gpu: [compute] pre-transform images before rendering

We're about to change the last stage of the compute pipeline to only
accept images, not sampled textures. This change prepares materials
for pixel-aligned image copying by pre-rendering images to a texture,
applying transforms.

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

gpu/shaders/scene.h

@@ -18,7 +18,7 @@ struct FillRef {
     uint offset;
 };
 
-struct FillTextureRef {
+struct FillImageRef {
     uint offset;
 };
 
@@ -88,14 +88,15 @@ FillRef Fill_index(FillRef ref, uint index) {
     return FillRef(ref.offset + index * Fill_size);
 }
 
-struct FillTexture {
-    uvec2 uv_bounds;
+struct FillImage {
+    uint index;
+    ivec2 offset;
 };
 
-#define FillTexture_size 8
+#define FillImage_size 8
 
-FillTextureRef FillTexture_index(FillTextureRef ref, uint index) {
-    return FillTextureRef(ref.offset + index * FillTexture_size);
+FillImageRef FillImage_index(FillImageRef ref, uint index) {
+    return FillImageRef(ref.offset + index * FillImage_size);
 }
 
 struct Stroke {
@@ -152,7 +153,7 @@ ClipRef Clip_index(ClipRef ref, uint index) {
 #define Element_Transform 10
 #define Element_BeginClip 11
 #define Element_EndClip 12
-#define Element_FillTexture 13
+#define Element_FillImage 13
 #define Element_size 36
 
 ElementRef Element_index(ElementRef ref, uint index) {
@@ -212,12 +213,13 @@ Fill Fill_read(FillRef ref) {
     return s;
 }
 
-FillTexture FillTexture_read(FillTextureRef ref) {
+FillImage FillImage_read(FillImageRef ref) {
     uint ix = ref.offset >> 2;
     uint raw0 = scene[ix + 0];
     uint raw1 = scene[ix + 1];
-    FillTexture s;
-    s.uv_bounds = uvec2(raw0, raw1);
+    FillImage s;
+    s.index = raw0;
+    s.offset = ivec2(int(raw1 << 16) >> 16, int(raw1) >> 16);
     return s;
 }
 
@@ -314,7 +316,7 @@ Clip Element_EndClip_read(ElementRef ref) {
     return Clip_read(ClipRef(ref.offset + 4));
 }
 
-FillTexture Element_FillTexture_read(ElementRef ref) {
-    return FillTexture_read(FillTextureRef(ref.offset + 4));
+FillImage Element_FillImage_read(ElementRef ref) {
+    return FillImage_read(FillImageRef(ref.offset + 4));
 }