Maxon Cinema 4D Forum
Irreversable hair changes
Irreversable hair changes
by Steve Bentley on Oct 10, 2019 at 9:20:49 am

I'm in tweak mode for a hair project and we've got our look down pretty well. Never one to leave well enough alone, I thought I'd tweak the thickness setting. Bam! (see before and after pics). Its like the soften filter that's on the post process has been removed. But now if I put that thickness value back to where it was (or change anything else for that matter) I can't get the silky look back - it's always a thin rope look. Restarting does help but not if I save the mangled file - its toast. I always have to go back to a safety file.
Is there a cache I don't know about that I can clear? Adding too many hairs can do this too on occasion.

Second issue. I've got 4 guides coming out of a single poly surface (pretty big poly) and I thought I'd move those guide in a little toward each other. So I unrooted them, moved them (or rather brushed them) to the new spot - contrary to the manual, moving does not work, you have to brush the roots along - and then I rerooted them. Looks great in the view port. But when I render the hairs are back at the original surface width where the guides used to be, even though the hairs being displayed in the viewport look like how I want them (yes, hairs, not just the guides). Does the hair always "fill" the poly no matter where the guides are? I'm thinking this is the case because the hairs should form a pretty nice tube but I'm now getting a cubic look. Whats the point of a preview in the view port if it can be this far off?
R19 Win7
Hmm. I'd upload the files but neither dragging them in or using the upload codes is working.

Re: Irreversable hair changes - images
by Steve Bentley on Oct 10, 2019 at 9:21:27 am

Re: Irreversable hair changes
by Brian Jones on Oct 10, 2019 at 2:05:38 pm

the image definitely look like thickness has not come back down, no experience there myself - the file could be interesting

2. AFAIK the hairs grow in their assigned surface (constrained by selections if present) and guides just guide hairs within their influence. Tightening the roots in shouldn't tighten where the hairs grow, I would try to use textures in the Length to control where it grows (assuming I'm understanding)

Re: Irreversable hair changes
by Steve Bentley on Oct 10, 2019 at 5:35:07 pm

Thanks Brian,
I figured that about the selection filling. Too bad the interactive preview doesn't reflect that.
But doesn't that mean that, given the hair will fill each poly in the selection (by the time you get a thick enough forest of hair), we're getting hair plugs?

Re: Irreversable hair changes
by Brian Jones on Oct 10, 2019 at 8:49:20 pm

it doesn't seem to, the hairs grow in an 'area' I think, so if hair count is the same distribution looks very similar if you grow hairs on a 20x20 plane or a 1x1 plane. The difference is the number of guides that get generated (at least by default) 4 as opposed to 400 but the hair looks the same, it's just way more controllable due to the number of guides on the 20x20.
With hairs it seems to be ignoring poly borders completely and just distributing evenly across the available surface. So if the area is limited by a poly selection the same number of hairs grows there, just way denser.

Re: Irreversable hair changes
by Steve Bentley on Oct 12, 2019 at 5:53:27 pm

Thanks Brian, you're right of course. I just have so many hairs in that one poly they are busting at the seams. Using a circle gradient in the density tab of the shader helped with that but that brought up a new problem. There is no spatial mapping setting for the gradient in the density tab (its grayed out - in what circumstances would it be available?). And I can't quite figure out the mapping.
If I set a plane to 9 divisions (3x3) and use the center poly to emit the hair, applying a gradient (in density) to that seems to map the gradient to the whole plane, using only a small fraction of the gradient for the center poly - that made sense. So I thought, hey if I delete the unemitting polys the gradient will map to just that one poly. Not so much.
So how does one determine what expanse the texture you are using to set where hairs aren't can stretch over? For a sphere for instance what mapping routine is used for that density "texture"?
Is there a way to apply the texture (in my case a gradient) to another object that will set the spatial nature of the map, and then point the density tab to that material on the other object like you would with a mograph shader effector (I mean I've always believed all of these cool toys are all based on the same system given the cloning nature of them).
And now that I've written that, I'm off to try a shader effector being use with the hair object. Mad Science! Frankenshader!

Re: Irreversable hair changes
by Brian Jones on Oct 13, 2019 at 4:42:00 am

Sounds interesting, unfortunately I’m out of town now until Wednesday, hope it goes well.

Re: Irreversable hair changes
by Steve Bentley on Nov 20, 2019 at 6:20:46 pm

Here we go again. R19 Win7
Its been going well and now suddenly, what I thought was a cache issue has turned out to be a viewport vs render issue. Attached are the files and images from view port render and the render engine.
The view port view is reasonable and an expected result (and it also matches a non viewport-render viewport working view). But the render version is just out to lunch. But of course the render version is the one that matters. I can't imagine how C4d gets to the render version given the single guide hair.
I've turned off all the waves and curl etc in the shader to try and simplify and target the problem. I've removed all other hair objects in case its a memory issue (but on a 128GB machine I can't imagine that).
This has happened in the past and as per the sage advice of others here I've turned off the cache in the hair object (which just makes manipulation in the viewport handleable anyway). This cache-off solution has worked everytime this has happened so far. But not this time.
I've sent this file to other machines, I've restarted, i've used chicken blood and howled at the moon. I'm stuck.