Repeating part of texture over another texture

Question

So I'm trying to replace a part of a texture over another in GLSL, first step in a grand scheme. So I have a image, 2048x2048, with 3 textures on the top left, each 512x512. For testing purposes I'm trying to just repeatedly draw the first one.

//get coord of smaller texture
coord = vec2(int(gl_TexCoord[0].s)%512,int(gl_TexCoord[0].t)%512);

//grab color from it and return it 
fragment = texture2D(textures, coord);
gl_FragColor = fragment;

It seems that it only grabs the same pixel, I get one color from the texture returned to me. Everything ends up grey. Anyone know what's off?

Answer 1

Unless that's a rectangle texture (which is isn't since you're using texture2D ), your texture coordinates are normalized . That means that the range [0, 1] maps to the entire range of the texture. 0.5 always means halfway, whether for a 256 sized texture or a 8192 one.

Therefore, you need to stop passing non-normalized texture coordinates (texel values). Pass normalized texture coordinates and adjust those.