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"
 #include "SkCanvas.h"
 #include "SkDrawable.h"
 #include "SkInterpolator.h"
 #include "SkPictureRecorder.h"
 #include "SkRandom.h"
+#include "sk_tool_utils.h"
 
 const SkRect gUnitSquare = { -1, -1, 1, 1 };
 
 static void color_to_floats(SkColor c, SkScalar f[4]) {
     f[0] = SkIntToScalar(SkColorGetA(c));
     f[1] = SkIntToScalar(SkColorGetR(c));
     f[2] = SkIntToScalar(SkColorGetG(c));
     f[3] = SkIntToScalar(SkColorGetB(c));
 }
 
@@ skipping 62 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());
+            sk_tool_utils::rotate_about(canvas, 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);