Question

I am new to OpenGL and am currently trying to render a cube with four faces, each with a different texture.

As you all know, having a separate texture for each face type is very memory intensive and makes the application slow.

At the moment I am trying to use a texture sheet for the sprite. I have the graphic file with each texture 16×16 pixels with 256 sprites arranged in a square (16×16).

I know that

GL11.glTexCoord2f(1.0f, 0.0f);
GL11.glVertex3f(1.0f, 1.0f,  1.0f);
GL11.glTexCoord2f(0.0f, 0.0f);
GL11.glVertex3f(0.0f, 1.0f, 1.0f);
GL11.glTexCoord2f(0.0f, 1.0f);
GL11.glVertex3f(0.0f, 0.0f, 1.0f);
GL11.glTexCoord2f(1.0f, 1.0f);
GL11.glVertex3f(1.0f, 0.0f, 1.0f);

gives me a rectangle with the whole sprite sheet so u and v of glTexCoord2f have to be less than 1.0f.

What I need now is a formula which will calculate the u and v of any sprite id in the texture.

The IDs go as following in the texture bitmap:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
17 18 16 20 21 22 23 24...

and I’d like to have a u and v for any of these IDs. The last bit isn’t explained very well, so I’ll explain it better if you would like.

Thank you in advance!

Answer 1

The locations of the sprites’ texture in the image are in a 16 x 16 array, so the location of a texture (if you count the first one as 0) are:

row = texNo / 16;
col = texNo % 16;

The coordinates are then:

u0 = row / 16;
u1 = (row + 1) / 16;

v0 = col / 16;
v1 = (col + 1) / 16; 

Then replace 1.0f with u1 or v1 as appropriate and 0.0f with u0 or v0 in the glTexCoord2Df calls.