android/opengl/GLSurfaceView.java

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.opengl;

import java.io.Writer;
import java.lang.ref.WeakReference;

import javax.microedition.khronos.egl.EGL10;
import javax.microedition.khronos.egl.EGL11;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.egl.EGLContext;
import javax.microedition.khronos.egl.EGLDisplay;
import javax.microedition.khronos.egl.EGLSurface;
import javax.microedition.khronos.opengles.GL;
import javax.microedition.khronos.opengles.GL10;

import android.content.Context;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Looper;
import android.os.Trace;
import android.util.AttributeSet;
import android.util.Log;
import android.view.Choreographer;
import android.view.SurfaceHolder;
import android.view.SurfaceView;

/**
 * An implementation of SurfaceView that uses the dedicated surface for
 * displaying OpenGL rendering.
 * <p>
 * A GLSurfaceView provides the following features:
 * <p>
 * <ul>
 * <li>Manages a surface, which is a special piece of memory that can be
 * composited into the Android view system.
 * <li>Manages an EGL display, which enables OpenGL to render into a surface.
 * <li>Accepts a user-provided Renderer object that does the actual rendering.
 * <li>Renders on a dedicated thread to decouple rendering performance from the
 * UI thread.
 * <li>Supports both on-demand and continuous rendering.
 * <li>Optionally wraps, traces, and/or error-checks the renderer's OpenGL calls.
 * </ul>
 *
 * <div class="special reference">
 * <h3>Developer Guides</h3>
 * <p>For more information about how to use OpenGL, read the
 * <a href="{@docRoot}guide/topics/graphics/opengl.html">OpenGL</a> developer guide.</p>
 * </div>
 *
 * <h3>Using GLSurfaceView</h3>
 * <p>
 * Typically you use GLSurfaceView by subclassing it and overriding one or more of the
 * View system input event methods. If your application does not need to override event
 * methods then GLSurfaceView can be used as-is. For the most part
 * GLSurfaceView behavior is customized by calling "set" methods rather than by subclassing.
 * For example, unlike a regular View, drawing is delegated to a separate Renderer object which
 * is registered with the GLSurfaceView
 * using the {@link #setRenderer(Renderer)} call.
 * <p>
 * <h3>Initializing GLSurfaceView</h3>
 * All you have to do to initialize a GLSurfaceView is call {@link #setRenderer(Renderer)}.
 * However, if desired, you can modify the default behavior of GLSurfaceView by calling one or
 * more of these methods before calling setRenderer:
 * <ul>
 * <li>{@link #setDebugFlags(int)}
 * <li>{@link #setEGLConfigChooser(boolean)}
 * <li>{@link #setEGLConfigChooser(EGLConfigChooser)}
 * <li>{@link #setEGLConfigChooser(int, int, int, int, int, int)}
 * <li>{@link #setGLWrapper(GLWrapper)}
 * </ul>
 * <p>
 * <h4>Specifying the android.view.Surface</h4>
 * By default GLSurfaceView will create a PixelFormat.RGB_888 format surface. If a translucent
 * surface is required, call getHolder().setFormat(PixelFormat.TRANSLUCENT).
 * The exact format of a TRANSLUCENT surface is device dependent, but it will be
 * a 32-bit-per-pixel surface with 8 bits per component.
 * <p>
 * <h4>Choosing an EGL Configuration</h4>
 * A given Android device may support multiple EGLConfig rendering configurations.
 * The available configurations may differ in how may channels of data are present, as
 * well as how many bits are allocated to each channel. Therefore, the first thing
 * GLSurfaceView has to do when starting to render is choose what EGLConfig to use.
 * <p>
 * By default GLSurfaceView chooses a EGLConfig that has an RGB_888 pixel format,
 * with at least a 16-bit depth buffer and no stencil.
 * <p>
 * If you would prefer a different EGLConfig
 * you can override the default behavior by calling one of the
 * setEGLConfigChooser methods.
 * <p>
 * <h4>Debug Behavior</h4>
 * You can optionally modify the behavior of GLSurfaceView by calling
 * one or more of the debugging methods {@link #setDebugFlags(int)},
 * and {@link #setGLWrapper}. These methods may be called before and/or after setRenderer, but
 * typically they are called before setRenderer so that they take effect immediately.
 * <p>
 * <h4>Setting a Renderer</h4>
 * Finally, you must call {@link #setRenderer} to register a {@link Renderer}.
 * The renderer is
 * responsible for doing the actual OpenGL rendering.
 * <p>
 * <h3>Rendering Mode</h3>
 * Once the renderer is set, you can control whether the renderer draws
 * continuously or on-demand by calling
 * {@link #setRenderMode}. The default is continuous rendering.
 * <p>
 * <h3>Activity Life-cycle</h3>
 * A GLSurfaceView must be notified when the activity is paused and resumed. GLSurfaceView clients
 * are required to call {@link #onPause()} when the activity pauses and
 * {@link #onResume()} when the activity resumes. These calls allow GLSurfaceView to
 * pause and resume the rendering thread, and also allow GLSurfaceView to release and recreate
 * the OpenGL display.
 * <p>
 * <h3>Handling events</h3>
 * <p>
 * To handle an event you will typically subclass GLSurfaceView and override the
 * appropriate method, just as you would with any other View. However, when handling
 * the event, you may need to communicate with the Renderer object
 * that's running in the rendering thread. You can do this using any
 * standard Java cross-thread communication mechanism. In addition,
 * one relatively easy way to communicate with your renderer is
 * to call
 * {@link #queueEvent(Runnable)}. For example:
 * <pre class="prettyprint">
 * class MyGLSurfaceView extends GLSurfaceView {
 *
 *     private MyRenderer mMyRenderer;
 *
 *     public void start() {
 *         mMyRenderer = ...;
 *         setRenderer(mMyRenderer);
 *     }
 *
 *     public boolean onKeyDown(int keyCode, KeyEvent event) {
 *         if (keyCode == KeyEvent.KEYCODE_DPAD_CENTER) {
 *             queueEvent(new Runnable() {
 *                 // This method will be called on the rendering
 *                 // thread:
 *                 public void run() {
 *                     mMyRenderer.handleDpadCenter();
 *                 }});
 *             return true;
 *         }
 *         return super.onKeyDown(keyCode, event);
 *     }
 * }
 * </pre>
 *
 */
public class GLSurfaceView extends SurfaceView implements SurfaceHolder.Callback {
    private final static String TAG = "GLSurfaceView";
    private final static boolean LOG_ATTACH_DETACH = false;
    private final static boolean LOG_THREADS = false;
    private final static boolean LOG_SURFACE = false;
    private final static boolean LOG_RENDERER = false;
    private final static boolean LOG_RENDERER_DRAW_FRAME = false;
    private final static boolean LOG_EGL = false;
    private final static boolean TRACE_ENABLED = false;

    private final WeakReference<GLSurfaceView> mThisWeakRef =
            new WeakReference<GLSurfaceView>(this);
    private GLThread mGLThread;
    private Renderer mRenderer;
    private boolean mDetached;
    private EGLConfigChooser mEGLConfigChooser;
    private EGLContextFactory mEGLContextFactory;
    private EGLWindowSurfaceFactory mEGLWindowSurfaceFactory;
    private GLWrapper mGLWrapper;
    private int mDebugFlags;
    private int mEGLContextClientVersion;
    private boolean mPreserveEGLContextOnPause;

    /**
     * The renderer only renders
     * when the surface is created, or when {@link #requestRender} is called.
     *
     * @see #getRenderMode()
     * @see #setRenderMode(int)
     * @see #requestRender()
     */
    public final static int RENDERMODE_WHEN_DIRTY = 0;
    /**
     * The renderer is called
     * continuously to re-render the scene.
     *
     * @see #getRenderMode()
     * @see #setRenderMode(int)
     */
    public final static int RENDERMODE_CONTINUOUSLY = 1;

    /**
     * Check glError() after every GL call and throw an exception if glError indicates
     * that an error has occurred. This can be used to help track down which OpenGL ES call
     * is causing an error.
     *
     * @see #getDebugFlags
     * @see #setDebugFlags
     */
    public final static int DEBUG_CHECK_GL_ERROR = 1;

    /**
     * Log GL calls to the system log at "verbose" level with tag "GLSurfaceView".
     *
     * @see #getDebugFlags
     * @see #setDebugFlags
     */
    public final static int DEBUG_LOG_GL_CALLS = 2;

    /**
     * Standard View constructor. In order to render something, you
     * must call {@link #setRenderer} to register a renderer.
     */
    public GLSurfaceView(Context context) {
        super(context);
        init();
    }

    /**
     * Standard View constructor. In order to render something, you
     * must call {@link #setRenderer} to register a renderer.
     */
    public GLSurfaceView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    @Override
    protected void finalize() throws Throwable {
        try {
            if (mGLThread != null) {
                // GLThread may still be running if this view was never
                // attached to a window.
                mGLThread.quitSafely();
            }
        } finally {
            super.finalize();
        }
    }

    private void init() {
        // Install a SurfaceHolder.Callback so we get notified when the
        // underlying surface is created and destroyed
        SurfaceHolder holder = getHolder();
        holder.addCallback(this);
    }

    /**
     * Set the glWrapper. If the glWrapper is not null, its
     * {@link GLWrapper#wrap(GL)} method is called
     * whenever a surface is created. A GLWrapper can be used to wrap
     * the GL object that's passed to the renderer. Wrapping a GL
     * object enables examining and modifying the behavior of the
     * GL calls made by the renderer.
     * <p>
     * Wrapping is typically used for debugging purposes.
     * <p>
     * The default value is null.
     * @param glWrapper the new GLWrapper
     */
    public void setGLWrapper(GLWrapper glWrapper) {
        mGLWrapper = glWrapper;
    }

    /**
     * Set the debug flags to a new value. The value is
     * constructed by OR-together zero or more
     * of the DEBUG_CHECK_* constants. The debug flags take effect
     * whenever a surface is created. The default value is zero.
     * @param debugFlags the new debug flags
     * @see #DEBUG_CHECK_GL_ERROR
     * @see #DEBUG_LOG_GL_CALLS
     */
    public void setDebugFlags(int debugFlags) {
        mDebugFlags = debugFlags;
    }

    /**
     * Get the current value of the debug flags.
     * @return the current value of the debug flags.
     */
    public int getDebugFlags() {
        return mDebugFlags;
    }

    /**
     * Control whether the EGL context is preserved when the GLSurfaceView is paused and
     * resumed.
     * <p>
     * If set to true, then the EGL context may be preserved when the GLSurfaceView is paused.
     * Whether the EGL context is actually preserved or not depends upon whether the
     * Android device that the program is running on can support an arbitrary number of EGL
     * contexts or not. Devices that can only support a limited number of EGL contexts must
     * release the  EGL context in order to allow multiple applications to share the GPU.
     * <p>
     * If set to false, the EGL context will be released when the GLSurfaceView is paused,
     * and recreated when the GLSurfaceView is resumed.
     * <p>
     *
     * The default is false.
     *
     * @param preserveOnPause preserve the EGL context when paused
     */
    public void setPreserveEGLContextOnPause(boolean preserveOnPause) {
        mPreserveEGLContextOnPause = preserveOnPause;
    }

    /**
     * @return true if the EGL context will be preserved when paused
     */
    public boolean getPreserveEGLContextOnPause() {
        return mPreserveEGLContextOnPause;
    }

    /**
     * Set the renderer associated with this view. Also starts the thread that
     * will call the renderer, which in turn causes the rendering to start.
     * <p>This method should be called once and only once in the life-cycle of
     * a GLSurfaceView.
     * <p>The following GLSurfaceView methods can only be called <em>before</em>
     * setRenderer is called:
     * <ul>
     * <li>{@link #setEGLConfigChooser(boolean)}
     * <li>{@link #setEGLConfigChooser(EGLConfigChooser)}
     * <li>{@link #setEGLConfigChooser(int, int, int, int, int, int)}
     * </ul>
     * <p>
     * The following GLSurfaceView methods can only be called <em>after</em>
     * setRenderer is called:
     * <ul>
     * <li>{@link #getRenderMode()}
     * <li>{@link #onPause()}
     * <li>{@link #onResume()}
     * <li>{@link #queueEvent(Runnable)}
     * <li>{@link #requestRender()}
     * <li>{@link #setRenderMode(int)}
     * </ul>
     *
     * @param renderer the renderer to use to perform OpenGL drawing.
     */
    public void setRenderer(Renderer renderer) {
        checkRenderThreadState();
        if (mEGLConfigChooser == null) {
            mEGLConfigChooser = new SimpleEGLConfigChooser(true, mEGLContextClientVersion);
        }
        if (mEGLContextFactory == null) {
            mEGLContextFactory = new DefaultContextFactory(mEGLContextClientVersion);
        }
        if (mEGLWindowSurfaceFactory == null) {
            mEGLWindowSurfaceFactory = new DefaultWindowSurfaceFactory();
        }
        mRenderer = renderer;

        mGLThread = new GLThread(mThisWeakRef);
        mGLThread.start();
    }

    /**
     * Install a custom EGLContextFactory.
     * <p>If this method is
     * called, it must be called before {@link #setRenderer(Renderer)}
     * is called.
     * <p>
     * If this method is not called, then by default
     * a context will be created with no shared context and
     * with a null attribute list.
     */
    public void setEGLContextFactory(EGLContextFactory factory) {
        checkRenderThreadState();
        mEGLContextFactory = factory;
    }

    /**
     * Install a custom EGLWindowSurfaceFactory.
     * <p>If this method is
     * called, it must be called before {@link #setRenderer(Renderer)}
     * is called.
     * <p>
     * If this method is not called, then by default
     * a window surface will be created with a null attribute list.
     */
    public void setEGLWindowSurfaceFactory(EGLWindowSurfaceFactory factory) {
        checkRenderThreadState();
        mEGLWindowSurfaceFactory = factory;
    }

    /**
     * Install a custom EGLConfigChooser.
     * <p>If this method is
     * called, it must be called before {@link #setRenderer(Renderer)}
     * is called.
     * <p>
     * If no setEGLConfigChooser method is called, then by default the
     * view will choose an EGLConfig that is compatible with the current
     * android.view.Surface, with a depth buffer depth of
     * at least 16 bits.
     * @param configChooser
     */
    public void setEGLConfigChooser(EGLConfigChooser configChooser) {
        checkRenderThreadState();
        mEGLConfigChooser = configChooser;
    }

    /**
     * Install a config chooser which will choose a config
     * as close to 16-bit RGB as possible, with or without an optional depth
     * buffer as close to 16-bits as possible.
     * <p>If this method is
     * called, it must be called before {@link #setRenderer(Renderer)}
     * is called.
     * <p>
     * If no setEGLConfigChooser method is called, then by default the
     * view will choose an RGB_888 surface with a depth buffer depth of
     * at least 16 bits.
     *
     * @param needDepth
     */
    public void setEGLConfigChooser(boolean needDepth) {
        setEGLConfigChooser(new SimpleEGLConfigChooser(needDepth, mEGLContextClientVersion));
    }

    /**
     * Install a config chooser which will choose a config
     * with at least the specified depthSize and stencilSize,
     * and exactly the specified redSize, greenSize, blueSize and alphaSize.
     * <p>If this method is
     * called, it must be called before {@link #setRenderer(Renderer)}
     * is called.
     * <p>
     * If no setEGLConfigChooser method is called, then by default the
     * view will choose an RGB_888 surface with a depth buffer depth of
     * at least 16 bits.
     *
     */
    public void setEGLConfigChooser(int redSize, int greenSize, int blueSize,
            int alphaSize, int depthSize, int stencilSize) {
        setEGLConfigChooser(new ComponentSizeChooser(redSize, greenSize,
                blueSize, alphaSize, depthSize, stencilSize, mEGLContextClientVersion));
    }

    /**
     * Inform the default EGLContextFactory and default EGLConfigChooser
     * which EGLContext client version to pick.
     * <p>Use this method to create an OpenGL ES 2.0-compatible context.
     * Example:
     * <pre class="prettyprint">
     *     public MyView(Context context) {
     *         super(context);
     *         setEGLContextClientVersion(2); // Pick an OpenGL ES 2.0 context.
     *         setRenderer(new MyRenderer());
     *     }
     * </pre>
     * <p>Note: Activities which require OpenGL ES 2.0 should indicate this by
     * setting @lt;uses-feature android:glEsVersion="0x00020000" /> in the activity's
     * AndroidManifest.xml file.
     * <p>If this method is called, it must be called before {@link #setRenderer(Renderer)}
     * is called.
     * <p>This method only affects the behavior of the default EGLContexFactory and the
     * default EGLConfigChooser. If
     * {@link #setEGLContextFactory(EGLContextFactory)} has been called, then the supplied
     * EGLContextFactory is responsible for creating an OpenGL ES 2.0-compatible context.
     * If
     * {@link #setEGLConfigChooser(EGLConfigChooser)} has been called, then the supplied
     * EGLConfigChooser is responsible for choosing an OpenGL ES 2.0-compatible config.
     *
     * This method must be called before:
     * <ul>
     * <li>{@link #setEGLConfigChooser(boolean)}
     * <li>{@link #setEGLConfigChooser(int, int, int, int, int, int)}
     * </ul>
     *
     * @param version The EGLContext client version to choose. Use 2 for OpenGL ES 2.0
     */
    public void setEGLContextClientVersion(int version) {
        checkRenderThreadState();
        mEGLContextClientVersion = version;
    }

    /**
     * Set the rendering mode. When renderMode is
     * RENDERMODE_CONTINUOUSLY, the renderer is called
     * repeatedly to re-render the scene. When renderMode
     * is RENDERMODE_WHEN_DIRTY, the renderer only rendered when the surface
     * is created, or when {@link #requestRender} is called. Defaults to RENDERMODE_CONTINUOUSLY.
     * <p>
     * Using RENDERMODE_WHEN_DIRTY can improve battery life and overall system performance
     * by allowing the GPU and CPU to idle when the view does not need to be updated.
     * <p>
     * This method can only be called after {@link #setRenderer(Renderer)}
     *
     * @param renderMode one of the RENDERMODE_X constants
     * @see #RENDERMODE_CONTINUOUSLY
     * @see #RENDERMODE_WHEN_DIRTY
     */
    public void setRenderMode(int renderMode) {
        switch (renderMode) {
            case RENDERMODE_WHEN_DIRTY:
            case RENDERMODE_CONTINUOUSLY:
                break;
            default:
                throw new IllegalArgumentException("renderMode");
        }
        mGLThread.setRenderMode(renderMode);
    }

    /**
     * Get the current rendering mode. May be called
     * from any thread. Must not be called before a renderer has been set.
     * @return the current rendering mode.
     * @see #RENDERMODE_CONTINUOUSLY
     * @see #RENDERMODE_WHEN_DIRTY
     */
    public int getRenderMode() {
        return mGLThread.getRenderMode();
    }

    /**
     * Request that the renderer render a frame.
     * This method is typically used when the render mode has been set to
     * {@link #RENDERMODE_WHEN_DIRTY}, so that frames are only rendered on demand.
     * May be called
     * from any thread. Must not be called before a renderer has been set.
     */
    public void requestRender() {
        mGLThread.requestRender();
    }

    /**
     * This method is part of the SurfaceHolder.Callback interface, and is
     * not normally called or subclassed by clients of GLSurfaceView.
     */
    public void surfaceCreated(SurfaceHolder holder) {
        mGLThread.surfaceCreated();
    }

    /**
     * This method is part of the SurfaceHolder.Callback interface, and is
     * not normally called or subclassed by clients of GLSurfaceView.
     */
    public void surfaceDestroyed(SurfaceHolder holder) {
        // Surface will be destroyed when we return
        mGLThread.surfaceDestroyed();
    }

    /**
     * This method is part of the SurfaceHolder.Callback interface, and is
     * not normally called or subclassed by clients of GLSurfaceView.
     */
    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        mGLThread.onWindowResize(w, h);
    }

    /**
     * Inform the view that the activity is paused. The owner of this view must
     * call this method when the activity is paused. Calling this method will
     * pause the rendering thread.
     * Must not be called before a renderer has been set.
     */
    public void onPause() {
        mGLThread.onPause();
    }

    /**
     * Inform the view that the activity is resumed. The owner of this view must
     * call this method when the activity is resumed. Calling this method will
     * recreate the OpenGL display and resume the rendering
     * thread.
     * Must not be called before a renderer has been set.
     */
    public void onResume() {
        mGLThread.onResume();
    }

    /**
     * Queue a runnable to be run on the GL rendering thread. This can be used
     * to communicate with the Renderer on the rendering thread.
     * Must not be called before a renderer has been set.
     * @param r the runnable to be run on the GL rendering thread.
     */
    public void queueEvent(Runnable r) {
        mGLThread.queueEvent(r);
    }

    /**
     * This method is used as part of the View class and is not normally
     * called or subclassed by clients of GLSurfaceView.
     */
    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        if (LOG_ATTACH_DETACH) {
            Log.d(TAG, "onAttachedToWindow reattach =" + mDetached);
        }

        final int renderMode = mGLThread != null ?
                mGLThread.mRenderMode : RENDERMODE_CONTINUOUSLY;

        if (mDetached && (mRenderer != null)) {
            mGLThread = new GLThread(mThisWeakRef);
            mGLThread.setRenderMode(renderMode);
            mGLThread.start();
        }
        mDetached = false;
    }

    /**
     * This method is used as part of the View class and is not normally
     * called or subclassed by clients of GLSurfaceView.
     * Must not be called before a renderer has been set.
     */
    @Override
    protected void onDetachedFromWindow() {
        if (LOG_ATTACH_DETACH) {
            Log.d(TAG, "onDetachedFromWindow");
        }
        if (mGLThread != null) {
            mGLThread.quitSafely();
            try {
                mGLThread.join();
            } catch (InterruptedException ex) {
            }
        }
        mDetached = true;
        super.onDetachedFromWindow();
    }

    // ----------------------------------------------------------------------

    /**
     * An interface used to wrap a GL interface.
     * <p>Typically
     * used for implementing debugging and tracing on top of the default
     * GL interface. You would typically use this by creating your own class
     * that implemented all the GL methods by delegating to another GL instance.
     * Then you could add your own behavior before or after calling the
     * delegate. All the GLWrapper would do was instantiate and return the
     * wrapper GL instance:
     * <pre class="prettyprint">
     * class MyGLWrapper implements GLWrapper {
     *     GL wrap(GL gl) {
     *         return new MyGLImplementation(gl);
     *     }
     *     static class MyGLImplementation implements GL,GL10,GL11,... {
     *         ...
     *     }
     * }
     * </pre>
     * @see #setGLWrapper(GLWrapper)
     */
    public interface GLWrapper {
        /**
         * Wraps a gl interface in another gl interface.
         * @param gl a GL interface that is to be wrapped.
         * @return either the input argument or another GL object that wraps the input argument.
         */
        GL wrap(GL gl);
    }

    /**
     * A generic renderer interface.
     * <p>
     * The renderer is responsible for making OpenGL calls to render a frame.
     * <p>
     * GLSurfaceView clients typically create their own classes that implement
     * this interface, and then call {@link GLSurfaceView#setRenderer} to
     * register the renderer with the GLSurfaceView.
     * <p>
     *
     * <div class="special reference">
     * <h3>Developer Guides</h3>
     * <p>For more information about how to use OpenGL, read the
     * <a href="{@docRoot}guide/topics/graphics/opengl.html">OpenGL</a> developer guide.</p>
     * </div>
     *
     * <h3>Threading</h3>
     * The renderer will be called on a separate thread, so that rendering
     * performance is decoupled from the UI thread. Clients typically need to
     * communicate with the renderer from the UI thread, because that's where
     * input events are received. Clients can communicate using any of the
     * standard Java techniques for cross-thread communication, or they can
     * use the {@link GLSurfaceView#queueEvent(Runnable)} convenience method.
     * <p>
     * <h3>EGL Context Lost</h3>
     * There are situations where the EGL rendering context will be lost. This
     * typically happens when device wakes up after going to sleep. When
     * the EGL context is lost, all OpenGL resources (such as textures) that are
     * associated with that context will be automatically deleted. In order to
     * keep rendering correctly, a renderer must recreate any lost resources
     * that it still needs. The {@link #onSurfaceCreated(GL10, EGLConfig)} method
     * is a convenient place to do this.
     *
     *
     * @see #setRenderer(Renderer)
     */
    public interface Renderer {
        /**
         * Called when the surface is created or recreated.
         * <p>
         * Called when the rendering thread
         * starts and whenever the EGL context is lost. The EGL context will typically
         * be lost when the Android device awakes after going to sleep.
         * <p>
         * Since this method is called at the beginning of rendering, as well as
         * every time the EGL context is lost, this method is a convenient place to put
         * code to create resources that need to be created when the rendering
         * starts, and that need to be recreated when the EGL context is lost.
         * Textures are an example of a resource that you might want to create
         * here.
         * <p>
         * Note that when the EGL context is lost, all OpenGL resources associated
         * with that context will be automatically deleted. You do not need to call
         * the corresponding "glDelete" methods such as glDeleteTextures to
         * manually delete these lost resources.
         * <p>
         * @param gl the GL interface. Use <code>instanceof</code> to
         * test if the interface supports GL11 or higher interfaces.
         * @param config the EGLConfig of the created surface. Can be used
         * to create matching pbuffers.
         */
        void onSurfaceCreated(GL10 gl, EGLConfig config);

        /**
         * Called when the surface changed size.
         * <p>
         * Called after the surface is created and whenever
         * the OpenGL ES surface size changes.
         * <p>
         * Typically you will set your viewport here. If your camera
         * is fixed then you could also set your projection matrix here:
         * <pre class="prettyprint">
         * void onSurfaceChanged(GL10 gl, int width, int height) {
         *     gl.glViewport(0, 0, width, height);
         *     // for a fixed camera, set the projection too
         *     float ratio = (float) width / height;
         *     gl.glMatrixMode(GL10.GL_PROJECTION);
         *     gl.glLoadIdentity();
         *     gl.glFrustumf(-ratio, ratio, -1, 1, 1, 10);
         * }
         * </pre>
         * @param gl the GL interface. Use <code>instanceof</code> to
         * test if the interface supports GL11 or higher interfaces.
         * @param width
         * @param height
         */
        void onSurfaceChanged(GL10 gl, int width, int height);

        /**
         * Called to draw the current frame.
         * <p>
         * This method is responsible for drawing the current frame.
         * <p>
         * The implementation of this method typically looks like this:
         * <pre class="prettyprint">
         * void onDrawFrame(GL10 gl) {
         *     gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
         *     //... other gl calls to render the scene ...
         * }
         * </pre>
         * @param gl the GL interface. Use <code>instanceof</code> to
         * test if the interface supports GL11 or higher interfaces.
         */
        void onDrawFrame(GL10 gl);
    }

    /**
     * An interface for customizing the eglCreateContext and eglDestroyContext calls.
     * <p>
     * This interface must be implemented by clients wishing to call
     * {@link GLSurfaceView#setEGLContextFactory(EGLContextFactory)}
     */
    public interface EGLContextFactory {
        EGLContext createContext(EGL10 egl, EGLDisplay display, EGLConfig eglConfig);
        void destroyContext(EGL10 egl, EGLDisplay display, EGLContext context);
    }

    private static class DefaultContextFactory implements EGLContextFactory {
        private final int mEGLContextClientVersion;

        public DefaultContextFactory(int version) {
            mEGLContextClientVersion = version;
        }

        public EGLContext createContext(EGL10 egl, EGLDisplay display, EGLConfig config) {
            int[] attrib_list = {EGL14.EGL_CONTEXT_CLIENT_VERSION, mEGLContextClientVersion,
                    EGL10.EGL_NONE };

            return egl.eglCreateContext(display, config, EGL10.EGL_NO_CONTEXT,
                    mEGLContextClientVersion != 0 ? attrib_list : null);
        }

        public void destroyContext(EGL10 egl, EGLDisplay display,
                EGLContext context) {
            if (!egl.eglDestroyContext(display, context)) {
                Log.e(TAG, "display:" + display + " context: " + context);
                if (LOG_THREADS) {
                    Log.d(TAG, "tid=" + Thread.currentThread().getId());
                }
                EglHelper.throwEglException("eglDestroyContex", egl.eglGetError());
            }
        }
    }

    /**
     * An interface for customizing the eglCreateWindowSurface and eglDestroySurface calls.
     * <p>
     * This interface must be implemented by clients wishing to call
     * {@link GLSurfaceView#setEGLWindowSurfaceFactory(EGLWindowSurfaceFactory)}
     */
    public interface EGLWindowSurfaceFactory {
        /**
         *  @return null if the surface cannot be constructed.
         */
        EGLSurface createWindowSurface(EGL10 egl, EGLDisplay display, EGLConfig config,
                Object nativeWindow);
        void destroySurface(EGL10 egl, EGLDisplay display, EGLSurface surface);
    }

    private static class DefaultWindowSurfaceFactory implements EGLWindowSurfaceFactory {

        public EGLSurface createWindowSurface(EGL10 egl, EGLDisplay display,
                EGLConfig config, Object nativeWindow) {
            EGLSurface result = null;
            try {
                result = egl.eglCreateWindowSurface(display, config, nativeWindow, null);
            } catch (IllegalArgumentException e) {
                // This exception indicates that the surfaceflinger surface
                // is not valid. This can happen if the surfaceflinger surface has
                // been torn down, but the application has not yet been
                // notified via SurfaceHolder.Callback.surfaceDestroyed.
                // In theory the application should be notified first,
                // but in practice sometimes it is not. See b/4588890
                Log.e(TAG, "eglCreateWindowSurface", e);
            }
            return result;
        }

        public void destroySurface(EGL10 egl, EGLDisplay display,
                EGLSurface surface) {
            egl.eglDestroySurface(display, surface);
        }
    }

    /**
     * An interface for choosing an EGLConfig configuration from a list of
     * potential configurations.
     * <p>
     * This interface must be implemented by clients wishing to call
     * {@link GLSurfaceView#setEGLConfigChooser(EGLConfigChooser)}
     */
    public interface EGLConfigChooser {
        /**
         * Choose a configuration from the list. Implementors typically
         * implement this method by calling
         * {@link EGL10#eglChooseConfig} and iterating through the results. Please consult the
         * EGL specification available from The Khronos Group to learn how to call eglChooseConfig.
         * @param egl the EGL10 for the current display.
         * @param display the current display.
         * @return the chosen configuration.
         */
        EGLConfig chooseConfig(EGL10 egl, EGLDisplay display);
    }

    private static abstract class BaseConfigChooser
            implements EGLConfigChooser {

        public BaseConfigChooser(int[] configSpec, int version) {
            mConfigSpec = filterConfigSpec(configSpec, version);
        }

        public EGLConfig chooseConfig(EGL10 egl, EGLDisplay display) {
            int[] num_config = new int[1];
            if (!egl.eglChooseConfig(display, mConfigSpec, null, 0,
                    num_config)) {
                throw new IllegalArgumentException("eglChooseConfig failed");
            }

            int numConfigs = num_config[0];

            if (numConfigs <= 0) {
                throw new IllegalArgumentException(
                        "No configs match configSpec");
            }

            EGLConfig[] configs = new EGLConfig[numConfigs];
            if (!egl.eglChooseConfig(display, mConfigSpec, configs, numConfigs,
                    num_config)) {
                throw new IllegalArgumentException("eglChooseConfig#2 failed");
            }
            EGLConfig config = chooseConfig(egl, display, configs);
            if (config == null) {
                throw new IllegalArgumentException("No config chosen");
            }
            return config;
        }

        abstract EGLConfig chooseConfig(EGL10 egl, EGLDisplay display,
                EGLConfig[] configs);

        protected int[] mConfigSpec;

        private int[] filterConfigSpec(int[] configSpec, int version) {
            if (version != 2) {
                return configSpec;
            }
            /* We know none of the subclasses define EGL_RENDERABLE_TYPE.
             * And we know the configSpec is well formed.
             */
            int len = configSpec.length;
            int[] newConfigSpec = new int[len + 2];
            System.arraycopy(configSpec, 0, newConfigSpec, 0, len-1);
            newConfigSpec[len-1] = EGL10.EGL_RENDERABLE_TYPE;
            newConfigSpec[len] = EGL14.EGL_OPENGL_ES2_BIT;
            newConfigSpec[len+1] = EGL10.EGL_NONE;
            return newConfigSpec;
        }
    }

    /**
     * Choose a configuration with exactly the specified r,g,b,a sizes,
     * and at least the specified depth and stencil sizes.
     */
    private static class ComponentSizeChooser extends BaseConfigChooser {
        public ComponentSizeChooser(int redSize, int greenSize, int blueSize,
                int alphaSize, int depthSize, int stencilSize, int version) {
            super(new int[] {
                    EGL10.EGL_RED_SIZE, redSize,
                    EGL10.EGL_GREEN_SIZE, greenSize,
                    EGL10.EGL_BLUE_SIZE, blueSize,
                    EGL10.EGL_ALPHA_SIZE, alphaSize,
                    EGL10.EGL_DEPTH_SIZE, depthSize,
                    EGL10.EGL_STENCIL_SIZE, stencilSize,
                    EGL10.EGL_NONE}, version);
            mValue = new int[1];
            mRedSize = redSize;
            mGreenSize = greenSize;
            mBlueSize = blueSize;
            mAlphaSize = alphaSize;
            mDepthSize = depthSize;
            mStencilSize = stencilSize;
        }

        @Override
        public EGLConfig chooseConfig(EGL10 egl, EGLDisplay display,
                EGLConfig[] configs) {
            for (EGLConfig config : configs) {
                int d = findConfigAttrib(egl, display, config,
                        EGL10.EGL_DEPTH_SIZE, 0);
                int s = findConfigAttrib(egl, display, config,
                        EGL10.EGL_STENCIL_SIZE, 0);
                if ((d >= mDepthSize) && (s >= mStencilSize)) {
                    int r = findConfigAttrib(egl, display, config, EGL10.EGL_RED_SIZE, 0);
                    int g = findConfigAttrib(egl, display, config, EGL10.EGL_GREEN_SIZE, 0);
                    int b = findConfigAttrib(egl, display, config, EGL10.EGL_BLUE_SIZE, 0);
                    int a = findConfigAttrib(egl, display, config, EGL10.EGL_ALPHA_SIZE, 0);
                    if ((r == mRedSize) && (g == mGreenSize)
                            && (b == mBlueSize) && (a == mAlphaSize)) {
                        return config;
                    }
                }
            }
            return null;
        }

        private int findConfigAttrib(EGL10 egl, EGLDisplay display,
                EGLConfig config, int attribute, int defaultValue) {

            if (egl.eglGetConfigAttrib(display, config, attribute, mValue)) {
                return mValue[0];
            }
            return defaultValue;
        }

        private int[] mValue;
        // Subclasses can adjust these values:
        protected int mRedSize;
        protected int mGreenSize;
        protected int mBlueSize;
        protected int mAlphaSize;
        protected int mDepthSize;
        protected int mStencilSize;
    }

    /**
     * This class will choose a RGB_888 surface with
     * or without a depth buffer.
     *
     */
    private static class SimpleEGLConfigChooser extends ComponentSizeChooser {
        public SimpleEGLConfigChooser(boolean withDepthBuffer, int version) {
            super(8, 8, 8, 0, withDepthBuffer ? 16 : 0, 0, version);
        }
    }

    /**
     * An EGL helper class.
     */

    private static class EglHelper {
        public EglHelper(WeakReference<GLSurfaceView> glSurfaceViewWeakRef) {
            mGLSurfaceViewWeakRef = glSurfaceViewWeakRef;
        }

        /**
         * Initialize EGL for a given configuration spec.
         * @param configSpec
         */
        public void initialize() {
            if (LOG_EGL) {
                Log.d(TAG, "initialize() tid=" + Thread.currentThread().getId());
            }
            /*
             * Get an EGL instance
             */
            mEgl = (EGL10) EGLContext.getEGL();

            /*
             * Get to the default display.
             */
            mEglDisplay = mEgl.eglGetDisplay(EGL10.EGL_DEFAULT_DISPLAY);

            if (mEglDisplay == EGL10.EGL_NO_DISPLAY) {
                throw new RuntimeException("eglGetDisplay failed");
            }

            /*
             * We can now initialize EGL for that display
             */
            int[] version = new int[2];
            if(!mEgl.eglInitialize(mEglDisplay, version)) {
                throw new RuntimeException("eglInitialize failed");
            }
            GLSurfaceView view = mGLSurfaceViewWeakRef.get();
            if (view == null) {
                mEglConfig = null;
                mEglContext = null;
            } else {
                mEglConfig = view.mEGLConfigChooser.chooseConfig(mEgl, mEglDisplay);

                /*
                * Create an EGL context. We want to do this as rarely as we can, because an
                * EGL context is a somewhat heavy object.
                */
                mEglContext = view.mEGLContextFactory.createContext(mEgl, mEglDisplay, mEglConfig);
            }
            if (mEglContext == null || mEglContext == EGL10.EGL_NO_CONTEXT) {
                mEglContext = null;
                throwEglException("createContext");
            }
            if (LOG_EGL) {
                Log.d(TAG, "createContext " + mEglContext + " tid=" + Thread.currentThread().getId());
            }

            mEglSurface = null;
        }

        /**
         * Create an egl surface for the current SurfaceHolder surface. If a surface
         * already exists, destroy it before creating the new surface.
         *
         * @return true if the surface was created successfully.
         */
        public boolean createSurface() {
            if (LOG_EGL) {
                Log.d(TAG, "createSurface()  tid=" + Thread.currentThread().getId());
            }
            /*
             * Check preconditions.
             */
            if (mEgl == null) {
                throw new RuntimeException("egl not initialized");
            }
            if (mEglDisplay == null) {
                throw new RuntimeException("eglDisplay not initialized");
            }
            if (mEglConfig == null) {
                throw new RuntimeException("mEglConfig not initialized");
            }

            /*
             *  The window size has changed, so we need to create a new
             *  surface.
             */
            destroySurfaceImp();

            /*
             * Create an EGL surface we can render into.
             */
            GLSurfaceView view = mGLSurfaceViewWeakRef.get();
            if (view != null) {
                mEglSurface = view.mEGLWindowSurfaceFactory.createWindowSurface(mEgl,
                        mEglDisplay, mEglConfig, view.getHolder());
            } else {
                mEglSurface = null;
            }

            if (mEglSurface == null || mEglSurface == EGL10.EGL_NO_SURFACE) {
                int error = mEgl.eglGetError();
                if (error == EGL10.EGL_BAD_NATIVE_WINDOW) {
                    Log.e(TAG, "createWindowSurface returned EGL_BAD_NATIVE_WINDOW.");
                }
                return false;
            }

            /*
             * Before we can issue GL commands, we need to make sure
             * the context is current and bound to a surface.
             */
            if (!mEgl.eglMakeCurrent(mEglDisplay, mEglSurface, mEglSurface, mEglContext)) {
                /*
                 * Could not make the context current, probably because the underlying
                 * SurfaceView surface has been destroyed.
                 */
                logEglErrorAsWarning(TAG, "eglMakeCurrent", mEgl.eglGetError());
                // we fall-through to "true" here because we do have a
                // valid EGLSurface at this point.
            }

            return true;
        }

        /**
         * Create a GL object for the current EGL context.
         * @return
         */
        public GL createGL() {
            GL gl = mEglContext.getGL();
            GLSurfaceView view = mGLSurfaceViewWeakRef.get();
            if (view != null) {
                if (view.mGLWrapper != null) {
                    gl = view.mGLWrapper.wrap(gl);
                }

                if ((view.mDebugFlags & (DEBUG_CHECK_GL_ERROR | DEBUG_LOG_GL_CALLS)) != 0) {
                    int configFlags = 0;
                    Writer log = null;
                    if ((view.mDebugFlags & DEBUG_CHECK_GL_ERROR) != 0) {
                        configFlags |= GLDebugHelper.CONFIG_CHECK_GL_ERROR;
                    }
                    if ((view.mDebugFlags & DEBUG_LOG_GL_CALLS) != 0) {
                        log = new LogWriter();
                    }
                    gl = GLDebugHelper.wrap(gl, configFlags, log);
                }
            }
            return gl;
        }

        /**
         * Display the current render surface.
         * @return the EGL error code from eglSwapBuffers.
         */
        public int swap() {
            if (! mEgl.eglSwapBuffers(mEglDisplay, mEglSurface)) {
                return mEgl.eglGetError();
            }
            return EGL10.EGL_SUCCESS;
        }

        public void destroySurface() {
            if (LOG_EGL) {
                Log.d(TAG, "destroySurface()  tid=" + Thread.currentThread().getId());
            }
            destroySurfaceImp();
        }

        private void destroySurfaceImp() {
            if (mEglSurface != null && mEglSurface != EGL10.EGL_NO_SURFACE) {
                mEgl.eglMakeCurrent(mEglDisplay, EGL10.EGL_NO_SURFACE,
                        EGL10.EGL_NO_SURFACE,
                        EGL10.EGL_NO_CONTEXT);
                GLSurfaceView view = mGLSurfaceViewWeakRef.get();
                if (view != null) {
                    view.mEGLWindowSurfaceFactory.destroySurface(mEgl, mEglDisplay, mEglSurface);
                }
                mEglSurface = null;
            }
        }

        public void terminate() {
            if (LOG_EGL) {
                Log.d(TAG, "terminate() tid=" + Thread.currentThread().getId());
            }
            if (mEglContext != null) {
                GLSurfaceView view = mGLSurfaceViewWeakRef.get();
                if (view != null) {
                    view.mEGLContextFactory.destroyContext(mEgl, mEglDisplay, mEglContext);
                }
                mEglContext = null;
            }
            if (mEglDisplay != null) {
                mEgl.eglTerminate(mEglDisplay);
                mEglDisplay = null;
            }
        }

        private void throwEglException(String function) {
            throwEglException(function, mEgl.eglGetError());
        }

        public static void throwEglException(String function, int error) {
            String message = formatEglError(function, error);
            if (LOG_THREADS) {
                Log.e(TAG, "throwEglException tid=" + Thread.currentThread().getId() + " "
                        + message);
            }
            throw new RuntimeException(message);
        }

        public static void logEglErrorAsWarning(String tag, String function, int error) {
            Log.w(tag, formatEglError(function, error));
        }

        public static String formatEglError(String function, int error) {
            return function + " failed: " + EGLLogWrapper.getErrorString(error);
        }

        private WeakReference<GLSurfaceView> mGLSurfaceViewWeakRef;
        EGL10 mEgl;
        EGLDisplay mEglDisplay;
        EGLSurface mEglSurface;
        EGLConfig mEglConfig;
        EGLContext mEglContext;
    }

    /**
     * A generic GL Thread. Takes care of initializing EGL and GL. Delegates
     * to a Renderer instance to do the actual drawing. Can be configured to
     * render continuously or on request.
     */

    static class GLThread extends HandlerThread {
        // only accessed from GLThread
        private GL10 mGLContext;
        private int mWidth;
        private int mHeight;
        private boolean mSizeChanged;
        // current render mode
        private int mRenderMode;
        // the EGLSurface exists but isn't working for some reason
        private boolean mEglSurfaceIsBad;
        // we have an EGLContext
        private boolean mHaveEglContext;
        // we have an EGLSurface
        private boolean mHaveEglSurface;
        // we have a Surface (i.e.: EGLNativeWindowType)
        private boolean mHasSurface;
        // activity is paused
        private boolean mPaused;

        // constants
        private EglHelper mEglHelper;
        private Handler mGLHandler;
        private Choreographer mChoreographer;

        // this runnable could be called often, so we keep an instance around
        class GetRenderModeRunnable implements Runnable {
            volatile public int renderMode;
            @Override
            public void run() {
                renderMode = doGetRenderMode();
            }
        };

        private final GetRenderModeRunnable mGetRenderModeRunnable = new GetRenderModeRunnable();

        /*
         * Set once at thread construction time, nulled out when the parent view is garbage
         * called. This weak reference allows the GLSurfaceView to be garbage collected while
         * the GLThread is still alive.
         */
        private final WeakReference<GLSurfaceView> mGLSurfaceViewWeakRef;

        private final Runnable mExecuteDrawAction = new Runnable() {
            private int mTraceVsyncCounter = 0;
            @Override
            public void run() {
                if (TRACE_ENABLED) {
                    Trace.traceCounter(Trace.TRACE_TAG_GRAPHICS,
                            "GLSurfaceView VSYNC counter", (mTraceVsyncCounter++) & 0xf);
                }
                executeDraw();
            }
        };

        public GLThread(WeakReference<GLSurfaceView> glSurfaceViewWeakRef) {
            super("GLThread", android.os.Process.THREAD_PRIORITY_DISPLAY);
            if (LOG_THREADS) {
                Log.d(TAG, "*** Starting GLThread ***");
            }
            mWidth = 0;
            mHeight = 0;
            mRenderMode = RENDERMODE_CONTINUOUSLY;
            mGLSurfaceViewWeakRef = glSurfaceViewWeakRef;
        }

        private void readyToRun() {
            mChoreographer = Choreographer.getInstance();
            mEglHelper = new EglHelper(mGLSurfaceViewWeakRef);
        }

        @Override
        public void start() {
            super.start();
            // getLooper() blocks until the thread is running
            Looper looper = getLooper();
            mGLHandler = new Handler(looper);
            // don't return until the GLThread state has been initialized
            mGLHandler.runWithScissors(new Runnable() {
                @Override
                public void run() {
                    readyToRun();
                }
            }, 0);
        }

        @Override
        public void run() {
            try {
                super.run();
            } finally {
                // by definition the GLThread is not running anymore here
                stopEglContext();
                stopEglSurface();
            }
        }

        // only call from the GLThread
        private void stopEglSurface() {
            if (mHaveEglSurface) {
                if (LOG_SURFACE) {
                    Log.d(TAG, "releasing EGL surface because paused tid=" + getId());
                }
                mHaveEglSurface = false;
                mEglHelper.destroySurface();
            }
        }

        // only call from the GLThread
        private void stopEglContext() {
            if (mHaveEglContext) {
                mEglHelper.terminate();
                mHaveEglContext = false;
                if (LOG_SURFACE) {
                    Log.d(TAG, "releasing EGL context because paused tid=" + getId());
                }
            }
        }

        private void updateState() {
            final boolean wasAbleToDraw = isAbleToDraw();
            if (!isReadyToDraw()) {
                return;
            }

            if (!mHaveEglSurface || mSizeChanged) {
                // create EGL context if needed
                boolean reportSurfaceCreated = false;
                if (!mHaveEglContext) {
                    mEglHelper.initialize();
                    mHaveEglContext = true;
                    reportSurfaceCreated = true;
                }

                // get the GL interface for the active EGLContext
                mGLContext = (GL10)mEglHelper.createGL();

                // create EGL Surface
                mHaveEglSurface = mEglHelper.createSurface();
                mEglSurfaceIsBad = !mHaveEglSurface;
                mSizeChanged = false;

                // notify use of surface size change
                GLSurfaceView view = mGLSurfaceViewWeakRef.get();
                if (view != null) {
                    if (reportSurfaceCreated) {
                        if (LOG_RENDERER) {
                            Log.d(TAG, "onSurfaceCreated");
                        }
                        view.mRenderer.onSurfaceCreated(mGLContext, mEglHelper.mEglConfig);
                    }

                    if (LOG_RENDERER) {
                        Log.d(TAG, "onSurfaceChanged(" + mWidth + ", " + mHeight + ")");
                    }
                    view.mRenderer.onSurfaceChanged(mGLContext, mWidth, mHeight);
                }
            }

            // see if we should kick the rendering loop
            if (!wasAbleToDraw && isAbleToDraw()) {
                // we're now able to draw
                if (mRenderMode == RENDERMODE_CONTINUOUSLY) {
                    requestRender();
                }
            }

            // By design, this is the only place in a GLThread thread where we wait().
            if (LOG_THREADS) {
                Log.d(TAG, "waiting tid=" + getId()
                        + " mHaveEglContext: " + mHaveEglContext
                        + " mHaveEglSurface: " + mHaveEglSurface
                        + " mPaused: " + mPaused
                        + " mHasSurface: " + mHasSurface
                        + " mSurfaceIsBad: " + mEglSurfaceIsBad
                        + " mWidth: " + mWidth
                        + " mHeight: " + mHeight
                        + " mRenderMode: " + mRenderMode);
            }
        }

        private void executeDraw() {
            if (TRACE_ENABLED) {
                Trace.traceBegin(Trace.TRACE_TAG_GRAPHICS, "executeDraw");
            }

            if (isAbleToDraw()) {
                if (mRenderMode == RENDERMODE_CONTINUOUSLY) {
                    requestRender();
                }

                if (LOG_RENDERER_DRAW_FRAME) {
                    Log.d(TAG, "onDrawFrame tid=" + getId());
                }

                GLSurfaceView view = mGLSurfaceViewWeakRef.get();
                if (view != null) {
                    view.mRenderer.onDrawFrame(mGLContext);
                    int swapError = mEglHelper.swap();
                    switch (swapError) {
                        case EGL10.EGL_SUCCESS:
                            break;
                        case EGL11.EGL_CONTEXT_LOST:
                            if (LOG_SURFACE) {
                                Log.d(TAG, "egl context lost tid=" + getId());
                            }
                            stopEglSurface();
                            stopEglContext();
                            break;
                        default:
                            // Other errors typically mean that the current surface is bad,
                            // probably because the SurfaceView surface has been destroyed,
                            // but we haven't been notified yet.
                            // Log the error to help developers understand why rendering stopped.
                            EglHelper.logEglErrorAsWarning(TAG, "eglSwapBuffers", swapError);
                            mEglSurfaceIsBad = true;
                            break;
                    }
                }
            }

            if (TRACE_ENABLED) {
                Trace.traceEnd(Trace.TRACE_TAG_GRAPHICS);
            }
        }

        private boolean isAbleToDraw() {
            return mHaveEglContext && mHaveEglSurface && isReadyToDraw();
        }

        private boolean isReadyToDraw() {
            return (!mPaused) && mHasSurface && (!mEglSurfaceIsBad)
                && (mWidth > 0) && (mHeight > 0);
        }

        private boolean isEglContextReleasedWhenPausing() {
            GLSurfaceView view = mGLSurfaceViewWeakRef.get();
            return (view != null) ? !view.mPreserveEGLContextOnPause : false;
        }

        public void queueEvent(Runnable r) {
            if (r == null) {
                throw new IllegalArgumentException("Runnable r must not be null");
            }
            mGLHandler.post(r);
        }

        /*
         * the call-backs below all run on the GLThread and implement state
         * changes of the GLSurfaceView and Activity life cycle.
         */

        private void doSurfaceCreated() {
            mHasSurface = true;
            updateState();
        }

        private void doSurfaceDestroyed() {
            if (mHasSurface) {
                if (LOG_SURFACE) {
                    Log.d(TAG, "noticed surfaceView surface lost tid=" + getId());
                }
                stopEglSurface();
            }
            mHasSurface = false;
        }

        private void doPause() {
            if (mPaused == false) {
                mPaused = true;
                stopEglSurface();
                // When pausing, optionally release the EGL Context:
                if (mHaveEglContext && isEglContextReleasedWhenPausing()) {
                    stopEglContext();
                }
            }
        }

        private void doResume() {
            mPaused = false;
            updateState();
            if (mRenderMode == RENDERMODE_WHEN_DIRTY) {
                requestRender();
            }
        }

        private void doWindowResize(int width, int height) {
            // we were not drawing yet. Update the window size and
            // state and attempt to draw a frame.
            mSizeChanged = (mWidth != width || mHeight != height);
            mWidth = width;
            mHeight = height;
            updateState();
            // we always (attempt to) draw a frame before returning
            executeDraw();
        }

        private void doSetRenderMode(int renderMode) {
            mRenderMode = renderMode;
        }


        private int doGetRenderMode() {
            return mRenderMode;
        }

        /*
         * the call-backs below run on the main UI thread, they just
         * wait while executing work on the GLThread.
         */

        public void surfaceCreated() {
            mGLHandler.runWithScissors(new Runnable() {
                @Override
                public void run() {
                    doSurfaceCreated();
                }
            }, 0);
        }

        public void surfaceDestroyed() {
            mGLHandler.runWithScissors(new Runnable() {
                @Override
                public void run() {
                    doSurfaceDestroyed();
                }
            }, 0);
        }

        public void onPause() {
            mGLHandler.runWithScissors(new Runnable() {
                @Override
                public void run() {
                    doPause();
                }
            }, 0);
        }

        public void onResume() {
            mGLHandler.runWithScissors(new Runnable() {
                @Override
                public void run() {
                    doResume();
                }
            }, 0);
        }

        public void onWindowResize(int w, int h) {
            final int width = w;
            final int height = h;
            mGLHandler.runWithScissors(new Runnable() {
                @Override
                public void run() {
                    doWindowResize(width, height);
                }
            }, 0);
        }

        /*
         * the methods below can be called from any thread
         */

        public void requestRender() {
            if (mRenderMode == RENDERMODE_CONTINUOUSLY) {
                mChoreographer.postCallback(Choreographer.CALLBACK_ANIMATION,
                        mExecuteDrawAction, null);
            } else {
                /*
                 * in RENDERMODE_WHEN_DIRTY we schedule the draw callback
                 * immediately because the developer is manager her
                 * timing loop manually -- in particular she could be
                 * using the Choreographer already.
                 */
                mGLHandler.post(mExecuteDrawAction);
            }
        }

        public void setRenderMode(final int renderMode) {
            mGLHandler.runWithScissors(new Runnable() {
                @Override
                public void run() {
                    doSetRenderMode(renderMode);
                }
            }, 0);
        }

        public int getRenderMode() {
            mGLHandler.runWithScissors(mGetRenderModeRunnable, 0);
            return mGetRenderModeRunnable.renderMode;
        }
    } // class GLThread

    static class LogWriter extends Writer {
        @Override
        public void close() {
            flushBuilder();
        }

        @Override
        public void flush() {
            flushBuilder();
        }

        @Override
        public void write(char[] buf, int offset, int count) {
            for (int i = 0; i < count; i++) {
                char c = buf[offset + i];
                if (c == '\n') {
                    flushBuilder();
                } else {
                    mBuilder.append(c);
                }
            }
        }

        private void flushBuilder() {
            if (mBuilder.length() > 0) {
                Log.v(TAG, mBuilder.toString());
                mBuilder.delete(0, mBuilder.length());
            }
        }

        private StringBuilder mBuilder = new StringBuilder();
    }

    private void checkRenderThreadState() {
        if (mGLThread != null) {
            throw new IllegalStateException(
                    "setRenderer has already been called for this instance.");
        }
    }
}