Hi, I'm currently working on an adventure-game (ref: the recent Myst IV) and I'm a bit stuck on a problem. In my background I want moving skies and the like, so I render out my scenes with an alpha mask to allow a moving background. Yet since I save my images as .jpg to save (disk)space (pre-rendered games get so terribly large), I have no way to save alpha in the same file. 2 things I have tried are either copying data from the Alpha-file to the rgb-texture on load time, thus making it a rgba texture, or using a simple pixel shader where I use 2 different textures, the RGB and the Alpha, to be combined at rendertime. Now, the 2nd method appears best to me, as it's proven to be faster as the first (terrible load times with the first, due to the locking/unlocking/etc. The real question is: what method is best - or is there a better solution? Additionaly, are pixelshaders v1.1 supported widely enough to use them (I presume they are, but I must admit I don't know for sure)?.. Looking forward for your input, thanks for reading.

Quote:Original post by The Parrot
Yet since I save my images as .jpg to save (disk)space (pre-rendered games get so terribly large), I have no way to save alpha in the same file.

Try PNGs. They support alpha, and compress well.

Quote:2 things I have tried are either copying data from the Alpha-file to the rgb-texture on load time, thus making it a rgba texture, or using a simple pixel shader where I use 2 different textures, the RGB and the Alpha, to be combined at rendertime.

I believe you can do it without any pixel shaders, using some texture stage state magic. Basically, put the texture in stage 0, and the alpha texture in stage 1. Then do:
device->SetTextureStageState(0, D3DTSS_COLOROP, D3DTSS_SELECTARG1);
device->SetTextureStageState(0, D3DTSS_COLORARG1, D3DTA_TEXTURE);
device->SetTextureStageState(0, D3DTSS_ALPHAOP, D3DTSS_SELECTARG1);
device->SetTextureStageState(0, D3DTSS_ALPHAARG1, D3DTA_CURRENT);

device->SetTextureStageState(1, D3DTSS_COLOROP, D3DTSS_SELECTARG1);
// If the alpha texture has white color info (0xaaffffff), you can replace
// TFACTOR with TEXTURE. Otherwise you can set TFACTOR to 0xffffffff
// Also, if vertices have no diffuse, you could say DIFFUSE
// which would result in 0xffffffff
device->SetTextureStageState(1, D3DTSS_COLORARG1, D3DTA_TFACTOR);
device->SetTextureStageState(1, D3DTSS_ALPHAOP, D3DTSS_SELECTARG1);
device->SetTextureStageState(1, D3DTSS_ALPHAARG1, D3DTA_TEXTURE);

device->SetTextureStageState(2, D3DTSS_COLOROP, D3DTOP_DISABLE);
device->SetTextureStageState(2, D3DTSS_ALPHAOP, D3DTOP_DISABLE);