Fix for fat stroked roundrects.

The original method did not correctly compute the distance value along
the inner edge, so the antialiasing was not quite correct. This fixes
that by adding additional vertices and setting a different outerRadius.
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2275423002

Review-Url: https://codereview.chromium.org/2275423002

diff --git a/src/gpu/GrOvalRenderer.cpp b/src/gpu/GrOvalRenderer.cpp
index add634d..e5eb665 100644 (file)
--- a/src/gpu/GrOvalRenderer.cpp
+++ b/src/gpu/GrOvalRenderer.cpp
@@ -1350,7 +1350,8 @@ private:
 //
 // For circular roundrects, in the case where the stroke width is greater than twice
 // the corner radius (overstroke), we add additional geometry to mark out the rectangle
-// in the center:
+// in the center. The shared vertices are duplicated so we can set a different outer radius
+// for the fill calculation.
 //    ____________
 //   |_|________|_|
 //   | |\ ____ /| |
@@ -1364,10 +1365,10 @@ private:
 static const uint16_t gRRectOverstrokeIndices[] = {
     // overstroke quads
     // we place this at the beginning so that we can skip these indices when rendering normally
-    5, 6, 17, 5, 17, 16,
-    17, 6, 10, 17, 10, 19,
-    10, 9, 18, 10, 18, 19,
-    18, 9, 5, 18, 5, 16,
+    16, 17, 19, 16, 19, 18,
+    19, 17, 23, 19, 23, 21,
+    21, 23, 22, 21, 22, 20,
+    22, 16, 18, 22, 18, 20,
 
     // corners
     0, 1, 5, 0, 5, 4,
@@ -1393,7 +1394,7 @@ static const int kIndicesPerOverstrokeRRect = SK_ARRAY_COUNT(gRRectOverstrokeInd
 static const int kIndicesPerFillRRect = kIndicesPerOverstrokeRRect - 6*4 + 6;
 static const int kIndicesPerStrokeRRect = kIndicesPerFillRRect - 6;
 static const int kVertsPerStandardRRect = 16;
-static const int kVertsPerOverstrokeRRect = 20;
+static const int kVertsPerOverstrokeRRect = 24;
 static const int kNumRRectsInIndexBuffer = 256;
 
 enum RRectType {
@@ -1611,20 +1612,34 @@ private:
                 verts++;
             }
             // Add the additional vertices for overstroked rrects.
+            // Effectively this is an additional rrect, drawn inside out,
+            // with outerRadius == -innerRadius. This will give us correct AA in the center.
             //
             // Note that args.fInnerRadius is negative in this case.
             // Also, the offset is a constant vector pointing to the right, which guarantees
             // that the distance value along the inner rectangle is constant, which
             // is what we want to get nice anti-aliasing.
             if (kOverstroke_RRectType == fType) {
-                // outerRadius = originalOuter + 0.5, and innerRadius = originalInner - 0.5.
-                // What we want is originalOuter - originalInner + 0.5, so we subtract 0.5.
-                SkScalar inset = outerRadius - args.fInnerRadius - SK_ScalarHalf;
+                verts->fPos = SkPoint::Make(bounds.fLeft + outerRadius, yCoords[1]);
+                verts->fColor = color;
+                verts->fOffset = SkPoint::Make(0, 0);
+                verts->fOuterRadius = -args.fInnerRadius;
+                verts->fInnerRadius = innerRadius;
+                verts++;
+
+                verts->fPos = SkPoint::Make(bounds.fRight - outerRadius, yCoords[1]);
+                verts->fColor = color;
+                verts->fOffset = SkPoint::Make(0, 0);
+                verts->fOuterRadius = -args.fInnerRadius;
+                verts->fInnerRadius = innerRadius;
+                verts++;
+
+                SkScalar inset = outerRadius - args.fInnerRadius;
                 verts->fPos = SkPoint::Make(bounds.fLeft + inset,
                                             bounds.fTop + inset);
                 verts->fColor = color;
                 verts->fOffset = SkPoint::Make(1, 0);
-                verts->fOuterRadius = outerRadius;
+                verts->fOuterRadius = -args.fInnerRadius;
                 verts->fInnerRadius = innerRadius;
                 verts++;
 
@@ -1632,7 +1647,7 @@ private:
                                             bounds.fTop + inset);
                 verts->fColor = color;
                 verts->fOffset = SkPoint::Make(1, 0);
-                verts->fOuterRadius = outerRadius;
+                verts->fOuterRadius = -args.fInnerRadius;
                 verts->fInnerRadius = innerRadius;
                 verts++;
 
@@ -1640,7 +1655,7 @@ private:
                                             bounds.fBottom - inset);
                 verts->fColor = color;
                 verts->fOffset = SkPoint::Make(1, 0);
-                verts->fOuterRadius = outerRadius;
+                verts->fOuterRadius = -args.fInnerRadius;
                 verts->fInnerRadius = innerRadius;
                 verts++;
 
@@ -1648,7 +1663,21 @@ private:
                                             bounds.fBottom - inset);
                 verts->fColor = color;
                 verts->fOffset = SkPoint::Make(1, 0);
-                verts->fOuterRadius = outerRadius;
+                verts->fOuterRadius = -args.fInnerRadius;
+                verts->fInnerRadius = innerRadius;
+                verts++;
+
+                verts->fPos = SkPoint::Make(bounds.fLeft + outerRadius, yCoords[2]);
+                verts->fColor = color;
+                verts->fOffset = SkPoint::Make(0, 0);
+                verts->fOuterRadius = -args.fInnerRadius;
+                verts->fInnerRadius = innerRadius;
+                verts++;
+
+                verts->fPos = SkPoint::Make(bounds.fRight - outerRadius, yCoords[2]);
+                verts->fColor = color;
+                verts->fOffset = SkPoint::Make(0, 0);
+                verts->fOuterRadius = -args.fInnerRadius;
                 verts->fInnerRadius = innerRadius;
                 verts++;
             }