Factor code to rotate a canvas about a point.

samplecode/SampleHT.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SampleCode.h"
 #include "SkAnimTimer.h"
 #include "SkView.h"
@@ skipping 77 matching lines @@
 
         SkPaint paint;
         paint.setAntiAlias(true);
 
         if (fInterp) {
             SkScalar values[5];
             SkInterpolator::Result res = fInterp->timeToValues(fTime, values);
             fColor = floats_to_color(values);
 
             canvas->save();
-            canvas->translate(fR.centerX(), fR.centerY());
-            canvas->rotate(values[4]);
-            canvas->translate(-fR.centerX(), -fR.centerY());
+            canvas->rotate(values[4], fR.centerX(), fR.centerY());
 
             switch (res) {
                 case SkInterpolator::kFreezeEnd_Result:
                     delete fInterp;
                     fInterp = nullptr;
                     break;
                 default:
                     break;
             }
         }
@@ skipping 66 matching lines @@
     }
 
 private:
     typedef SampleView INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 static SkView* MyFactory() { return new HTView; }
 static SkViewRegister reg(MyFactory);