why "gradient" vex function can't work in sinppet?

[yaohaosquall]

Hi,masters!

I want to test sinppet node in volume vop sop,and I try to use "gradient" function to calculate the gradient of the density field,but it turns out an error saying that "Call to undefined function vector gradient...".So,is there any restrction of using vex fuction in sinppet?

thanks!

[magneto]

I think that means gradient is not available in CVEX if I am not wrong. Might have to ask SESI for an RFE

[symek]

gradient() computes its values using shading grid which is available during rendering. Other than that:

http://www.sidefx.com/docs/houdini12.5/nodes/sop/volumeanalysis

[DanBode]

Maybe you're looking for the volumegradient() function?

http://www.sidefx.com/docs/houdini12.5/vex/functions/volumegradient

[yaohaosquall]

Thanks,Magneto!I don't know much about the differents between CVEX and VEX,gonna have a look on it!

Symek,I think you gave me the right answer,Maybe that is why it always works in a shader network.thanks!

And DanBode,yeah I'm looking for a method does the same thing as volumegradient() function,but not this one.I'm trying to implement a for loop in vop network that can recursively modify a level set like l_n = F(l_n-1),so volumegradient vop may not be a appropriate choice because it always references to a sop data that is outside of the vop network which means it can't be modifyed dynamically.I tryed to do it in a foreach node where I can just use a volumegradient to do the right thing but it was not as efficient as i expected, so I'm seeking for a vop loop implementation. thanks anyway!

[ikarus]

Unfortunately in order to do any differentiation you need access to nearby voxels which isn't available in an immediate context since voxels(and points) are run independently of each other in vex, this is why vex is fast.