Rendering hair

[Jon.Topps]

I've made three hair projects now, and two of them have completely crashed my computer when trying to render. If a render takes forever, I'm cool with that, but obviously destroying my computer is not good, lol, so help understanding why this is happening would be appreciated.

In one project, I gave the default cube hair, and combed the hair. Then I threw on a three point lighting set up. This rendered fine, and even quite quickly.

In another project, I made a very simple model of a blobfish, then gave it three particle systems for hair (head, mustache, and eyebrows). I brought the hair count to zero for all three of them, and then painted in hair where I wanted it to be. It was working fine, but then rendering it, it said it was doing the BVH or something (I'm scared to hit render again), and crashed the comp.

In my latest project I have a llama head I'm working on, and applied a material to. I put one particle system of hair on it, turned up the hair count to 3000, and made it slightly clumpy, and made it brown, that's it. I didn't even comb it. I tried to make a render, and again, it said something like doing BVH, but it started getting a percentage, it went up to 65%, then crashed Blender and nearly crashed my computer.

I'm not really doing anything all too complicated, but did I do something wrong? Is there a trick to it? Is it just chance? I would like to be able to get good at hair, but this is kind of discouraging me.

[Girlgamer87]

Are your pc specs good?

Which render mode are you using?
Evee/cycles/..

Have you tried disabling children? (That sounds so wrong) Each hair strand has x number of children.

[Girlgamer87]

"BVH" is calculating the geometrical structure of the scene. Crashing at 65% doesn't sound good but sometimes blender becomes unresponsive for some time - all resources go to the render and none to the ui. It may 'recover' and continue the render but it's usually an indication of some issue, RAM etc

[Kaulann]

i would suggest you try sticking to around 1000 hair particals and setting the interpolated children to about 50 insted of 100 than if it dosent look like enough hair you can up that number a little or play around with the size of the hair strands.

on if you did something wrong i would say no. it sounds like you just added a bit to much for your compuuter to handle. i have crashed my pc a bunch of times getting blender stuck on what seems like very simple things.

[*P0P$*FR3$H3NM3Y3R*]

BVH is the Bounding Volume Hierarchy. A calculation of what is visible to the camera in what order. IF it crashes at the same spot it might suggest that there is some issue with lack of memory eventually?

[Jon.Topps]

Thanks for the advice! So I reduced it a bunch, and it works great. I was using cycles to try and render the hair before. The weird thing is, it renders SUPER quick. I don't understand how it can go from crashing, to rendering in seconds...?

Anyways new problem, this makes no sense at all to me. I created a new particle group for the fine fair. I shortened the length, took the hair count to zero, and then started drawing in hairs where they belong. I rendered it, and it worked, and looked fine, but I had forgotten the children. So, I added simple children, and BAM! Check out the pic below. Woah this is a mess. Shortening the length of the children doesn't help. All the children still float around, and it looks like sawdust filling the air. Why in the world would this happen?
Combing it doesn't help. I don't even know what to adjust to try and fix this...
EDIT: It seems changing the radius helps, but then I'm stuck to having the hairs all super packed tightly together, where I would like them more evenly distributed. Is this a bug?

https://steamcommunity.com/sharedfiles/filedetails/?id=2116790121
https://steamcommunity.com/sharedfiles/filedetails/?id=2116790798

[Kaulann]

i try not to use simple childern for that very reason. it never seems to do what i want. Also that is a very good lama. i love the eyes. anyway try using either no children or interpolated. if you really want to use simple than you might need to just mess around with the settings on it. i havent messed with simple children really so i dont know much about how to make it look good.

[Jon.Topps]

Originally posted by Kaulann:

i try not to use simple childern for that very reason. it never seems to do what i want. Also that is a very good lama. i love the eyes. anyway try using either no children or interpolated. if you really want to use simple than you might need to just mess around with the settings on it. i havent messed with simple children really so i dont know much about how to make it look good.

Thanks! Here's how I finally got it. The eyes I had in the previous pic weren't fully rendered because Eevee can't do what I did.
I ended up basically killing the rotation on the simple children. I used interpolated on the longer hair, and you're right, it worked much better. That's so dumb that simple children make the radius cause hair to spawn in mid air... I also drew in thousands of hairs for the fine hair, which is strange it didn't crash blender, and actually rendered quite fast. I still don't really get why it crashed in the first place.
https://steamcommunity.com/sharedfiles/filedetails/?id=2116990403

[Kaulann]

that looks really good. great job.

[Jon.Topps]

Thanks so much!
Another issue I've had with hair, is Blender creating hairs where I don't have any. Here's an example. I don't get why, when I've put the hairs to zero, then drawn them in, why would there be hair where it should be smooth? It looks wrong too, but I don't even know how to begin thinking about what to do to fix this.
https://steamcommunity.com/sharedfiles/filedetails/?id=2113251195