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I've been unsuccessful so far in finding information on, or working out how to control the angle that a particle is emitted from using a normal map.

What I'm trying to do is create a texture or UV map and bake a normal map and use that texture to effect the normal that is used by the particle system to create the vectors of the particles.

Ideally I would like to be able to:

Emit a wave or hemisphere pattern from a plane.

Paint on a direction for particular patches of grass or hair.

Paint a set normal in order to simulate fabrics or faux fur that is manufactured with a direction. (eg, default blue is upright. various changes in colour tilt the hair direction)

Have I missed something simple or is this currently not possible?

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  • $\begingroup$ Would manipulating the normals by geometry also be OK for you? $\endgroup$ – stacker Dec 14 '13 at 19:27
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    $\begingroup$ You could try using textured force fields and enabling Use force field for generating hair. I'm not sure if this is what you want though. $\endgroup$ – gandalf3 Dec 14 '13 at 22:05
  • $\begingroup$ if a texture force field can use the UV map of the model and a normal texture to set the initial direction of a particle at the emission surface this would be ideal. I'll take another look at the texture force field, I've so far been unable to make them effect changes to particles. $\endgroup$ – SleepyMolecule Dec 15 '13 at 3:56
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I don't know a way to incorporate normal maps, you could achieve the effect you described by Subdividing W the plane several times. And deform it e.g. using Proportional Editing.

enter image description here

This way you would also be able to animate the geometry with Shape Keys

enter image description here

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  • $\begingroup$ If a shape key could still effect the particles while being set to 0 on the actual model this would be a step in the right direction. I'll look in to it, thanks. $\endgroup$ – SleepyMolecule Dec 15 '13 at 4:19
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If it is something like this you would like, there is the comb tool (like combing hair).

combed hair

Add a particles system, then, go from Object mode to Particle edit. Select the comb tool. Comb. Since you stated that you intended to paint the normal map, I guess this would be better.

If you want to render your particle system. You must leave Particle edit.

Also, if you need to change some of the parameters for the particle system, you must discard the combing information and comb it again. It doesn't matter, combing is fun. :-)

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  • $\begingroup$ Thanks for the reply! Combing is amazing but in this case I would love to avoid it if possible (It also only applies to hair?). The advantages being speed, settings still available, unable to comb a uniform angle to the surface (afaik). $\endgroup$ – SleepyMolecule Dec 15 '13 at 4:14
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It sounds like you are assuming that the emitter and the visible object have to be the same.

You can have a low res mesh visible with particles coming through it that are emitted from an underlying high res mesh. You can even have several emitters hidden from view.

enter image description here

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  • $\begingroup$ I just did something similar myself. Using the XYZ texture type and baking a deform. It had Mixed results, mostly it was missing a constant angle for all fur. $\endgroup$ – SleepyMolecule Dec 15 '13 at 12:37
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I'm leaning towards the answer to my question being currently a no.

I've tried many combinations without the desired result, however I have found a work around!

In particle settings under Velocity are the setting Tangent and Rot (rotation). By taking sections of a model and making vertex groups you can control what angle particles in that area spawn at relative to the surface normal. However! You must use very very small amounts of both Normal (same as length) and Tangent as adding Tangent seems to wildly increase the hair length. A Normal of 0.002 and a Tangent of 0.03 is a good start. Dialing the rotation (Rot) from -1 to 1 spins the hairs direction though a full rotation.

To save time, creating the particle effect should be done first. When adding a new area, select the original hair setting and make it Single User before dialing the Rot to its desired angle.

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