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examples/gkurve: explain frag_bary coordinates intent

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Signed-off-by: Stephen Gutekanst <stephen@hexops.com>
This commit is contained in:
Stephen Gutekanst 2022-05-21 11:05:16 -07:00
parent eae2a090c6
commit 2b718c6de1
1 changed files with 15 additions and 3 deletions
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18
examples/gkurve/vert.wgsl
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@ -6,7 +6,7 @@ struct VertexUniform {
struct VertexOut { struct VertexOut {
@builtin(position) position_clip: vec4<f32>, @builtin(position) position_clip: vec4<f32>,
@location(0) frag_uv: vec2<f32>, @location(0) frag_uv: vec2<f32>,
@interpolate(linear) @location(1) frag_bary: vec3<f32>, @interpolate(linear) @location(1) frag_bary: vec2<f32>,
@interpolate(flat) @location(2) triangle_index: u32, @interpolate(flat) @location(2) triangle_index: u32,
} }
@ -18,10 +18,22 @@ struct VertexOut {
var output : VertexOut; var output : VertexOut;
output.position_clip = ubo.matrix * position; output.position_clip = ubo.matrix * position;
output.frag_uv = uv; output.frag_uv = uv;
output.frag_bary = vec3<f32>(
// Generates [0, 0], [0.5, 0.0], [1.0, 1.0]
//
// Equal to:
//
// if ((vertex_index+1u) % 3u == 0u) {
// output.frag_bary = vec2<f32>(0.0, 0.0);
// } else if ((vertex_index+1u) % 3u == 1u) {
// output.frag_bary = vec2<f32>(0.5, 0.0);
// } else {
// output.frag_bary = vec2<f32>(1.0, 1.0);
// }
//
output.frag_bary = vec2<f32>(
f32(((vertex_index+2u) % 3u * 2u) % 3u), f32(((vertex_index+2u) % 3u * 2u) % 3u),
f32(((vertex_index+2u) % 3u * 2u) & 2u) * 2.0, f32(((vertex_index+2u) % 3u * 2u) & 2u) * 2.0,
0.0,
); );
output.triangle_index = vertex_index / 3u; output.triangle_index = vertex_index / 3u;
return output; return output;