GDC 2019 - Part Three

The is the final post on my trip to GDC19, find the first here and the second here.

The last three days of GDC there was also the expo on which we had a booth as part of the Belgian pavilion, so I had less time to attend talks. This last post wraps up the talks I attended during those three days.

The Making of 'Divinity: Original Sin 2'

I just had to go to this session by my former employer, Swen Vincke. He talked about the rough ride Original Sin 2 was. Partly a trip down memory lane for me, as nothing changed much at Larian ;). Very nice to meet-up with ex-Larian-colleague Kenzo Ter Elst who was attending the same talk!

"Shadows" of the Tomb Raider: Ray Tracing Deep Dive

Somehow this happened to be the first talk I did on ray tracing, which is my favorite subject of all, while I had actually planned for many more. I still had time :)

I just read that the all the slides of the GDC19 talks by NVidia are online, so you can already check those!

The good thing of this talk is that it brought me somewhat up to speed with the all the new RT stuff. I mean, I "know" raytracers, having written quite a few as a student, but it has been +10 years since I actively did anything with ray tracing!

There are a bunch of new shaders we can write; rays are generated per light type by "raygen" shaders, we have anyhit and closesthit shaders. Even translucency gets handled by these shaders.

What I did not realize before GDC, but now fully understand, is the importance of the denoising step in the RT pipeline. GI in raytracing always yielded noisy results unless you calculated a massive amount of rays. In all appliances of RT I've seen at GDC, only one ray was cast per step of a path, yielding incredibly noisy results. So denoising is a central part of real time raytracing. A lot of optimization needs to go in this step, for example in this talk they showed a penumbra mask, areas where we know there is a half-shadow, and only denoised on those areas.

Interesting too were the acceleration structure concepts, BLAS and TLAS (Bottom Level Acceleration Structure and Top LAS). In Tomb Raider BLAS were used on a per mesh base, TLAS were regarded as scenes.

Real-Time Path Tracing and Denoising in 'Quake 2'

Another RT focused talk, this time how a Quake II build received ray tracing. It started as research project called q2vkpt that can be found entirely on github. After Christophs part of the talk came Alexey from NVidia detailing what extra features and optimizations they added.

I played the game at the NVidia booth for a while and had a short talk there with Eric Haines (some guy who apparently just released a book on ray tracing, nice timing). In the demo, with my nose to the screen, I could easily see what is called "fireflies", pixels that are outliers in intensity that do not really de-noise so very well.

No matter how good the raytracing, something still looks off if you ask me, but this was explained in the talk: the original textures of Quake contained baked lighting and while they did an effort to remove that, it was not entirely possible.

'Marvel's Spider-Man': A Technical Postmortem

I think this talk was the best I've seen at GDC19. Elan Ruskin announced that he would go fast through his slides and it would not be possible to take pictures of his slides. Boy, was he right! It was amazing, he went super fast, almost never missed, was always crystal clear. Luckily his slides can be found here.

Some things that stood out to me:

• They worked on it for three years, producing 154MB worth of source code.
• They use scaleform for their UI, we used that at Larian too, not sure if they still do though.
• Concurrent components are hard
• Scenes were build with Houdini, they defined a json format for their levels that could easily be exported from and into houdini. It's that "into" that struck me as odd, I learned that when you have a loop in your art tools that you run into issues, but hey, if it worked for them...
• They used 128m grid size for their tiles, which were hexes! Hex3es allow for better streaming because three tiles cover almost 180 degrees of what you're going to see next, while with square tiles you'd need to stream 5 of them.
• During motion blur (while swooping through the city) no extra mipmaps get streamed
• There are a few cutscenes that can't be skipped in the game: they are actually just animated load screens; it was cool to see how everything outside the cutscene got unloaded and then loaded in.
• At some point the game covered 90% of a blu ray disc and still it needed to grow, so they had to quite some little clever compression tricks to get everything on one disc.
• One example was instead of using a classic index buffer they used offsets (+1, +2, etc) which yielded better compression results.

This talk is a must watch! Good thing it's available on the vault for free!

Back to the Future! Working with Deterministic Simulation in 'For Honor'

Last but definitely not least was this session on lockstep deterministic simulation by Jennifer Henry. In For Honor only player input is send over the network. There is no central authority, meaning that every peer simulates every step of the game. Every player keeps a history of 5 seconds worth of input. If a delayed input arrives, since the simulation is done completely deterministic, the whole simulation gets redone starting from the delayed input.

This proved to be hard, for starters: floating points are different between AMD and Intel, there's multithreading, random values, etc...

Central take-away: "don't underestimate desync". Jennifer showed a few cases. In debug mode desyncs get reported to Jira, but in a live build a snapshot gets recorded. Then the game either tries to recover, kicks the diverging peer or disbands the entire session.

Input gets processed quickly: 8 times per frame! The physics steps with 0.5ms:

Definitely worth to watch on the vault!

Wrap-up

So that's it! On Friday after the expo closed we went sightseeing a bit in SF and found this cool museum of very very old arcade machines! My smartphone takes really bad pictures so I cannot show much of them, but this one was really cool:

We went for dinner in "Boudin", which is a restaurant + bakery, where you could buy bread in all kinds of weird shapes, this one was nice:

Thanks for reading!