Hello everyone

Do you know if there is any plan about caustics in Karma ?

I would really like to switch my workflow to Houdini/Solaris, but as I mainly do commercial projects around perfume and alcohol bottles, I need to be able to handle caustics. For the moment I'm using Blender / Cycles, which is far from incredible for this use, but at least with the "Lightpath" node trick, I can have more or less control over the rendering of fake caustic, which often does the job. Maybe there is a similar trick in karma, but never see how to....

So for the moment, this lack of caustics or control over fake caustics, prevents me from professionally switching to this software that I really like...

since Karma supports both pathtraced as well as fake caustics you may want to ask more specific question

do you have issue with it's speed, quality or do you have issues making caustic to work at all?

keep in mind that pathtraced caustics in Karma are mostly bruteforce, can be aided a bit by path guiding in CPU, but outside of that don't make use of any dedicated caustic sampler or unbiased photonampping techiques at the moment

You’re right, it’s not really specific

So, can we expect any dedicated caustic sampler or unbiased photonmapping ?

Other question, how can we customize the fake caustics ?

I tried to do it like I do in blender : one glass material, one « transparent material (I don’t know how to do it with material x so I create a glass material with an ior of 1), then I tryed to made the dot product of normals and different things import with « ray import » (don’t know how I can import « incoming » like in blender), connected to a ramp, connected to the transmission color, but it wasn’t really working…

How do you guys do ?

(You can see the trick at like 30sec :



)

There is no dedicated sampler for caustics in Karma yet.

However, you may take a look at Render Geometry Settings for caustics and fake caustics options which give control
over enabling/disabling caustics, the fake caustics color and opacity:
https://www.sidefx.com/docs/houdini/nodes/lop/rendergeometrysettings.html [www.sidefx.com]

Yes I already saw that, but I want/need more control over fake caustics ? Can’t we access it by a different path, a bit like in blender where you can control the shape and brightness off it ?

philippepetitpas
Yes I already saw that, but I want/need more control over fake caustics ? Can’t we access it by a different path, a bit like in blender where you can control the shape and brightness off it ?

You can easily do this with a vex material. I'm not sure if there is the state information to do a ray switch on shadowray with MaterialX though.

But vex material doesn’t work with karma xpu right ?

Ok, I may have find something. First screenshot is with caustics activated (of course it is the most realistic, but SOOOOO noisy...), second is with the original fake caustics (I just tweeked a little bit the "fake caustics color" in material properties).
The third screenshot is a custom one with which is not realistic, but a bit more interesting than the original fake caustics. If anyone have ideas to do better, you're welcome (I shared the original file too, if someone want to try a better solution)