Unreal Engine 5 demo and misconceptions...

There's been quite a few articles covering how HDDs simply can't keep up with the moment-to-moment streaming enabled by the PS5 and SX. But, again this really misses the point of PCs - PCs are engines of brute force. Consoles are beasts that are designed to streamline and work past limitations through optimisation. Yes, the next gen consoles are generally much more powerful than the average PC out there right now but they are still highly optimised pieces of hardware because they are static and will quickly be outclassed by new PC technologies appearing on the near-term horizon.

Yes, the rate of improvement of CPUs and GPUs is quite phenomenal at this point in time!

This is all self-evident, but why am I writing another post so close to the previous one when I'm covering much of the same ground? Well, that's because the Unreal Engine 5 tech demo was released, running on PS5, alongside an interview with key personnel at EPIC Games and there is, as far as I understand things, one primary misconception being repeated over and over again. To paraphrase:

You can't fit all of this detail in the scene into memory on a PC - it's not possible.

This is, at best, a misunderstanding of nomenclature... at worst, it's a lie.

Let's pull up the entire quote from Nick Penwarden:

"So, Nanite enabled the artists to build a scene with geometric complexity that would have been impossible before. There are ten of billions of triangles in that scene and we simply couldn't have them all in memory at once. And so, what we end up needing to do is streaming in triangles as the camera is moving throughout the environment. And the I/O capabilities of playstation 5 are one of the key hardware features that enable us to achieve that level of realism."

This statement has been used by various outlets to imply that this is some sort of impossible feat that current PCs are incapable of. I don't blame them because it sounds impossible when stated like this. But digging deeper, all is not as it appears...

This boils down to words and how we use them.

Traditionally, a "scene" is a short clip in a TV show or movie or a static set change covering limited time in a stage play. These two forms as essentially analogous, with film-making allowing for a greater range of exceptions and allowances. A scene could last for a single fight sequence but the sequence itself could be 10 minutes long with multiple camera cuts.

However, a "scene" in game design parlance is basically any element that encompasses a single experience. This can be a simple menu screen or map interface, to an entire "level" or world as we would normally think of such a term in game design. The two definitions are completely at odds with each other: The scene where Lumen walks through the canyon is not the entire "scene" of the level.

So, with that knowledge, let's re-read that quote from Nick Penwarden:

So, Nanite enabled the artists to increase the amount of detail contained within a single level and have that information organised in a data structure that allowed more dynamic streaming into video memory from the storage drive faster than was possible on Unreal Engine 4. We are doing the same thing as previously - streaming in new parts of the level as the camera moves around it - but our data management allows that to occur more dynamically in terms of geometric and texture LOD. The new SSD on the PS5 allows us to do that faster on that console.

This is just describing streaming of world data - same as we've seen in Assassin's Creed games, same as we've seen in GTA games and Elder Scrolls games... and same as we've seen in every other AAA single player game in existence. A level doesn't fit entirely into RAM and so the data needs to be managed off of the storage device during play. Why is this being dressed up as something new?

This is a scene that is totally possible on mid-range PCs right now. See Destiny's Mars environment, for example...

Going back to that scene in the canyon - it can absolutely be contained within 8 GB of memory and, as Lumen is moving through the canyon, further detail of the upcoming assets can be streamed into the RAM and then VRAM (on PC) from the storage drive. On PS5 and Xbox Series X, that translates to being moved into the unified memory pool from the SSD. In fact, it's ironic that at 3 mins and 34 secs Lumen has to move through a visually occluding barrier to reach the next section - which traditionally denotes a loading transition. This transition is supposed to be a thing of the past, btw.

I actually went and signed up for a free account on Quixel and downloaded some free assets. What I found was that an 8K texture (including normal map and material properties) usually ran around 200-300 MB and an asset, like a cliff (i.e. vertice positional data) added an extra 200-300 MB on top of that. That's at the highest fidelity possible and, more than likely, the PS5 is not streaming those assets and textures into memory with that level of fidelity - this is where we start getting into discussions on LOD and MIP levels.

So, yes, you can stream a movie-quality level of detail to your memory but that's not likely going to be happening on only 16 GB total device memory. At that point, Nanite steps in and downsamples textures and assets until they are manageable. I suspect that most assets are 2k or below in resolution in this demo because the camera doesn't get that close to them

Going back to that loading transition, it takes approximately 10 seconds. That's a HUGE amount of time. Let me put that into perspective:

What is happening over that 10 second period?

The Series X can transfer 16 GB in 6.67 seconds of uncompressed data, the PS5 can do it in 2.91 seconds. Over 10 seconds, a SATA 3 SSD can transfer 5 GB whereas a traditional 7200 rpm HDD can just scrape through just over 1 GB. It's not even worth considering the NVMe drives in this comparison because PC and next gen consoles do not even need to transfer (or display) more than 8-16 GB of data in 10 seconds.

I don't know what's happening in that time frame but it's very suspiciously indicative that the demo is platform agnostic. Looking more closely, the "lock-in" to the transition animation occurs at 3:35 when the focus shift happens and releases around 3:55 when Lumen starts walking - a 20 second period, effectively doubling the previous numbers. Do I believe a SATA 3 HDD can pull into memory the dig hole scene directly after that transition? Bluntly, yes - I think 2.4 GB would be enough to hold that geometry and reused/repeating textures - this is not a transition to a completely different environment, requiring a complete wipe of the RAM.

We get another tranisition animation from approximately 5:14 to 5:21 where loading likely takes place, enough time for an HDD to load those statues into memory (~800 MB). You'll also note that from this point on, duplicated meshes are used extensively, meaning less assets brought into active RAM from the storage drive. There's another loading transition at 5:48 to 5:51 in order to load the new mesh statue just around the corner and a final loading transition from 7:40 to around 7:52. That's not to mention that from 6:17 to around 6:40 appears to be a pre-baked transition followed by 6:45 to 7:31 where it appears to be mostly controlled camera perspectives and limited "player" interaction.

All in all, there's more in-engine cutscene here than an Uncharted game!

The final flight through the city isn't that impressive because most of the meshes and textures are probably lower quality due to the speed at which they're passing the camera and thus not that demanding on I/O. If Oblivion could do it in 2006 on the Xbox 360, then I am not that impressed in 2020 by this portion of the demo...

They did this in 2006 on a console with 512 MB of DDR3... (okay, so this is probably pre-rendered on the 360)

Conclusion...

I haven't seen anything super impressive in this demo. The technology is impressive but I see nothing that is saying "adiós" to the spinning platter hard disc drive... I *AM* excited for what SSDs can bring to the gaming landscape but nothing on show with this demo is purely a result of that.

Think I'm wrong about this? Let me know why I'm wrong in the comments. :)