Crytek’s Ray Tracing Demo Wasn’t Fully Ray Traced

Update: Okay, maybe I went a bit too overboard. Yes, I am quite sure that part of the demo isn’t ray traced, but the rest of it does seem to leverage real-time ray tracing. I’ve confirmed this with a few industry experts as well. If you have something constructive to share, please do so in the comments below.

Remember that demo Crytek showed off at GDC this year? The one that was developed using the Cry Engine and supposedly had real-time ray tracing? The one that prompted NVIDIA to release a driver enabling ray tracing on the GTX GPUs. Well, guess what? It was fake, or at least part of it was. In this post, I’ll show you a few images from that very demo where the reflections don’t match with the casting objects. Real-time ray tracing is quite accurate, there may be blurriness, but the objects and their reflections should be identical which isn’t the case here.

Crytek’s Ray Tracing Demo was Fake: Case 1- The Bullet Casings

Have a look at the bullet casings. The circular inscriptions on the back of the bullets don’t match the ones in the reflections. The pattern on the bullets has a smaller radius, while the reflections look like the back of a can. Furthermore, as if this wasn’t bad enough, the bullets’ look like they’re floating. Here’s a closeup in case you didn’t get that:

Case 2: Window Reflections Don’t Match the Source

Here’s the second clear indication that Crytek’s ray tracing demo is fake. Look at the puddle of water on the window-sill. Its reflection is completely inaccurate. Secondly, there’s a thin streak of light being reflected by the water in the puddle. However, if you look at the reflection on the window, it’s missing. This is yet another indicator.

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Again, here’s a closeup:

See the reflection is quite noticeably different. I’m surprised that no one noticed this. This first came to my attention while discussing the possibility of AMD’s Navi 20 GPUs supporting any form of real-time ray tracing (on the TechPowerUp Forums). It seemed like a solid lead, and then I combed through the demo myself and whaddya know, it’s fake!

So What’s up, Crytek?

Alright, so if this isn’t real-time ray tracing, then what trickery is it? I did a bit of asking around, and the most common answer I got was that this is more of a Voxel-Based solution than real-time ray tracing. You can read up on Voxel-based Illumination here.

The main steps of the VXGI technique consist of the voxelization of the scene, encoding the opacity and emittance information in the clipmap and then voxel cone tracing is used to compute global illumination.

This allows rendering of the shadows and reflections cast by objects that are absent from the scene but are close enough that their reflection/shadow should be visible. SSAO or Screen Space Ambient Occlusion only considers the objects that are visible on the screen, hence many reflections and shadows are missed. An excellent example of this can be seen in Rise of the Tomb Raider, where switching from HBAO+ to VXAO (Voxel-Based AO) dramatically improves the ambient shadowing, not only making it more accurate but also improving the quality.

Well, what are you waiting for. Watch Crytek’s “real-time ray tracing” demo and see for yourself. Here. You don’t even have to search for it:

What do you think? Are there any other irregularities that we missed? Let us know in the comments below.