GLES学习笔记---OpenGL绘制到ImageReader

一、ImageReader简介

ImageReader 之前经常使用在camera应用里面，创建一个ImageReader，然后获取surface，配流和下发request时候将surface下发给framework，中间具体对ImageReader做了什么没有具体研究过，等到Hal层camera回帧的时候，ImageReader的onFrameAvailable就会回调上来，通过reader就可以获取图片了。

虽然使用上很简单，但是其实ImageReader里面要学习的东西还是很多的。

ImageReader本质上就是封装了BufferQueue和Surface的一些东西，init的时候创建了一个生产者消费者的队列，以下是init的主要代码

二、使用ImageReader接收Opengl绘制结果

为啥用ImageReader接收绘制结果呢？之前写过使用glReadPixels将绘制结果读取到内存，但是glReadPixels在读取较大图片时候很耗时的，尤其是低端机上，因为glReadPixels是直接从显存拷贝到内存，所以并不使用频繁读取的情况。

通过分析ImageReader源码大概可以简单了解到ImageReader基于BufferQueue和Surface的，那我们可以猜到ImageReader相关的内存应该是GraphicBuffer，GraphicBuffer方便于GPU&CPU共享。

下面这段是创建EGL环境的代码，主要就是：

media_status_t status = AImageReader_new(4000, 3000, AIMAGE_FORMAT_RGBA_8888, 3, &imageReader);  创建ImageReader

status = AImageReader_setImageListener(imageReader, &listener);  设置帧回调

ANativeWindow *nwin;
status = AImageReader_getWindow(imageReader, &nwin); 获取ANativeWindow, 作为

eglCreateWindowSurface的输入，也就是我们之后绘制的载体了。

JNIEXPORT void JNICALL Java_com_sprd_opengl_test_MyNdk_init2
        (JNIEnv *env, jobject obj, jobject surface) {
    // egl ------------------------------------------------------------------- start
    LOGD("init");

    AImageReader *imageReader;
    media_status_t status = AImageReader_new(4000, 3000, AIMAGE_FORMAT_RGBA_8888, 3, &imageReader);
    LOGD("AImageReader_new status: %d", status);

    listener.onImageAvailable = onFrameAvailable;
    status = AImageReader_setImageListener(imageReader, &listener);
    LOGD("AImageReader_setImageListener status: %d", status);

    ANativeWindow *nwin;
    status = AImageReader_getWindow(imageReader, &nwin);
    LOGD("AImageReader_getWindow status: %d", status);

    gl_cxt.nw = nwin;
    gl_cxt.reader = imageReader;

    EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
    if (display == EGL_NO_DISPLAY) {
        LOGD("egl display failed");
        return;
    }

    if (EGL_TRUE != eglInitialize(display, 0, 0)) {
        LOGD("eglInitialize failed");
        return;
    }

    EGLConfig eglConfig;
    EGLint configNum;
    EGLint configSpec[] = {
            EGL_RED_SIZE, 8,
            EGL_GREEN_SIZE, 8,
            EGL_BLUE_SIZE, 8,
            EGL_ALPHA_SIZE, 8,
            EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
            EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
            EGL_RECORDABLE_ANDROID, EGL_TRUE,
            EGL_NONE
    };

    if (EGL_TRUE != eglChooseConfig(display, configSpec, &eglConfig, 1, &configNum)) {
        LOGD("eglChooseConfig failed");
        return;
    }

    EGLSurface winSurface = eglCreateWindowSurface(display, eglConfig, nwin, 0);
    if (winSurface == EGL_NO_SURFACE) {
        LOGD("eglCreateWindowSurface failed");
        return;
    }

    const EGLint ctxAttr[] = {
            EGL_CONTEXT_CLIENT_VERSION, 2,
            EGL_NONE
    };

    EGLContext context = eglCreateContext(display, eglConfig, EGL_NO_CONTEXT, ctxAttr);
    if (context == EGL_NO_CONTEXT) {
        LOGD("eglCreateContext failed");
        return;
    }

    if (EGL_TRUE != eglMakeCurrent(display, winSurface, winSurface, context)) {
        LOGD("eglMakeCurrent failed");
        return;
    }
    gl_cxt.display = display;
    gl_cxt.winSurface = winSurface;
    gl_cxt.context = context;

    // egl ------------------------------------------------------------------- end

    // shader ------------------------------------------------------------------- start
    GLint vsh = initShader(vertexSimpleShape, GL_VERTEX_SHADER);
    GLint fsh = initShader(fragSimpleShape, GL_FRAGMENT_SHADER);

    GLint program = glCreateProgram();
    if (program == 0) {
        LOGD("glCreateProgram failed");
        return;
    }

    glAttachShader(program, vsh);
    glAttachShader(program, fsh);

    glLinkProgram(program);
    GLint status2 = 0;
    glGetProgramiv(program, GL_LINK_STATUS, &status2);
    if (status2 == 0) {
        LOGD("glLinkProgram failed");
        return;
    }
    gl_cxt.program = program;
    LOGD("glLinkProgram success");
    // shader ------------------------------------------------------------------- end
}

这段是绘制的代码，里面有不少无用的代码，主要是绘制完成之后

eglSwapBuffers一下就可以了，这样才会触发onFrameAvailable回调。

JNIEXPORT void JNICALL Java_com_sprd_opengl_test_MyNdk_process2
        (JNIEnv *env, jobject obj, jobject bitmap) {
    LOGD("process2  1");
    glUseProgram(gl_cxt.program);
    AndroidBitmapInfo bitmapInfo;
    if (AndroidBitmap_getInfo(env, bitmap, &bitmapInfo) < 0) {
        LOGE("AndroidBitmap_getInfo() failed ! ");
        return;
    }
    void *bmpPixels;
    LOGD("process2  2, format: %d, stride: %d", bitmapInfo.format, bitmapInfo.stride);
    AndroidBitmap_lockPixels(env, bitmap, &bmpPixels);
    LOGD("process2  3");

    unsigned int textureId;
    glGenTextures(1, &textureId);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textureId);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    int width = bitmapInfo.width;
    int height = bitmapInfo.height;

    LOGD("process2  4");
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, bmpPixels);
    unsigned char *pOri = (unsigned char *)bmpPixels;
    LOGD("process2  5     %d, %d, %d, %d, %d, %d, %d, %d", *(pOri), *(pOri+1), *(pOri+2), *(pOri+3),
         *(pOri+114), *(pOri+115), *(pOri+116), *(pOri+117));
    glBindTexture(GL_TEXTURE_2D, 0);
    AndroidBitmap_unlockPixels(env, bitmap);

    unsigned int offTexture, fbo;
    glGenTextures(1, &offTexture);
    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, offTexture);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    // 没有这句调用, glCheckFramebufferStatus 返回 36054
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
    glGenFramebuffers(1, &fbo);
    LOGD("fb status: %d, error: %d" , glCheckFramebufferStatus(GL_FRAMEBUFFER), glGetError());
    glBindFramebuffer(GL_FRAMEBUFFER, fbo);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, offTexture, 0);
    LOGD("fb status: %d, error: %d" , glCheckFramebufferStatus(GL_FRAMEBUFFER), glGetError());
    glBindTexture(GL_TEXTURE_2D, 0);
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    /*顶点               纹理*/
    float vertices[] = {-1.0f, -1.0f, 0.0f, 0.0f, 0.0f,
                        -1.0f, 1.0f,  0.0f, 0.0f, 1.0f,
                        1.0f,  -1.0f, 0.0f, 1.0f, 0.0f,
                        1.0f,  1.0f,  0.0f, 1.0f, 1.0f};

    unsigned int indices[] = {
            0, 1, 2, // first triangle
            1, 2, 3  // second triangle
    };

    // optimal
    unsigned int VBO, EBO, VAO;
    glGenVertexArrays(1, &VAO);
    glBindVertexArray(VAO);

    glGenBuffers(1, &VBO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)((0 + 3)*sizeof(float)));
    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);

    glGenBuffers(1, &EBO);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

    glBindVertexArray(0);


    glBindVertexArray(VAO);
    glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

    // draw to offline texture.
    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, offTexture);
    glBindFramebuffer(GL_FRAMEBUFFER, fbo);
    LOGD("fb status: %d, error: %d" , glCheckFramebufferStatus(GL_FRAMEBUFFER), glGetError());
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, (void*)0);
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    glBindTexture(GL_TEXTURE_2D, 0);


    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textureId);
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, (void*)0);
    glBindTexture(GL_TEXTURE_2D, 0);

    glFinish();

    glDisableVertexAttribArray(0);
    glDisableVertexAttribArray(1);
    glBindVertexArray(0);

    eglSwapBuffers(gl_cxt.display, gl_cxt.winSurface);
    LOGD("process2 X");

最后就是onFrameAvailable回调了，绘制完成之后onFrameAvailable就会触发，可以暂时不考虑我的memcpy那一段

AHardwareBuffer_lock耗时就十几毫秒（4000*3000*4的数据），所以很快就能从内存得到绘制结果了。

static void onFrameAvailable(void *context, AImageReader *reader) {
    LOGD("MyNdk onFrameAvailable");

    AImage *image = nullptr;
    media_status_t status = AImageReader_acquireNextImage(reader, &image);
    LOGD("AImageReader_acquireNextImage status: %d, image: %p", status, image);

    AHardwareBuffer *inBuffer = nullptr;
    status = AImage_getHardwareBuffer(image, &inBuffer);
    LOGD("AImage_getHardwareBuffer status: %d, inBuffer: %p", status, inBuffer);

    int width;
    int height;
    AImage_getWidth(image, &width);
    AImage_getHeight(image, &height);
    unsigned char *ptrReader = nullptr;
    unsigned char *dstBuffer = static_cast<unsigned char *>(malloc(width * height * 4));
    LOGD("AHardwareBuffer_lock E, w:%d, h:%d", width, height);
    AHardwareBuffer_lock(inBuffer, AHARDWAREBUFFER_USAGE_CPU_READ_OFTEN, -1, nullptr,
                         (void **) &ptrReader);
    LOGD("AHardwareBuffer_lock X");
    memcpy(dstBuffer, ptrReader, width * height * 4);
    AHardwareBuffer_unlock(inBuffer, nullptr);
    LOGD("%d, %d, %d, %d", *ptrReader, *(ptrReader+1), *(ptrReader+2), *(ptrReader+3));

    AImage_delete(image);
}