Bug 711959 - Add RenderTask and the necessary mechanisms to use it. r=kats

mobile/android/base/gfx/RenderTask.java

@@ -0,0 +1,80 @@
+/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.gecko.gfx;
+
+/**
+ * A class used to schedule a callback to occur when the next frame is drawn.
+ * Subclasses must redefine the internalRun method, not the run method.
+ */
+public abstract class RenderTask {
+    /**
+     * Whether to run the task after the render, or before.
+     */
+    public final boolean runAfter;
+
+    /**
+     * Time when this task has first run, in ns. Useful for tasks which run for a specific duration.
+     */
+    private long mStartTime;
+
+    /**
+     * Whether we should initialise mStartTime on the next frame run.
+     */
+    private boolean mResetStartTime = true;
+
+    /**
+     * The callback to run on each frame. timeDelta is the time elapsed since
+     * the last call, in nanoseconds. Returns true if it should continue
+     * running, or false if it should be removed from the task queue. Returning
+     * true implicitly schedules a redraw.
+     *
+     * This method first initializes the start time if resetStartTime has been invoked,
+     * then calls internalRun.
+     *
+     * Note : subclasses should override internalRun.
+     *
+     * @param timeDelta the time between the beginning of last frame and the beginning of this frame, in ns.
+     * @param currentFrameStartTime the startTime of the current frame, in ns.
+     * @return true if animation should be run at the next frame, false otherwise
+     * @see RenderTask#internalRun(long, long)
+     */
+    public final boolean run(long timeDelta, long currentFrameStartTime) {
+        if (mResetStartTime) {
+            mStartTime = currentFrameStartTime;
+            mResetStartTime = false;
+        }
+        return internalRun(timeDelta, currentFrameStartTime);
+    }
+
+    /**
+     * Abstract method to be overridden by subclasses.
+     * @param timeDelta the time between the beginning of last frame and the beginning of this frame, in ns
+     * @param currentFrameStartTime the startTime of the current frame, in ns.
+     * @return true if animation should be run at the next frame, false otherwise
+     */
+    protected abstract boolean internalRun(long timeDelta, long currentFrameStartTime);
+
+    public RenderTask(boolean aRunAfter) {
+        runAfter = aRunAfter;
+    }
+
+    /**
+     * Get the start time of this task.
+     * It is the start time of the first frame this task was run on.
+     * @return the start time in ns
+     */
+    public long getStartTime() {
+        return mStartTime;
+    }
+
+    /**
+     * Schedule a reset of the recorded start time next time {@link RenderTask#run(long, long)} is run.
+     * @see RenderTask#getStartTime()
+     */
+    public void resetStartTime() {
+        mResetStartTime = true;
+    }
+}