I'm locking the backbuffer in direct3D 9 and copying an image to it. I noticed on one computer that when the image is stretched to the screen, it becomes blurry. On another computer I tested on, it's completely unfiltered (pixelated). Is there a way to specify how the backbuffer is sampled to the screen, or is it controlled by something else?
I've tried
Device->SetSamplerState(0, D3DSAMP_MAGFILTER, D3DTEXF_POINT);
However it had no effect; I think it only affects textures.
SetSamplerState does not affect how the backbuffer is drawn to the screen. AFAIK most drivers will use point sampling, which means pixels will be lost or doubled, resulting in bad quality. BTW, what was the GPU/driver on the machine where it looked fine (you can't/shouldn't depend on this behavior everywhere)?
The right way to do this is to copy the image to a texture and render a screen aligned quad so you can use hardware sampling to smooth the result for you.
If for whatever reason you cannot use a texture + rendering pass, you can use IDirect3DDevice9::StretchRect to filter the image when copying to the backbuffer. To actually load the image from system memory, you'll have to use another surface, either locking and copying it or using D3DXLoadSurfaceFromMemory.
