[SOLVED] Why must the position rest for a noise to behave consistently in shader ?

[Mael_P 3]

Hello,

For all my time in Houdini I have never shaded a lot. I however have played with pointVop quite bit, so I was surprised when I tried to make a noisy shader and I kept following the camera ?
Let me explain what the scene is :

- a grid, that has a principledshader

- a rotating null, parenting a camera

- 3 lights

In the shader, I take the position of a Global Variable, plug it into a noise, and in the basecolor of the principledshader.
Why is that, that when I render different frames (so the camera has moved), the noise stays the same. I can see the lights are not coming from the same angle, which is normal since the camera moved, but the noise is pixel for pixel displaying the same way.
I fixed it by pluging a restpost between the Global Variable and the input of my noise, but I can't wrap my head around why I have to do this in the first place ? Normaly everything makes sense in Houdini but this doesn't.
As I said I know my ways around Point Vops, so should I expect other different behaviors in the shader context ?

 

 

 

 

 

 

shader_must_rest.hiplc

Edited December 19, 2020 by Mael_P
title

[symek 389]

4 hours ago, Mael_P said:

I fixed it by pluging a restpost between the Global Variable and the input of my noise, but I can't wrap my head around why I have to do this in the first place ? Normaly everything makes sense in Houdini but this doesn't.
As I said I know my ways around Point Vops, so should I expect other different behaviors in the shader context ?

Change in your shader behavior compared to PointVops comes from a single fact - stack it on top of everything you already know,  and all of this will make sense again. Fact is: in Mantra (as probably any other renderer) world origin is at the camera position.

[Mael_P 3]

15 hours ago, symek said:

Change in your shader behavior compared to PointVops comes from a single fact - stack it on top of everything you already know,  and all of this will make sense again. Fact is: in Mantra (as probably any other renderer) world origin is at the camera position.

That's good to know, thanks you !