Ray Tracing, Transparency and Particles?

Now here’s a thing. Take a mesh, say a UVsphere, add a material and a clouds texture, get it to emit particles from the texture. Add IPOs for the material colour and animate for say 100 frames. Particles fly out, change colour etc. Groovy. Now add a bigger UVsphere, add a material and texture, make it partially transparent by going to the Material buttons and turning Render Pipeline>ZTransp on and setting and Material>A to say 0.4. Put the emitter mesh in the centre of the transparent sphere and render. Particles fly out, change colour, all visible through the transparent sphere. All good. But the transparent sphere is pretty ordinary looking. So go to Mirror Transp, turn on Ray Transp (ZTransp seems to automatically turn off), maybe add some Fresnel. Render. Transparent sphere looks much better, but the particles have disappeared completely. So I can either have particles in the middle of a crappy transparent sphere, or a good transparent sphere with no particles in it. Aargh! I’m sure I’m missing something obvious here: can anyone point me in the right direction? Thanks, Clive.

ZTransp is transparency based on the Z value, or distance from the camera; stuff further away from the camera, behind a transparent thing, is rendered. Ray Tracing is a completely different way to render, based on tracing the path of a photon from a light source as it reaches the camera; that is why RayTracing and ZTransp are mutually exclusive.

Particles are special little beasts that are not light sources and don’t have mass or substance, so they cannot be traced. If you want a glowing center of stuffs inside your sphere, create light sources (lamps) - lots of them, and animate them.

Now I was hoping you weren’t going to say that - I’ve tried dupliverting lamps onto particles in the past and it never really seems to work out very well. Anyway, thanks for clearing that up for me. Now I know.

A trick, though, is dupliverting textured planes onto your particles. These can have a spherical blend onto them so they look like particles, but because they are actual objects they will show up in ray transparency.

Ok… i’m having the same issue but with grass trough a window… hmmm…