uv not being passed through from vertex to surface shader

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Hi

I'm getting up to scratch writing shaders in unity, and am trying to get the uv from the verts through to the surface shader. However for some reason when I declare a variable for the surface shader input named 'uv_x', it isn't filled in with the uv from the mesh. To verify the uvs weren't wrong, I tried just manually passing it through in a variable called 'hello' and get the expected result. This is my code (or a snippet of it)

     SubShader 
     {
 
 
 
         
         CGPROGRAM
         #pragma surface surf Lambert vertex:vert
         #pragma glsl
         #pragma target 3.0
 
         sampler2D _SDF_Texture;
         
         struct Input 
         {
             float3 pos;
             float2 uv_sdf;
             float2 hello;
         };
 
         void vert (inout appdata_full v, out Input OUT)
         {
             UNITY_INITIALIZE_OUTPUT(Input, OUT);
 
             //manually forcing through the uv value has no effect
             //OUT.uv_sdf = v.texcoord;
 
             //try passing uv value through just as a general parameter
             OUT.hello = v.texcoord;
         }
 
         void surf (Input IN, inout SurfaceOutput o) 
         {
             //always black (i.e. uv_sdf is always 0s)
             //float4 color = float4(IN.uv_sdf.x,IN.uv_sdf.y,0,1);
 
             //shows the colour gradient correctly across a quad (i.e. bl=black, tl=green, br=red, tr=yellow)
             float4 color = float4(IN.uv_sdf.x,IN.uv_sdf.y,0,1);
 
             o.Albedo = color.rgb;
             o.Alpha = 1.0;
         }
         ENDCG
     }

I'm a little baffled. Manually forcing uv_sdf to be the right value has no effect, which suggests its being automatically overwritten with something, but not the uvs from the mesh. I tried explicitly marking uv_sdf as TEXCOORD0 but still no luck.

Anyone any thoughts on this one?

cheers

-Chris

Answer 1

Answer by moosefetcher · Jan 21, 2016 at 06:36 PM

I've just spent the best part of a day figuring this out - I couldn't find a version of this question with an answer, so I'll attempt to answer it here: (Sorry this is 4 months late - I'm new to Unity)

First up you need to name your texture in your Input struct, with the format uv followed by TextureName:

 float2 uv_MainTex;

You'll then be able to access the UV coordinates in the surf struct and add an offset to sample MainTex in an alternate location, like this:

 void surf (Input IN, inout SurfaceOutput o) {
        float2 offsetUVs = IN.uv_MainTex;
        offsetUVs.y += _adjustmentAmount;
        _surfaceColour = saturate(tex2D (_MainTex, offsetUVs).rgba * _offsetColour.rgba);
 }

The tex2D method takes a sampler2D and a float2 as parameters, so you can make a change to the float2 from the input struct (IN.uv_MainTex) and pass the altered float2 into the tex2D method instead. I hope that works for you.

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