GZDoom Sector Rendering

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GZDoom Sector Rendering

Postby shoober » Sat Dec 01, 2012 1:24 am

I was reading a thread about ZDoom vs GZDOOM and came across a comment that stated that GZDoom doesn't render the sector effects as accurately as ZDoom does, because of software rendering. Is this true? I'm a purist and want to replay Doom how it should truly look instead of GZDoom emulating the sector effects (unless GZDoom emulates the sector effects with 100% accuracy). I even set my compatibility options to Doom (strict) just so I have a authentic Doom experience this time around. I used GZDoom the last time I played through it.

One thing though, I can't stand not being able to use Mouselook to aim, unless I'm playing Wolfenstein 3D where looking up and down is pointless. I can't tolerate autoaim of any sort, I just have to aim at the enemies no matter what. I just played a couple levels with ZDoom and couldn't help but notice this strange effect that happens when you look up and down. Its like it zooms in on everything and bends it. Its kind of headache inducing, though bearable. I know Doom was originally designed with no mouselook in mind, hence this problem. This made me miss using GZDoom where this phenomenon doesn't occur.

So what I want to know is, does GZDoom render the sector effects as accurately as the original software render does?
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Re: GZDoom Sector Rendering

Postby Blue Shadow » Sat Dec 01, 2012 3:25 am

The way I see it is that if you don't mind playing the game with freelook, then something like how sector lighting (that's probably what you mean by "sector effects") differs between both renderers shouldn't be a concern, in the first place.

I mean, you're not a Doom purist if you use freelook.
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Re: GZDoom Sector Rendering

Postby Nash » Sat Dec 01, 2012 4:28 am

"Purists" use doom2.exe. :P If you want a close to vanilla Doom experience on a modern system, use Chocolate Doom. Look up/down doesn't exist. :P
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Re: GZDoom Sector Rendering

Postby shoober » Sat Dec 01, 2012 5:13 am

Besides mouselook, I want an authentic Doom experience VISUALLY. Sure, most purists would not use mouselook, but then they might enable texture filtering. Its just personal preference. If I didn't mind how ZDoom and GZDoom render the sectors, then I wouldn't of made a thread about it in the first place. If you like to use autoaim in video games that's fine with me, I just prefer to actually aim at my enemies to kill them. Some people need a little help with aiming I guess.

But anyway, I would really like to get back onto the subject. Could someone explain if GZDoom can render the sector effects exactly how they are rendered using the software render?
Last edited by wildweasel on Sat Dec 01, 2012 6:51 pm, edited 1 time in total.
Reason: Fixed doomwiki links to point to the real, canon DoomWiki.org.
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Re: GZDoom Sector Rendering

Postby edward850 » Sat Dec 01, 2012 5:47 am

FYI, you may want to reference all your links to the new wiki location, Doomwiki.org. The Wikia site only exists still because it can't be taken down, and thus any information on it may not be up-to-date or even correct.

Anyway.
As Doom isn't 3D, flats (floors and ceilings) are rendered with some flood fill-esc algorithm. Each texture is rendered to fill all possible space, stretching out until they reach another flat or the edge of the screen. However, GZdoom (and any other port that uses true 3D to represent everything) cannot do this, due to all surfaces being rendered as proper polygons.
GZdoom, therefor, emulates the results by extending out floor and ceiling textures past their logical end to re-create the flood fill effect in various circumstances. This works in most conditions (such as with deep water effect), but it can never work in 100% of cases.
Walls become an issue because they cannot be rendered outside of the logical rendering order. If a wall texture is above or below a floor or ceiling texture, it cannot be seen, regardless if it could in the software render.

You can read a lot about Doom's rendering here.
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Re: GZDoom Sector Rendering

Postby ibm5155 » Sat Dec 01, 2012 1:59 pm

Well so why not use zdoom?
is like this, if you want to play vanilla, goto vanilla doom/2 or prboom.

I don´t see a problem with gzdoom not being 100% on the way it render not being like the vanilla (and it´s not software render :p)
The good part is gzdoom/zdoom don´t have many bugs that have on vanilla, and on the other side we have a great port for modders with 3D models, 180 look,... support *__*

So, that´s it, i really would not like to use gzdoom/zdoom for play the way it was done, i was just use dosbox + doom2.exe...
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Re: GZDoom Sector Rendering

Postby shoober » Sat Dec 01, 2012 3:36 pm

I would of used Dosbox to play Doom, but I want mouselook. I just can't stand not being about to look up and down (unless I'm playing Wolfenstein 3D where you don't need to). I like to aim at my enemies, not just have my bullets magically go to the top or bottom of the screen when I aim in the direction of the enemy. This is why I want to use ZDoom, so I can have mouselook. What I'm trying to do is, have ZDoom render Doom the way it would look if I did run it through Dosbox.

I want an authentic look for Doom visually and everything else besides the mouselook. But, there is one thing, if GZDoom can render all the sector effects the same as they look in software mode, I would rather use GZDoom then. Then, I could look up and down without the map warping and so on. But I would rather have this happen, then the sector effects being rendered not as accurate as they are in software mode.

So, does GZDoom render all those sector effects as accurate as the original software mode does?
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Re: GZDoom Sector Rendering

Postby InsanityBringer » Sat Dec 01, 2012 4:02 pm

Really, it depends on the level. Stock Doom levels never used any of these tricks (aside from maybe some levels in Final Doom), and they should render just fine. Most basic effects should also work, too. Maps that make very heavy usage of trickery (this is usually mentioned in the description or text file) might have issues, but most general maps should be fine.

Now, there are still going to be many things in GZDoom that don't look like software (and therefore "unauthentic"), regardless of the map. Doom's diminished lighting effects aren't 100% accurately replicated in GZDoom, as doing so would be difficult, for example
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Re: GZDoom Sector Rendering

Postby shoober » Sat Dec 01, 2012 5:10 pm

Interesting. Is there anything else besides the lighting effects that GZDoom can't render as accurate as software render does?
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Re: GZDoom Sector Rendering

Postby Gez » Sat Dec 01, 2012 5:31 pm

Color depth loss from palettization (red that turns into brown, etc.)
Geometry distortion when looking up and down
Sprites "bleeding" into the floor or ceiling
Sprites getting cut oddly by geometry
Partial invisibility effect (a.k.a. fuzz)
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Re: GZDoom Sector Rendering

Postby shoober » Sat Dec 01, 2012 7:27 pm

Well, with that information, I have made up my mind. I'm going to stick with ZDoom that uses the software render. I want an authentic look to Doom visually. I want everything about Doom to be authentic, except added mouselook. Actually aiming and shooting at the enemies makes it way more fun and challenging then just pointing the gun in there general direction and having the bullets magically hit them. Thank you InsanityBringer and Gez for answering my question.
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Re: GZDoom Sector Rendering

Postby ibm5155 » Sun Dec 02, 2012 6:50 am

The best fog for gzdoom should be doom, and not the stock dark (actualy i prefer more the doom fog ^^)
EDIT:if i remember right, someone did a mod that the fuz is 100% identical to the software fuz effect, i just can´t remember where I finded that mod =/
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Re: GZDoom Sector Rendering

Postby Gez » Sun Dec 02, 2012 7:11 am

ibm5155 wrote:EDIT:if i remember right, someone did a mod that the fuz is 100% identical to the software fuz effect, i just can´t remember where I finded that mod =/

No, nobody did anything where the fuzz is 100% identical, because it is absolutely impossible.

Let's look at a small pixel grid:
123
456
789

To render pixel 5, the software fuzz effect will "borrow" a pixel from 2, 4, 6, or 8 from the background (not the actual sprite) and then darken its color by shifting it through the colormap.

With OpenGL shaders, you cannot get pixels from the background (strictly impossible) and also you do not use the colormap. Finally, shaders do not have access to pixels (or texels) at all, they don't know the dimensions of the image they're changing. They work with relative coordinates in floating point (so that 0.0 is left or top, and 1.0 is right or bottom), meaning that any attempt at making it pixely like the original effect will fail since you won't get the same pixel size on a fuzzy clip as you'll get on a fuzzy spider mastermind.

Being 100% identical to software is therefore absolutely impossible on at least three counts.
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Re: GZDoom Sector Rendering

Postby ibm5155 » Sun Dec 02, 2012 7:41 am

viewtopic.php?f=3&t=28139
well I like what i see. It´s not 100% but it´s near =D
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Re: GZDoom Sector Rendering

Postby Gez » Sun Dec 02, 2012 8:01 am

And these shaders are in GZDoom now. They've been included for a while. It even says so in the wiki article I linked to.
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