Judgement Day - Work in Progress #5 (Patreon)

Shot 4 Full Render Preview

Oh boy, another WIP! I've got a lot to share this time, starting with the fourth shot of the animation! I showed this off last time and I've made some visual tweaks since to fill out the shot.

Shot 5 Full Render Preview

This was a fun one! Shot 5 was relatively simple to make, but I do want to mention some details that you all might be interested in putting into your own work.

Camera Movement

Creating the camera movement for this shot was actually quite a challenge! I wanted to have the camera rotate around Legacy from front to back and hand keying the camera motion wasn't cutting it.

Instead, I decided to do something a bit unorthodox, yet simple. I cut a circle in half and converted it to a curve, parenting that curve to Legacy with a child of constraint so it follows his motion forward. I then parent the camera to the curve using the "follow curve" constraint.

The damped track constraint points the camera in the right direction so it's always facing Legacy. This ended up being a problem, though, as it was rotating the camera along its local Z (tilt) axis. I ended up having to hand key the camera's rotation to get the desired effect.

Soldiers and Mocap

I'm beginning to use motion capture libraries more in my work, and this shot provided an excellent opportunity to work with some of the assets I've purchased.

All of my resources were provided from Actorcore, run be Reallusion. They have some pretty awesome high quality models and motion capture data for background characters. I ended up picking a couple of their (pricey) sets for this shot.

Shot 6 Preview

This shot is currently rendering as I'm writing this but it has roughly 46 hours to go before it's done. I have a LOT to talk about for this shot, so buckle up!

New MPM Techniques

This shot required Legacy's paw to scrape through the ground and pull up a bunch of the road. This is a pretty difficult effect to achieve in itself, and unfortunately MPM isn't built for high velocity breakage.

The main issue I was having post-sim was that I had floating debris once the simulation was finished, shown below.

This was due to the a few things, mainly that MPM isn't meant to simulate rigid object like concrete structures. This resulted in floating particles, which in turn caused the pieces to float in mid air.

The fix for this problem actually ended up being much, much simpler than anticipated. Instead of relying JUST on MPM particles for simulation, I switched all of the pieces that would end up floating to a RBD simulation. The node tree is below.

The reason this even works is because of the velocity attribute that is already on each point of the simulation. When I pack the geometry for simulation (converting "piece" of geometry into its own packed mesh), Houdini normalizes the velocity attribute for each different packed mesh.

This means that the velocity it transferred perfectly from the MPM simulation, creating a seamless transition between the MPM solver and the RBD solver. On a side note, Houdini treats packed geometry as a single point rather than a set of points. This means with a simple group expression node, you can select entire pieces above a certain height.

These "packed primitives" are then sent into an RBD bullet solver to get the final result!

Custom SOP Solvers

A really cool aspect of Houdini is the ability to make custom SOP level solvers. This means that you can create custom simulations for geometry that Houdini's other solvers (such as pyro, RBD, MPM, vellum, etc) can't do. I ended up having to use the SOP solver for a cool shield impact effect on Legacy's paw.

The setup for this is relatively simple. The general idea is that the solver needs to look at the proximity of each bullet particle and add value to an attribute at the points that are within the given proximity.

The POPnet in the above screenshot is the source for our bullets while the right tree with the alembic is Legacy's paw mesh that I'm bringing in. Inside of the solver, the "previous frame" DOP import node does exactly what it says. It looks at each previous frame of Legacy's paw, and import that's into the solver.

This last part of the node tree is the important part. The attribute transfer node looks at the proximity of each bullet particle to Legacy's paw and then will transfer the attribute "impact" from the particles onto his paw. It checks this every frame, saving the last frame in "memory" so that the attribute will carry over. Additionally, multiplying the impact by 0.9 every frame slowly fades out the effect. I then add an attribute blur to slowly spread the effect outwards.

That's all for this WIP! All of the shots are essentially done and I'll be able to move onto compositing and sound design within the next day or so. Thank you all for your continued support! <3