Factor code to rotate a canvas about a point.

samplecode/SampleCircle.cpp

 /*
  * Copyright 2011 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 "SkCanvas.h"
 #include "SkPaint.h"
@@ skipping 69 matching lines @@
         SkScalar step = SK_ScalarPI * 2 / n;
         SkScalar angle = 0;
         for (int i = 1; i < n; i++) {
             angle += step;
             SkScalar c, s = SkScalarSinCos(angle, &c);
             path->lineTo(c, s);
         }
         path->close();
     }
 
-    static void rotate(SkCanvas* canvas, SkScalar angle, SkScalar px, SkScalar py) {
-        canvas->translate(-px, -py);
-        canvas->rotate(angle);
-        canvas->translate(px, py);
-    }
-
     virtual void onDrawContent(SkCanvas* canvas) {
         SkPaint paint;
         paint.setAntiAlias(true);
         paint.setStyle(SkPaint::kStroke_Style);
-//        canvas->drawCircle(250, 250, 220, paint);
         SkMatrix matrix;
         matrix.setScale(SkIntToScalar(100), SkIntToScalar(100));
         matrix.postTranslate(SkIntToScalar(200), SkIntToScalar(200));
         canvas->concat(matrix);
         for (int n = 3; n < 20; n++) {
             SkPath path;
             make_poly(&path, n);
             SkAutoCanvasRestore acr(canvas, true);
             canvas->rotate(SkIntToScalar(10) * (n - 3));
             canvas->translate(-SK_Scalar1, 0);
             canvas->drawPath(path, paint);
         }
     }
 
 private:
     int fN;
     typedef SampleView INHERITED;
 };
 
 const SkScalar CircleView::ANIM_DX(SK_Scalar1 / 67);
 const SkScalar CircleView::ANIM_DY(SK_Scalar1 / 29);
 const SkScalar CircleView::ANIM_RAD(SK_Scalar1 / 19);
 
 //////////////////////////////////////////////////////////////////////////////
 
 static SkView* MyFactory() { return new CircleView; }
 static SkViewRegister reg(MyFactory);