I’m trying a map an image of the Earth onto an icosahedron. I got the code tess.c and sphere.c from the glut distribution. The sphere looks much better than a gluSphere.
Has anybody already done this? The test code I wrote yesterday doesn’t handle the places where the texture has to wrap, the triangles don’t line up with the edge of the texture, and I’m slightly concerned with the poles.
I would convert the vertex coordinates into polar coordinates, map longitude and latitudes from 0 to 1 (edit: for triangle vertices wich cross the border you need to either add or subtract 1 to get the wrapping right!), set GL_TEXTURE_WRAP_S to GL_REPEAT, that should solve the border not fitting argument for longitudes,
and GL_TEXTURE_WRAP_T to GL_CLAMP_TO_EDGE.
And there is an orientation of the icosahedron where you have a vertex on north and south pole.
The usual planet textures are mapping the poles to a full line anyway, so the texture is already distorted.
If you have a better map, you need to inverse there projection to a sphere.
[This message has been edited by Relic (edited 01-31-2003).]
Everything works except for where a triangle has vertices on either side of the texture boundary because the longitude wraps 0-2*PI.
I’ll have to check the vertices of all my triangle strips to see which ones wrap.
Decide on a longitude, and duplicate your vertices down that longitude; one set has a u coordinate that’s 1 greater than the other set. Then the other vertices have values inbetween, and texture repeat will match it all up for you.