From 3f467d121229142177ef1b2f417fe87c7bf7fdf2 Mon Sep 17 00:00:00 2001
From: Jim Eckerlein <jim.eckerlein@icloud.com>
Date: Sun, 24 Sep 2023 15:10:19 +0200
Subject: Compute vertex position in shader

---
 wgpu/src/shader/quad.wgsl          | 8 ++++++++
 wgpu/src/shader/quad/gradient.wgsl | 4 ++--
 wgpu/src/shader/quad/solid.wgsl    | 4 ++--
 3 files changed, 12 insertions(+), 4 deletions(-)

(limited to 'wgpu/src/shader')

diff --git a/wgpu/src/shader/quad.wgsl b/wgpu/src/shader/quad.wgsl
index f919cfe2..555e81bb 100644
--- a/wgpu/src/shader/quad.wgsl
+++ b/wgpu/src/shader/quad.wgsl
@@ -37,3 +37,11 @@ fn select_border_radius(radi: vec4<f32>, position: vec2<f32>, center: vec2<f32>)
     rx = select(rx, ry, position.y > center.y);
     return rx;
 }
+
+// Compute the normalized quad coordinates based on the vertex index.
+fn vertex_position(vertex_index: u32) -> vec2<f32> {
+    // #: 0 1 2 3 4 5
+    // x: 1 1 0 0 0 1
+    // y: 1 0 0 0 1 1
+    return vec2<f32>((vec2(1u, 2u) + vertex_index) % 6u < 3u);
+}
diff --git a/wgpu/src/shader/quad/gradient.wgsl b/wgpu/src/shader/quad/gradient.wgsl
index 0754e97f..36cae61c 100644
--- a/wgpu/src/shader/quad/gradient.wgsl
+++ b/wgpu/src/shader/quad/gradient.wgsl
@@ -1,5 +1,5 @@
 struct GradientVertexInput {
-    @location(0) v_pos: vec2<f32>,
+    @builtin(vertex_index) vertex_index: u32,
     @location(1) @interpolate(flat) colors_1: vec4<u32>,
     @location(2) @interpolate(flat) colors_2: vec4<u32>,
     @location(3) @interpolate(flat) colors_3: vec4<u32>,
@@ -48,7 +48,7 @@ fn gradient_vs_main(input: GradientVertexInput) -> GradientVertexOutput {
         vec4<f32>(pos - vec2<f32>(0.5, 0.5), 0.0, 1.0)
     );
 
-    out.position = globals.transform * transform * vec4<f32>(input.v_pos, 0.0, 1.0);
+    out.position = globals.transform * transform * vec4<f32>(vertex_position(input.vertex_index), 0.0, 1.0);
     out.colors_1 = input.colors_1;
     out.colors_2 = input.colors_2;
     out.colors_3 = input.colors_3;
diff --git a/wgpu/src/shader/quad/solid.wgsl b/wgpu/src/shader/quad/solid.wgsl
index ebd6d877..5fc5b13a 100644
--- a/wgpu/src/shader/quad/solid.wgsl
+++ b/wgpu/src/shader/quad/solid.wgsl
@@ -1,5 +1,5 @@
 struct SolidVertexInput {
-    @location(0) v_pos: vec2<f32>,
+    @builtin(vertex_index) vertex_index: u32,
     @location(1) color: vec4<f32>,
     @location(2) pos: vec2<f32>,
     @location(3) scale: vec2<f32>,
@@ -40,7 +40,7 @@ fn solid_vs_main(input: SolidVertexInput) -> SolidVertexOutput {
         vec4<f32>(pos - vec2<f32>(0.5, 0.5), 0.0, 1.0)
     );
 
-    out.position = globals.transform * transform * vec4<f32>(input.v_pos, 0.0, 1.0);
+    out.position = globals.transform * transform * vec4<f32>(vertex_position(input.vertex_index), 0.0, 1.0);
     out.color = input.color;
     out.border_color = input.border_color;
     out.pos = pos;
-- 
cgit