gpu, cmaa: don't blend the leftmost and bottom-most edges in the BLUR_EDGES path.

gpu/command_buffer/service/gles2_cmd_apply_framebuffer_attachment_cmaa_intel.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gpu/command_buffer/service/gles2_cmd_apply_framebuffer_attachment_cmaa_intel.h"
 
 #include "base/logging.h"
 #include "gpu/command_buffer/service/framebuffer_manager.h"
 #include "gpu/command_buffer/service/gles2_cmd_decoder.h"
 #include "ui/gl/gl_context.h"
@@ skipping 1420 matching lines @@
       //     any(greaterThan(numberOfEdges4, uvec4(1))) ? 1.0 : 0.0;
 
       gl_FragDepth =
           any(greaterThan(outEdge4, uvec4(1))) ? 1.0 : 0.0;
     }
     \n#endif\n  // COMBINE_EDGES
 
     \n#ifdef BLUR_EDGES\n
     layout(early_fragment_tests) in;
     void BlurEdges() {
-      int _i;
-
+      // Each |gl_FragCoord| updates 4 texels of the original texture, which are
+      // 2x|gl_FragCoord| + (-1 or 0, -1 or 0) in the unnormalized texture
+      // coordinate, which is the coordinate used by texelFetch().
+      // e.g. when gl_FragCoord == (3.5, 3.5), this fragment shader covers
+      // (6,6) (6,7) (7,6) (7,7) texels.
+      // Note: gl_FragCoord == (0.5, 0.5) (i.e. left-bottom-most fragment)
+      // covers (0,0) (0,1) (1,0) (1,1) texels
+      // gl_FragCoord == ((w/2)-0.5, (h/2)-0.5) (i.e. right-top-most fragment)
+      // covers (w-2,h-2) (w-2,h-1) (w-1,h-2) (w-1,h-1)
       ivec3 screenPosIBase = ivec3(ivec2(gl_FragCoord.xy) * 2, 0);
       vec3 screenPosBase = vec3(screenPosIBase);
+
+      // When gl_FragCoord == (0.5, 0.5) (i.e. left-bottom-most fragment),
+      // |sampA| textureGatherOffset() looks up (-1,-1), (-1,0), (0,-1), (0,0).
+      // (-1,-1), (-1,0), (0,-1) must be handled.
+      // Note: textureGatherOffset() on out of range gives an undefined value.
+      uvec2 notBottomLeft = uvec2(notEqual(screenPosIBase.xy, ivec2(0, 0)));
+      // When gl_FragCoord == ((w/2)-0.5, (h/2)-0.5) (i.e. right-top-most
+      // fragment), |sampD| looks up (w-1, h-1), (w-1, h), (w, h-1), (w, h).
+      // (w-1, h), (w, h-1), (w, h) must be handled.
+      uvec2 notTopRight = uvec2(
+          notEqual((screenPosIBase.xy + 2), textureSize(g_src0TextureFlt, 0)));
+
       uint forFollowUpCount = 0u;
       ivec4 forFollowUpCoords[4];
 
       uint packedEdgesArray[4 * 4];
 
       uvec4 sampA = uvec4(
           textureGatherOffset(g_src0TextureFlt,
                               screenPosBase.xy * g_OneOverScreenSize,
                               ivec2(0, 0)) *255.5);
       uvec4 sampB = uvec4(
           textureGatherOffset(g_src0TextureFlt,
                               screenPosBase.xy * g_OneOverScreenSize,
                               ivec2(2, 0)) *255.5);
       uvec4 sampC = uvec4(
           textureGatherOffset(g_src0TextureFlt,
                               screenPosBase.xy * g_OneOverScreenSize,
                               ivec2(0, 2)) *255.5);
       uvec4 sampD = uvec4(
           textureGatherOffset(g_src0TextureFlt,
                               screenPosBase.xy * g_OneOverScreenSize,
                               ivec2(2, 2)) *255.5);
 
-      packedEdgesArray[(0) * 4 + (0)] = sampA.w;
-      packedEdgesArray[(1) * 4 + (0)] = sampA.z;
-      packedEdgesArray[(0) * 4 + (1)] = sampA.x;
+      packedEdgesArray[(0) * 4 + (0)] =
+          sampA.w * notBottomLeft.x * notBottomLeft.y;
+      packedEdgesArray[(1) * 4 + (0)] = sampA.z * notBottomLeft.y;
+      packedEdgesArray[(0) * 4 + (1)] = sampA.x * notBottomLeft.x;
       packedEdgesArray[(1) * 4 + (1)] = sampA.y;
-      packedEdgesArray[(2) * 4 + (0)] = sampB.w;
-      packedEdgesArray[(3) * 4 + (0)] = sampB.z;
+      packedEdgesArray[(2) * 4 + (0)] = sampB.w * notBottomLeft.y;
+      packedEdgesArray[(3) * 4 + (0)] =
+          sampB.z * notBottomLeft.y * notTopRight.x;
       packedEdgesArray[(2) * 4 + (1)] = sampB.x;
-      packedEdgesArray[(3) * 4 + (1)] = sampB.y;
-      packedEdgesArray[(0) * 4 + (2)] = sampC.w;
+      packedEdgesArray[(3) * 4 + (1)] = sampB.y * notTopRight.x;
+      packedEdgesArray[(0) * 4 + (2)] = sampC.w * notBottomLeft.x;
       packedEdgesArray[(1) * 4 + (2)] = sampC.z;
-      packedEdgesArray[(0) * 4 + (3)] = sampC.x;
-      packedEdgesArray[(1) * 4 + (3)] = sampC.y;
+      packedEdgesArray[(0) * 4 + (3)] =
+          sampC.x * notBottomLeft.x * notTopRight.y;
+      packedEdgesArray[(1) * 4 + (3)] = sampC.y * notTopRight.y;
       packedEdgesArray[(2) * 4 + (2)] = sampD.w;
-      packedEdgesArray[(3) * 4 + (2)] = sampD.z;
-      packedEdgesArray[(2) * 4 + (3)] = sampD.x;
-      packedEdgesArray[(3) * 4 + (3)] = sampD.y;
+      packedEdgesArray[(3) * 4 + (2)] = sampD.z * notTopRight.x;
+      packedEdgesArray[(2) * 4 + (3)] = sampD.x * notTopRight.y;
+      packedEdgesArray[(3) * 4 + (3)] = sampD.y * notTopRight.x * notTopRight.y;
 
-      for (_i = 0; _i < 4; _i++) {
+      for (int _i = 0; _i < 4; _i++) {
         int _x = _i % 2;
         int _y = _i / 2;
 
         ivec3 screenPosI = screenPosIBase + ivec3(_x, _y, 0);
 
         uint packedEdgesC = packedEdgesArray[(1 + _x) * 4 + (1 + _y)];
 
         uvec4 edges = UnpackEdge(packedEdgesC);
         vec4 edgesFlt = vec4(edges);
 
@@ skipping 366 matching lines @@
       \n#ifdef OUT_FBO\n
         outColor = pixel;
       \n#else\n
         imageStore(outTexture, screenPosI, pixel);
       \n#endif\n
       }
     );
 /* clang-format on */
 
 }  // namespace gpu