在着色器上实现 GL_REPEAT

Question

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);

my shader code looks like this:

 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);

Answer 1

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.