Fix non-uniform scale for stroked ellipses

src/gpu/GrOvalRenderer.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrOvalRenderer.h"
 
 #include "GrEffect.h"
@@ skipping 402 matching lines @@
 {
     GrDrawState* drawState = target->drawState();
 #ifdef SK_DEBUG
     {
         // we should have checked for this previously
         bool isAxisAlignedEllipse = drawState->getViewMatrix().rectStaysRect();
         SkASSERT(paint.isAntiAlias() && isAxisAlignedEllipse);
     }
 #endif
 
+    // do any matrix crunching before we reset the draw state for device coords
     const SkMatrix& vm = drawState->getViewMatrix();
     GrPoint center = GrPoint::Make(ellipse.centerX(), ellipse.centerY());
     vm.mapPoints(&center, 1);
-    SkRect xformedRect;
-    vm.mapRect(&xformedRect, ellipse);
-    SkScalar xRadius = SkScalarHalf(xformedRect.width());
-    SkScalar yRadius = SkScalarHalf(xformedRect.height());
+    SkScalar ellipseXRadius = SkScalarHalf(ellipse.width());
+    SkScalar ellipseYRadius = SkScalarHalf(ellipse.height());
+    SkScalar xRadius = SkScalarAbs(vm[SkMatrix::kMScaleX]*ellipseXRadius + 
+                                   vm[SkMatrix::kMSkewY]*ellipseYRadius);
+    SkScalar yRadius = SkScalarAbs(vm[SkMatrix::kMSkewX]*ellipseXRadius + 
+                                   vm[SkMatrix::kMScaleY]*ellipseYRadius);
     if (SkScalarDiv(xRadius, yRadius) > 2 || SkScalarDiv(yRadius, xRadius) > 2) {
         return false;
     }
 
+    // do (potentially) anisotropic mapping of stroke
+    SkVector scaledStroke;
+    SkScalar strokeWidth = stroke.getWidth();
+    scaledStroke.fX = SkScalarAbs(strokeWidth*(vm[SkMatrix::kMScaleX] + vm[SkMatrix::kMSkewY]));
+    scaledStroke.fY = SkScalarAbs(strokeWidth*(vm[SkMatrix::kMSkewX] + vm[SkMatrix::kMScaleY]));
+
     GrDrawState::AutoDeviceCoordDraw adcd(drawState);
     if (!adcd.succeeded()) {
         return false;
     }
 
     // position + edge
     static const GrVertexAttrib kVertexAttribs[] = {
         {kVec2f_GrVertexAttribType, 0, kPosition_GrVertexAttribBinding},
         {kVec2f_GrVertexAttribType, sizeof(GrPoint), kEffect_GrVertexAttribBinding},
         {kVec4f_GrVertexAttribType, 2*sizeof(GrPoint), kEffect_GrVertexAttribBinding}
@@ skipping 21 matching lines @@
     GrEffectRef* effect = EllipseEdgeEffect::Create(isStroked);
     static const int kEllipseCenterAttrIndex = 1;
     static const int kEllipseEdgeAttrIndex = 2;
     drawState->setEffect(kEdgeEffectStage, effect,
                          kEllipseCenterAttrIndex, kEllipseEdgeAttrIndex)->unref();
 
     SkScalar innerXRadius = 0.0f;
     SkScalar innerRatio = 1.0f;
 
     if (SkStrokeRec::kFill_Style != style) {
-        SkScalar strokeWidth = stroke.getWidth();
 
-        // do (potentially) anisotropic mapping
-        SkVector scaledStroke;
-        scaledStroke.set(strokeWidth, strokeWidth);
-        vm.mapVectors(&scaledStroke, 1);
 
         if (SkScalarNearlyZero(scaledStroke.length())) {
             scaledStroke.set(SK_ScalarHalf, SK_ScalarHalf);
         } else {
             scaledStroke.scale(0.5f);
         }
 
         // this is legit only if scale & translation (which should be the case at the moment)
         if (SkStrokeRec::kStroke_Style == style || SkStrokeRec::kHairline_Style == style) {
             SkScalar innerYRadius = SkMaxScalar(0, yRadius - scaledStroke.fY);
@@ skipping 46 matching lines @@
     verts[3].fPos = SkPoint::Make(bounds.fRight, bounds.fBottom);
     verts[3].fOuterXRadius = xRadius;
     verts[3].fInnerXRadius = innerXRadius;
     verts[3].fOuterOffset = SkPoint::Make(xRadius, outerRatio*yRadius);
     verts[3].fInnerOffset = SkPoint::Make(xRadius, innerRatio*yRadius);
 
     target->drawNonIndexed(kTriangleStrip_GrPrimitiveType, 0, 4, &bounds);
 
     return true;
 }