Hi there.
I have to render some particles inside a bowl that reflects a lot, and i need to get the refelctions of the particles.
Is there a way to get reflections in the matte objects?
Cheers.
There are a couple of ways.
In Krakatoa MX 2, you can set up a Krakatoa Atmospheric effect and select the particle objects (PRT Loaders, PRT Volumes, PRT FumeFX etc.) that you want to show in reflections. You could in theory save only a Reflection Render Element if you are interested only in that component. The main drawback is that the KRAtmospheric renders a voxel grid, so the reflection might not look exactly like point rendering (depending on the settings and number of particles). If you are rendering voxels in Krakatoa, then you might be better off rendering everything with the Krakatoa Atmospheric since it interacts with the scene completely including reflections, refractions and shadows. Here is an overview: thinkboxsoftware.com/krak-us … ric-effect
Note that mental ray is not supported yet, only renderers that support 3ds Max atmospherics like Scanline, VRay and Brazil will work.
Also note that in some other cases, you can use the ability of particles to reflect the matte objects to create complex interactions - see the bottom of this page: thinkboxsoftware.com/krakato … eflections
But for your particular cases, the Krakatoa Atmospheric is probably the way to go.
And then there is the hack where you could render 6 90 degrees cameras in Particle mode in Krakatoa MX and then load the resulting images or image sequences as a user-defined Cubic Reflection Map in a Reflect/Refract material. But this is quite difficult to set up and while I have done it in the past and it looked relatively convincing, the Krakatoa Atmpsheric is still the way to go…
So ther is no way to render real particles reflections?
If there is no other solution i’ll go with the atmospheric, the bad part is that the volumetric renderer considerably slower than the particle one :S
is this under dev or in hte list?
Cheers and thanks as always!
The Krakatoa Atmospheric was mainly developed to covert this exact case.
Just think about it - how would you reflect particles in a complex surface without first putting them on a grid?
We do the opposite - we can raytrace matte geometry and atmospherics (including Krakatoa’s) with the Krakatoa Material when rendering points.
So if you cover a geometry object with particles, you can make them raytrace other objects and atmospherics. But you cannot raytrace infinitely small points without putting them on a grid first - the ray has to hit something with actual volume.
That’s why the only two approaches are atmospherics (particles on a grid), and cubic reflection maps. We have discussed creating reflection maps automatically (by setting up the 6 cameras and rendering in point mode to produce the necessary data the way Max has Automatic Cubic Reflection Maps), but we felt the atmospheric approach is much more flexible. Reflection maps only work on mostly spherical objects, while most people really want raytraced reflections…
Understood 
Atmospheric is the solution then.
Another question (this is more basic, but I have my head a bit slow today) when i get the reflection of the particles in atmospheric, i can extract the reflection channel, but i don’t have a mask for the reflected particles in the alpha, my solution will be to extract the reflections with a pure green as background and do a strict chroma key, but is there a way to get the mask of the reflections?
(Also right now is coming to my mind that maybe doing a second render with pure white can help, but this doubles the render time too).
Cheers!
EDIT: Another idea to get particle reflections could be using the atmospheric grid to define their position and fill it with particles, something similar to using frost to define a volume to create tons of particles with a PRT Volume object, this way maybe you can render the reflections in particle mode, i don’t know if this is something plausible or not, it’s just an idea that just came to my mind.
I am not sure I follow (slow day here too?)
You said “when i get the reflection of the particles in atmospheric”
My understanding is that you want particles reflected in a reflective mesh. You are reflecting the Atmospheric in a Raytraced material, not the other way round. Can you please post a step by step explanation of what you are reflecting in what, images would be useful too.
Im sorry, i expressed myself in a very wrong manner hahaha
What i wanted to say os “when i get the reflection of the particles (as an atmospheric effect) in the objects”, so it is exactly what you think it is.
The thing is, i launch a render, and i have my reflection layer, i can see just the reflection in the objects surrounding the particles (that’s great), if i check the alpha of that reflection layer, i don’t have the alpha of the reflected particles, i have a standard alpha, because the particles are just reflections.
For compositing my layer order will be (from bottom to top, like photoshop)
- Krakatoa particle render
- Krakatoa/Scanline reflection layer (just over the beauty, no multiply or overlay or nothing, just over iRay because i want the particles reflection to hide the original iRay reflection)
- iRay beauty render
The problem comes with the intermediate layer because i don’t have a clean alpha/matte/mask of the reflection, because it’s meant to be used with add or with another layer comp mode, so the only solution that comes to my mind, apart from duplicating the render, is to launch the reflection layer with a green background and use a chroma key to get the matte.
Cheers.
Wouldn’t it work to render the bottom layer WITHOUT reflections, then ADD the middle reflection layer instead of trying to replace the reflections? No Alpha needed for additive comping…
Please keep in mind I am not a very good 2D comper
I can’t.
Since the beauty pass is rendered with iRay, i can’t separate passes from the beauty, and the render is about a complex metal machine which is very reflective with different types of reflections, so i will need to play with the different objects.
That’s why i need the particle reflection with a matte, to work with it in a completely solid manner.
BTW did you saw the other post i did?
http://forums.thinkboxsoftware.com/viewtopic.php?f=22&t=8282
Do you know why i get that error baking the particles?
Cheers.