opengl - 使用 glReadPixels 检索位图时，抗锯齿功能丢失

Question

我使用 OpenGL 编写了一个程序。它实现了一个简单的功能：画一个茶壶。为了让它在屏幕上看起来不错，我启用了多重采样抗锯齿。它确实如此。看下面的位图：

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但是当我将它保存为bmp图片时，它看起来很糟糕。我使用 FBO 和 PBO 来做到这一点。现在我在这里发布我的部分代码：

glGenFramebuffers(1,&m_frameBuffer);
glBindFramebuffer(GL_FRAMEBUFFER,m_frameBuffer);

glGenRenderbuffers(1,&m_renderBufferColor);
glBindRenderbuffer(GL_RENDERBUFFER,m_renderBufferColor);
glRenderbufferStorage(GL_RENDERBUFFER,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);
glRenderbufferStorage(GL_RENDERBUFFER,GL_DEPTH_COMPONENT,
    m_subImageWidth,m_subImageHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER,GL_DEPTH_ATTACHMENT,
    GL_RENDERBUFFER,m_renderBufferDepth);

glBindFramebuffer(GL_FRAMEBUFFER,0);

glBindFramebuffer(GL_FRAMEBUFFER,m_frameBuffer);



glGenBuffers(1,m_subImageBuffer);
glBindBuffer(GL_PIXEL_PACK_BUFFER,m_subImageBuffer);
        glBufferData(GL_PIXEL_PACK_BUFFER,m_bufferSize,
            NULL,GL_STREAM_READ);

glBindFramebuffer(GL_FRAMEBUFFER,m_frameBuffer);

glBindBuffer(GL_PIXEL_PACK_BUFFER,m_subImageBuffer);
glPixelStorei(GL_PACK_ALIGNMENT,1);
//注意：以BGR的顺序读取
glReadPixels(0,0,m_subImageWidth,m_subImageHeight,
        GL_BGR,GL_UNSIGNED_BYTE,bufferOffset(0));
GLUtils::checkForOpenGLError(__FILE__,__LINE__);
m_subPixels[i] = static_cast<GLubyte*>(glMapBuffer(GL_PIXEL_PACK_BUFFER,GL_READ_ONLY));
gltGenBMP(subImageFile,GLT_BGR,m_subImageWidth,m_subImageHeight,m_subPixels[i]);
glBindBuffer(GL_PIXEL_PACK_BUFFER,0);
glUnmapBuffer(GL_PIXEL_PACK_BUFFER);
glBindBuffer(GL_PIXEL_PACK_BUFFER,0);

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