Texture Mapping Triangles

clipping is done in hardware (means you dont worry about it).

Quote:

Original post by dpadam450 clipping is done in hardware (means you dont worry about it).

Perhaps he wants to do it in software (e.g. for a CSG algorithm)?

I assume you want to do something like this, where you have a quad (with vertex positions and tex coords) [1], then find some points to clip the quad [2], then produce a new polygon [3]. Is this right?

[1]       [2]       [3]A-----B   A--F--B     /F--B|     |   |     |    /    ||     |   E     |   E     ||     |   |     |   |     |D-----C   D-----C   D-----C

Would a simple weighted average work?
I.e.
weighting = distance(F,A)/distance(A,B)
F.tex.u = weighting *A.tex.u + (1-weighting)*B.tex.u
F.tex.v = weighting *A.tex.v + (1-weighting)*B.tex.v

If you grab a text-book on computer graphics, there'll probably be a whole chapter on clipping algorithms. Unfortunately, I don't have one handy though...

Yes, thats right. In that case you simply alter the texture coordinates along with the vertex positions.

So if p0 and p1 were the endpoints of an edge when you decide to clip it at distance t, and tex0 and tex1 were the texture coordinates at the corresponding points:

p_new = (1-t)*p0 + t*p1
tex_new = (1-t)*tex0 + t*tex1

However, I'm not sure the OP is asking about that, since he mentions loading a Q3 BSP. dpadam450 gave most of the answer, but a more full one would be that Q3 maps store faces in a very nice format for rendering, all you need to do is determine whether a strip or fan should be drawn (I think you determine that via the sign of the vert or index count), then just feed the coordinates to OpenGL using glVertex* and glTexCoord2*. It really is that simple :) (of course, you should use VBOs!)

I think I gave a bad explanation. I'm actually loading a non-compiled map file (map extension). Each brush is given as a series of intersecting planes and I am generating triangles from this data. What I meant about the quad is that, to generate the triangles I create a quad on the surface of one of the planes and then clip it against all the other planes in the brush generating a face. What I don't know how to do is apply a texture to the face (some number of triangles) after it's been clipped so the texture is correct.

JuNC:
It sounds like I need to be computing the texture co-ordinates while clipping each quad, and not figure them out during rendering, is this correct?

[Edited by - AsOne on September 6, 2007 3:10:57 PM]

Quote:

Original post by AsOne JuNC: It sounds like I need to be computing the texture co-ordinates while clipping each quad, and not figure them out during rendering, is this correct?

I'd definitely calculate the vertex data (i.e. tex-coords) at the same time as the clipping, not during the rendering stage.