Fix transformed stroke width in GrAALinearizingConvexPathRenderer.

BUG=520476

Review URL: https://codereview.chromium.org/1302503003

3 files changed, 97 insertions, 5 deletions

diff --git a/gm/scaledstrokes.cpp b/gm/scaledstrokes.cpp
new file mode 100644
index 0000000000..59c3efb1cc
--- /dev/null
+++ b/gm/scaledstrokes.cpp
@@ -0,0 +1,84 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+#include "SkCanvas.h"
+#include "SkRRect.h"
+#include "SkPath.h"
+
+class ScaledStrokesGM : public skiagm::GM {
+public:
+    ScaledStrokesGM() {}
+
+protected:
+
+    SkString onShortName() override {
+        return SkString("scaledstrokes");
+    }
+
+    SkISize onISize() override {
+        return SkISize::Make(640, 320);
+    }
+
+    static void draw_path(SkScalar size, SkCanvas* canvas, SkPaint paint) {
+        SkScalar c = 0.551915024494f * size;
+        SkPath path;
+        path.moveTo(0.0f, size);
+        path.cubicTo(c, size, size, c, size, 0.0f);
+        path.cubicTo(size, -c, c, -size, 0.0f, -size);
+        path.cubicTo(-c, -size, -size, -c, -size, 0.0f);
+        path.cubicTo(-size, c, -c, size, 0.0f, size);
+        canvas->drawPath(path, paint);
+    }
+
+    void onDraw(SkCanvas* canvas) override {
+        SkPaint paint;
+        SkPath path;
+        paint.setStyle(SkPaint::Style::kStroke_Style);
+        canvas->translate(5.0f, 5.0f);
+        const SkScalar size = 60.0f;
+        for (int i = 0; i < 2; i++) {
+            paint.setAntiAlias(i == 1);
+            canvas->save();
+            for (int j = 0; j < 4; j++) {
+                SkScalar scale = 4.0f - j;
+                paint.setStrokeWidth(4.0f / scale);
+                canvas->save();
+                canvas->translate(size / 2.0f, size / 2.0f);
+                canvas->scale(scale, scale);
+                draw_path(size / 2.0f / scale, canvas, paint);
+                canvas->restore();
+
+                canvas->save();
+                canvas->translate(size / 2.0f, 80.0f + size / 2.0f);
+                canvas->scale(scale, scale);
+                canvas->drawCircle(0.0f, 0.0f, size / 2.0f / scale, paint);
+                canvas->restore();
+
+                canvas->save();
+                canvas->translate(0.0f, 160.0f);
+                canvas->scale(scale, scale);
+                canvas->drawRect(SkRect::MakeXYWH(0.0f, 0.0f, size / scale, size / scale), paint);
+                canvas->restore();
+
+                canvas->save();
+                canvas->translate(0.0f, 240.0f);
+                canvas->scale(scale, scale);
+                canvas->drawLine(0.0f, 0.0f, size / scale, size / scale, paint);
+                canvas->restore();
+
+                canvas->translate(80.0f, 0.0f);
+            }
+        }
+
+    }
+
+private:
+    typedef GM INHERITED;
+};
+
+DEF_GM( return new ScaledStrokesGM; )
diff --git a/src/gpu/GrAAConvexTessellator.cpp b/src/gpu/GrAAConvexTessellator.cpp
index e38ba3c3ae..db10086741 100644
--- a/src/gpu/GrAAConvexTessellator.cpp
+++ b/src/gpu/GrAAConvexTessellator.cpp
@@ -201,10 +201,14 @@ bool GrAAConvexTessellator::tessellate(const SkMatrix& m, const SkPath& path) {
     }
 
     SkScalar coverage = 1.0f;
+    SkScalar scaleFactor = 0.0f;
     if (fStrokeWidth >= 0.0f) {
+        SkASSERT(m.isSimilarity()); 
+        scaleFactor = m.getMaxScale(); // x and y scale are the same
+        SkScalar effectiveStrokeWidth = scaleFactor * fStrokeWidth;
         Ring outerStrokeRing;
-        this->createOuterRing(fInitialRing, fStrokeWidth / 2 - kAntialiasingRadius, coverage,
-                              &outerStrokeRing);
+        this->createOuterRing(fInitialRing, effectiveStrokeWidth / 2 - kAntialiasingRadius, 
+                              coverage, &outerStrokeRing);
         outerStrokeRing.init(*this);
         Ring outerAARing;
         this->createOuterRing(outerStrokeRing, kAntialiasingRadius * 2, 0.0f, &outerAARing);
@@ -216,8 +220,9 @@ bool GrAAConvexTessellator::tessellate(const SkMatrix& m, const SkPath& path) {
     // the bisectors are only needed for the computation of the outer ring
     fBisectors.rewind();
     if (fStrokeWidth >= 0.0f && fInitialRing.numPts() > 2) {
+        SkScalar effectiveStrokeWidth = scaleFactor * fStrokeWidth;
         Ring* insetStrokeRing;
-        SkScalar strokeDepth = fStrokeWidth / 2 - kAntialiasingRadius;
+        SkScalar strokeDepth = effectiveStrokeWidth / 2 - kAntialiasingRadius;
         if (this->createInsetRings(fInitialRing, 0.0f, coverage, strokeDepth, coverage, 
                              &insetStrokeRing)) {
             Ring* insetAARing;
diff --git a/src/gpu/GrAALinearizingConvexPathRenderer.cpp b/src/gpu/GrAALinearizingConvexPathRenderer.cpp
index fc72a8f60f..899c6b1ef1 100644
--- a/src/gpu/GrAALinearizingConvexPathRenderer.cpp
+++ b/src/gpu/GrAALinearizingConvexPathRenderer.cpp
@@ -50,8 +50,11 @@ bool GrAALinearizingConvexPathRenderer::onCanDrawPath(const CanDrawPathArgs& arg
         return false;
     }
     if (args.fStroke->getStyle() == SkStrokeRec::kStroke_Style) {
-        return args.fViewMatrix->isSimilarity() && args.fStroke->getWidth() >= 1.0f && 
-                args.fStroke->getWidth() <= kMaxStrokeWidth && !args.fStroke->isDashed() && 
+        if (!args.fViewMatrix->isSimilarity()) {
+            return false;
+        }
+        SkScalar strokeWidth = args.fViewMatrix->getMaxScale() * args.fStroke->getWidth();
+        return strokeWidth >= 1.0f && strokeWidth <= kMaxStrokeWidth && !args.fStroke->isDashed() && 
                 SkPathPriv::LastVerbIsClose(*args.fPath) &&
                 args.fStroke->getJoin() != SkPaint::Join::kRound_Join;
     }