Id Tech VS Unreal Engine \ VOGONS

Id Tech VS Unreal Engine

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First post, by silikone

Posted on 2017-10-24, 09:37

silikone Offline

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It is widely known among benchmarkers that Unreal Engine and Id Tech (3) each have their strengths and weaknesses, with the former being infamous for an insane amount of reliance on CPU horsepower.
Now, I wanted to delve into the reasons as to why, but all I could really find is that Id Tech is rather lazy on overdraw prevention, relying on the principle used since Doom. Unreal on the other hand is in many cases perfect down to the pixels when it comes depth simplification. A great example is mirrors. The very first room in Quake 3 showcases both a portal and a mirror in action, but they are otherwise used sparingly, owing to their impact on the performance. Unreal was not reluctant to throw reflective surfaces at you, managing to do so without stressing the graphics hardware too much.
Yet it is supposedly exactly these savings on the rendering side that end up handicapping Unreal Engine, while the brute force of fast GPUs absolutely destroy in Id Tech.
Is there additional information on the matter?

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Reply 1 of 5, by Fusion

Posted on 2017-10-24, 17:43

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I was under the impression that the reflective floors in Unreal were just mirrored geometry with a transparent floor texture.

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Reply 2 of 5, by leileilol

Posted on 2017-10-24, 21:55

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Unreal being a portal-driven engine probably helps, though Quake already dabbled in that area in early development and wasn't much beneficial for the software renderer (apparently portals weren't very tolerable of complex architecture) so that's scrapped out since with only a few references to portals left in the source.

Sadly, mentioning a game engine having portals probably misleads into the concept of Portal these days

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Reply 3 of 5, by Errius

Posted on 2017-10-24, 22:09

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I never played Portal back in the day. The first time I encountered the phrase "the cake is a lie" was in a custom Quake map made by some guy on a server I often played on.

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Reply 4 of 5, by vladstamate

Posted on 2017-10-25, 14:52

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leileilol wrote:
Unreal being a portal-driven engine probably helps, though Quake already dabbled in that area in early development and wasn't much beneficial for the software renderer (apparently portals weren't very tolerable of complex architecture) so that's scrapped out since with only a few references to portals left in the source.

Sadly, mentioning a game engine having portals probably misleads into the concept of Portal these days

I thought Quake's BSP algorithms act like portals in a way. In the sense that once you establish your BSP tree you raycast visibility between different cells. This is all done offline so time is of no issue. So you know that when player is in cell A it can see cell B but not C. So when in A draw B but not C.

Parsing BSP at runtime is incredibly fast, should not use a lot of CPU power.

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Reply 5 of 5, by silikone

Posted on 2017-10-26, 01:25

silikone Offline

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Real-time or not, the overdraw amount is still pretty high in comparison.

leileilol wrote:
Unreal being a portal-driven engine probably helps, though Quake already dabbled in that area in early development and wasn't much beneficial for the software renderer (apparently portals weren't very tolerable of complex architecture) so that's scrapped out since with only a few references to portals left in the source.

What about this quote from John Carmack? Didn't Quake's software renderer also use scan-lines to "completely" abolish overdraw?

The options are to either do PVS with a simplified version of the world, or ignore the geometry and just work with portal topology.

Unreal used a scan-line visibility algorithm, which crippled it's ability to have high poly counts or high framerates with hardware accelerators.

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