Obj merging hair: should it work?

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Hello

I have several characters with hair, rendering in Redshift. Everything is hunky dory. For certain reasons I want to obj_merge the characters. The polymeshes, obj_merged, work as expected but the hair_generate objects, obj_merged, don't render. I tick some likely looking tickbox on the merged hair object(see below) and the hair now renders but not as expected. (I tried variations of hair width and ticking the use Houdini hair thickness box but to no good end)

Should I expect this to work? Am I merging hair using the correct method?

I'd be grateful for any pointers in the right direction
Edited by alastair - Aug. 14, 2021 06:44:32

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Capture.JPG (13.2 KB)
hair_merge.jpg (85.4 KB)

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It might be a problem for Houdini in shifting to a new renderer.
You will have to wait until new version of Houdini is released.
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one potential cause ould be if your object is scaled on object level and you are object merging with Into This Object option
which will apply the transform to the geometry to compensate for that
however this would not be reflected in @pscele or @width attribute
so you will have to scale those yourself by the same factor
Tomas Slancik
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tamte
one potential cause ould be if your object is scaled on object level and you are object merging with Into This Object option
which will apply the transform to the geometry to compensate for that
however this would not be reflected in @pscele or @width attribute
so you will have to scale those yourself by the same factor

Hi Tomas
Thanks for responding. I made a very simple scene to test my problem and it doesn't look to be a transformation issue (see attached scene). I'm beginning to suspect that hair_generate objects are not meant to be merged. I wonder if anyone has actually done this? Is using the object merge node the wrong process?

Alastair
Edited by alastair - Aug. 15, 2021 05:37:31

Attachments:
hair_merge_test.hiplc (1007.7 KB)

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ifree
It might be a problem for Houdini in shifting to a new renderer.
You will have to wait until new version of Houdini is released.

Hi ifree
Thanks for responding. If it's a mismatch between Houdini and redshift should the original individual hair objects also not display the same non-rendering problem?

Alastair
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Interestingly the simple scene above works as expected in Mantra. So it looks like some sort of Redshift issue, or at the least the operation of redshift issue.

A
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"merged_hair" renders fine for me if I enable "Render Polygons as Hair" in its Redshift OBJ properties. My guess is that Redshift treats Hair Generate nodes differently, and for the rest we need to tick that parameter.
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pabcou
"merged_hair" renders fine for me if I enable "Render Polygons as Hair" in its Redshift OBJ properties. My guess is that Redshift treats Hair Generate nodes differently, and for the rest we need to tick that parameter.

Thanks pabcou. As you can see from my original post I mention getting the hair to render by ticking "Render Polygons as Hair" but as you can see from the included image it's very different in look from the the contributing single hair objects.
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Hi, when rendering hair using Redshift, I would avoid merging hair with a "head" because Render Polygons as Hair will usually try to render the "head" as hair. The different look you can see could be caused by this or the hair width/thickness which Houdini and Redshift treat differently. ie. Houdini = radius, Redshift = width/diameter (or visa versa, I can't remember). This is what Match Houdini/Mantra Hair Thickness is for.

Rob
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robsdesign
Hi, when rendering hair using Redshift, I would avoid merging hair with a "head" because Render Polygons as Hair will usually try to render the "head" as hair. The different look you can see could be caused by this or the hair width/thickness which Houdini and Redshift treat differently. ie. Houdini = radius, Redshift = width/diameter (or visa versa, I can't remember). This is what Match Houdini/Mantra Hair Thickness is for.

Rob
Thanks Rob. I should have been clearer; I'm merging the hair and head objects in two separate objects, so no hair and head mixing. I'm beginning to think that some redshift attributes get left behind when merging the hair. The individual hair objects render fine WITHOUT the render-polygons-as hair ticked and the merged hair object renders as expected in Mantra. I may be missing something but I think it's an un-catered for Redshift scenario.
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It might be worth checking on the Redshift forum because of the new hair shader as this could be a (another) potential bug.

ie. Testing your sample scene, checking/unchecking match thickness isn't visibly doing anything whereas something should be happening. If the original looks correct in Mantra but not Redshift, this would be the first setting I'd check as the thickness is what looks different (to me) between your two original renders. (and is *supposed* to be the main difference between Redshift/Mantra hair)

As a quick test, does doubling the hair thickness give correct results?
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