Add blurcircles2 GM

gm/SkAnimTimer.h

 /*
  * 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 "SkTime.h"
 
 #ifndef SkAnimTimer_DEFINED
@@ skipping 86 matching lines @@
      *  Returns 0 if the timer is stopped.
      */
     SkScalar scaled(SkScalar speed, SkScalar period = 0) const {
         double value = this->secs() * speed;
         if (period) {
             value = ::fmod(value, SkScalarToDouble(period));
         }
         return SkDoubleToScalar(value);
     }
 
+    /**
+     * Transitions from ends->mid->ends linearly over period seconds. The phase specifies a phase
+     * shift in seconds.
+     */

[robertphillips, 2016/05/13 18:44:16]

Isn't this more commonly known as ping-pong?

[bsalomon, 2016/05/13 18:58:10]

Done.

+    SkScalar pulse(SkScalar period, SkScalar phase, SkScalar ends, SkScalar mid) const {
+        return Pulse(this->secs(), period, phase, ends, mid);
+    }
+
+    /** Helper for computing a pulse value without a SkAnimTimer object */
+    static SkScalar Pulse(SkScalar t, SkScalar period, SkScalar phase, SkScalar ends,
+                          SkScalar mid) {
+        double value = ::fmod(t + phase, period);
+        double half = period / 2.0;
+        double diff = ::fabs(value - half);
+        return ends + (1.0 - diff / half) * (mid - ends);
+    }
+
 private:
     double  fBaseTimeNanos;
     double  fCurrTimeNanos;
     State   fState;
 
     void setState(State newState) {
         switch (newState) {
             case kStopped_State:
                 fBaseTimeNanos = fCurrTimeNanos = 0;
                 fState = kStopped_State;
@@ skipping 16 matching lines @@
                     case kRunning_State:
                         break;
                 }
                 fState = kRunning_State;
                 break;
         }
     }
 };
 
 #endif