GPU "fix" for thin stroked rects

src/gpu/GrAARectRenderer.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrAARectRenderer.h"
 #include "GrRefCnt.h"
 #include "GrGpu.h"
@@ skipping 710 matching lines @@
     GrAssert(sizeof(GrPoint) + sizeof(GrColor) == vsize);
 
     // We create vertices for four nested rectangles. There are two ramps from 0 to full
     // coverage, one on the exterior of the stroke and the other on the interior.
     // The following pointers refer to the four rects, from outermost to innermost.
     GrPoint* fan0Pos = reinterpret_cast<GrPoint*>(verts);
     GrPoint* fan1Pos = reinterpret_cast<GrPoint*>(verts + 4 * vsize);
     GrPoint* fan2Pos = reinterpret_cast<GrPoint*>(verts + 8 * vsize);
     GrPoint* fan3Pos = reinterpret_cast<GrPoint*>(verts + 12 * vsize);
 
+    // TODO: this only really works if the X & Y margins are the same all around
+    // the rect
+    SkScalar inset = SkMinScalar(SK_Scalar1, devOutside.fRight - devInside.fRight);

[bsalomon, 2013/06/26 15:47:49]

As in square scale? Have we checked that anywhere?

[robertphillips, 2013/06/26 17:33:05]

This code path explicitly expects non-uniform stroking (see handling in
GrAARectRenderer::strokeAARect).

+    inset = SkMinScalar(inset, devInside.fLeft - devOutside.fLeft);
+    inset = SkMinScalar(inset, devInside.fTop - devOutside.fTop);
+    inset = SK_ScalarHalf * SkMinScalar(inset, devOutside.fBottom - devInside.fBottom);
+    SkASSERT(inset >= 0);
+
     // outermost
     set_inset_fan(fan0Pos, vsize, devOutside, -SK_ScalarHalf, -SK_ScalarHalf);
-    set_inset_fan(fan1Pos, vsize, devOutside,  SK_ScalarHalf,  SK_ScalarHalf);
-    set_inset_fan(fan2Pos, vsize, devInside,  -SK_ScalarHalf, -SK_ScalarHalf);
+    // inner two
+    set_inset_fan(fan1Pos, vsize, devOutside,  inset,  inset);
+    set_inset_fan(fan2Pos, vsize, devInside,  -inset, -inset);
     // innermost
     set_inset_fan(fan3Pos, vsize, devInside,   SK_ScalarHalf,  SK_ScalarHalf);
 
     // The outermost rect has 0 coverage
     verts += sizeof(GrPoint);
     for (int i = 0; i < 4; ++i) {
         *reinterpret_cast<GrColor*>(verts + i * vsize) = 0;
     }
 
+    int scale;
+    if (inset < SK_ScalarHalf) {
+        scale = SkScalarFloorToInt(512.0f * inset / (inset + SK_ScalarHalf));
+        SkASSERT(scale >= 0 && scale <= 255);
+    } else {
+        scale = 0xff;
+    }
+
     // The inner two rects have full coverage
     GrColor innerColor;
     if (useVertexCoverage) {
-        innerColor = 0xffffffff;
+        innerColor = scale | (scale << 8) | (scale << 16) | (scale << 24);

[bsalomon, 2013/06/26 15:47:49]

Can we use GrColorParckRGBA()?

[robertphillips, 2013/06/26 17:33:05]

Done.

     } else {
-        innerColor = target->getDrawState().getColor();
+        if (0xff == scale) {
+            innerColor = target->getDrawState().getColor();
+        } else {
+            innerColor = SkAlphaMulQ(target->getDrawState().getColor(), scale);

[bsalomon, 2013/06/26 15:47:49]

maybe just call this unconditionally?

[robertphillips, 2013/06/26 17:33:05]

Done.

+        }
     }
+
     verts += 4 * vsize;
     for (int i = 0; i < 8; ++i) {
         *reinterpret_cast<GrColor*>(verts + i * vsize) = innerColor;
     }
 
     // The innermost rect has 0 coverage
     verts += 8 * vsize;
     for (int i = 0; i < 4; ++i) {
         *reinterpret_cast<GrColor*>(verts + i * vsize) = 0;
     }
@@ skipping 16 matching lines @@
     // can't call mapRect for devInside since it calls sort
     combinedMatrix.mapPoints((SkPoint*)&devInside, (const SkPoint*)&rects[1], 2);
 
     if (devInside.isEmpty()) {
         this->fillAARect(gpu, target, devOutside, SkMatrix::I(), devOutside, useVertexCoverage);
         return;
     }
 
     this->geometryStrokeAARect(gpu, target, devOutside, devInside, useVertexCoverage);
 }