add SkAnimTimer, SPACE = pause/resume, ESP = stop

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
+#define SkAnimTimer_DEFINED
+
+/**
+ *  Class to track a "timer". It supports 3 states: stopped, paused, running.
+ *
+ *  The caller must call updateTime() to resync with the clock (typically just before
+ *  using the timer). Forcing the caller to do this ensures that the timer's return values
+ *  are consistent if called repeatedly, as they only reflect the time since the last
+ *  calle to updateTimer().
+ */
+class SkAnimTimer {
+public:
+    enum State {
+        kStopped_State,
+        kPaused_State,
+        kRunning_State
+    };
+
+    /**
+     *  Class begins in the "stopped" state.
+     */
+    SkAnimTimer() : fBaseTime(0), fCurrTime(0), fState(kStopped_State) {}
+
+    bool isStopped() const { return kStopped_State == fState; }
+    bool isRunning() const { return kRunning_State == fState; }
+    bool isPaused() const { return kPaused_State == fState; }
+
+    /**
+     *  Stops the timer, and resets it, such that the next call to run or togglePauseResume
+     *  will begin at time 0.
+     */
+    void stop() {
+        this->setState(kStopped_State);
+    }
+
+    /**
+     *  If the timer is paused or stopped, it will resume (or start if it was stopped).
+     */
+    void run() {
+        this->setState(kRunning_State);
+    }
+
+    /**
+     *  If the timer is stopped, this has no effect, else it toggles between paused and running.
+     */
+    void togglePauseResume() {
+        if (kRunning_State == fState) {
+            this->setState(kPaused_State);
+        } else {
+            this->setState(kRunning_State);
+        }
+    }
+
+    /**
+     *  Call this each time you want to sample the clock for the timer. This is NOT done
+     *  automatically, so that repeated calls to msec() or secs() will always return the
+     *  same value.
+     *
+     *  This may safely be called with the timer in any state.
+     */
+    void updateTime() {
+        if (kRunning_State == fState) {
+            fCurrTime = SkTime::GetMSecs();
+        }
+    }
+
+    /**
+     *  Return the time in milliseconds the timer has been in the running state.
+     *  Returns 0 if the timer is stopped.
+     */
+    SkMSec msec() const { return fCurrTime - fBaseTime; }
+
+    /**
+     *  Return the time in seconds the timer has been in the running state.
+     *  Returns 0 if the timer is stopped.
+     */
+    double secs() const {
+        return this->msec() * 0.001;
+    }
+
+    /**
+     *  Return the time in seconds the timer has been in the running state,
+     *  scaled by "speed" and (if not zero) mod by period.
+     *  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);
+    }
+
+private:
+    SkMSec  fBaseTime;
+    SkMSec  fCurrTime;
+    State   fState;
+
+    void setState(State newState) {
+        switch (newState) {
+            case kStopped_State:
+                fBaseTime = fCurrTime = 0;
+                fState = kStopped_State;
+                break;
+            case kPaused_State:
+                if (kRunning_State == fState) {
+                    fState = kPaused_State;
+                } // else stay stopped or paused
+                break;
+            case kRunning_State:
+                switch (fState) {
+                    case kStopped_State:
+                        fBaseTime = fCurrTime = SkTime::GetMSecs();
+                        break;
+                    case kPaused_State: {// they want "resume"
+                        SkMSec now = SkTime::GetMSecs();
+                        fBaseTime += now - fCurrTime;
+                        fCurrTime = now;
+                    } break;

[bsalomon, 2015/02/02 20:54:25]

minor, thought we put the break inside:

    fCurrTime = now;
    break;
}

+                    case kRunning_State:
+                        break;
+                }
+                fState = kRunning_State;
+                break;
+        }
+    }
+};
+
+#endif