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About many games you can say "oh that's the Unreal engine for sure", "this was made by upgrading GTA 4", etc. We can often recognize the engine used for a game just by looking at its graphics (disregarding menus and such).

I'm wondering, why is this? All game engines use the same 3D rendering technology that we all use, and the different games usually have a distinct art style, so what's left to recognize?

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For GTA4, it's stipple transparency that gives it away ;) –  drxzcl Aug 24 '10 at 11:31
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All people are based on the same technology, all cars are, all movies are, all oil paintings on canvas are. The technology influences only a fraction of a final product. –  Kaj Aug 25 '10 at 0:40
    
@Kaj: Apparently so. I wasn't previously aware of how much of the rendering process is custom made. –  Bart van Heukelom Aug 25 '10 at 9:15
    
Chronicles Of Riddick look like Doom 3 engine. –  user712092 Jun 23 '11 at 9:15
    
@Kaj but we have races so we know approximately these guys are from Asia and these from Africa... –  user712092 Jun 23 '11 at 9:16
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Primarily I'd imagine this is down to the shaders. For example, the Unreal engine will have a certain method of handling HDR, a certain method of handling bump mapping, a certain method of handling light scatter, etc.

They will also have a uniform level of clarity in terms of constraints such as texture sizes and colour support.

Additionally the algorithms will be similar. Objects will be tessellated using the same algorithms. AI will make decisions according to the same decision-making architectures.

If the bump mapping is causing insane specular and reacts strongly to changes in lighting for example, you immediately start thinking Doom 3 engine. That's because that shader code is shared between every game using the engine. You wouldn't want to rip something like that out.

"All game engines use the same 3D rendering technology that we all use"

The technology is the same, but the rules that govern how the world actually looks (eg. lighting, tessellation, LOD , etc) are all written by the developer. The 3D rendering technology doesn't have that much to do with the visual quality of the things on screen. Even the rules for applying flat ambient lighting is left up to the developer (assuming you're not using Fixed-Function Pipelines).

You can make your OpenGL app look just like your DirectX app with often trivial difficulty. The underlying rendering technology really doesn't have that much impact except with regards to speed.

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There are other things that give it away, too. Source Engine games sometimes provide a recognisable set of options, for instance, and use the loading screen you'd recognise from HL2. –  Jonathan Hobbs Mar 3 '12 at 1:35
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UE3 is instantly recognizable from the model/texture LOD levels popping in after background-lateload. Which is a damn sweet feature by the way. –  Noora Apr 20 '13 at 16:21
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Why?

  • For similar design situations You use same engine methods.
  • Common environment technology is typical for concrete engine (Grass Trees).
  • Ground material mixing
  • Trigers and events systems have similar errors .
  • Lods and Loding systems are big mark of engines.
  • Shadow handling.
  • Postprocess handling.
  • Z-Buffers/Depth buffers make same errors on same distances .
  • A.I. behavior issues. Scripts handling.
  • Smoke, fire, rain, dust, snow, water, clouds, reflection
  • same noise textures/detail textures everybody likes to use :) in one engine.
  • Sky handling/sky boxes.
  • Caching
  • materials preset
  • and render math. All engines use their own variants of same math.

    EDITED: @ wkerslake adds

  • level size/streaming
  • phys in general
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Back when I was involved in 3D graphics I could tell at a glance which rendering engine an application used. While there were less to choose from and the graphics weren't as advanced there were tell-tale giveaways like these listed here. –  ChrisF Aug 24 '10 at 13:10
    
Yup, the days of fixed-function pipelines when the rendering engine was responsible for things such as lighting and blending. In the post-FFP era those aspects are completely replaced with developer-written code though. Irritatingly, I learnt FFP in university - just as it became completely obsolete. –  Rushyo Aug 24 '10 at 13:45
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This is a pretty comprehensive list, only things I'd add are level size/streaming and the handling of destructible geometry. –  wkerslake Aug 24 '10 at 17:00
    
@Rushyo - it's not problem, you have to know old things to do new things right :)... BUt You are right, new engines are about quick and easy contruction of everything on any level. –  samboush Aug 25 '10 at 0:27
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It's funny because it's true, the lighting and further post-process effects can easily expose the underlying engine.

Engine Comparison

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Haha, I love the Doom 3 one. –  Nate C-K Apr 2 '13 at 13:56
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Animations also give it away. Every engine handles them in a different way and they also look and feel different while playing.

You can spot engine limitations on animations and tell which engine was used by that too.

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I never knew you could really do that.

Easiest ways to tell:

  • Very often they have big 'Unity Engine' or 'Unreal Technology' logos on startup.
  • Companies reusing game engines - A 'Rockstar Games' open world game is almost certainly going to use a GTA tweaked engine.
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Well to be honest I often don't see it either, but people around me instantly do. –  Bart van Heukelom Aug 24 '10 at 11:12
    
"Very often they have big 'Unity Engine' or 'Unreal Technology' logos on startup." Thank you, Captain Obvious! :P –  Paul Manta Mar 5 '12 at 18:22
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There are subtle differences in the engines and what they're good and bad at that is easy to spot from game to game.

The exact combination of these traits can often identify the engine.

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You can tell Unreal games because they all use the same incredibly bad skin shader, and the same stupid "physics" puzzles.

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Theres a reason they're named "Unreal" ;) –  RCIX Aug 26 '10 at 6:32
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Aside from the 3D graphics, we also recognize common shared behaviors in the game engine itself. There are a lot of little variables that go into every part of a game, and certain combinations, once set, remain a part of all games using that engine.

Such variables could include: character move speed, character movement acceleration, camera pan speed, camera pan acceleration, camera pan smoothness, and so on.

This is very apparent with mods or games that started as mods (hello Source engine games) because once the design is past the basics, rarely will anyone go back to tweak something like the acceleration rate of a jump. The effect of all those little variables is that the games "feel similar" but in a way that's hard to pin down.

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A lot of what people say is a typical engine is actually more art related. Engines empower or impose restrictions on art assets but the design and execution of how things feel is largely an art issue. Take for example the faces in Oblivion; So many people were blaming the engine for the slightly less than convincing characters. This was clearly an issue with the art, or if not that then the section of Bethesda's code that blended faces together, rather than the whole 'engine'. Similarly, when people see shiny, grimy, steroid abusing space marines they'll think 'Unreal' but this is more of an art direction, rather than a facet of the underlying engine that displays that art. Even though different studios make grimy space marine games they'll often use unreal because it's been proven to be able to make that sort of game.

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I think there are more subtle signs than what you see. Quake felt the same on OpenGL, Software, and PowerVR - despite unique looks on each.

For instance, the Quake-Engine games, to me felt more solid, whereas Build engine felt more flimsy, and Unreal felt kind of abstracted.

This is largely physics - and I suspect something to do with the game loop as well.

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Wow - I never realized it but I've felt the exact same way about those engines ever since I've been familiar with them. Perhaps instead of some concrete example of what kind of thing defines an engine it's much more of this kind of "feel" that one gets when interacting with it? –  PfhorSlayer May 15 '12 at 18:43
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I've found that facial animations are usually a dead giveaway. There is a lot of variation and even with different art you can still see the same patterns in the textures.

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-1 Facial animation has nothing to do with Engine identification. Either its manual morph or bone animation or its FaceFX. FaceFX gives away itself, and many many engine uses it. –  iamcreasy Mar 5 '12 at 9:46
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I often recognize engines by their physics. Most notable here is the Source engine, particularly the part which picks up objects. You'll notice that in many games picking stuff up is similar. I believe this is due to the engine. I also agree that different engines handle light differently, so you can recognize them by that.

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