glBlitFramebuffer 导致 OpenGL 错误

Question

我想使用多重采样抗锯齿并将我绘制的内容保存到 BMP。我使用 FBO 进行多重采样和普通 FBO。我参考了这篇文章：GL_framebuffer_multisample。

但是当我使用 glBlitFramebuffer 将数据从 FBO 复制到正常的 FBO 以进行多重采样时，会发生 OpenGL 错误。现在我在这里发布我的部分代码：

首先，创建两个 FBO：

glGenFramebuffers(1,&m_frameBuffer);
glBindFramebuffer(GL_FRAMEBUFFER,m_frameBuffer);
glGenRenderbuffers(1,&m_renderBufferColor);
glBindRenderbuffer(GL_RENDERBUFFER,m_renderBufferColor);
//在FBO里开启多重采样
glRenderbufferStorageMultisample(GL_RENDERBUFFER,4,
    GL_RGB,m_subImageWidth,m_subImageHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER,GL_COLOR_ATTACHMENT0,
    GL_RENDERBUFFER,m_renderBufferColor);
glGenRenderbuffers(1,&m_renderBufferDepth);
glBindRenderbuffer(GL_RENDERBUFFER,m_renderBufferDepth);
glRenderbufferStorageMultisample(GL_RENDERBUFFER,4,
    GL_DEPTH_COMPONENT24,m_subImageWidth,m_subImageHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER,GL_DEPTH_ATTACHMENT,
    GL_RENDERBUFFER,m_renderBufferDepth);
glBindFramebuffer(GL_FRAMEBUFFER,0);//解除绑定
//generate standard FBO for blitting
glGenFramebuffers(1,&m_frameBufferBlit);
glBindFramebuffer(GL_FRAMEBUFFER,m_frameBufferBlit);
glGenRenderbuffers(1,&m_renderBufferColorBlit);
glBindRenderbuffer(GL_RENDERBUFFER,m_renderBufferColorBlit);
glRenderbufferStorage(GL_RENDERBUFFER,GL_RGB,
    m_subImageWidth,m_subImageHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER,GL_COLOR_ATTACHMENT0,
    GL_RENDERBUFFER,m_renderBufferColorBlit);
glGenRenderbuffers(1,&m_renderBufferDepthBlit);
glBindRenderbuffer(GL_RENDERBUFFER,m_renderBufferDepthBlit);
glRenderbufferStorage(GL_RENDERBUFFER,GL_DEPTH_COMPONENT24,
    m_subImageWidth,m_subImageHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER,GL_DEPTH_ATTACHMENT,
    GL_RENDERBUFFER,m_renderBufferDepth);
glBindFramebuffer(GL_FRAMEBUFFER,0);//解除绑定

然后画一些东西：

glBindFramebuffer(GL_FRAMEBUFFER,m_frameBuffer);
GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
if (status != GL_FRAMEBUFFER_COMPLETE)
{
    cout << "The frame buffer status is not complete!" << endl;
    return;
}
drawing();//draw something
glBindFramebuffer(GL_FRAMEBUFFER,0);
    int temp1 = GLUtils::checkForOpenGLError(__FILE__,__LINE__);
    //blitting
    glBindFramebuffer(GL_DRAW_FRAMEBUFFER,m_frameBufferBlit);
    glBindFramebuffer(GL_READ_FRAMEBUFFER,m_frameBuffer);
    int temp2 = GLUtils::checkForOpenGLError(__FILE__,__LINE__);
    glBlitFramebuffer(0,0,m_subImageWidth,m_subImageHeight,
        0,0,m_subImageWidth,m_subImageHeight,
        GL_COLOR_BUFFER_BIT,GL_LINEAR);
    int temp3 = GLUtils::checkForOpenGLError(__FILE__,__LINE__);
    glBindFramebuffer(GL_READ_FRAMEBUFFER,0);
    glBindFramebuffer(GL_DRAW_FRAMEBUFFER,0);
    //glBindFramebuffer(GL_FRAMEBUFFER,m_frameBuffer);
    glBindBuffer(GL_PIXEL_PACK_BUFFER,m_subImageBuffer[i]);
    glPixelStorei(GL_PACK_ALIGNMENT,1);
    glBindFramebuffer(GL_FRAMEBUFFER,m_frameBufferBlit);
    //注意：以BGR的顺序读取
    glReadPixels(0,0,m_subImageWidth,m_subImageHeight,
        GL_BGR,GL_UNSIGNED_BYTE,bufferOffset(0));
    int temp4 = GLUtils::checkForOpenGLError(__FILE__,__LINE__);
    m_subPixels[i] = static_cast<GLubyte*>(glMapBuffer(GL_PIXEL_PACK_BUFFER,GL_READ_ONLY));
    if (m_subPixels[i] == NULL)
    {
        cout << "NULL pointer" << endl;
    }
    gltGenBMP(subImageFile[i],GLT_BGR,m_subImageWidth,m_subImageHeight,m_subPixels[i]);
    glUnmapBuffer(GL_PIXEL_PACK_BUFFER);
    glBindBuffer(GL_PIXEL_PACK_BUFFER,0);
    glBindFramebuffer(GL_FRAMEBUFFER,0);

函数 GLUtils：：checkForOpenGLError 用于检查是否发生 OpenGL 错误（返回 1 表示发生错误）。绘画是为了渲染一些东西。gltGenBMP的功能是将数据保存为BMP。它们都工作得很好。我发现 temp1 和 temp2 是 0，temp3 和 temp4 是 1.So 我得出的结论：函数 glBlitFramebuffer 有问题。但是为什么？有没有设置错误？

---

更新：当我检查正常的 FBO m_frameBufferBlit时：

glBindFramebuffer(GL_DRAW_FRAMEBUFFER,m_frameBufferBlit);
status = glCheckFramebufferStatus(GL_DRAW_FRAMEBUFFER);
if (status != GL_FRAMEBUFFER_COMPLETE)
{
    cout << "The frame buffer status is not complete!" << endl;
    return;
}

我发现它不完整。所以我没有正确创建 FBO？

怎么了？

Answer 1

回想一下帧缓冲完整性的条件可能很有用：

• 必须至少有一个图像附加到帧缓冲
• 所有附件必须完整
• 所有活动的绘制缓冲区都必须具有关联的图像
• 读取缓冲区（如果处于活动状态）必须具有关联的图像
• 所有附加的图像必须具有相同数量的样本

以及附加图像完整性的条件：

• 图像的宽度和高度必须为非零
• 图像内部格式必须与连接点匹配（例如：深度图像必须附加到深度附件）

请注意，这些规则是对实际规则的简化，实际规则稍微复杂一些。