Hi there,
When I turn on the Prune option, under the Optimization tab on the Hair Generate, I would expect it to keep the exact same look but just show a percentage of the groom.
What seems to happen though, is that the hair is being regenerated with every new pruning Ratio, which means points are being created in different positions and completely changing the look.
This means a hair that is showing on the pruned version, may not be there on the full version!
Is it possible to prune the hair to show a percentage of the final hair, without creating new point position?
This means the pruned version would be actually part of the full version.
Thanks!
Care to share some edifying images?
I don't think there's any seed like characteristic to the Pruning feature, but I might be wrong. Hence, pics please.
I don't think there's any seed like characteristic to the Pruning feature, but I might be wrong. Hence, pics please.
Hi there,
Here are some pictures to better show what I mean.
The 3 images show the full fur (no prune), same fur pruned at 0.3, and same fur pruned at 0.7.
As you can see, clumps/strands are being generated in different places (specially noticed in the silhouette)
Here are some pictures to better show what I mean.
The 3 images show the full fur (no prune), same fur pruned at 0.3, and same fur pruned at 0.7.
As you can see, clumps/strands are being generated in different places (specially noticed in the silhouette)
The problem is that I don't see, or at least not something that obvious to convince me that your hypothesis is correct. Did you try to analyze (and post those images if it's not too much to ask) with the “thicken strands” (I don't recall its exact name) feature off and see if there's actually a difference?
The issue about working with a small percentage of the generated hair and then looking a bit, or eve a lot, different than what's expected, is not new for most hair grooming artists as far as I know. Of course it depends on the system, but talking strictly about Houdini, there shouldn't be a seed like behavior with pruning.
There are a few parameters that work with vicinity distance, which is of course incumbent on the number of hairs, for clumping as well as for the hairgen itself, and if those are calculated after the pruning ratio, then you've discovered an workflow defect. Pruning should be a simple random purge of already generated hairs.
Please go with this to Support - they'll figure out what's what after you'll give them enough info.
The issue about working with a small percentage of the generated hair and then looking a bit, or eve a lot, different than what's expected, is not new for most hair grooming artists as far as I know. Of course it depends on the system, but talking strictly about Houdini, there shouldn't be a seed like behavior with pruning.
There are a few parameters that work with vicinity distance, which is of course incumbent on the number of hairs, for clumping as well as for the hairgen itself, and if those are calculated after the pruning ratio, then you've discovered an workflow defect. Pruning should be a simple random purge of already generated hairs.
Please go with this to Support - they'll figure out what's what after you'll give them enough info.
Hi again,
I have attached a new image that I think will be easier to see.
I also did another test where I manually deleted part of primitives of the generated fur, and I got the result I wanted - The left over is just part of those initial strands with no change in position whatsoever. The only problem with my “prune” is that I don't have any gain in performance - my partially deleted fur plays at the same speed as the full fur, which defeats the purpose here.
So in the image attached:
- the top row is using the Houdini default prune option (left to right: no prune, prune 30%, prune 70%)
If you focus on the fur inside the blue rectangle you can clearly notice the the profile changes considerably - no strand is the same.
- the bottom row was my “ manually deleted” version (left to right: no delete, delete 30%, delete 70%)
An in this case you can clearly see the profile is constant, and you can even identity strands of fur that are there intact on the 3 versions.
I will try support now, but anyone has any ideas about this?
Thanks!
I have attached a new image that I think will be easier to see.
I also did another test where I manually deleted part of primitives of the generated fur, and I got the result I wanted - The left over is just part of those initial strands with no change in position whatsoever. The only problem with my “prune” is that I don't have any gain in performance - my partially deleted fur plays at the same speed as the full fur, which defeats the purpose here.
So in the image attached:
- the top row is using the Houdini default prune option (left to right: no prune, prune 30%, prune 70%)
If you focus on the fur inside the blue rectangle you can clearly notice the the profile changes considerably - no strand is the same.
- the bottom row was my “ manually deleted” version (left to right: no delete, delete 30%, delete 70%)
An in this case you can clearly see the profile is constant, and you can even identity strands of fur that are there intact on the 3 versions.
I will try support now, but anyone has any ideas about this?
Thanks!
I should've asked you a scene files, not more pics, because I have no idea what's going on there.
It's best to do that when you send the problem to Support.
It's best to do that when you send the problem to Support.
Yes, you are right - a scene file would have probably been better 
Attached is a very simple example scene file:
- I have a simple setup to create a fur look. If you go the Hairgen/Optimization tab and turn the Prune option ON (which I set with a Pruning Ration of 0.3) you will clearly see the fur change look
I have also included my custom prune setup inside the Hairgen node and included a toggle on the top node called Custom Prune 0.3. If you try to turn ON and OFF my custom Prune you will see the fur look doesn't change
See image below - In Green Houdini Prune | In Red my “Custom Prune”
Let me know what you think!
Attached is a very simple example scene file:
- I have a simple setup to create a fur look. If you go the Hairgen/Optimization tab and turn the Prune option ON (which I set with a Pruning Ration of 0.3) you will clearly see the fur change look
I have also included my custom prune setup inside the Hairgen node and included a toggle on the top node called Custom Prune 0.3. If you try to turn ON and OFF my custom Prune you will see the fur look doesn't change
See image below - In Green Houdini Prune | In Red my “Custom Prune”
Let me know what you think!
Your “custom_prune” behaves like one would expect a “regular” prune to behave. I didn't notice this before, but apparently, Houdini's prune works by a different logic and whichever that might be, it's not very useful when getting more performance viewport is not the only thing the user's after.
“stable pruning” spells like a feature that would achieve the “normal” behavior, but it doesn't and the documentation's oblivious about its existence.
Definitely file a RFE for this.
BTW, I'm getting better FPS with your custom prune. Make sure RT toggle is off./
“stable pruning” spells like a feature that would achieve the “normal” behavior, but it doesn't and the documentation's oblivious about its existence.
Definitely file a RFE for this.
BTW, I'm getting better FPS with your custom prune. Make sure RT toggle is off./
Yes, exactly my point - Houdini's prune is not very useful if it changes the “look” when pruning…
I already submitted for support and I am waiting for their reply.
Regarding the FPS, it might be the case on this simple setup, but in a more complex setup, I am getting exactly the same FPS on the full fur not pruned and my custom Prune - 14 FPM - while with Houdini's prune it goes to 22 FPM with a 0.5 pruning ratio, and up to 30 FPM with a 0.7 pruning ratio.
I already submitted for support and I am waiting for their reply.
Regarding the FPS, it might be the case on this simple setup, but in a more complex setup, I am getting exactly the same FPS on the full fur not pruned and my custom Prune - 14 FPM - while with Houdini's prune it goes to 22 FPM with a 0.5 pruning ratio, and up to 30 FPM with a 0.7 pruning ratio.
Please share what you'll have learned.
Hi there,
So after a few days, Side FX finally replied and here is their answer to this Prune issue:
“Hi, thanks for the detailed explanation. The first thing to do is enable ”stable pruning“. It is not the default because it can be a lot slower. In this mode all the root points are still generated, but hair is only generated for a percentage of them. Hence the id and position of the remaining points is stable.
Clumps can still jump around though, as clump curves are picked at random from the input hair. When hairs disappear due to pruning, different clumps will be picked. You can avoid this though by generating custom clump curves using a hairgen SOP within the Hair Generate object. This should allow you to get a very similar look, with more control and stability.
See the attached file. Hope that helps!”
I have tried their example and although it is much closer now, it is not a perfect solution - it still changes slightly the look of the hair, but at least it is a better way than before.
So it is something we should be aware of…
Hope this helps everyone!
Cheers
So after a few days, Side FX finally replied and here is their answer to this Prune issue:
“Hi, thanks for the detailed explanation. The first thing to do is enable ”stable pruning“. It is not the default because it can be a lot slower. In this mode all the root points are still generated, but hair is only generated for a percentage of them. Hence the id and position of the remaining points is stable.
Clumps can still jump around though, as clump curves are picked at random from the input hair. When hairs disappear due to pruning, different clumps will be picked. You can avoid this though by generating custom clump curves using a hairgen SOP within the Hair Generate object. This should allow you to get a very similar look, with more control and stability.
See the attached file. Hope that helps!”
I have tried their example and although it is much closer now, it is not a perfect solution - it still changes slightly the look of the hair, but at least it is a better way than before.
So it is something we should be aware of…
Hope this helps everyone!
Cheers
Thanks for the update.