Houdini 20 Bubble Scene Beginner Tips (Patreon)

Houdini 20 is here! SideFX added a bunch of scenes to their content library, showcasing many of H20's new features. I've been testing them out and I noticed some issues that might give new users trouble. I remember when I first started using Houdini I would often hit a brick wall when demo scenes didn't work out of the box.

Let's start with a few beginner tips to get this cool bubbles scene working.

First off, you'll notice when opening the file for the first time that there are no bubbles!

The reason for this is that the scene is set to read cached geometry from disk, but the download doesn't include it. (It would be a multi-gigabyte download if it did.)

Dive into the lol node and you'll find two File Cache nodes: float_pts and bubbles_meshed.

Load from Disk is checked, but since there are no files present it shows a warning and loads nothing. To get this working, click the Save to Disk button. This will process the entire node tree and save out each frame of the animation.

Note that it might take up to an hour or more to finish. I you want faster results, go to the remeshbubbles2 node and lower the Resolution Frequency from 6 to 3. This will make for less smooth bubbles and won't look good in a final render, but for the purposes of exploring the scene it will be fine.

After caching the geo, we've got bubbles!

Next up, there are a few issues that need to be fixed before rendering the scene.

Navigate back to /obj and dive into the lopnet1 node.

Contained within is a full Solaris scene that imports the animated geometry and adds lights, materials and other rendering-related essentials.

Fire up a Karma XPU render and you'll find things aren't looking right at all:

There are several reasons for this. First, the path to the geo in the background material assignment is wrong. Click on assignmaterial2 and change the Primitives value from /bkg/ to /bd/.

The background is rendering now, but the look still isn't quite right.

The last issue to address is that the textures used in the scene are also missing. The most important one to fix is in domelight1:

Simply replace this with one of your own HDR environment maps. There are also a few that come with Houdini, located in $HH/pic/hdri.

The other missing texture is in kma_lfilter_gobo1 in lightfilterlibrary1. This one is not very important to the look of the final scene, so you can simply delete the Texture path and leave it blank. You could also use your own alpha matte texture. The idea here is that a texture is used to block out parts of the light.

Success!

One last tip! The scene is set to render at 4K resolution in the Karma Render Settings (the node is named 1080_2048). This is overkill when just exploring and studying the scene and might take many hours to render. Feel free to lower the resolution to 1080p or even 720p for a much more responsive experience.