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:
int width = source.width / 2;
int height = source.height / 2;
RenderTexture currentDestination = RenderTexture.GetTemporary(
width, height, 0
);
Graphics.Blit(source, currentDestination, bloom, BoxDownPrefilterPass);
But i need this to be done in the shader.
Something like this:
GrabPass
{
"_BackgroundTexture"
}
//this next line is just an example of what i'd like to do. is this possible?
_BackgroundTexture.setSize = halfSize;
col = tex2D(_BackgroundTexture, i.grabPos);
Thanks for any help all 
hey @bgolus , thanks for the reply.
Ending up doing this in the end:
half4 frag(v2f i) : SV_Target
{
half4 col = 0;
float2 newUVPos;
//Sample the grab pass texture at the same point for multiple
//fragments. Eg, if fragment is 0.0, 0.1, and 0.2, then sample
//from the texture at uv 0.0. if 0.3, 0.4, 0.5, then sample
//at 0.3 etc. this gives the effect of lower resolution.
//uv coords start out 0 to 1. Multiply by 10X or more so
//we get an integer. eg, uv.x = 0.51. X by 10 = 5.1;
newUVPos.x = i.grabPos.x * _SmootherFactor;
newUVPos.y = i.grabPos.y * _SmootherFactor;
//then round to the nearest int. Eg 5.1 will be 5.0
newUVPos.x = round(newUVPos.x);
newUVPos.y = round(newUVPos.y );
//then convert back into a 0 to 1 uv coords range.
//Eg 5.0 will become 0.5
newUVPos.x /= _SmootherFactor;
newUVPos.y /= _SmootherFactor;
//sample from the grab pass texture
col = tex2D(_BackgroundTexture, newUVPos);
return col;
}
