allow GMs to animate

gm/addarc.cpp

 /*
  * Copyright 2015 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 "SkRandom.h"
 
 class AddArcGM : public skiagm::GM {
+public:
+    AddArcGM() : fRotate(0) {}
+
 protected:
     SkString onShortName() SK_OVERRIDE { return SkString("addarc"); }
 
     SkISize onISize() SK_OVERRIDE { return SkISize::Make(1040, 1040); }
 
     void onDraw(SkCanvas* canvas) SK_OVERRIDE {
         canvas->translate(20, 20);
 
         SkRect r = SkRect::MakeWH(1000, 1000);
 
         SkPaint paint;
         paint.setAntiAlias(true);
         paint.setStyle(SkPaint::kStroke_Style);
         paint.setStrokeWidth(15);
 
         const SkScalar inset = paint.getStrokeWidth() + 4;
         const SkScalar sweepAngle = 345;
         SkRandom rand;
 
+        SkScalar sign = 1;
         while (r.width() > paint.getStrokeWidth() * 3) {
             paint.setColor(rand.nextU() | (0xFF << 24));
             SkScalar startAngle = rand.nextUScalar1() * 360;
 
+            SkScalar speed = SkScalarSqrt(16 / r.width()) * 0.5f;
+            startAngle += fRotate * 360 * speed * sign;
+
             SkPath path;
             path.addArc(r, startAngle, sweepAngle);
             canvas->drawPath(path, paint);
 
             r.inset(inset, inset);
-
+            sign = -sign;
         }
     }
 
+    bool onAnimatePulse(SkMSec curr) SK_OVERRIDE {
+        fRotate = curr / SkIntToScalar(1000);
+        return true;
+    }
+
 private:
+    SkScalar fRotate;
     typedef skiagm::GM INHERITED;
 };
 DEF_GM( return new AddArcGM; )