This is the code for accessing pixel data from the backbuffer in a D3D9 application. Keywords: LPDIRECT3DSURFACE9 read backbuffer copy back buffer directly access back buffer Direct3D device DirectX 9

How to Access Data in the Backbuffer in Direct3D 9.cpp

void demoExtractBackBufferPixels(LPDIRECT3DDEVICE9 d3d_device) {
  
  // TODO: In your app, add FAILED() macros to check the HRESULTs passed back
  //       by each of the API calls. I leave these out for clarity.
  
  // Grab the backbuffer from the Direct3D device
  LPDIRECT3DSURFACE9 back_buffer = NULL;
  d3d_device->GetBackBuffer(0, 0, D3DBACKBUFFER_TYPE_MONO, &back_buffer);
  
  // Get the buffer's description and make an offscreen surface in system memory.
  // We need to do this because the backbuffer is in video memory and can't be locked
  // unless the device was created with a special flag (D3DPRESENTFLAG_LOCKABLE_BACKBUFFER).
  // Unfortunately, a video-memory buffer CAN be locked with LockRect.  The effect is
  // that it crashes your app when you try to read or write to it.
  D3DLOCKED_RECT d3dlr;
  D3DSURFACE_DESC desc;
  LPDIRECT3DSURFACE9 offscreen_surface = NULL;
  back_buffer->GetDesc(&desc);
  d3d_device->CreateOffscreenPlainSurface(desc.Width, desc.Height, desc.Format,
                                          D3DPOOL_SYSTEMMEM, &offscreen_surface, NULL);

  // Copy from video memory to system memory
  d3d_device->GetRenderTargetData(back_buffer, offscreen_surface);
  
  // Lock the surface using some flags for optimization
  offscreen_surface->LockRect(&d3dlr, NULL, D3DLOCK_NO_DIRTY_UPDATE|D3DLOCK_READONLY);
  
  // TODO: do some processing based on the pixel format, d3dlr and desc.Width/desc.Height
  switch (desc.Format) {
  case D3DFMT_R8G8B8:
  case D3DFMT_X1R5G5B5:
  case D3DFMT_R5G6B5:
  case D3DFMT_A8R8G8B8:
  case D3DFMT_X8R8G8B8:
  default:
  }
  
  // Release all of our references
  offscreen_surface->UnlockRect();
  offscreen_surface->Release();
  back_buffer->Release();
  
}