Stormie
07-06-2001, 05:37 AM
Hi all. I have a couple of questions concerning multitexturing. These may be answered in the Red Book, but it's Friday afternoon.. I'm at work.. my Red Book is at home.. so humour me, please!
First question: Assuming you wish to render a polygon with a texture map and a light map, can you get the same result with multipass rendering as with multitexture? I found an article on delphi3d (http://www.delphi3d.net/articles/viewarticle.php?article=lightmapping.htm) that seems to say flat out that you can't, and has pictures to prove it. It says you have to invert your lightmap and do subtractive blending, because "OpenGL does not support multiplicative alpha blending".
But surely you could get the desired result by rendering the polygon with the texture map, then rendering it again with the lightmap as texture format GL_LUMINANCE? Doesn't that produce the result C = CfLt, which is what we'd want?
Second question: So how widely supported is the multitexture extension? I assume most (all?) "modern" PC hardware supports it (but with how many texture units?), but if you demanded it, how much hardware would you be cutting out? That article I mentioned above said that a Voodoo2 supported multitexturing.. surely there's not much around that's older than that?
[This message has been edited by Stormie (edited 07-06-2001).]
First question: Assuming you wish to render a polygon with a texture map and a light map, can you get the same result with multipass rendering as with multitexture? I found an article on delphi3d (http://www.delphi3d.net/articles/viewarticle.php?article=lightmapping.htm) that seems to say flat out that you can't, and has pictures to prove it. It says you have to invert your lightmap and do subtractive blending, because "OpenGL does not support multiplicative alpha blending".
But surely you could get the desired result by rendering the polygon with the texture map, then rendering it again with the lightmap as texture format GL_LUMINANCE? Doesn't that produce the result C = CfLt, which is what we'd want?
Second question: So how widely supported is the multitexture extension? I assume most (all?) "modern" PC hardware supports it (but with how many texture units?), but if you demanded it, how much hardware would you be cutting out? That article I mentioned above said that a Voodoo2 supported multitexturing.. surely there's not much around that's older than that?
[This message has been edited by Stormie (edited 07-06-2001).]