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Procedural shader aliasing problems


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Hi houdinks.

I am trying to add detail to very low resolution gmetry of a fern.

The idea is that all the details should came from a displacement/bump shader, usign a map or using a procedural.

To get the veins pattern I have reuse the leaf material that came with Houdini, which is a sine based pattern that simply apply a sine function to make the veins.

Also the surface is glass, so is like a fern made of glass.

The problem with the procedural way is the these kind of patterns, and specially with tis high frequency detail in a glass surface is creating a lot of alias/flickering, the look in a still image is great but when the geom is moving problems begin.

So anyone have tried to solve the aliasing problems with sine based patterns before?

I have attached an scene where the fern geo is using a material with the default glass shader and the problematic displacement shader, I have also included the VOP Network so anybody can have a better idea about the problem.

Thanks a lot.


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At a glance, there are at least two things that jump out as being aliasing sources:

1. The Trig VOP does not filter.

2. The Absolute VOP does not filter either.

The funny thing is that the main VOP header file "$HH/vex/include/voplib.h" does have a filtered version of sin() and cos() (the functions are called vop_FilteredSin() and vop_FilteredCos()), but they haven't made a VOP wrapper for them -- meaning you'd have to call them from an inline vop.

Unfortunately though, instead of just computing the integral analytically and calling it a day, they then also go ahead and fade it to the average value (which for these functions is zero), and which IMHO is just wrong -- the visual result is that your sine-based features will go completely smooth way faster than they should. I have no idea why they've done this, but I wouldn't use it as is; just write your own without the fade-to-average bit.

Bad news #3 is that voplib.h has no filtered abs(), so you have to write that one yourself as well.

Anyway, I added a quick Inline VOP that computes a filtered version of abs(sin(x)), and this seems to cure most of the aliasing. I did notice some other VOPs (like filterstep) in there that may need some love as well, so this may not be a complete fix.


I left the control for the filter width as a constant VOP in there, but feel free to make it a parameter.


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Hi Mario.

Thanks for he help to busy that I forget respond this.

Well, at the moment I have solved the problem using texture maps that renders nicely.

But it hard to get the same detail as with the procedural pattern.

Hopefully tomorrow I can take a look at your shader and to give to the procedurl pattern another chance.


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