I'm trying to implement GL_REPEAT on glsl. I wrote something using the mod function but there's a problem where the two textures combine. Could you explain why it doesn't work right?
in main:
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
in vec2 TextureCoord;
float yCoord = mod(TextureCoord.y + 0.5, 1.0);
emission = texture(material.emission,vec2(TextureCoord.x, yCoord)).rgb;
//result
vec3 result = emission;
FragColor = vec4(result, 1.0f);
The wrap mode is honored during texture filtering. You set the GL_LINEAR filter mode, hence it will always use a 2x2 texel footprint. If that footprint happens to be at the border, the selected wrap mode will apply to selecting each individual texel. In your case, if you get near the border, you told it to filter into the textrue border color, which a filter with GL_REPEAT wrap mode never would have done, it would have used the texel data from the opposing border instead.
So if you want to re-implement that manually in the shader, you must also implement the texel selection and the filtering itself. Since you also use mipmapping, doing so will be quite complex, and slow.