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struct Camera {
scale: vec2f,
centre: vec2f,
};
struct Particle {
position: vec2f,
data: u32,
life: f32,
};
@group(0) @binding(0) var<uniform> camera: Camera;
@group(0) @binding(1) var<storage, read> palette: array<vec4f>;
@group(0) @binding(2) var<storage, read> particles: array<Particle>;
struct VertexOutput {
@builtin(position) clip_position: vec4f,
@location(0) world: vec2f,
@location(1) @interpolate(flat) instance: u32,
@location(2) @interpolate(flat) material: u32,
@location(3) @interpolate(flat) life: f32,
};
@vertex
fn vs_main(
@builtin(vertex_index) i: u32,
@builtin(instance_index) n: u32,
) -> VertexOutput {
let particle = particles[n];
// (0,0),(1,0),(0,1),(1,1)
let corner = vec2f(f32(i & 1u), f32((i >> 1u) & 1u));
let world = particle.position + corner;
var out: VertexOutput;
out.clip_position = vec4f((world - camera.centre) * camera.scale, 0.0, 1.0);
out.world = world;
out.instance = n;
out.material = particle.data & 0xFF;
out.life = particle.life;
return out;
}
@fragment
fn fs_main(in: VertexOutput) -> @location(0) vec4f {
let particle = particles[in.instance];
// TODO can pack more in here and shift
let c = palette[in.material];
// if life is less than 1, smoothly reduce alpha to 0
return vec4f(c.r, c.g, c.b, c.a * smoothstep(0.0, 1, in.life));
}
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