FBO 渲染到纹理和 glReadPixels答案

【问题标题】：FBOs render to texture and glReadPixelsFBO 渲染到纹理和 glReadPixels
【发布时间】：2010-10-21 14:12:20
【问题描述】：

我已经设置了 FBO（GL_FRAMEBUFFER_EXT、颜色和深度缓冲区），并且我的应用正在使用 NULL 图像将简单的 OpenGL 3D 对象（旋转茶壶）渲染为纹理。我正在尝试使用 glReadPixels 捕获像素数据。我在屏幕上正确地看到了 3D 对象。但是 glReadPixels 给出了垃圾数据。我想知道我哪里出错了。任何帮助/指针表示赞赏。

   Code is given below (in brief) -

    glEnable(GL_TEXTURE_2D); // Enable texturing so we can bind our frame buffer texture
    glEnable(GL_DEPTH_TEST); // Enable depth testing

    // Initialize the FBO
    int WIDTH=window_width;
    int HEIGHT=window_height;

    glGenTextures(1, &fbo_texture); // Generate one texture
    glBindTexture(GL_TEXTURE_2D, fbo_texture); // Bind the texture fbo_texture

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, window_width, window_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL); // Create a standard texture with the width and height of our window

        // Setup the basic texture parameters
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

   ......
   ......
   // setup depth buffer
   glGenRenderbuffersEXT(1, &fbo_depth); // Generate one render buffer and store the ID in fbo_depth
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, fbo_depth); // Bind the fbo_depth render buffer

glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT, window_width, window_height); // Set the render buffer storage to be a depth component, with a width and height of the window

glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, fbo_depth); // Set the render buffer of this buffer to the depth buffer

   ....
   .....
  //set up FBO
  glGenFramebuffersEXT(1, &fbo); // Generate one frame buffer and store the ID in fbo
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo); // Bind our frame buffer

glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, fbo_texture, 0); // Attach the texture fbo_texture to the color buffer in our frame buffer

glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, fbo_depth); // Attach the depth buffer fbo_depth to our frame buffer

GLenum status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT); // Check that status of our generated frame buffer

if (status != GL_FRAMEBUFFER_COMPLETE_EXT) // If the frame buffer does not report back as complete
{
    std::cout << "Couldn't create frame buffer" << std::endl; // Output an error to the console
    exit(0); // Exit the application
}


    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo); // Bind our frame buffer for rendering
    glPushAttrib(GL_VIEWPORT_BIT | GL_ENABLE_BIT); // Push our glEnable and glViewport states
    glViewport(0, 0, window_width, window_height); // Set the size of the frame buffer view port

    glClearColor (0.0f, 0.0f, 1.0f, 1.0f); // Set the clear colour
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear the depth and colour buffers
    glLoadIdentity(); // Reset the modelview matrix

    glTranslatef(0.0f, 0.0f, -5.0f); // Translate back 5 units

    glRotatef(rotation_degree, 1.0f, 1.0f, 0.0f); // Rotate according to our rotation_degree value

    glutSolidTeapot(1.0f); // Render a teapot
    glPopAttrib(); // Restore our glEnable and glViewport states

    glReadPixels(0, 0, window_width, window_height, GL_RGBA, GL_UNSIGNED_BYTE, pixels[i]);

    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); // Unbind our texture

    //now display

    ....
    ....

    glutSwapBuffers();
    }

【问题讨论】：

标签： opengl

【解决方案1】：

您需要先绑定您的 FBO，然后调用 glFramebufferTexture2D 和其他 FBO 调用。

同样为避免此类问题，您需要使用 glCheckFramebufferStatus 检查帧缓冲区状态，首先绑定 FBO，它会告诉您帧缓冲区是否完整并准备好渲染。

另外，如果你绘制到一个纹理，你可以使用 glGetTexImage 获取纹理数据。

【讨论】：

我正在绑定 FBO。正如我所说，我在屏幕上看到了 3D 对象，它工作正常。我只是无法让 glReadPixels 工作。
绑定贴图，解绑FBO。
glGetTexImage 成功，但所有像素都设置为 ff 00 00, 00 ff 00, 00 00 ff 并重复。

【解决方案2】：

您正在传递像素[i]。看起来很可疑。像素被声明为什么？从你发的内容我看不出来。我最希望看到类似

glReadPixels(0, 0, window_width, window_height, GL_RGBA, GL_UNSIGNED_BYTE, pixels);

或

glReadPixels(0, 0, window_width, window_height, GL_RGBA, GL_UNSIGNED_BYTE, &pixels[0]);

但这一切都取决于您对像素数组的意图。

【讨论】：