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====== Shader Compiler ======

==== "sampler_texname not found" compile error when sharing samplers ====

Consider this code:

<code>
#pragma shader_feature_local_fragment _ _ALBEDO;
TEXTURE2D(_Albedo);
TEXTURE2D(_Normal);
SAMPLER(sampler_Albedo);

half4 Frag(v2f i)
{
   #if _ALBEDO
      return SAMPLE_TEXTURE2D(_Albedo, sampler_Albedo, i.uv);
   #endif
   
   return SAMPLE_TEXTURE2D(_Normal, sampler_Albedo, i.uv); // we share the albedo sampler
}
</code>

When compiling, two variants are created, one for when albedo is on, another for when it's off. This will throw an error saying that sampler_albedo cannot be found ((Note: this error will only be thrown on some platforms (windows)) ((the spelling of the error is wrong, as it's all lowercase when the variable is not))

DX9 associates samplers with textures, and so Unity does too. When you set a Unity Texture to ''Clamp'', it sets '-''clamp'' on sampler_<TEXTURENAME>. When the variant with ''_ALBEDO'' not defined is compiled, the compiler strips the albedo texture because it's not being used.

**However**, Unity assumes that since ''sampler_Albedo'' is associated with the ''_Albedo'' texture, it should be stripped as well, even though the sampler is also being used by the ''_Normal''.

Possible workarounds:
  * Give the _Normal texture its own sampler
  * Use a sampler not associated with a texture (which means the user cannot edit it via the texture settings)
  * Make sure you always sample the texture associated with the sampler so it doesn't get stripped. Something like:

<code>
result *= saturate(1 + SAMPLE_TEXTURE2D_LOD(_Albedo, sampler_Albedo, float2(0,0), 11));
return result;
</code>

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