OpenGL API学习记录 glBlitFramebuffer

glBlitFramebuffer

将FBO中指定的东西copy到指定地方去 配合bind函数使用 下面例子拷贝的颜色缓存 在延迟渲染时 可以拷贝GL_DEPTH_BUFFER_BIT来结合正向渲染和延迟渲染

glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
glBindFramebuffer(GL_DRAW_FRAMEBUFFER, intermediateFBO);
glBlitFramebuffer(0, 0, SCR_WIDTH, SCR_HEIGHT, 0, 0, SCR_WIDTH, SCR_HEIGHT, GL_COLOR_BUFFER_BIT, GL_NEAREST);

具体用法在后期MSAA中 先有一个FBO承载第一次绘制 使用multi纹理和multiRBO 再将他的内容copy到另一个FBO作为最后画在呈现在屏幕那个矩形的texture

// configure MSAA framebuffer
    // --------------------------
    unsigned int framebuffer;
    glGenFramebuffers(1, &framebuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
    // create a multisampled color attachment texture
    unsigned int textureColorBufferMultiSampled;
    glGenTextures(1, &textureColorBufferMultiSampled);
    glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, textureColorBufferMultiSampled);
    glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, 4, GL_RGB, SCR_WIDTH, SCR_HEIGHT, GL_TRUE);
    glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, 0);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D_MULTISAMPLE, textureColorBufferMultiSampled, 0);
    // create a (also multisampled) renderbuffer object for depth and stencil attachments
    unsigned int rbo;
    glGenRenderbuffers(1, &rbo);
    glBindRenderbuffer(GL_RENDERBUFFER, rbo);
    glRenderbufferStorageMultisample(GL_RENDERBUFFER, 4, GL_DEPTH24_STENCIL8, SCR_WIDTH, SCR_HEIGHT);
    glBindRenderbuffer(GL_RENDERBUFFER, 0);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, rbo);

    if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
        cout << "ERROR::FRAMEBUFFER:: Framebuffer is not complete!" << endl;
    glBindFramebuffer(GL_FRAMEBUFFER, 0);

    // configure second post-processing framebuffer
    unsigned int intermediateFBO;
    glGenFramebuffers(1, &intermediateFBO);
    glBindFramebuffer(GL_FRAMEBUFFER, intermediateFBO);
    // create a color attachment texture
    unsigned int screenTexture;
    glGenTextures(1, &screenTexture);
    glBindTexture(GL_TEXTURE_2D, screenTexture);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, screenTexture, 0);  // we only need a color buffer

    if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
        cout << "ERROR::FRAMEBUFFER:: Intermediate framebuffer is not complete!" << endl;
    glBindFramebuffer(GL_FRAMEBUFFER, 0);

glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // 1. draw scene as normal in multisampled buffers
        glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        glEnable(GL_DEPTH_TEST);

        // set transformation matrices    
        shader.use();
        glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 1000.0f);
        shader.setMat4("projection", projection);
        shader.setMat4("view", camera.GetViewMatrix());
        shader.setMat4("model", glm::mat4(1.0f));

        glBindVertexArray(cubeVAO);
        glDrawArrays(GL_TRIANGLES, 0, 36);

        // 2. now blit multisampled buffer(s) to normal colorbuffer of intermediate FBO. Image is stored in screenTexture
        glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);
        glBindFramebuffer(GL_DRAW_FRAMEBUFFER, intermediateFBO);
        glBlitFramebuffer(0, 0, SCR_WIDTH, SCR_HEIGHT, 0, 0, SCR_WIDTH, SCR_HEIGHT, GL_COLOR_BUFFER_BIT, GL_NEAREST);

        // 3. now render quad with scene's visuals as its texture image
        glBindFramebuffer(GL_FRAMEBUFFER, 0);
        glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
        glDisable(GL_DEPTH_TEST);

        // draw Screen quad
        screenShader.use();
        glBindVertexArray(quadVAO);
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, screenTexture); // use the now resolved color attachment as the quad's texture
        glDrawArrays(GL_TRIANGLES, 0, 6);