Dependent Texture Read

Unity Engine
1

Does anyone know if moving a UV coord into a local variable causes a dependent texture read ?

float2 mainUV = i.uv;
fixed4 col = tex2D ( _MainTex, mainUV );

2

I’m not an expert in this stuff - far from it, but my understanding would be in that example no - not unless you change the values in mainUV in some way. In fact, in that example above, I’d imagine that the interim step would get optimised out at compile time.

3

Yeah thats what I am assuming also, but I would like to know for sure
Like is the driver smart enough to know the UV was moved to a local var ?

I am doing this because sometimes I do modify the UV like…

float2 mainUV = i.uv;

#ifdef ECHO_DISTORTION_ON
change mainUV here
#endif

fixed4 col = tex2D ( _MainTex, mainUV );

I’m hoping when the keyword ECHO_DISTORTION_ON is not active there are no dependent texture reads.

4

UPDATE: in a small test it seems unity optimizes out the mainUV variable if nothing changes it and uses the TEXCOORD directly

5

The shader compiler optimizes this away. Nothing to do with Unity itself FYI.

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