使用glReadPixels檢索位圖時會失去抗鋸齒功能

我使用OpenGL編寫程序。它實現了一個簡單的功能：繪製一個茶壺。爲了使它在屏幕上看起來不錯，我啓用了多重取樣抗鋸齒功能。它確實如此。請看下面的位圖：使用glReadPixels檢索位圖時會失去抗鋸齒功能

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但是當我將它保存爲bmp圖片，它看起來不錯。我使用FBO和PBO來做到這一點。現在，我在後部分我的代碼在這裏：

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的順序讀取 
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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