How to scale and offset a cubemap using sphere mapping

Question

I am trying to scale and repeat a Cubemap with Latitude-Longitude mapping layout just as you would do with classical UV mapping but without any interesting result. This should be used as a skybox.

This comes from the fact that the coordinates are in 3D space and we can't apply this simple formula texcoord.xy * scale.xy + offset.xy

How would you handle such features : scaling which involves tiling and offsetting.

samplerCUBE _TexCube;
texCUBE(_TexCube, float3);

Answer 1

This doesn't really answer the question but is a workaround. Beware it's hack time :)

Instead of using the texCUBE and samplerCube I'll be using the tex2D method and a simple sampler to sample the texture.

As I am using a sphere mesh, I generate 2D UVs like this.

float x = atan2(vertex.x, vertex.z) / PI;
x = x / 2.0 + 0.5; // To remap from 0 to 1
float y = vertex.y / 2.0 + 0.5; // Also remap from 0 to 1
float3 color = tex2D(sampler, float2(x, y) * scale.xy + offset.xy);

It's a bit hacky but using this I have 2D texture coordinates for my texture.