Method ReadPixels

Rendering/OpenGL2/vtkOpenGLRenderWindow.cxx:1304–1476

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//------------------------------------------------------------------------------
int vtkOpenGLRenderWindow::ReadPixels(
  const vtkRecti& rect, int front, int glformat, int gltype, void* data, int right)
{
  // set the current window
  this->MakeCurrent();

  if (rect.GetWidth() < 0 || rect.GetHeight() < 0)
  {
    // invalid box
    return VTK_ERROR;
  }

  // Must clear previous errors first.
#ifdef VTK_REPORT_OPENGL_ERRORS
  while (glGetError() != GL_NO_ERROR)
  {
  }
#endif

  this->GetState()->vtkglDisable(GL_SCISSOR_TEST);

  // Calling pack alignment ensures that we can grab the any size window
  this->GetState()->vtkglPixelStorei(GL_PACK_ALIGNMENT, 1);

  this->GetState()->PushReadFramebufferBinding();

  if (front)
  {
    this->DisplayFramebuffer->Bind(GL_READ_FRAMEBUFFER);
    this->DisplayFramebuffer->ActivateReadBuffer(right ? 1 : 0);
  }
  else
  {
    this->RenderFramebuffer->Bind(GL_READ_FRAMEBUFFER);
    this->RenderFramebuffer->ActivateReadBuffer(0);

    // Let's determine if we're reading from an FBO.
    bool resolveMSAA = this->GetBufferNeedsResolving();

    if (resolveMSAA)
    {
      this->GetState()->PushDrawFramebufferBinding();
      int* fbsize = this->RenderFramebuffer->GetLastSize();
      this->ResolveFramebuffer->Resize(fbsize[0], fbsize[1]);
      this->ResolveFramebuffer->Bind(GL_DRAW_FRAMEBUFFER);

      // Now blit to resolve the MSAA and get an anti-aliased rendering in
      // resolvedFBO.
      this->GetState()->vtkglBlitFramebuffer(rect.GetLeft(), rect.GetBottom(), rect.GetRight(),
        rect.GetTop(), rect.GetLeft(), rect.GetBottom(), rect.GetRight(), rect.GetTop(),
        GL_COLOR_BUFFER_BIT, GL_NEAREST);
      this->GetState()->PopDrawFramebufferBinding();

      // Now make the resolvedFBO the read buffer and read from it.
      this->ResolveFramebuffer->Bind(GL_READ_FRAMEBUFFER);
      this->ResolveFramebuffer->ActivateReadBuffer(0);
    }
  }