From 2b718c6de12226c2664e72010ed364795d8efac6 Mon Sep 17 00:00:00 2001
From: Stephen Gutekanst <stephen@hexops.com>
Date: Sat, 21 May 2022 11:05:16 -0700
Subject: [PATCH] examples/gkurve: explain frag_bary coordinates intent

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>
---
 examples/gkurve/vert.wgsl | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/examples/gkurve/vert.wgsl b/examples/gkurve/vert.wgsl
index 87439458..18d9fe0e 100644
--- a/examples/gkurve/vert.wgsl
+++ b/examples/gkurve/vert.wgsl
@@ -6,7 +6,7 @@ struct VertexUniform {
 struct VertexOut {
     @builtin(position) position_clip: vec4<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,
 }
 
@@ -18,10 +18,22 @@ struct VertexOut {
     var output : VertexOut;
     output.position_clip = ubo.matrix * position;
     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) & 2u) * 2.0,
-        0.0,
     );
     output.triangle_index = vertex_index / 3u;
     return output;