Problem: HtoA Solaris Rendering Animated Caustics with a Gobo Lightfilter

gogofrgl12345 — Fri, 20 Jan 2023 16:49:37 GMT

Hi!

I am currently working on an underwater project for my demoreel which is supposed to have caustics in it. I am working inside Houdini with Arnold and Solaris and I want to create the look of caustics using a gobo for my main light. I found this approach to connecting a gobo lightfilter to my light inside the arnold documentation. (https://help.autodesk.com/view/ARNOL/ENU/?guid=arnold_for_houdini_solaris_ah_Light_Filters__html) After trying this approach I found that it doesn't really work for me as I have a couple of problems.

First Problem: Connecting the gobo the way it is showed in the documentation I don't get any result at all. (Screenshot A) Connecting a light_decay into the light_filter instead of the gobo is surprisingly working. Connecting a barndoor on the other hand is also not working. Although I get the gobo working when I connect the image directly into the color of the output instead of the light_filter. (Screenshot B) Connecting the Image Sequence into the texture of the area light is also working (only for arealights) but I would like to know which approach would be the correct one and how to make it work.

Second Problem: I can't animate the caustics this way. (Screenshot B) I have an image sequence with animated caustics but I can't use $F4 for example to get the image sequence into it as I get the warning: "Cannot have channels which depend on time." (Screenshot D) Driving the value for the frame with a relative reference from somewhere else in my network also doesn't seem to work as it also detects that it is an animated value and I get the same warning.

Third Problem: This approach seems to mostly only work with the arealight. If possible I would like to use a distantlight for creating the caustics as I could probably make them fairly sharp (which I want) and with using the arealight the caustics get very blurry, very quickly, when the distance between the light and the plane gets bigger. I already set the spread of the arealight to 0 but it still gets blurry very quickly and I can't get the shadows to be sharper.

I would be really grateful if there's anyone who could help me make this work. If you know what I did wrong or if there is an alternative way to get a gobo with an image sequence working inside Houdini with Arnold and Solaris that would be awesome. Also if you have some general tips or thoughts in mind for creating convincing caustics I would enjoy reading that too.

Thanks in advance and I wish all of you a great rest of the day wherever you are.

(A) supposedly correct way (image, gobo, light_filter) (not working)

(B) current way (image, color) (working)

(D) Warning when using $F4 for using an image sequence for the animated caustics

Re: Problem: HtoA Solaris Rendering Animated Caustics with a Gobo Lightfilter

srlasset — Mon, 31 Mar 2025 12:32:14 GMT

Gobos still don't work in Solaris as of the latest version.

topic Re: Problem: HtoA Solaris Rendering Animated Caustics with a Gobo Lightfilter in Arnold for Houdini Forum

Problem: HtoA Solaris Rendering Animated Caustics with a Gobo Lightfilter

Re: Problem: HtoA Solaris Rendering Animated Caustics with a Gobo Lightfilter