As Houdini (solaris) is going towards serious lighting (which I am very happy about). I decided to start doing serious tests and ask serious lighting questions
All renders below were done using IPR on Houdini 18.0.566
#1 Transparency shadows.
With Mantra, transparency and shadows was always the issue. Even with Physical Rendering, we could not get proper shadows (and I understand, it's not a easy problem to solve).
starting as a “base” geometry :
(btw, please notice white line on the corners of inside of the box)
With a CLASSIC mantra shader, we would get effect like so:
Which of course, is a problem as shadow is way too dark for such transparent object.
Now, to deal with those shadows, we have 2 options:
#1 Totally remove shadows from equation (which could be sufficient for some scenarios but it's definitely not a “physically correct” solution)
or
#2 Calculate caustic light. In very simple example caustic light will work but in example like this one, it starts to fall apart:
(This render took >35mins, comparing to the previous one which took 30seconds, + it has tons of major issues)
Switching to the printipled shader, of course we will have same shadow issue (no caustic light):
With principled shader, SideFX has introduced “Fake Caustics” option which helps getting rid of bad shadows(no caustic light):
Now, switching to Karma - a base render with 1 diffuse bounce (same as mantra) gave little bit different result:
Adding transparent glass object to it (with principle “fake caustics”):
My question is - is there something I am doing wrong in my setup, something that I am missing or I should do other way ?
How do You approach an issue with transparent shadows in your scenes ?
Don't want to compare to other renderers here, but Mantra and Karma is not performing well and I want to make sure I am not doing anything wrong before treating it as a formal bug.
