Factor code to rotate a canvas about a point.

samplecode/SampleDither.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 "SkView.h"
 #include "SkCanvas.h"
 #include "SkGradientShader.h"
 #include "SkPath.h"
 #include "SkRegion.h"
 #include "SkShader.h"
 #include "SkUtils.h"
 #include "Sk1DPathEffect.h"
 #include "SkCornerPathEffect.h"
 #include "SkPathMeasure.h"
 #include "SkRandom.h"
 #include "SkColorPriv.h"
 #include "SkColorFilter.h"
 #include "SkDither.h"
+#include "sk_tool_utils.h"
 
 static void draw_sweep(SkCanvas* c, int width, int height, SkScalar angle) {
     SkRect  r;
     SkPaint p;
 
     p.setAntiAlias(true);
 //    p.setDither(true);
     p.setStrokeWidth(SkIntToScalar(width/10));
     p.setStyle(SkPaint::kStroke_Style);
 
     r.set(0, 0, SkIntToScalar(width), SkIntToScalar(height));
 
     //    SkColor colors[] = { SK_ColorRED, SK_ColorBLUE, SK_ColorGREEN, SK_ColorCYAN };
     SkColor colors[] = { 0x4c737373, 0x4c737373, 0xffffd300 };
     p.setShader(SkGradientShader::MakeSweep(r.centerX(), r.centerY(),
                                             colors, nullptr, SK_ARRAY_COUNT(colors)));
 
     SkAutoCanvasRestore acr(c, true);
-
-    c->translate(r.centerX(), r.centerY());
-    c->rotate(angle);
-    c->translate(-r.centerX(), -r.centerY());
+    sk_tool_utils::rotate_about(c, angle, r.centerX(), r.centerY());
 
     SkRect bounds = r;
     r.inset(p.getStrokeWidth(), p.getStrokeWidth());
     SkRect innerBounds = r;
 
     if (true) {
         c->drawOval(r, p);
     } else {
         SkScalar x = r.centerX();
         SkScalar y = r.centerY();
@@ skipping 113 matching lines @@
     }
 
 private:
     typedef SampleView INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 static SkView* MyFactory() { return new DitherView; }
 static SkViewRegister reg(MyFactory);