[msbarnett]

> This is exactly the case for CD Projekt Red. They built their own engine (RED Engine) for Witcher 1 and built on top of it for the two Witcher sequels and also pushed it to its very limits for Cyberpunk 2077.

Close. REDEngine was created for Witcher 2: Assassins of Kings. Witcher 1 was built on a modified copy of Bioware's Aurora Engine (the Neverwinter Nights engine).

REDEngine versions were:

REDEngine 1: The Witcher 2: Assassins of Kings

REDEngine 2: The Witcher 2: Assassins of Kings – Enhanced Edition

REDEngine 3: The Witcher 3

REDEngine 4: Cyberpunk 2077

[daemin]

To add to that (since I'm somewhat of an expert on this), the engine for Cyberpunk 2077 was completely rewritten from scratch, and only small bits were either ported from W3 or inspired by what was done in W3.

[profile53]

Huh that’s super interesting — full rewrites aren’t super common. Do you know why they elected to rewrite the engine completely?

[daemin]

I have to be careful here, but the simple reason is that the previous engine was not designed to handle the density nor the verticality of the CP77 world.

Not that Unreal Engine 5 can handle a world like CP77 either, despite what people may think with the Matrix demo.

[robswc]

Game dev isn't my field, I always find it fascinating though.

Why can't Unreal handle something like CP2077? Could be an "explain like I'm five" - details would be cool but I'm not sure I would even fully understand them, haha.

[danielbarla]

I'm not an expert on the topic either, but from similar discussions I've followed, the answer tends to be that out of the box and with the base settings, an engine like UE5 will be optimised for certain use cases. Different genres will have different specific needs, and may require your developers to do a lot of heavy lifting to make the engine performant under their specific conditions. A good example might be sim racing titles, which generally have the player moving a lot faster than the default scenario for an engine (which is mostly a slow-moving FPS, for example). At these relatively high speeds, the default antialiasing methods may result in serious graphical artifacts, and at the rate at which physics needs to be calculated (90-300 hertz) the default physics of the engine may be less useful, and you're forced to implement your own from scratch. That's not to say it's impossible, but you're opting out from a lot of the engine features, or in some cases, it's actively making your life hard.

[robswc]

Awesome answer. Thanks for those examples, makes a ton of sense!

I just assumed in 99% of cases, you could just "tweak" Unreal but if its issues with core components of the engine... I could see why an engine from scratch may work better.

[P5fRxh5kUvp2th]

"can't handle" here means "can't handle performantly".

Think of it like using the wrong data structure for the problem.

[daemin]

And not just for the game itself but for creating the world in the first place. Often you need radically different data structures for the creation and editing of the data as compared to what you need for running the game on player's machines.

[voidr]

In Cyberpunk 2077: you can go from one end of the open world to the other, without ever seeing a loading screen, you can even install a mod that allows your car to fly and you can see the whole city from the top, I haven't seen a game like that in UE5 at that level therefore there is a possibility that it would struggle with something like that if it's not designed to cope with it.

Video games use a trick called Level Of Detail, which means if something is far away, you only render a very low definition version of that object, UE5 has it as well, however we don't know if it's capable enough for something like Night City, obviously the RED engine was built with a very hardcore LOD system that might be a massive pain to do in UE5.

[robswc]

So the investment into seeing if UE5 would work with something like CP2077 would be greater than the investment into a new engine? Or perhaps the risks are greater? I could see getting 75% of the way there and realizing its starting to buckle would be pretty detrimental.

[anotherman554]

If Unreal Engine 5 can't handle a world like CP77, why are they making the sequel to CP77 in Unreal Engine? Are they betting on the engine being ready for CP77's sequel when they need it to be?

[Cyph0n]

Interesting! I’m not at all familiar with game engine design or even game dev, but the only game series I can think of that reliably handles large, open-world scale well is GTA.

Here’s a dumb question: in theory, would Rockstar’s internal engine (RAGE) have worked for CP77, or are the technical challenges simply too different?

[WorldMaker]

The easiest dumb answer is that Rockstar has never licensed RAGE to an external developer and presumably doesn't develop the engine with that in mind at all so it is probably under-documented and hard to work with for any team that isn't Rockstar.

Also, I think there are other engines that do as well as RAGE, but none of them are licensed for external use either and are secret sauce to their various developers.

[Cyph0n]

I think that’s fairly self-evident, hence my inclusion of “in theory” :)

Are there other internal engines that have been used for open-world games with detail and scale at the level of GTA or RDR?

[kranke155]

How is Unreal limited in a way that prevents it from doing something like CP77?

[ffhhj]

Do they license their engine? Building it just for CP77 would be a shame.

[somat]

And if i remember correctly the aurora engine started life as MDK2.

[bashmelek]

I remember Neverwinter Nights 2. Decently fun game, but extremely buggy. It had some strange local lag where it wasn’t that unusual to command a character to move only to have them freeze in place then teleport back where they were 10 seconds before.

[belthesar]

NWN2 was such an odd duck from an engine reuse perspective. When development on NWN2 began, Obsidian was handed a much older version of the Aurora engine source than what was currently available. While they did do amazing work with what they had, many weird bugs that were addressed by updated versions of mainline Aurora were now things Obsidian had to address in addition to the challenges they had to update the engine for the new game.