Mapping a texture using UV's in the vertex function of a surface shader

Does anyone know how to do this, i'm aware of mapping tex2Dlod and how to get uv_Maintex into the vertex function, however using the two together doesn't seem to give any results. Any thoughts?

 

The Surface Shader's vertex function runs before uv_MainTex has been calculated, so while you can access the value in the Input struct, it is going to be the default uninitialized value of float2(0,0). If you want to get the equivalent value, you'll have to calculate the UV yourself like you would if you were writing a vertex fragment shader.

float2 uv_MainTex = TRANSFORM_TEX(v.texcoord.xy, _MainTex);

 

Thanks for the explanation dude, I just figured it out and was about to post it, but I didn't know the reason so great!! I was just trying to find the documentation for the variable name that represents 'vertex' in surf shader, being texcoord. Thanks again for the explanation!