Add GM case for arc truncation error bug

gm/hairlines.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 "gm.h"
 #include "SkCanvas.h"
 #include "SkTArray.h"
@@ skipping 115 matching lines @@
         }
 
         {
             // A right angle (crbug.com/137465 and crbug.com/256776)
             SkPath* bug2 = &fPaths.push_back();
 
             bug2->moveTo(5.5f, 5.5f);
             bug2->lineTo(5.5f, 0.5f);
             bug2->lineTo(0.5f, 0.5f);
         }
+
+        {
+            // Arc example to test imperfect truncation bug (crbug.com/295626) 
+            static const SkScalar kRad = SkIntToScalar(2000);
+            static const SkScalar kStartAngle = SkFloatToScalar(262.59717f);
+            static const SkScalar kSweepAngle = SkScalarHalf(SkFloatToScalar(17.188717f));
+
+            SkPath* bug = &fPaths.push_back();
+
+            // Add a circular arc
+            SkRect circle = SkRect::MakeLTRB(-kRad, -kRad, kRad, kRad);
+            bug->addArc(circle, kStartAngle, kSweepAngle);
+
+            // Now add the chord that should cap the circular arc
+            SkScalar cosV, sinV = SkScalarSinCos(SkDegreesToRadians(kStartAngle), &cosV);
+
+            SkPoint p0 = SkPoint::Make(kRad * cosV, kRad * sinV);
+
+            sinV = SkScalarSinCos(SkDegreesToRadians(kStartAngle + kSweepAngle), &cosV);
+
+            SkPoint p1 = SkPoint::Make(kRad * cosV, kRad * sinV);
+
+            bug->moveTo(p0);
+            bug->lineTo(p1);
+        }
     }
 
     virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
         static const SkAlpha kAlphaValue[] = { 0xFF, 0x40 };
 
         enum {
             kMargin = 5,
         };
         int wrapX = canvas->getDeviceSize().fWidth - kMargin;
 
@@ skipping 41 matching lines @@
     SkTArray<SkPath> fPaths;
     typedef GM INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 static GM* MyFactory(void*) { return new HairlinesGM; }
 static GMRegistry reg(MyFactory);
 
 }