From c0596179bd8582e4f4b5289cdeee8de4fa3de464 Mon Sep 17 00:00:00 2001
From: Robert Krahn <robert.krahn@gmail.com>
Date: Thu, 3 Nov 2022 00:35:01 +0100
Subject: non uniform border radius for quads

---
 wgpu/src/shader/quad.wgsl | 47 +++++++++++++++++++++++++++++++++--------------
 1 file changed, 33 insertions(+), 14 deletions(-)

(limited to 'wgpu/src/shader')

diff --git a/wgpu/src/shader/quad.wgsl b/wgpu/src/shader/quad.wgsl
index 73edd97c..cf4f7e4d 100644
--- a/wgpu/src/shader/quad.wgsl
+++ b/wgpu/src/shader/quad.wgsl
@@ -11,7 +11,7 @@ struct VertexInput {
     @location(2) scale: vec2<f32>,
     @location(3) color: vec4<f32>,
     @location(4) border_color: vec4<f32>,
-    @location(5) border_radius: f32,
+    @location(5) border_radius: vec4<f32>,
     @location(6) border_width: f32,
 }
 
@@ -21,7 +21,7 @@ struct VertexOutput {
     @location(1) border_color: vec4<f32>,
     @location(2) pos: vec2<f32>,
     @location(3) scale: vec2<f32>,
-    @location(4) border_radius: f32,
+    @location(4) border_radius: vec4<f32>,
     @location(5) border_width: f32,
 }
 
@@ -32,9 +32,12 @@ fn vs_main(input: VertexInput) -> VertexOutput {
     var pos: vec2<f32> = input.pos * globals.scale;
     var scale: vec2<f32> = input.scale * globals.scale;
 
-    var border_radius: f32 = min(
-        input.border_radius,
-        min(input.scale.x, input.scale.y) / 2.0
+    var min_border_radius = min(input.scale.x, input.scale.y) * 0.5;
+    var border_radius: vec4<f32> = vec4<f32>(
+        min(input.border_radius.x, min_border_radius),
+        min(input.border_radius.y, min_border_radius),
+        min(input.border_radius.z, min_border_radius),
+        min(input.border_radius.w, min_border_radius)
     );
 
     var transform: mat4x4<f32> = mat4x4<f32>(
@@ -76,6 +79,18 @@ fn distance_alg(
     return sqrt(dist.x * dist.x + dist.y * dist.y);
 }
 
+// Based on the fragement position and the center of the quad, select one of the 4 radi.
+// Order matches CSS border radius attribute:
+// radi.x = top-left, radi.y = top-right, radi.z = bottom-right, radi.w = bottom-left
+fn select_border_radius(radi: vec4<f32>, position: vec2<f32>, center: vec2<f32>) -> f32 {
+    var rx = radi.x;
+    var ry = radi.y;
+    rx = select(radi.x, radi.y, position.x > center.x);
+    ry = select(radi.w, radi.z, position.x > center.x);
+    rx = select(rx, ry, position.y > center.y);
+    return rx;
+}
+
 
 @fragment
 fn fs_main(
@@ -83,14 +98,17 @@ fn fs_main(
 ) -> @location(0) vec4<f32> {
     var mixed_color: vec4<f32> = input.color;
 
+    var border_radius = select_border_radius(
+        input.border_radius,
+        input.position.xy,
+        (input.pos + input.scale * 0.5).xy
+    );
+
     if (input.border_width > 0.0) {
-        var internal_border: f32 = max(
-            input.border_radius - input.border_width,
-            0.0
-        );
+        var internal_border: f32 = max(border_radius - input.border_width, 0.0);
 
         var internal_distance: f32 = distance_alg(
-            vec2<f32>(input.position.x, input.position.y),
+            input.position.xy,
             input.pos + vec2<f32>(input.border_width, input.border_width),
             input.scale - vec2<f32>(input.border_width * 2.0, input.border_width * 2.0),
             internal_border
@@ -109,13 +127,14 @@ fn fs_main(
         vec2<f32>(input.position.x, input.position.y),
         input.pos,
         input.scale,
-        input.border_radius
+        border_radius
     );
 
     var radius_alpha: f32 = 1.0 - smoothstep(
-        max(input.border_radius - 0.5, 0.0),
-        input.border_radius + 0.5,
-        dist);
+        max(border_radius - 0.5, 0.0),
+        border_radius + 0.5,
+        dist
+    );
 
     return vec4<f32>(mixed_color.x, mixed_color.y, mixed_color.z, mixed_color.w * radius_alpha);
 }
-- 
cgit