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Edward850

ZDoom rendering piece-by-piece

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You've probably seen how Doom renders a scene. But what about ZDoom, and its vastly more complex maps? Watch and learn how the software renderer constructs everything piece by piece.


(This isn't quite pixel by pixel, because if it was we'd be here forever watching it generate a 1920x1080 scene, with overdraw. That's not fun.)

Maps in order of appearance:
CyberCrime3 - Map04
Abandonedrig (CutmanMike)
KDIZD - Z1M8
Back to Saturn X E1 - Map01
Frozen Time - Map01
DWFORUMS3
KDIZD - Z1M5
ZArena - Map01
ZDoom Community Map Project 2
Crusharghs ( http://crantime.org/wads.html )
KDIZD - Z1M10
Vela Pax - Map05

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Linguica said:

Geez, at 9:00 is some serious OVERDRAW AHOY


to think a mordeth bridge could've solved that.

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Heh, that's from Frozen Time. Most apt name for a map ever, since when one of those bridges (or ten, as the map layout is wont to do) comes into view, your CPU gets frozen in time.

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I originally did that scene from a different angle, however it got hung up drawing texture masks in a place I couldn't even see. There's something very funky about that bridge setup.

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Since it's in the video description on youtube, but not in the OP:

CyberCrime3 - Map04
Abandonedrig (CutmanMike)
KDIZD - Z1M8
Back to Saturn X E1 - Map01
Frozen Time - Map01
DWFORUMS3
KDIZD - Z1M5
ZArena - Map01
ZDoom Community Map Project 2
Crusharghs ( http://crantime.org/wads.html )
KDIZD - Z1M10
Vela Pax - Map05

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Linguica said:

Geez, at 9:00 is some serious OVERDRAW AHOY


Well, those 3D bridge effects rely a lot on masked textures, and AFAIK there's no software rendered port with a mechanism in place to avoid overdrawing those.

They are even explicitly excluded from the "smart" BSP overdraw avoidance mechanism, and if I recall they are even drawn after sprites.

Of course that's not a problem with normal maps at vanilla resolutions, but I see how they can become a bottleneck if they are abused to create all sorts of special visual and architectural effects at higher resolutions.

Ports like RoRDoom or CDoom are even worse, as they overdraw not only masked textures but floors as well, in order to create "Room over Room" effects, often mangling sprites in the process.

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At about 17 minutes in, it starts drawing a scene from ZDCMP2 which features 3D floors (translucent swimmable water and an opaque bridge). It gets to rendering them at circa 19 minutes. It's a lot faster than the Frozen Time midtex bridge.

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Gez said:

At about 17 minutes in, it starts drawing a scene from ZDCMP2 which features 3D floors (translucent swimmable water and an opaque bridge). It gets to rendering them at circa 19 minutes. It's a lot faster than the Frozen Time midtex bridge.


This is the perfect candidate for a 3D floor. 200 of those floors could have been drawn in the time it took for one of those bridges.

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By the way, I'm not sure exactly how the rendering demo was set up, but it seems to be set up to take a constant time (or at least a constant pause) between each successive "piece", regardless of actual pixel count.

Of course that makes numerous small renders appear very slow, while in reality the Doom renderer is quite linear and proportional to the number of pixels that are drawn.

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Indeed. Actual time taken isn't properly reflected in a lot of cases, such as transparency.
Still, Frozen Time does actually run faster with all of its bridges changed to 3Dfloors, but only because of the insatiable masked count when looking from the inside out.

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Edward850 said:

You've probably seen how Doom renders a scene.

I haven't. Where is it?

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Wow, that video was fun to watch (and it actually taught me something new). Well played. ;)

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Where's all the portals and polyobjects and other fun stuff though? :P Some of these had little that vanilla wouldn't pull off, sans limits (one at least IS a vanilla compatible map).

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Polyobjects aren't actually interesting, due to the dynamic BSP. They just become normal segs in a room.

Although, the old rendering method sure would be funny in an "outtakes" video.

There was surprisingly little examples of portals I could find at the time.

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Edward850 said:

There was surprisingly little examples of portals I could find at the time.

Urban Brawl probably produces some good scenes.

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