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Multires spikes
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Description

System Information
OS: Windows 7 Professional SP1
Graphics card: nvidia geforce 560ti

Blender Version
Broken: 2.69.1 r61064

Short description of error
Multires occasionally messes up the geometry which leads to un-fixable spikes. When you try to smooth out the problem area on one multires level, it makes it even worse on other multires levels.

Exact steps for others to reproduce the error

I'm not sure how to get a sculpt into a state where this happens. In bugReport.blend, you'll see the spikes at multires level 3 near the knees. If you try to smooth them out, you'll get different spikes on multires level 4. Trying to smooth out the problem area on level 2 makes the level 3 spikes worse.

I attempted to reproduce the bug on a simpler model in bugReport2.blend and it took a long time to get it into this state where this bug happens. I used the crease, grab, smooth, and clay strips brush a lot, scaled down the object and applied the scale (not sure if that matters), and did some more sculpting. When you smooth out the problem area on multires level 1, you get issues on higher levels.

Here's a .zip of the files mentioned above: https://dl.dropboxusercontent.com/u/17578055/multires.zip

Details

Type
Bug

Event Timeline

Kevin Hays (haysk) added a project: BF Blender.
Kevin Hays (haysk) set Type to Bug.
Kevin Hays (haysk) created this task.
Kevin Hays (haysk) raised the priority of this task from to Needs Triage by Developer.
Brecht Van Lommel (brecht) claimed this task.

This is an issue on the todo list:
http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/Tools#Multires_Modifier

It's due to the multires representation used, some mesh shapes give this problem, but fixing it requires a pretty big change in how we store and calculate multiresolution levels that is not so much a bugfix but likely more of a partial rewrite of the system.

Do any of the current core devs have the expertise to make the fix/rewrite eventually (even if a year from now), or is it something that will require another dev altogether? thanks. I'm concerned about how opensubdiv will effect everything.

It's mostly a matter of having time, not expertise, everyone who could do this is pretty busy with other things.

@Brecht Van Lommel (brecht) I gather from your response, the issue has been identified, but just no one is available to fix it? if so, thats at least some good news. I had thought it was just unsolvable by the team, thus my "expertise" comment, thanks for your time.

Would a quick fix be to add Edit mode to the levels? So that I could just edit out the spike manually?

We are at the gates of 2.80... so sad that this is not fix yet... I hope to be able to use multirres in the near future for sculpting, not just for copy details...