OES External Texture Render - tonykwok/made-mistakes-again GitHub Wiki

/*
 * Copyright (C) 2021 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.mediav2.cts;

import android.graphics.SurfaceTexture;
import android.opengl.EGL14;
import android.opengl.EGLConfig;
import android.opengl.EGLContext;
import android.opengl.EGLDisplay;
import android.opengl.EGLSurface;
import android.util.Log;
import android.view.Surface;

/**
 * Holds state associated with a Surface used for MediaCodec decoder output.
 * <p>
 * The (width,height) constructor for this class will prepare GL, create a SurfaceTexture,
 * and then create a Surface for that SurfaceTexture.  The Surface can be passed to
 * MediaCodec.configure() to receive decoder output.  When a frame arrives, we latch the
 * texture with updateTexImage, then render the texture with GL to a pbuffer.
 * <p>
 * The no-arg constructor skips the GL preparation step and doesn't allocate a pbuffer.
 * Instead, it just creates the Surface and SurfaceTexture, and when a frame arrives
 * we just draw it on whatever surface is current.
 * <p>
 * By default, the Surface will be using a BufferQueue in asynchronous mode, so we
 * can potentially drop frames.
 */
class OutputSurface implements SurfaceTexture.OnFrameAvailableListener {
    private static final String TAG = "OutputSurface";
    private static final boolean VERBOSE = false;

    private EGLDisplay mEGLDisplay = EGL14.EGL_NO_DISPLAY;
    private EGLContext mEGLContext = EGL14.EGL_NO_CONTEXT;
    private EGLSurface mEGLSurface = EGL14.EGL_NO_SURFACE;

    private SurfaceTexture mSurfaceTexture;
    private Surface mSurface;

    private Object mFrameSyncObject = new Object();     // guards mFrameAvailable
    private boolean mFrameAvailable;

    private TextureRender mTextureRender;

    /**
     * Creates an OutputSurface backed by a pbuffer with the specified dimensions.  The new
     * EGL context and surface will be made current.  Creates a Surface that can be passed
     * to MediaCodec.configure().
     */
    public OutputSurface(int width, int height, boolean useHighBitDepth) {
        this(width, height, useHighBitDepth, /* useYuvSampling */ false);
    }

    public OutputSurface(int width, int height, boolean useHighBitDepth, boolean useYuvSampling) {
        if (width <= 0 || height <= 0) {
            throw new IllegalArgumentException();
        }

        eglSetup(width, height, useHighBitDepth, useYuvSampling);
        makeCurrent();

        setup(this, useYuvSampling);
    }

    /**
     * Creates an OutputSurface using the current EGL context (rather than establishing a
     * new one).  Creates a Surface that can be passed to MediaCodec.configure().
     */
    public OutputSurface() {
        setup(this, /* useYuvSampling */ false);
    }

    public OutputSurface(final SurfaceTexture.OnFrameAvailableListener listener) {
        setup(listener, /* useYuvSampling */ false);
    }

    /**
     * Creates instances of TextureRender and SurfaceTexture, and a Surface associated
     * with the SurfaceTexture.
     */
    private void setup(SurfaceTexture.OnFrameAvailableListener listener, boolean useYuvSampling) {
        assertTrue(EGL14.eglGetCurrentContext() != EGL14.EGL_NO_CONTEXT);
        assertTrue(EGL14.eglGetCurrentDisplay() != EGL14.EGL_NO_DISPLAY);
        assertTrue(EGL14.eglGetCurrentSurface(EGL14.EGL_DRAW) != EGL14.EGL_NO_SURFACE);
        assertTrue(EGL14.eglGetCurrentSurface(EGL14.EGL_READ) != EGL14.EGL_NO_SURFACE);
        mTextureRender = new TextureRender();
        mTextureRender.setUseYuvSampling(useYuvSampling);
        mTextureRender.surfaceCreated();

        // Even if we don't access the SurfaceTexture after the constructor returns, we
        // still need to keep a reference to it.  The Surface doesn't retain a reference
        // at the Java level, so if we don't either then the object can get GCed, which
        // causes the native finalizer to run.
        if (VERBOSE) Log.d(TAG, "textureID=" + mTextureRender.getTextureId());
        mSurfaceTexture = new SurfaceTexture(mTextureRender.getTextureId());

        // This doesn't work if OutputSurface is created on the thread that CTS started for
        // these test cases.
        //
        // The CTS-created thread has a Looper, and the SurfaceTexture constructor will
        // create a Handler that uses it.  The "frame available" message is delivered
        // there, but since we're not a Looper-based thread we'll never see it.  For
        // this to do anything useful, OutputSurface must be created on a thread without
        // a Looper, so that SurfaceTexture uses the main application Looper instead.
        //
        // Java language note: passing "this" out of a constructor is generally unwise,
        // but we should be able to get away with it here.
        mSurfaceTexture.setOnFrameAvailableListener(listener);

        mSurface = new Surface(mSurfaceTexture);
    }

    /**
     * Prepares EGL.  We want a GLES 2.0 context and a surface that supports pbuffer.
     */
    private void eglSetup(int width, int height, boolean useHighBitDepth, boolean useYuvSampling) {
        mEGLDisplay = EGL14.eglGetDisplay(EGL14.EGL_DEFAULT_DISPLAY);
        if (mEGLDisplay == EGL14.EGL_NO_DISPLAY) {
            throw new RuntimeException("unable to get EGL14 display");
        }
        int[] version = new int[2];
        if (!EGL14.eglInitialize(mEGLDisplay, version, 0, version, 1)) {
            mEGLDisplay = null;
            throw new RuntimeException("unable to initialize EGL14");
        }

        // Configure EGL for pbuffer and OpenGL ES 2.0.  We want enough RGB bits
        // to be able to tell if the frame is reasonable.
        int eglColorSize = useHighBitDepth ? 10: 8;
        int eglAlphaSize = useHighBitDepth ? 2: 0;
        int[] attribList = {
                EGL14.EGL_RED_SIZE, eglColorSize,
                EGL14.EGL_GREEN_SIZE, eglColorSize,
                EGL14.EGL_BLUE_SIZE, eglColorSize,
                EGL14.EGL_ALPHA_SIZE, eglAlphaSize,
                EGL14.EGL_RENDERABLE_TYPE, EGL14.EGL_OPENGL_ES2_BIT,
                EGL14.EGL_SURFACE_TYPE, EGL14.EGL_PBUFFER_BIT,
                EGL14.EGL_NONE
        };
        EGLConfig[] configs = new EGLConfig[1];
        int[] numConfigs = new int[1];
        if (!EGL14.eglChooseConfig(mEGLDisplay, attribList, 0, configs, 0, configs.length,
                numConfigs, 0)) {
            throw new RuntimeException("unable to find RGB888+recordable ES2 EGL config");
        }

        // Configure context for OpenGL ES 3.0/2.0.
        int eglContextClientVersion = useYuvSampling ? 3: 2;
        int[] attrib_list = {
                EGL14.EGL_CONTEXT_CLIENT_VERSION, eglContextClientVersion,
                EGL14.EGL_NONE
        };
        mEGLContext = EGL14.eglCreateContext(mEGLDisplay, configs[0], EGL14.EGL_NO_CONTEXT,
                attrib_list, 0);
        checkEglError("eglCreateContext");
        if (mEGLContext == null) {
            throw new RuntimeException("null context");
        }

        // Create a pbuffer surface.  By using this for output, we can use glReadPixels
        // to test values in the output.
        int[] surfaceAttribs = {
                EGL14.EGL_WIDTH, width,
                EGL14.EGL_HEIGHT, height,
                EGL14.EGL_NONE
        };
        mEGLSurface = EGL14.eglCreatePbufferSurface(mEGLDisplay, configs[0], surfaceAttribs, 0);
        checkEglError("eglCreatePbufferSurface");
        if (mEGLSurface == null) {
            throw new RuntimeException("surface was null");
        }
    }

    /**
     * Discard all resources held by this class, notably the EGL context.
     */
    public void release() {
        if (mEGLDisplay != EGL14.EGL_NO_DISPLAY) {
            EGL14.eglDestroySurface(mEGLDisplay, mEGLSurface);
            EGL14.eglDestroyContext(mEGLDisplay, mEGLContext);
            EGL14.eglReleaseThread();
            EGL14.eglTerminate(mEGLDisplay);
        }

        mSurface.release();

        mSurfaceTexture.release();

        mEGLDisplay = EGL14.EGL_NO_DISPLAY;
        mEGLContext = EGL14.EGL_NO_CONTEXT;
        mEGLSurface = EGL14.EGL_NO_SURFACE;

        mTextureRender = null;
        mSurface = null;
        mSurfaceTexture = null;
    }

    /**
     * Makes our EGL context and surface current.
     */
    public void makeCurrent() {
        if (!EGL14.eglMakeCurrent(mEGLDisplay, mEGLSurface, mEGLSurface, mEGLContext)) {
            throw new RuntimeException("eglMakeCurrent failed");
        }
    }

    /**
     * Returns the Surface that we draw onto.
     */
    public Surface getSurface() {
        return mSurface;
    }

    /**
     * Replaces the fragment shader.
     */
    public void changeFragmentShader(String fragmentShader) {
        mTextureRender.changeFragmentShader(fragmentShader);
    }

    /**
     * Latches the next buffer into the texture.  Must be called from the thread that created
     * the OutputSurface object, after the onFrameAvailable callback has signaled that new
     * data is available.
     */
    public void awaitNewImage() {
        final int TIMEOUT_MS = 2000;

        synchronized (mFrameSyncObject) {
            while (!mFrameAvailable) {
                try {
                    // Wait for onFrameAvailable() to signal us.  Use a timeout to avoid
                    // stalling the test if it doesn't arrive.
                    mFrameSyncObject.wait(TIMEOUT_MS);
                    if (!mFrameAvailable) {
                        // TODO: if "spurious wakeup", continue while loop
                        throw new RuntimeException("Surface frame wait timed out");
                    }
                } catch (InterruptedException ie) {
                    // shouldn't happen
                    throw new RuntimeException(ie);
                }
            }
            mFrameAvailable = false;
        }

        // Latch the data.
        mTextureRender.checkGlError("before updateTexImage");
        mSurfaceTexture.updateTexImage();
    }

    /**
     * Wait for new image to become available or until timeout, whichever comes first.
     * @param timeoutMs
     * @return true if new image is available. false for no new image until timeout.
     */
    public boolean checkForNewImage(int timeoutMs) {
        synchronized (mFrameSyncObject) {
            while (!mFrameAvailable) {
                try {
                    // Wait for onFrameAvailable() to signal us.  Use a timeout to avoid
                    // stalling the test if it doesn't arrive.
                    mFrameSyncObject.wait(timeoutMs);
                    if (!mFrameAvailable) {
                        return false;
                    }
                } catch (InterruptedException ie) {
                    // shouldn't happen
                    throw new RuntimeException(ie);
                }
            }
            mFrameAvailable = false;
        }

        // Latch the data.
        mTextureRender.checkGlError("before updateTexImage");
        mSurfaceTexture.updateTexImage();
        return true;
    }

    /**
     * Draws the data from SurfaceTexture onto the current EGL surface.
     */
    public void drawImage() {
        mTextureRender.drawFrame(mSurfaceTexture);
    }

    public void latchImage() {
        mTextureRender.checkGlError("before updateTexImage");
        mSurfaceTexture.updateTexImage();
    }

    @Override
    public void onFrameAvailable(SurfaceTexture st) {
        if (VERBOSE) Log.d(TAG, "new frame available");
        synchronized (mFrameSyncObject) {
            if (mFrameAvailable) {
                throw new RuntimeException("mFrameAvailable already set, frame could be dropped");
            }
            mFrameAvailable = true;
            mFrameSyncObject.notifyAll();
        }
    }

    /**
     * Checks for EGL errors.
     */
    private void checkEglError(String msg) {
        int error = EGL14.eglGetError();
        if (error != EGL14.EGL_SUCCESS) {
            throw new RuntimeException(msg + ": EGL error: 0x" + Integer.toHexString(error));
        }
    }

    private static void assertTrue(boolean condition) {
        if (!condition) {
            throw new AssertionError();
        }
    }
}
/*
 * Copyright (C) 2021 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.mediav2.cts;

import android.graphics.Bitmap;
import android.graphics.SurfaceTexture;
import android.opengl.GLES11Ext;
import android.opengl.GLES20;
import android.opengl.Matrix;
import android.util.Log;

import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

/**
 * Code for rendering a texture onto a surface using OpenGL ES 2.0.
 */
class TextureRender {
    private static final String TAG = "TextureRender";

    private static final int FLOAT_SIZE_BYTES = 4;
    private static final int TRIANGLE_VERTICES_DATA_STRIDE_BYTES = 5 * FLOAT_SIZE_BYTES;
    private static final int TRIANGLE_VERTICES_DATA_POS_OFFSET = 0;
    private static final int TRIANGLE_VERTICES_DATA_UV_OFFSET = 3;
    private final float[] mTriangleVerticesData = {
            // X, Y, Z, U, V
            -1.0f, -1.0f, 0.0f, 0.0f, 0.0f,
             1.0f, -1.0f, 0.0f, 1.0f, 0.0f,
            -1.0f,  1.0f, 0.0f, 0.0f, 1.0f,
             1.0f,  1.0f, 0.0f, 1.0f, 1.0f,
    };

    private FloatBuffer mTriangleVertices;

    private static final String VERTEX_SHADER_RGB =
            "uniform mat4 uMVPMatrix;\n" +
            "uniform mat4 uSTMatrix;\n" +
            "attribute vec4 aPosition;\n" +
            "attribute vec4 aTextureCoord;\n" +
            "varying vec2 vTextureCoord;\n" +
            "void main() {\n" +
            "  gl_Position = uMVPMatrix * aPosition;\n" +
            "  vTextureCoord = (uSTMatrix * aTextureCoord).xy;\n" +
            "}\n";

    private static final String FRAGMENT_SHADER_RGB =
            "#extension GL_OES_EGL_image_external : require\n" +
            "precision mediump float;\n" +      // highp here doesn't seem to matter
            "varying vec2 vTextureCoord;\n" +
            "uniform samplerExternalOES sTexture;\n" +
            "void main() {\n" +
            "  gl_FragColor = texture2D(sTexture, vTextureCoord);\n" +
            "}\n";

    private static final String VERTEX_SHADER_YUV =
            "#version 300 es\n" +
            "uniform mat4 uMVPMatrix;\n" +
            "uniform mat4 uSTMatrix;\n" +
            "in vec4 aPosition;\n" +
            "in vec4 aTextureCoord;\n" +
            "out vec2 vTextureCoord;\n" +
            "void main() {\n" +
            "  gl_Position = uMVPMatrix * aPosition;\n" +
            "  vTextureCoord = (uSTMatrix * aTextureCoord).xy;\n" +
            "}\n";

    private static final String FRAGMENT_SHADER_YUV =
            "#version 300 es\n" +
            "#extension GL_OES_EGL_image_external : require\n" +
            "#extension GL_EXT_YUV_target : require\n" +
            "precision mediump float;\n" +      // highp here doesn't seem to matter
            "uniform __samplerExternal2DY2YEXT uTexSampler;\n" +
            "in vec2 vTextureCoord;\n" +
            "out vec4 outColor;\n" +
            "void main() {\n" +
            "    outColor = texture(uTexSampler, vTextureCoord);\n" +
            "}\n";

    private float[] mMVPMatrix = new float[16];
    private float[] mSTMatrix = new float[16];

    private int mProgram;
    private int mTextureID;
    private int muMVPMatrixHandle;
    private int muSTMatrixHandle;
    private int maPositionHandle;
    private int maTextureHandle;
    private boolean mUseYuvSampling;

    public TextureRender() {
        mTriangleVertices = ByteBuffer.allocateDirect(
            mTriangleVerticesData.length * FLOAT_SIZE_BYTES)
                .order(ByteOrder.nativeOrder()).asFloatBuffer();
        mTriangleVertices.put(mTriangleVerticesData).position(0);

        Matrix.setIdentityM(mSTMatrix, 0);
        mUseYuvSampling = false;
    }

    public void setUseYuvSampling(boolean useYuvSampling) {
        mUseYuvSampling = useYuvSampling;
    }

    public int getTextureId() {
        return mTextureID;
    }

    public void drawFrame(SurfaceTexture st) {
        checkGlError("onDrawFrame start");
        st.getTransformMatrix(mSTMatrix);

        GLES20.glClearColor(0.0f, 1.0f, 0.0f, 1.0f);
        GLES20.glClear(GLES20.GL_DEPTH_BUFFER_BIT | GLES20.GL_COLOR_BUFFER_BIT);

        GLES20.glUseProgram(mProgram);
        checkGlError("glUseProgram");

        GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
        GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, mTextureID);

        mTriangleVertices.position(TRIANGLE_VERTICES_DATA_POS_OFFSET);
        GLES20.glVertexAttribPointer(maPositionHandle, 3, GLES20.GL_FLOAT, false,
            TRIANGLE_VERTICES_DATA_STRIDE_BYTES, mTriangleVertices);
        checkGlError("glVertexAttribPointer maPosition");
        GLES20.glEnableVertexAttribArray(maPositionHandle);
        checkGlError("glEnableVertexAttribArray maPositionHandle");

        mTriangleVertices.position(TRIANGLE_VERTICES_DATA_UV_OFFSET);
        GLES20.glVertexAttribPointer(maTextureHandle, 2, GLES20.GL_FLOAT, false,
            TRIANGLE_VERTICES_DATA_STRIDE_BYTES, mTriangleVertices);
        checkGlError("glVertexAttribPointer maTextureHandle");
        GLES20.glEnableVertexAttribArray(maTextureHandle);
        checkGlError("glEnableVertexAttribArray maTextureHandle");

        Matrix.setIdentityM(mMVPMatrix, 0);
        GLES20.glUniformMatrix4fv(muMVPMatrixHandle, 1, false, mMVPMatrix, 0);
        GLES20.glUniformMatrix4fv(muSTMatrixHandle, 1, false, mSTMatrix, 0);

        GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
        checkGlError("glDrawArrays");
        GLES20.glFinish();
    }

    /**
     * Initializes GL state.  Call this after the EGL surface has been created and made current.
     */
    public void surfaceCreated() {
        if (mUseYuvSampling == false) {
            mProgram = createProgram(VERTEX_SHADER_RGB, FRAGMENT_SHADER_RGB);
        } else {
            mProgram = createProgram(VERTEX_SHADER_YUV, FRAGMENT_SHADER_YUV);
        }
        if (mProgram == 0) {
            throw new RuntimeException("failed creating program");
        }
        maPositionHandle = GLES20.glGetAttribLocation(mProgram, "aPosition");
        checkGlError("glGetAttribLocation aPosition");
        if (maPositionHandle == -1) {
            throw new RuntimeException("Could not get attrib location for aPosition");
        }
        maTextureHandle = GLES20.glGetAttribLocation(mProgram, "aTextureCoord");
        checkGlError("glGetAttribLocation aTextureCoord");
        if (maTextureHandle == -1) {
            throw new RuntimeException("Could not get attrib location for aTextureCoord");
        }

        muMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");
        checkGlError("glGetUniformLocation uMVPMatrix");
        if (muMVPMatrixHandle == -1) {
            throw new RuntimeException("Could not get attrib location for uMVPMatrix");
        }

        muSTMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uSTMatrix");
        checkGlError("glGetUniformLocation uSTMatrix");
        if (muSTMatrixHandle == -1) {
            throw new RuntimeException("Could not get attrib location for uSTMatrix");
        }


        int[] textures = new int[1];
        GLES20.glGenTextures(1, textures, 0);

        mTextureID = textures[0];
        GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, mTextureID);
        checkGlError("glBindTexture mTextureID");

        GLES20.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_MIN_FILTER,
                GLES20.GL_NEAREST);
        GLES20.glTexParameterf(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_MAG_FILTER,
                GLES20.GL_LINEAR);
        GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_WRAP_S,
                GLES20.GL_CLAMP_TO_EDGE);
        GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_WRAP_T,
                GLES20.GL_CLAMP_TO_EDGE);
        checkGlError("glTexParameter");
    }

    /**
     * Replaces the fragment shader.
     */
    public void changeFragmentShader(String fragmentShader) {
        GLES20.glDeleteProgram(mProgram);
        mProgram = createProgram(VERTEX_SHADER_RGB, fragmentShader);
        if (mProgram == 0) {
            throw new RuntimeException("failed creating program");
        }
    }

    private int loadShader(int shaderType, String source) {
        int shader = GLES20.glCreateShader(shaderType);
        checkGlError("glCreateShader type=" + shaderType);
        GLES20.glShaderSource(shader, source);
        GLES20.glCompileShader(shader);
        int[] compiled = new int[1];
        GLES20.glGetShaderiv(shader, GLES20.GL_COMPILE_STATUS, compiled, 0);
        if (compiled[0] == 0) {
            Log.e(TAG, "Could not compile shader " + shaderType + ":");
            Log.e(TAG, " " + GLES20.glGetShaderInfoLog(shader));
            GLES20.glDeleteShader(shader);
            shader = 0;
        }
        return shader;
    }

    private int createProgram(String vertexSource, String fragmentSource) {
        int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexSource);
        if (vertexShader == 0) {
            return 0;
        }
        int pixelShader = loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentSource);
        if (pixelShader == 0) {
            return 0;
        }

        int program = GLES20.glCreateProgram();
        checkGlError("glCreateProgram");
        if (program != 0) {
            GLES20.glAttachShader(program, vertexShader);
            checkGlError("glAttachShader");
            GLES20.glAttachShader(program, pixelShader);
            checkGlError("glAttachShader");
            GLES20.glLinkProgram(program);
            int[] linkStatus = new int[1];
            GLES20.glGetProgramiv(program, GLES20.GL_LINK_STATUS, linkStatus, 0);
            if (linkStatus[0] != GLES20.GL_TRUE) {
                Log.e(TAG, "Could not link program: ");
                Log.e(TAG, GLES20.glGetProgramInfoLog(program));
                GLES20.glDeleteProgram(program);
                program = 0;
            }
        } else {
            Log.e(TAG, "Could not create program");
        }

        return program;
    }

    public void checkGlError(String op) {
        int error;
        while ((error = GLES20.glGetError()) != GLES20.GL_NO_ERROR) {
            Log.e(TAG, op + ": glError " + error);
            throw new RuntimeException(op + ": glError " + error);
        }
    }

    /**
     * Saves the current frame to disk as a PNG image.  Frame starts from (0,0).
     * <p>
     * Useful for debugging.
     */
    public static void saveFrame(String filename, int width, int height) {
        // glReadPixels gives us a ByteBuffer filled with what is essentially big-endian RGBA
        // data (i.e. a byte of red, followed by a byte of green...).  We need an int[] filled
        // with native-order ARGB data to feed to Bitmap.
        //
        // If we implement this as a series of buf.get() calls, we can spend 2.5 seconds just
        // copying data around for a 720p frame.  It's better to do a bulk get() and then
        // rearrange the data in memory.  (For comparison, the PNG compress takes about 500ms
        // for a trivial frame.)
        //
        // So... we set the ByteBuffer to little-endian, which should turn the bulk IntBuffer
        // get() into a straight memcpy on most Android devices.  Our ints will hold ABGR data.
        // Swapping B and R gives us ARGB.  We need about 30ms for the bulk get(), and another
        // 270ms for the color swap.
        //
        // Making this even more interesting is the upside-down nature of GL, which means we
        // flip the image vertically here.

        ByteBuffer buf = ByteBuffer.allocateDirect(width * height * 4);
        buf.order(ByteOrder.LITTLE_ENDIAN);
        GLES20.glReadPixels(0, 0, width, height, GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, buf);
        buf.rewind();

        int pixelCount = width * height;
        int[] colors = new int[pixelCount];
        buf.asIntBuffer().get(colors);
        for (int i = 0; i < pixelCount; i++) {
            int c = colors[i];
            colors[i] = (c & 0xff00ff00) | ((c & 0x00ff0000) >> 16) | ((c & 0x000000ff) << 16);
        }

        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream(filename);
            Bitmap bmp = Bitmap.createBitmap(colors, width, height, Bitmap.Config.ARGB_8888);
            bmp.compress(Bitmap.CompressFormat.PNG, 90, fos);
            bmp.recycle();
        } catch (IOException ioe) {
            throw new RuntimeException("Failed to write file " + filename, ioe);
        } finally {
            try {
                if (fos != null) fos.close();
            } catch (IOException ioe2) {
                throw new RuntimeException("Failed to close file " + filename, ioe2);
            }
        }
        Log.d(TAG, "Saved " + width + "x" + height + " frame as '" + filename + "'");
    }
}