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struct Uniforms {
transform: mat4x4<f32>,
//xy = start, wz = end
position: vec4<f32>,
//x = start stop, y = end stop, zw = padding
stop_range: vec4<i32>,
}
struct Stop {
color: vec4<f32>,
offset: f32,
};
@group(0) @binding(0)
var<uniform> uniforms: Uniforms;
@group(0) @binding(1)
var<storage, read> color_stops: array<Stop>;
struct VertexOutput {
@builtin(position) position: vec4<f32>,
@location(0) raw_position: vec2<f32>
}
@vertex
fn vs_main(@location(0) input: vec2<f32>) -> VertexOutput {
var output: VertexOutput;
output.position = uniforms.transform * vec4<f32>(input.xy, 0.0, 1.0);
output.raw_position = input;
return output;
}
//TODO: rewrite without branching
@fragment
fn fs_main(input: VertexOutput) -> @location(0) vec4<f32> {
let start = uniforms.position.xy;
let end = uniforms.position.zw;
let start_stop = uniforms.stop_range.x;
let end_stop = uniforms.stop_range.y;
let v1 = end - start;
let v2 = input.raw_position.xy - start;
let unit = normalize(v1);
let offset = dot(unit, v2) / length(v1);
let min_stop = color_stops[start_stop];
let max_stop = color_stops[end_stop];
var color: vec4<f32>;
if (offset <= min_stop.offset) {
color = min_stop.color;
} else if (offset >= max_stop.offset) {
color = max_stop.color;
} else {
var min = min_stop;
var max = max_stop;
var min_index = start_stop;
var max_index = end_stop;
loop {
if (min_index >= max_index - 1) {
break;
}
let index = min_index + (max_index - min_index) / 2;
let stop = color_stops[index];
if (offset <= stop.offset) {
max = stop;
max_index = index;
} else {
min = stop;
min_index = index;
}
}
color = mix(min.color, max.color, smoothstep(
min.offset,
max.offset,
offset
));
}
return color;
}
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