Question How to downscale and upscale a grab pass texture in a shader

hey all. I'm working on a custom bloom shader.
It requires down sample and up sample steps.

I know this can be done in C#, eg:

Code (CSharp):

1. int width = source.width / 2;
2. int height = source.height / 2;
3.  
4. RenderTexture currentDestination = RenderTexture.GetTemporary(
5.             width, height, 0
6.         );
7.        
8.  
9. Graphics.Blit(source, currentDestination, bloom, BoxDownPrefilterPass);

But i need this to be done in the shader.
Something like this:

Code (CSharp):

1. GrabPass
2. {
3.      "_BackgroundTexture"
4. }
5.  
6. //this next line is just an example of what i'd like to do. is this possible?
7. _BackgroundTexture.setSize = halfSize;
8. col = tex2D(_BackgroundTexture, i.grabPos);

Thanks for any help all

 

Not possible.

 

hey @bgolus, thanks for the reply.

Ending up doing this in the end:

Code (CSharp):

1.             half4 frag(v2f i) : SV_Target
2.             {
3.                 half4 col = 0;
4.  
5.                 float2 newUVPos;
6.  
7.                 //Sample the grab pass texture at the same point for multiple
8.                 //fragments. Eg, if fragment is 0.0, 0.1, and 0.2, then sample
9.                 //from the texture at uv 0.0. if 0.3, 0.4, 0.5, then sample
10.                 //at 0.3 etc. this gives the effect of lower resolution.
11.                
12.                 //uv coords start out 0 to 1. Multiply by 10X or more so
13.                 //we get an integer. eg, uv.x = 0.51. X by 10 = 5.1;
14.                 newUVPos.x = i.grabPos.x * _SmootherFactor;
15.                 newUVPos.y = i.grabPos.y * _SmootherFactor;
16.  
17.                 //then round to the nearest int. Eg 5.1 will be 5.0
18.                 newUVPos.x = round(newUVPos.x);
19.                 newUVPos.y  = round(newUVPos.y );
20.  
21.                 //then convert back into a 0 to 1 uv coords range.
22.                 //Eg 5.0 will become 0.5
23.                 newUVPos.x /= _SmootherFactor;
24.                 newUVPos.y  /= _SmootherFactor;
25.  
26.                 //sample from the grab pass texture
27.                 col = tex2D(_BackgroundTexture, newUVPos);
28.                
29.                 return col;
30.                
31.             }