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macdubh
08-01-2006, 08:33 PM
Does anyone know of a way to select or control a subset of an objects vertices as a particle emitter ? For example, can a weightmap be used to define which vertices are preferred as the particle emitter. Also, does anyone know how layout actually decides which particular poly, or vertex, is used at any point in the sequence.

Any help much appreciated.

evenflcw
08-02-2006, 09:18 AM
In most cases ParticleFX just emitts randomly across a surface. But if you set Nozzle to Vertices and have Fixed Random checked it will emit according to point(creation)order. To limit where on a surface there should be emission you can use textures (T button beside birthrate; Weights aren't possible and UVs don't seem to work by me), however this does not seem to work with Nozzle set to Vertices. So if you need to limit what vertices emitt just copy that part of the object into a different layer and only attach the emitter to that layer.

EDIT:
ParticleFX is the oldest part of the FX suite and I would be surprised if it got updated soon. Atleast I can hope :)

macdubh
08-04-2006, 08:12 PM
Thanks for the tips evenflcw. I have now played around with the texture pane but, like you, I could not get any meaningful result with uv maps. I also experimented with gradients using a null and distance to object as the input but this didn't seem to work either. This is a shame since With LW9 I'm finding particleFX much speedier and therefore easier to work with.

evenflcw
08-05-2006, 07:43 AM
Null+Gradient set to Distance to Object acctually seems to works for me ... in 8.5 even and without calculations, which was kind of unexpected! Although it seems I have to hit File>Update if I change the motion on the null. Note also that Update should done on frame 0. If I do it on any other frame it'll only evaluate the pfx from that frame and on, anything before that will be static.

I attached the scene.

macdubh
08-06-2006, 12:54 AM
Thanks again. I studied your scene and found that I was not setting up the gradient correctly. Somewhat encouraged I tried an experiment which has subsequently disappointed. The attatched scene has the setup containing a basic capsule with one end involuted. At the apex of the interior is a small region (surfaced as "source") which has a Null in close proximity, used as the object in the distance to obect gradient. I deliberately chose the highest polygon numbers for this region. Now the particles are limited to the region of interest but are infrequently emitted and increasing the birth rate has no effect on the total number. Shifting the Null to the external top point of the capsule shows a similar effect. It appears that PFX is randomly choosing a polygon to emit and then deciding if that polygon falls within the gradient. If it doesn't then too bad, no particle. However it does not then decide, as it should, that there are still x number of particles to generate and keep going.

evenflcw
08-06-2006, 09:08 AM
You're analysis and conclusions seem to be correct. PFX does seem to randomly choose emission spots first, and only after that evaluate whether those spots are within the texture or not. Obviously this is bad because it means the numbers you input aren't reflected correctly in the output. I suggest you bug report this. I'll do the same.

Although you cannot trust the numbers it is still usable if you bump the numbers. If you really need to keep track of the particles I suggest you place those "source" polygons in a layer all to themselves and skip using textures altogether.