OK the initial drop is a different thing. that one actually is simple: To copyrect, you must lock the buffer so it gets downloaded to the System RAM. GPUs never were meant for that and are dead slow at it.
if you do it more than once it isn't needed anymore, the backbuffer is already present in the in the system ram and DX knows that it is here and where.
you can not grab anything from the VRAM directly, thats why Pixel Shaders were invented, to work on the GPU directly without using the ultra slow download solution anymore.
if you do it more than once it isn't needed anymore, the backbuffer is already present in the in the system ram and DX knows that it is here and where.
you can not grab anything from the VRAM directly, thats why Pixel Shaders were invented, to work on the GPU directly without using the ultra slow download solution anymore.