gpu/shaders: avoid first-class arrays

Safari's WebGL1 implementation (rightly) complains that first-class
array types are not supported as function result types. Define and
use a struct type instead.

While we're here, use const variables instead of functions.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/shaders/common.inc

@@ -1,38 +1,39 @@
 // SPDX-License-Identifier: Unlicense OR MIT
 
-// fboTextureTransform returns a transformation
+struct m3x2 {
+	vec3 r0;
+	vec3 r1;
+};
+
+// fboTextureTransform is the transformation
 // that cancels the implied transformation between
 // the framebuffer and its texture.
 // Only two rows are returned. The last is implied
 // to be [0, 0, 1].
-vec3[2] fboTextureTransform() {
-	vec3[2] t;
+const m3x2 fboTextureTransform = m3x2(
 #ifdef HLSL
-	t[0] = vec3(1.0, 0.0, 0.0);
-	t[1] = vec3(0.0, -1.0, 1.0);
+	vec3(1.0, 0.0, 0.0),
+	vec3(0.0, -1.0, 1.0)
 #else
-	t[0] = vec3(1.0, 0.0, 0.0);
-	t[1] = vec3(0.0, 1.0, 0.0);
+	vec3(1.0, 0.0, 0.0),
+	vec3(0.0, 1.0, 0.0)
 #endif
-	return t;
-}
+);
 
-// fboTransform returns a transformation
+// fboTransform is the transformation
 // that cancels the implied transformation between
 // the clip space and the framebuffer.
 // Only two rows are returned. The last is implied
 // to be [0, 0, 1].
-vec3[2] fboTransform() {
-	vec3[2] t;
+const m3x2 fboTransform = m3x2(
 #ifdef HLSL
-	t[0] = vec3(1.0, 0.0, 0.0);
-	t[1] = vec3(0.0, 1.0, 0.0);
+	vec3(1.0, 0.0, 0.0),
+	vec3(0.0, 1.0, 0.0)
 #else
-	t[0] = vec3(1.0, 0.0, 0.0);
-	t[1] = vec3(0.0, -1.0, 0.0);
+	vec3(1.0, 0.0, 0.0),
+	vec3(0.0, -1.0, 0.0)
 #endif
-	return t;
-}
+);
 
 // toClipSpace converts an OpenGL gl_Position value to a
 // native GPU position.
@@ -45,6 +46,6 @@ vec4 toClipSpace(vec4 pos) {
 #endif
 }
 
-vec3 transform3x2(vec3[2] t, vec3 v) {
-	return vec3(dot(t[0], v), dot(t[1], v), dot(vec3(0.0, 0.0, 1.0), v));
+vec3 transform3x2(m3x2 t, vec3 v) {
+	return vec3(dot(t.r0, v), dot(t.r1, v), dot(vec3(0.0, 0.0, 1.0), v));
 }

gpu/shaders/cover.vert

@@ -23,7 +23,6 @@ layout(location = 1) out vec2 vUV;
 void main() {
     gl_Position = toClipSpace(vec4(pos*transform.xy + transform.zw, z, 1));
 	vUV = uv*uvTransform.xy + uvTransform.zw;
-	vec3[2] fboTrans = fboTextureTransform();
-	vec3 uv3 = transform3x2(fboTrans, vec3(uv, 1.0));
+	vec3 uv3 = transform3x2(fboTextureTransform, vec3(uv, 1.0));
 	vCoverUV = (uv3*vec3(uvCoverTransform.xy, 1.0)+vec3(uvCoverTransform.zw, 0.0)).xy;
 }

gpu/shaders/intersect.vert

@@ -17,12 +17,10 @@ layout(binding = 0) uniform Block {
 layout(location = 0) out vec2 vUV;
 
 void main() {
-  vec3[2] fboTrans = fboTransform();
-  vec3 p = transform3x2(fboTrans, vec3(pos, 1.0));
+  vec3 p = transform3x2(fboTransform, vec3(pos, 1.0));
   gl_Position = vec4(p, 1);
-  vec3[2] fboTexTrans = fboTextureTransform();
-  vec3 uv3 = transform3x2(fboTexTrans, vec3(uv, 1.0));
+  vec3 uv3 = transform3x2(fboTextureTransform, vec3(uv, 1.0));
   vUV = uv3.xy*subUVTransform.xy + subUVTransform.zw;
-  vUV = transform3x2(fboTexTrans, vec3(vUV, 1.0)).xy;
+  vUV = transform3x2(fboTextureTransform, vec3(vUV, 1.0)).xy;
   vUV = vUV*uvTransform.xy + uvTransform.zw;
 }