Image mask support - shader side

Author: kvark

webrender/res/clip_shared.glsl

@@ -5,6 +5,8 @@
 
 flat varying vec4 vClipRect;
 flat varying vec4 vClipRadius;
+flat varying vec4 vClipMaskUvRect;
+flat varying vec4 vClipMaskScreenRect;
 
 #ifdef WR_VERTEX_SHADER
 void write_clip(Clip clip) {
@@ -13,6 +15,9 @@ void write_clip(Clip clip) {
                        clip.top_right.outer_inner_radius.x,
                        clip.bottom_right.outer_inner_radius.x,
                        clip.bottom_left.outer_inner_radius.x);
+    //TODO: interpolate the final mask UV
+    vClipMaskUvRect = clip.mask_rect.uv;
+    vClipMaskScreenRect = clip.mask_rect.screen;
 }
 #endif
 
@@ -46,6 +51,13 @@ float do_clip(vec2 pos) {
     // Apply a more gradual fade out to transparent.
     //distance_from_border -= 0.5;
 
-    return 1.0 - smoothstep(0.0, 1.0, distance_from_border);
+    float border_alpha = 1.0 - smoothstep(0.0, 1.0, distance_from_border);
+
+    vec2 vMaskUv = (pos - vClipMaskScreenRect.xy) / vClipMaskScreenRect.zw;
+    vec2 clamped_mask_uv = clamp(vMaskUv, vec2(0.0, 0.0), vec2(1.0, 1.0));
+    vec2 source_uv = clamped_mask_uv * vClipMaskUvRect.zw + vClipMaskUvRect.xy;
+    float mask_alpha = texture(sMask, source_uv).r; //careful: texture has type A8
+
+    return border_alpha * mask_alpha;
 }
 #endif

webrender/res/prim_shared.glsl

@@ -257,7 +257,6 @@ PrimitiveInstance fetch_instance(int index) {
 
     return pi;
 }
-
 struct Primitive {
     Layer layer;
     Tile tile;
@@ -298,7 +297,24 @@ ClipRect fetch_clip_rect(int index) {
     ivec2 uv = get_fetch_uv_2(index);
 
     rect.rect = texelFetchOffset(sData32, uv, 0, ivec2(0, 0));
-    rect.dummy = texelFetchOffset(sData32, uv, 0, ivec2(1, 0));
+    //rect.dummy = texelFetchOffset(sData32, uv, 0, ivec2(1, 0));
+    rect.dummy = vec4(0.0, 0.0, 0.0, 0.0);
+
+    return rect;
+}
+
+struct MaskRect {
+    vec4 uv;
+    vec4 screen;
+};
+
+MaskRect fetch_mask_rect(int index) {
+    MaskRect rect;
+
+    ivec2 uv = get_fetch_uv_2(index);
+
+    rect.uv = texelFetchOffset(sData32, uv, 0, ivec2(0, 0));
+    rect.screen = texelFetchOffset(sData32, uv, 0, ivec2(1, 0));
 
     return rect;
 }
@@ -325,6 +341,7 @@ struct Clip {
     ClipCorner top_right;
     ClipCorner bottom_left;
     ClipCorner bottom_right;
+    MaskRect mask_rect;
 };
 
 Clip fetch_clip(int index) {
@@ -335,6 +352,7 @@ Clip fetch_clip(int index) {
     clip.top_right = fetch_clip_corner(index + 2);
     clip.bottom_left = fetch_clip_corner(index + 3);
     clip.bottom_right = fetch_clip_corner(index + 4);
+    clip.mask_rect = fetch_mask_rect(index+5);
 
     return clip;
 }