Weight Painting and Particle Generation

zombiewhacker · October 5, 2008, 9:07pm

V. 2.47
Having trouble learning to weight paint. As a test, I painted different sections of a mesh weights of 1.0, .75, .5, and zero, respectively. I thought this meant that particles (hair, in this case) would generate from the heavily weighted faces of the mesh and none at all from the unweighted (blue) sections. Instead, all sections of the mesh are producing hair particles at the same rate and length.
What middle step am I missing here?
EDIT: Relevant tutorials here:
http://wiki.blender.org/index.php/Manual/Weight_Paint

Patel · October 6, 2008, 11:11am

Because you can have many vertexgroups on one mesh, you have to tell the particle system which vgroup is controlling a certain attribute.
You can do this in the ParticleButtons ExtraPanel: select the attribute you want to control and choose the correct vgroup.

Pat

harkyman · October 6, 2008, 3:21pm

Along with Patel’s response, I should point out that the attribute I usually key for with that control is: Density. No hair grows outside of your vert group then.

zombiewhacker · October 6, 2008, 7:11pm

Whoa, whoa, slow down. Remember, you’re talking to a n00b here.:spin:
Let’s take it step-by-step.
Assume a mesh with two vertex groups. Let’s say I’ve named the first group Red and the second Blue. These I then weight paint accordingly.
I switch to the Particles menu. Add New, then select hair.
Now I have the Particles ExtraPanel in front of me. Right under it, the first button is called GR. Near as I can tell this is the button you’re referring to. By default, it displays as greyed out (as opposed to light blue). When I click on it, it expects me to enter a value of some kind. What do I enter?

Patel · October 7, 2008, 11:40am

The GR: input is for effectors, which can be controled by vgroups as well, this field is expecting the name of the vgroup BTW.

Down in the ExtraPanel there is a Vertex group: section with three buttons.
The first is set to density by default - you can stay with this as harkyman pointed out.
The second is just for inverting the vgroupweighting.
The third gives you the choice of the vertexgroups existing for your particleobject.

zombiewhacker · October 7, 2008, 6:07pm

Thanks for being patient with me.
Okay, I found option box. If I select Red, red sprouts hair. Problem is, if I select Blue, blue sprouts hair. I thought weight painting it blue would prevent hair from growing. Instead, all “painting” seems to do is create a new vgroup, but not actually give it weight.
Another problem: when I render, mesh containing hair vanishes. I see hair but no mesh, like an invisible man effect. Is this supposed to happen?

Patel · October 8, 2008, 4:00am

Everybody does this vgroups stuff in a different way, so this is just a suggestion:

1.Create your vertexgroup in the Editbuttons by choosing “New” in the LinkandMaterialPanel, selecting the vertices and assigning them.
Don’t miss the “Assign” step like I do sometimes.
2. In WeightPaintMode you can activate the “Vgroup” button, to make sure you are just painting on the active vgroup.
3. Paint your density(or whatever) on the mesh.
4. Setup your particlesystem with the vgroup.
5. To render the emitterobject as well, there is an “Emitter” button in the VisualizationPanel.