If the format is for a texture or surface this means that the A8R8G8B8 format can have alpha values inside. Useful for color keying and blending.

Whereas X8R8G8B8 uses the same amount of memory, but 25% stay unused.

For a backbuffer this doesn't make any difference.


Notice: 25% unused may sound harsh, but it means a pixel is 32bit which fits todays architecture way better than 24bit. Most cards don't offer any 24bit acceleration nor the display modes for it.

Quote:For a backbuffer this doesn't make any difference.

I don't like to nit-pick, but you mean front buffer, right? [smile]

An alpha channel in the render-target/backbuffer allows the use of destination alpha during blend-op's. However this is all resolved in the front-buffer such that alpha isn't of any use anymore...

Check out the D3DFORMAT documentation for details - A8R8G8B8 is valid for back buffers, but not for front buffers.

hth
Jack

Oopsie, i consider my nit picked :)