particles from shader

tripathiutsav · Lurker Joined: 20 Aug 2010 Posts: 4 Location: kolkata

Can any body help me , i am finding the way that how to emit particles from shader which i have made in shop. like noise of black and white with different vop node. i assign the material on the sphere. i want to emit particle from sphere but only from dark value of shader.later if i modify the shader the particle must modify its birth place.

thanks a lot in advance, if anybody can help me, i really appreciate that.

ragupasta · Posted: Fri Jan 27, 2012 12:45 pm GMT Post subject:

There are probably lots of good ways to solve this, however I did find a hack.

Make your scene up and build your noise(s) in a vopsop. Basically you reference copy those vop nodes, and paste them inside your material network. (check shops)
Downside is that to change the noise values you would have to do it at the sop level and not shops.

It will be at least sunday before I can look for a better solution (working all weekend). Im sure others here will post a better soloution before then.

If you was using a texture map, you could bring it into cops, and use a pic() inside a point sop.

tripathiutsav · Lurker Joined: 20 Aug 2010 Posts: 4 Location: kolkata

thanks a lot for for your reply... ragupasta

i can use tex() and pic() expression functions to fetch the values from the disk and cop but they consume lot of memory to calculate , on the other hand if i use vopsop for Cd value than it deal with only point not with surface.So for emit particles from point i need to increase the density of point in geometry to get perfect noise color and again it would be too heavy.
Or i can directly put material sop node on particles to fetch same material of geometry from shop level but particle point are not giving Cd value , obiously its calculating in render processs.
Is there is any way to transfer the shop' Cf value to point's cd value in sop level, so that i could delete non required point on basis of cd.

and bake vex is not working on particles.

OR is there a any function like tex or pic to fetch value from shop Cf .

thanks

ragupasta · Posted: Sat Jan 28, 2012 7:32 am GMT Post subject:

Well you can't access the colour values directly from the material afaik (someone can correct me if they know better than I). The materialsop creates the "materialshop" attribute and not a Cd so thats the problem.

Increasing the geometry count to get a really good definition of the noise doesn't carry so big an overhead in terms of calculation, unless your using some really dense geometry, like a hard surface asset, or organic sub-d model.

As for the Cf attribute inside the material, all attributes in Houdini can be exported (example being rendering extra image planes), but directly accessing that inside of sops, I honestly don't know. You also say Cf value to sop and delete non required point based on Cd (promoted attrib). That still would require a large amount of geometry at achieve.
Deleting via a noisey surface still wants heavy geometry to look right, or you still would have a blocky surface to emit particles from.