For this week the main comments from our mentors were more about having more stuff going on. Last week we added a bunch of layers to the effects by using millions and millions of particles, but moving them from Houdini to Maya using Arnold’s ASS files was somewhat problematic. Especially at render time, they created all sorts of issues. My idea to solve this was to take the particle sims and convert them to VDBs, and basically on the first try I got a pretty good result. It even made me discard my pyro sims, since they added too little to the sim and were giving me a headache trying to control their behavior and cache sizes.
The first step was to take the existing particle sims to convert them to VDB. This was very straightforward. I just used a VDB From Particles node and using the particles’ velocities to create some sort of trail for the fog volume.
I tweaked the settings a little bit. Otherwise I would get super long streaks which were detrimental to the effect. So a little tweaking to the velocity multiplier was necessary.
After adjusting pscale and adjusting the velocity trails I smoothed the VDB a little by using a VDB smooth node (a side note worth mentioning is that VDB smooth SDF doesn’t work with density volumes). Smoothing it makes it look a little bit more like smoke dust .
Some of the layers of my particle sim didn’t collide with the geometry nor a ground plane given that they were small enough to allow me to get away with not having any realistic collisions. They were more about adding layers of detail, sourcing from the cracks and chunks of the road. But since optimizing is kind of a big deal for us, whatever was under the origin in the Y axis, I clipped off by using a VDB clip node, something that reduced the size of my VDB by a bit, but hey, every little improvement in file size counts.
The final stem was to adjust the density, we don’t want this to become an homage to Michael Bay, it’s not an explosive scene, we just need some dust going up, so I reduced the density by post multiplying it in a Volume Mix node. After that it was all about writing out 16-bit volumes (this by using a Primitive SOP and in the Volumes/VDB section of it enabling the “Write 16-bit Floats” option. After that you use the good old File Cache to write out the files and pass them along for rendering.
Now, I haven’t seen the render yet, but I am so looking forward to this new pass. I’m pretty sure it will look so much better than the previous one. There were additional tweaks made that are worth mentioning, but not breaking down in the same way. Those adjustments were the following:
- ASS files now have proper motion blur (hopefully they worked alrigh during render time)
- Todd wanted to see a bit more stuff going on, so I added a couple of extra chunks of asphalt being torn up (the larger ones)
- Asphalt geo was adjusted to have more subdivisions to enable displacement at render time
Almost done with this project. It really looks good, and I feel we have worked really hard to take it to the next level. I’m really happy about the results we are getting. Can’t wait to put this on my reel.
Until next post!