Algorithm for UV Coords generation for grid

OpenGL OpenGL: Advanced Coding
1

I have a landscape which is an array of vertices, and a matching array of texcoords.

I want to have an algorithm too generate the ST/UV coords for the grid.

an example of what i think the algorithm should look like;

for ( long y = 0; y < height; y++ )
{
	for ( long x = 0; x < width; x+=6 )
	{
		texcoords[y*(width*3)+x].s = ?;
		texcoords[y*(width*3)+x].t = ?;
		texcoords[y*(width*3)+x+1].s = ?;
		texcoords[y*(width*3)+x+1].t = ?;
		texcoords[y*(width*3)+x+2].s = ?;
		texcoords[y*(width*3)+x+2].t = ?;
		texcoords[y*(width*3)+x+3].s = ?;
		texcoords[y*(width*3)+x+3].t = ?;
		texcoords[y*(width*3)+x+4].s = ?;
		texcoords[y*(width*3)+x+4].t = ?;
		texcoords[y*(width*3)+x+5].s = ?;
		texcoords[y*(width*3)+x+5].t = ?;
	}
}
2

Ahem … if I understood well, this is fair easy …

Without any kind of optimisation :

for ( long y = 0; y < height; y++ )
{
for ( long x = 0; x < width; x++ )
{
texcoords[ywidth+x].s = (float)x/(float)(width-1);
texcoords[ywidth+x].t = (float)y/(float)(height-1);
}
}

texture coordinates are from 0.0 to 1.0.

[This message has been edited by paddy (edited 05-26-2001).]

3

The pronblem is, my array contains three points for every polygon, and each polygon is reversed;

even polygons;
(0)
|
|
(1)–(2)

odd polygons;
(1)–(0)
\ |
\ |
(2)

So the algorithm has to be cleverer to accomodate this?

4

Just asign the plane you want to your texture coords.

XY plane:
s=x
t=y

or…

XZ plane:
s=x
t=z

or…whatever you choose.

Once the texture coords are set up, then scale them to the appropriate size.

5

About your reversed polygon thing. It doesn’t matter because you’ll be assigning the texture coordinates the same forward and reversed vertices.

6

Of course!
So simple I could’nt see it :slight_smile:

Cheers.

7

Not to blame anyone but … I think there is an easier way to store an array for a landscape