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Particle Hair - Density texture bug
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Description

System Information
WIn7 x64
nVidia GF GTX 660

Blender Version
Broken: 2.7
Worked: 2.6

Short description of error

When I connect a texture to Particle/Hair Density parameter every time I click some, any button in Texture tab (or texture slot in PArticle tab) the position of hair strands changes.

Exact steps for others to reproduce the error

  1. Create any mesh (box will be fine), and a small plane which will take place of a feather
  2. Create Particle System, change:
    • from Emiter to Hair (Hair Length: 0.3 will do)
    • Render --> Object --> Dupli Object: the plane mesh you created
    • Textures --> click New
    • having it selected go to Textures tab, to Influence and click Density.

Attached blend file has it all set up.

Details

Type
Bug

Event Timeline

The screenshot below shows what`s happening with hair

Lukas, in case you feel like crunching hairy issues again… :/

Bastien Montagne (mont29) triaged this task as Normal priority.Apr 13 2014, 11:03 PM

I am not sure I understand the problem...As far as I have seen, textures -should- update the particle when tweaked. I just did a commit that avoids updating when the active texture is changed in the particle tab but I don't think changing the texture settings otherwise should not update.. Do I miss something here?

What I have seen however is that changing between textures in the particle tab strangely only updates half the sphere each time.

The problem here is that it updates itself when you click literally anything not necessarily involving texture.
And even if it should, the change shouldn`t be so dramatic, unpredictable, etc.

Look at the screenshots I`ve uploaded. The changes didn`t happen because I changed "density". I clicked some irrelevant checkbox somewhere. Also the density map covers almost the whole head where you can see there are totally bald areas, not to mention weird, changing amounts of feathers.

I can see the problem in the screenshot but it would help if the actual test file had a similar behaviour (which it doesn't, each "update" does the whole sphere). I can see how it would be nice for updates to only refresh the relevant areas though.

@Antony Riakiotakis (psy-fi) the problem is when influence=>density (texture) is ticked. Every time you click for example influence=>general=>time or some other texture/particle system settings like "hair lenght" (even without change the value) it exactly looks like particle system changes seeds value (seed is still "0", but hair change their location).

When influence=>density (texture) is unticked everything is ok.

@Antony Riakiotakis (psy-fi): Assigning to you in case you have an idea. But imo we can close as TODO, spending time on these issues seems like a waste.

Yes, this looks more like a todo actually, it requires being able to internally separate which slots should get full recalculation and which should not.