Particles Density from Image Texture - UV coordinates problem #41087

New Issue

filip mond · 2014-07-15T19:42:04+02:00

filip mond commented

2014-07-15 19:42:04 +02:00

System Information
OS X 10.8.5 NVIDIA GeForce GTX 780M 4096 MB

Blender Version
Blender 2.71 Hash:a1aa969

Short description of error
Image Texture used for particle density, doesn't accept UV mapping coordinates.

Exact steps for others to reproduce the error
When Image Texture is used for particles density with UV map coordinates, than image is stretched into square 2x2 units in center of scene.

test-Particles-Texture-Emitter.blend

Generated coordinates works.
Other types - I'm not sure (because I'm not sure how they should looks like.)

Tested with Cycles and BR engine, scene build from scratch with the same result.

**System Information** OS X 10.8.5 NVIDIA GeForce GTX 780M 4096 MB **Blender Version** Blender 2.71 Hash:a1aa969 **Short description of error** Image Texture used for particle density, doesn't accept UV mapping coordinates. **Exact steps for others to reproduce the error** When Image Texture is used for particles density with UV map coordinates, than image is stretched into square 2x2 units in center of scene. ![test-Particles-Texture-Emitter.jpg](https://archive.blender.org/developer/F97967/test-Particles-Texture-Emitter.jpg) [test-Particles-Texture-Emitter.blend](https://archive.blender.org/developer/F97969/test-Particles-Texture-Emitter.blend) Generated coordinates works. Other types - I'm not sure (because I'm not sure how they should looks like.) Tested with Cycles and BR engine, scene build from scratch with the same result.

filip mond commented

2014-07-15 19:42:04 +02:00

Changed status to: 'Open'

filip mond commented

2014-07-15 19:42:04 +02:00

Added subscriber: @FilipMond

Lukas Tönne was assigned by Bastien Montagne

2014-07-17 20:17:48 +02:00

Bastien Montagne commented

2014-07-17 20:17:48 +02:00

Added subscriber: @mont29

Bastien Montagne commented

2014-07-17 20:17:48 +02:00

Lukas, maybe this one is not a can of worms? ;)

Lukas Tönne commented

2014-07-18 18:35:57 +02:00

Changed status from 'Open' to: 'Archived'

Lukas Tönne closed this issue

2014-07-18 18:35:57 +02:00

Lukas Tönne commented

2014-07-18 18:35:57 +02:00

This is not a bug, the problem is simply that the particle emission mode is set to "Verts" - this can only emit particles directly on vertices and any density mapping of the UV map is ignored. Consider what would happen when then UV map is not contiguous, e.g. each face is scattered randomly over the UV map. UV coordinates are simply not defined for vertices themselves (unless they are actually corners of a face, which is not the case.

A kind of workaround is to use "Faces" emitter mode:
test-Particles-Texture-Emitter2.blend
Note that i reduced the number of particles in this file, otherwise you get multiple particles per face which looks weird. You can also switch the distribution from jittered to random if that is of interest.

This is not a bug, the problem is simply that the particle emission mode is set to "Verts" - this can only emit particles directly on vertices and any density mapping of the UV map is ignored. Consider what would happen when then UV map is not contiguous, e.g. each face is scattered randomly over the UV map. UV coordinates are simply not defined for vertices themselves (unless they are actually *corners* of a face, which is not the case. A kind of workaround is to use "Faces" emitter mode: [test-Particles-Texture-Emitter2.blend](https://archive.blender.org/developer/F98430/test-Particles-Texture-Emitter2.blend) Note that i reduced the number of particles in this file, otherwise you get multiple particles per face which looks weird. You can also switch the distribution from `jittered` to `random` if that is of interest.

filip mond commented

2014-07-18 22:44:59 +02:00

OK It make a sense now :(

Anyway … does exist any way how to give user feedback that UV will be ignored?
Just to protect others from my pain … it took me in two days eight hours of testing in what way are particles distributed.
It looks now like a lot of time, but there was at the same time a several factors that affect result when I was tested.
So if there is option like have UV in grey color on a list when Vert option is selected or so, it could save me (and maybe to others) a ton of time.

WORKAROUND
I tried your workaround (instead of Vert use Faces) - seems to work for my sample file, but it doesn't work for my braille text so well.

I tried also move texture from vert position to centers of faces, but it become even worse.

I would like to understand how it works, but I understand it's not a topic here.

My workaround in this case was at the end squared texture and grid resized to match the texture size 2x2 unit.
Thread BA

DETAILS (not necessary to read)
Initial plan was to restore braille text from image into vector file.
Image was to small for direct convert, so … precise circles emitted from precise grid seemed to me as the best choice.
At the end It was really hard to understand what cause my problem from reasons like:

character (style) of my braille image are just a few dots.
testing behavior on a plane with square texture where of course problem wasn't visible.
And all the time refresh cash if its not display problem.
… after all that I took this rectangle ABC texture, that shows me whats going on there.

OK It make a sense now :( Anyway **… does exist any way how to give user feedback that UV will be ignored?** Just to protect others from my pain … it took me in two days eight hours of testing in what way are particles distributed. It looks now like a lot of time, but there was at the same time a several factors that affect result when I was tested. So if there is option like have UV in grey color on a list when Vert option is selected or so, it could save me (and maybe to others) a ton of time. **WORKAROUND** I tried your workaround (instead of Vert use Faces) - seems to work for my sample file, but it doesn't work for my braille text so well. ![Screen_Shot_2014-07-18_at_21.31.00_copy.jpg](https://archive.blender.org/developer/F98449/Screen_Shot_2014-07-18_at_21.31.00_copy.jpg) I tried also move texture from vert position to centers of faces, but it become even worse. ![Screen_Shot_2014-07-18_at_21.29.49_copy.jpg](https://archive.blender.org/developer/F98451/Screen_Shot_2014-07-18_at_21.29.49_copy.jpg) I would like to understand how it works, but I understand it's not a topic here. My workaround in this case was at the end squared texture and grid resized to match the texture size 2x2 unit. [Thread BA ](http://blenderartists.org/forum/showthread.php?342637-Density-from-texture-%85-*-!!!&p=2684738&viewfull=1#post2684738) **DETAILS (not necessary to read)** Initial plan was to restore braille text from image into vector file. Image was to small for direct convert, so … precise circles emitted from precise grid seemed to me as the best choice. At the end It was really hard to understand what cause my problem from reasons like: - character (style) of my braille image are just a few dots. - testing behavior on a plane with square texture where of course problem wasn't visible. And all the time refresh cash if its not display problem. … after all that I took this rectangle ABC texture, that shows me whats going on there.

Lukas Tönne commented

2014-07-19 14:02:37 +02:00

Not sure about the Braille case, there could be lots of reasons for the result: bad texture mapping, insufficient base density (since the texture is just a filter), etc. Generally i'm not convinced that particles are the best approach for a braille "simulation" anyway, it would probably work a lot better with a plain object array and some scripting to raise/hide them.

Conveying such intricate details about which emission mode works with texture factors in the UI is not feasible unfortunately. The particle system is just a big black box with lots of buttons on it. Eventually we will get a more transparent system using nodes and clear data interfaces, where users can specify exactly what happens at each stage. This should help avoid the exponential number of possible and incompatible combinations that make particles so hard to use.

Not sure about the Braille case, there could be lots of reasons for the result: bad texture mapping, insufficient base density (since the texture is just a filter), etc. Generally i'm not convinced that particles are the best approach for a braille "simulation" anyway, it would probably work a lot better with a plain object array and some scripting to raise/hide them. Conveying such intricate details about which emission mode works with texture factors in the UI is not feasible unfortunately. The particle system is just a big black box with lots of buttons on it. Eventually we will get a more transparent system using nodes and clear data interfaces, where users can specify exactly what happens at each stage. This should help avoid the exponential number of possible and incompatible combinations that make particles so hard to use.

filip mond commented

2014-07-21 17:58:12 +02:00

Thank you for all your help.

I noticed that no one wants to touch them (particles).
But some visual feedback for user that coordinates aren't use would be helpful.
(if exist)

Thank you for all your help. I noticed that no one wants to touch them (particles). But some visual feedback for user that coordinates aren't use would be helpful. (if exist)

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Particles Density from Image Texture - UV coordinates problem #41087