Direct3D: efficient way to get system memory bitmap from IDirect3DSurface9 (default pool)?

Question

I have IDirect3DSurface9, default pool, YUV format. How can I efficiently get bitmap bits from it? At the moment I:

create render target:
device->CreateRenderTarget(surf_desc.Width, surf_desc.Height, D3DFMT_A8R8G8B8, D3DMULTISAMPLE_NONE, 0, TRUE, &render_target, NULL)

convert YUV to RGB32:
device->StretchRect(videomem_surf, NULL, render_target_, NULL, D3DTEXF_NONE)
(complete rectangle, no stretching)

create plain offscreen surface in system memory
device->CreateOffscreenPlainSurface(surf_desc.Width, surf_desc.Height, D3DFMT_A8R8G8B8, D3DPOOL_SYSTEMMEM, &sysmem_offscreen_surf, NULL)

copy data from video mem to sysmem:
device->GetRenderTargetData(render_target, sysmem_offscreen_surface)

GetDC from offscreen surface, create compatible DC and compatible bitmap, BitBlt from offscreen sufrace DC to compatible DC and copy bitmap bits to my buffer by GetDIBits()

this looks a bit of overhead, because of so many copying: from original surface to render target, then to offscreen surface, then to compatible bitmap, and then finally to my buffer. How can this be improved?

thanks

Answer 1

Since you create you render target in lockable mode (6th parameter to CreateRenderTarget), you can lock the render target with LockRect and copy the data directly from there.

MSDN does not recommend using lockable render targets, and says:

If you need read access to render targets, use GetRenderTargetData instead of lockable render targets.

So an alternative is to call GetRenderTargetData into the offscreen surface, and then lock the offscreen surface (instead of using DCs and bitmaps).