded_computes: std::collections::HashMap<std::path::PathBuf, Compute>,
    /// Effects loaded from files, by resolved path.
    pub loaded_effects: std::collections::HashMap<std::path::PathBuf, Effect>,
    /// The built-in terrain shader, once a terrain material needs it.
    pub terrain_shader: Option<Shader>,
    /// Shaders made so far (the built-in one is not counted).
    pub shaders: u32,
    /// Shaders loaded from files, by resolved path.
    pub loaded_shaders: std::collections::HashMap<std::path::PathBuf, Shader>,
    /// The material handed out for meshes without one.
    pub default_material: Option<Material>,
    /// Meshes loaded from files, by resolved path.
    pub loaded: std::collections::HashMap<std::path::PathBuf, Mesh>,
    /// Material handles survive geometry eviction; reloading must preserve
    /// user shader edits and must not allocate another material/texture set.
    pub file_materials: std::collections::HashMap<std::path::PathBuf, Vec<Material>>,
    /// Images that glTF files take from files of their own, by asset name
    /// (see `gltf::Loaded::image_sources`): many models share them.
    pub shared_images: std::collections::HashMap<String, crate::Texture>,
    /// Materials loaded from glTF files, by their name in the file, with
    /// what they were made from (`Ctx::loaded_materials`).
    pub loaded_materials: std::collections::HashMap<String, Vec<(Material, MaterialDesc)>>,
}

impl Assets3D {
    /// Mesh `id`'s bounds, unless there's no such mesh or it was freed.
    pub(crate) fn live_bounds(&self, id: u32) -> Option<(Vec3, f32)> {
        self.bounds.get(id as usize).copied().filter(|&(_, r)| r >= 0.0)
    }

    /// How mesh `id` binds to joints, if it's skinned.
    pub(crate) fn skin(&self, id: u32) -> Option<&MeshSkin> {
        self.skins.get(id as usize)?.as_deref()
    }

    /// Mesh `id`'s morph targets, if it has any.
    pub(crate) fn morph(&self, id: u32) -> Option<&MeshMorph> {
        self.morphs.get(id as usize)?.as_deref()
    }

    /// Whether mesh `id` casts shadows (the default).
    pub(crate) fn casts_shadows(&self, id: u32) -> bool {
        !self.shadowless.get(id as usize).copied().unwrap_or(false)
    }
}

/// sRGB color to linear RGBA, for the GPU.
pub(crate) fn linear(c: Color) -> [f32; 4] {
    // Most tints are white: skip the three `powf`s (this runs per instance).
    if c.r == 1.0 && c.g == 1.0 && c.b == 1.0 {
        return [1.0, 1.0, 1.0, c.a];
    }
    let lin = |v: f32| {
        if v <= 0.04045 {
            v / 12.92
        } else {
            ((v + 0.055) / 1.055).powf(2.4)
        }
    };
    [lin(c.r), lin(c.g), lin(c.b), c.a]
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn looking_at_points_minus_z_at_the_target() {
        for target in [Vec3::X, Vec3::NEG_X, Vec3::new(1.0, 2.0, -3.0), Vec3::Y, Vec3::NEG_Y] {
            let t = Transform3D::default().looking_at(target);
            assert!((t.forward() - target.normalize()).length() < 1e-5, "{target}");
        }
    }

    #[test]
    fn the_screen_center_ray_goes_where_the_camera_looks() {
        let mut camera = Camera3D::new(Vec2::new(800.0, 600.0));
        camera.position = Vec3::new(3.0, 4.0, 5.0);
        camera.look_at(Vec3::ZERO);
        let (from, dir) = camera.screen_ray(Vec2::new(400.0, 300.0));
        assert_eq!(from, camera.position);
        assert!((dir - camera.forward()).length() < 1e-4);
        // Left of center points left of forward.
        let (_, left) = camera.screen_ray(Vec2::new(0.0, 300.0));
        let right_axis = camera.rotation * Vec3::X;
        assert!(left.dot(right_axis) < 0.0);
    }

    #[test]
    fn the_view_projection_puts_the_target_in_the_middle() {
        let mut camera = Camera3D::new(Vec2::new(800.0, 600.0));
        camera.position = Vec3::new(0.0, 10.0, 10.0);
        camera.look_at(Vec3::new(1.0, 0.0, 0.0));
        let clip = camera.view_proj() * Vec4::new(1.0, 0.0, 0.0, 1.0);
        let ndc = clip.truncate() / clip.w;
        assert!(
            ndc.x.abs() < 1e-4 && ndc.y.abs() < 1e-4 && (0.0..1.0).contains(&ndc.z),
            "{ndc}"
        );
    }
}