Uncombable hairs and how to fix them?

I’m experimenting with combing fur and I’m frequently running into this problem, where a set of hair particles appear to get tangled up among themselves and cannot be combed:

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I think this situation is caused by releasing the left mouse button and then moving the mouse back to where the initial combing action started; Blender tends to be slow to respond when combing fur and it doesn’t always realize that I’ve let go of the mouse button and still thinks I’m combing. I’ve gotten Blender to respond a little better by turning off subdivision modifiers, but this situation still occurs a lot.

When I have “stuck” hairs like this, my first line of defense is to set the strength of the Comb tool to 1.000, but that doesn’t always work.

Sometimes I can fix this issue if I view the model from a different angle and try combing again.

Sometimes I can fix this issue if I uncheck Deflect Emitter, comb the problematic area (which usually makes the hairs hide inside the object), check Deflect Emitter, then comb the problematic area again (which makes the hairs pop outside the object).

However, there are other times when nothing appears to work. In fact, sometimes it seems impossible to select the individual particles using Box Select, Circle Select, hovering with the mouse and pressing the L key (for Select Linked), or left-clicking with the arrow tool. I can select the particles if I go to Select -> All, but that isn’t helpful since I’m then selecting everything. I have no idea why I can’t select these specific particles that are very clearly in the viewport. If they were vertices, I could easily select them, but as particles I can’t. It makes no sense.

I have been trying to work around/fix this problem for a couple days, and I can’t seem to figure out a technique that will reliably comb hair when the particles get “stuck” like this. (And they seem to get “stuck” a lot.)

How can I fix scenarios like this? My Blender file can be downloaded here: http://www.sundriftproductions.com/blenderartists/kitten_fur_05.zip


After a lot of further experimentation, I think I know what the problem is. Unlike many of the other tools in Blender that allow you to affect vertices/objects/etc., the Brush tool only combs particles that are within a certain apparent distance from the brush tool itself.

In other words, let’s say I’m combing the fur on a cat leg. I’m viewing the leg through the camera while I’m combing it, using the Lock to View feature on the camera. I’m pretty close to the leg when I’m combing it. If I pull back a certain amount (I’m not sure how far back, but there is some sort of internal threshold being used here) and then try combing the leg again, I won’t be able to comb any particles.

In fact, I can be zoomed in and combing the cat’s left leg and still see part of the cat’s right leg’s particles in the viewport…but the Brush tool will only affect the left leg (not the right leg). This is apparently because the particles that I can see on the right leg fall outside the magic distance threshold of what the Brush tool can touch.

I suspect that the behavior I described in my original post is what happens if some particles fall jusssssst outside of the range of the Brush tool. Because when I see this behavior now, I simply move in closer with the camera and then I can brush those particles.

I’m still not sure how Blender determines the distance where it allows the Brush tool to affect particles – I don’t see any relevant parameter in the N panel that would determine this. Instead, I suspect it’s just some sort of built-in preset distance and, if you fall outside the range of it, the Brush tool simply doesn’t touch those particles.