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Endemoniada

Same Alpha Map for Different Textures ?

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Hi guys, I'm using D3D for 2D and a lot of my textures use the exact same alpha map; it seems like a waste that each texture has its own alpha channel when they are all the same. Also, it would be nice if I could change the alpha map on the fly. So is something like this possible: BeginScene() for each blit { set alpha map set texture (RGB only, no A) blit } EndScene() That would be great. I'm still pretty new at D3D so maybe it can be done simply. Take care.

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It should be perfectly possible using pixel shaders; have 2 textures as inputs - one is your alpha channel, and one is your diffuse channel(s). Write the output as being a combination of the two textures.

However, if you don't wanna be messing with shaders...

You can probably do what you want by having multi-texture rendering.

I can never remember the correct ordering/setup of the texture blending operations, but you would have IDirect3DDevice9::SetTexture( 0, my_alpha ) and IDirect3DDevice9::SetTexture( 1, my_diffuse ) and then configure the texture stages so as to blend.

The difficulty is going to be in mixing the file formats. I'm not sure if you'll get away with a D3DFMT_A8 (or similar quantity) in one channel and have it blend correctly with a D3DFMT_X8R8G8B8 or D3DFMT_R8G8B8 texture in the second channel.

hth
Jack

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