C++ OpenGL FBO，MRT写入后台缓冲区

我在Mac上的OpenGL3.3中遇到了一个令人困惑的情况。我已经创建了一个FBO，有五个连接点，每个连接点的大小为512x512。我构建了一个着色器，它可以写入gl_FragData[0-4]，用于我的几何体的漫反射、法线、位置、镜面反射和发射。渲染场景时，后缓冲区和渲染目标将被更新，即使我只绑定了FBO

下面是一些代码：

    void OpenGLESDriver::setFrameBufferAttachments( u32 nAttachments, const u32* aAttachments ){
      pushText( "setFrameBufferAttachments" );
        #if USE_MRT
          GLint max;
          glGetIntegerv( GL_MAX_DRAW_BUFFERS, &max );
          GLenum aBuffers[max];
          if( nAttachments > max ){
            nAttachments = max;
          }
          for( u32 i=0; i<nAttachments; ++i ){
            aBuffers[i] = GL_COLOR_ATTACHMENT0+aAttachments[i];
          }
          for( u32 i=nAttachments; i<max; ++i ){
            aBuffers[i] = GL_NONE;
          }
          glDrawBuffers( max, aBuffers );
          glAssert();
        #else
          glDrawBuffer( GL_COLOR_ATTACHMENT0+aAttachments[0] );
          glAssert();
        #endif
      popText();
    }

因此，最终渲染代码如下所示：

        pushText( "Render MRT pass" );
          if( setFrameBuffer( m_tPostFx.buffers[0] )){
            setColorMask( true, true, true, true );
            clearZ();
            enableZBuffer( false );
            setColor( color );
            clearMRT( m_tPostFx.clearMRTShader );
            enableZBuffer( true );
            drawMRTPass();
          }
        popText();

---

出于某种原因，后台缓冲区正在呈现给FBO和FBO。我一定错过了什么，但不知道是什么。有人知道我做错了什么吗？

经过一番摸索，我终于找到了答案。我的渲染器使用渲染期间填充的RenderNode对象向量。在我完成后期效果后，我没有清除那个向量。出于某种原因，未填充向量将与下一个FBO目标一起渲染，该目标将在第二个FBO中再次绘制所有第一批几何体。通过在渲染过程开始和结束时清除向量，我解决了这个问题。我仍在尝试跟踪是谁再次提交了所有渲染节点。希望我粘贴的代码能够帮助任何希望做FBO的人，因为它毕竟可以工作。：）

实际上，我有点困惑，为什么这

GLenum aBuffers[max]max

不是常数时，code>编译。我假设

USE\u MRT

是未定义的，它是

setFrameBufferAttachments

中我们应该关注的第二个代码分支？在C++11中，max不需要是常量。诚然，它不是在VisualStudio下编译的，但这段代码是针对Android和OSX的。这没关系，因为我的Win32渲染器使用DirectX，而我的iOS渲染器使用Metal。Win32代码并没有采用这种技巧。

    FrameBuffer::handle OpenGLESDriver::createFrameBuffer( const FrameBuffer::ColorTargets& vColorTargets, const DepthTarget::handle& hDT ){

      //--------------------------------------------------------------------
      // Save off default FBO.
      //--------------------------------------------------------------------

      if( s_iFBOMaster < 0 ){
        glGetIntegerv( GL_FRAMEBUFFER_BINDING, &s_iFBOMaster );
        glAssert();
      }

      //--------------------------------------------------------------------
      // Generate frame buffer object.
      //--------------------------------------------------------------------

      GLuint fbo;
      glGenFramebuffers( 1, &fbo );
      glAssert();
      glBindFramebuffer( GL_FRAMEBUFFER, fbo );
      glAssert();

      //--------------------------------------------------------------------
      // Attach color RBO.
      //--------------------------------------------------------------------

      FrameBuffer::ColorTargets::const_iterator itCT = vColorTargets.getIterator();
      u32 mrtIndex = 0;
      while( itCT ){
        const ColorTarget::handle& hCT = itCT++;
        if( !hCT ){
          continue;
        }
        if( hCT->toTexID() ){
          glFramebufferTexture2D(
              GL_FRAMEBUFFER,
              GL_COLOR_ATTACHMENT0+mrtIndex,
              GL_TEXTURE_2D,
              hCT->toTexID(),
              0 );
        }else if( hCT->toRBO() ){
          glFramebufferRenderbuffer(
              GL_FRAMEBUFFER,
              GL_COLOR_ATTACHMENT0+mrtIndex,
              GL_RENDERBUFFER,
              hCT->toRBO() );
        }else{
          DEBUG_ASSERT_ALWAYS( "No color texture or RBO to attach!" );
        }
        glAssert();
        ++mrtIndex;
        if( !checkFBStatus() ){
          e_log( "GL", "Couldn't create color attachment!" );
          hCT.as<ColorTarget>()->toFlags()->bFailed = true;
        }
      }

      //--------------------------------------------------------------------
      // Attach depth RBO.
      //--------------------------------------------------------------------

      if( hDT ){
        if( hDT->toTexID() ){
          glFramebufferTexture2D(
              GL_FRAMEBUFFER,
              GL_DEPTH_ATTACHMENT,
              GL_TEXTURE_2D,
              hDT->toTexID(),
              0 );
        }else if( hDT->toRBO() ){
          glFramebufferRenderbuffer(
              GL_FRAMEBUFFER,
              GL_DEPTH_ATTACHMENT,
              GL_RENDERBUFFER,
              hDT->toRBO() );
        }else{
          DEBUG_ASSERT_ALWAYS( "No depth texture or RBO to attach!" );
        }
        glAssert();
        if( !checkFBStatus() ){
          e_log( "GL", "Couldn't create depth attachment!" );
          hDT.as<DepthTarget>()->toFlags()->bFailed = true;
        }
      }

      //--------------------------------------------------------------------
      // New handle.
      //--------------------------------------------------------------------

      glBindFramebuffer( GL_FRAMEBUFFER, 0 );
      glAssert();

      FrameBuffer::handle hFrameBuffer = e_new( FrameBuffer );
      hFrameBuffer->setColorTargets( vColorTargets );
      hFrameBuffer->setDepthTarget( hDT );
      hFrameBuffer->setFBO( u32( fbo ));
      return hFrameBuffer;
    }

    void OpenGLESDriver::setDefaultTarget(){
      pushText( "setDefaultTarget" );
        glBindFramebuffer( GL_FRAMEBUFFER, 0 );//s_iFBOMaster );
        glAssert();
        glViewport( 0, 0, IEngine::cxView(), IEngine::cyView() );
        glAssert();
      popText();
    }

        pushText( "Render MRT pass" );
          if( setFrameBuffer( m_tPostFx.buffers[0] )){
            setColorMask( true, true, true, true );
            clearZ();
            enableZBuffer( false );
            setColor( color );
            clearMRT( m_tPostFx.clearMRTShader );
            enableZBuffer( true );
            drawMRTPass();
          }
        popText();