Bug 1759526 - Refactor write_transform_vertex. r=gw

This patch separates the antialiasing code from write_vertex. It should not introduce any behavior change, but the resulting code is easier to understand.

Differential Revision: https://phabricator.services.mozilla.com/D141479

gfx/wr/webrender/res/brush.glsl

@@ -116,22 +116,13 @@ void brush_shader_main_vs(
         segment_data = segment_info[1];
     }
 
-    VertexInfo vi;
+    // Most of the time this is the segment rect, but when doing the edge AA
+    // it is inflated.
+    RectWithEndpoint adjusted_segment_rect = segment_rect;
 
     // Write the normal vertex information out.
     if (transform.is_axis_aligned) {
 
-        // Select the corner of the local rect that we are processing.
-        vec2 local_pos = mix(segment_rect.p0, segment_rect.p1, aPosition.xy);
-
-        vi = write_vertex(
-            local_pos,
-            ph.local_clip_rect,
-            ph.z,
-            transform,
-            pic_task
-        );
-
         // TODO(gw): transform bounds may be referenced by
         //           the fragment shader when running in
         //           the alpha pass, even on non-transformed
@@ -142,7 +133,7 @@ void brush_shader_main_vs(
         init_transform_vs(vec4(vec2(-1.0e16), vec2(1.0e16)));
 #endif
     } else {
-        vi = write_transform_vertex(
+        adjusted_segment_rect = clip_and_init_antialiasing(
             segment_rect,
             ph.local_rect,
             ph.local_clip_rect,
@@ -151,8 +142,24 @@ void brush_shader_main_vs(
             transform,
             pic_task
         );
+
+        // The clip was taken into account in clip_and_init_antialiasing, remove
+        // it so that it doesn't interfere with the aa.
+        ph.local_clip_rect.p0 = vec2(-1.0e16);
+        ph.local_clip_rect.p1 = vec2(1.0e16);
     }
 
+    // Select the corner of the local rect that we are processing.
+    vec2 local_pos = mix(adjusted_segment_rect.p0, adjusted_segment_rect.p1, aPosition.xy);
+
+    VertexInfo vi = write_vertex(
+        local_pos,
+        ph.local_clip_rect,
+        ph.z,
+        transform,
+        pic_task
+    );
+
     // For brush instances in the alpha pass, always write
     // out clip information.
     // TODO(gw): It's possible that we might want alpha

gfx/wr/webrender/res/prim_shared.glsl

@@ -151,13 +151,13 @@ vec2 intersect_lines(vec2 p0, vec2 p1, vec2 p2, vec2 p3) {
     return vec2(nx / d, ny / d);
 }
 
-VertexInfo write_transform_vertex(RectWithEndpoint local_segment_rect,
-                                  RectWithEndpoint local_prim_rect,
-                                  RectWithEndpoint local_clip_rect,
-                                  int edge_flags,
-                                  float z,
-                                  Transform transform,
-                                  PictureTask task) {
+RectWithEndpoint clip_and_init_antialiasing(RectWithEndpoint local_segment_rect,
+                                            RectWithEndpoint local_prim_rect,
+                                            RectWithEndpoint local_clip_rect,
+                                            int edge_flags,
+                                            float z,
+                                            Transform transform,
+                                            PictureTask task) {
     // Calculate a clip rect from local_rect + local clip
     RectWithEndpoint clip_rect = local_clip_rect;
     RectWithEndpoint segment_rect = local_segment_rect;
@@ -209,28 +209,7 @@ VertexInfo write_transform_vertex(RectWithEndpoint local_segment_rect,
     local_segment_rect.p1 += extrude_distance.zw;
 #endif
 
-    // Select the corner of the local rect that we are processing.
-    vec2 local_pos = mix(local_segment_rect.p0, local_segment_rect.p1, aPosition.xy);
-
-    // Convert the world positions to device pixel space.
-    vec2 task_offset = task.task_rect.p0 - task.content_origin;
-
-    // Transform the current vertex to world space.
-    vec4 world_pos = transform.m * vec4(local_pos, 0.0, 1.0);
-    vec4 final_pos = vec4(
-        world_pos.xy * task.device_pixel_scale + task_offset * world_pos.w,
-        z * world_pos.w,
-        world_pos.w
-    );
-
-    gl_Position = uTransform * final_pos;
-
-    VertexInfo vi = VertexInfo(
-        local_pos,
-        world_pos
-    );
-
-    return vi;
+    return local_segment_rect;
 }
 
 void write_clip(vec4 world_pos, ClipArea area, PictureTask task) {