gpu: pack 2D transforms in vec4 values

Instead of separate 2d scale and transform, pack them into a single
4d value.

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

gpu/shaders/cover.vert

@@ -7,13 +7,10 @@ precision highp float;
 #include <common.inc>
 
 layout(binding = 0) uniform Block {
+	vec4 transform;
+	vec4 uvCoverTransform;
+	vec4 uvTransform;
 	float z;
-	vec2 scale;
-	vec2 offset;
-	vec2 uvCoverScale;
-	vec2 uvCoverOffset;
-	vec2 uvScale;
-	vec2 uvOffset;
 };
 
 layout(location = 0) in vec2 pos;
@@ -24,9 +21,9 @@ layout(location = 1) in vec2 uv;
 layout(location = 1) out vec2 vUV;
 
 void main() {
-    gl_Position = vec4(pos*scale + offset, z, 1);
-	vUV = uv*uvScale + uvOffset;
+    gl_Position = 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));
-	vCoverUV = (uv3*vec3(uvCoverScale, 1.0)+vec3(uvCoverOffset, 0.0)).xy;
+	vCoverUV = (uv3*vec3(uvCoverTransform.xy, 1.0)+vec3(uvCoverTransform.zw, 0.0)).xy;
 }