Slimetrails

[SirBardCat]

Before I begin I'd like to make it very clear that I hate legacy with a passion, and if it were not a program, inatimate, I would rape it and then burn it down until nothing but ashes remained. Then I'd take a crap on whatever was left of it, and let my dog roll around in it.

I'm creating a rather large map containing sectors quite close together. It only gives me slimetrails in legacy, (it's a legacy specific map), and only on the sectors that are close together (2-3 units apart). I'm not sure what's causing this. In fact, I have no CLUE. I've run it through BSP32 and Zennode. Of course, this is only a cosmetic issue, but it's not just 1 or 2 slimetrails, it's ALOT of slimetrails, concetrated in a small area. And, well, that looks awful.
I doubt it can be fixed at this point, but theres also people that know alot more about how the engine works, as well as nodes and such. So bring on teh suggestions. Oh, and in case you missed it, this ONLY happens when I run it with Legacy.

[CodeImp]

Try a different nodebuilder. The way a nodebuilder splits could reduce slime trails, but I dont know of any nodebuilder that is good enough to get rid of them all. Other than that, there is AFAIK nothing to do about this. Its a doom bug and it can only be fixed by modifying doom.... that sets me thinking, why does randy not try to fix or at lest reduce slime trails in zdoom?

[Graf Zahl]

Why am I not surprised that this is only a problem in Legacy?

The reason for this is simple:

The node builder has to create additional vertices to create its data. But to save space it completely discards the fractional part of it so if a vertex is placed on coodinate (37.5,40.5) it becomes (37,40)

With these small sectors these precision inaccuracies in the vertex coordinates become rather severe (half a unit off of 2 is 25%) so the effects become more visible. Unfortunately Legacy is the only major source port that doesn't do anything about it.

All Boom derivates (PrBoom, Eternity, ZDoom) try to fix these inaccuracies while loading a level and those which use GL nodes don't have to bother because GL nodes are much more precise.

End result: You probably won't be able to do anything about this problem if you use Legacy.

[deathbringer]

How legacy specific is it? if it has boom and 3D floors you could go for EDGE, If it just has boom you could go for...anything really, and if it has Boom, 3D floors and Fragglescript..doesnt eternity have all those?

[Graf Zahl]

deathbringer said:

How legacy specific is it? if it has boom and 3D floors you could go for EDGE, If it just has boom you could go for...anything really, and if it has Boom, 3D floors and Fragglescript..doesnt eternity have all those?

Eternity doesn't have 3D floors and it doesn't have FraggleScript anymore (due to stability issues.) So unless this map requires 3D floors a switch to a different engine is higly recommended - and if this is part of a larger project, well - too bad about it.

[SirBardCat]

Well this is quite a large project. It's pretty legacy specific. (3d floors, FS) I could live without the 3d floors, but fragglescript is absolutely nessecary. This won't be released for a long while, so hopefully these problems will be fixed within the next few releases.

Edit: Heh, I'm not removing anything, I refuse to let a shitty port limit my creativity, so if this persists, then I guess it'll just hafto be in the final release. :\

[Graf Zahl]

I doubt it. They don't even fix much more annoying stuff like the missing voodoo dolls. What makes you think they might fix something most people won't even notice?

(Well I like to be proven wrong though...)

[Darkhaven]

Use ZDoom. Anything Legacy can do, ZDoom can do alot better (excluding Legacy's cool 3D floors), and ZDoom has many more editing features than any other port will ever have. For example, slopes, things with a possible Z Height, the "Transfer Lights" system, the new texture system... I'm just getting started.

[SirBardCat]

Darkhaven said:

Use ZDoom. Anything Legacy can do, ZDoom can do alot better (excluding Legacy's cool 3D floors), and ZDoom has many more editing features than any other port will ever have. For example, slopes, things with a possible Z Height, the "Transfer Lights" system, the new texture system... I'm just getting started.

Heh, this wad is being built on scripting. I don't know ACS, and right now, I don't CARE to learn it. So poo on you.

[Sporku]

Yes.. Jump on the ZDoom bandwagon why don't you? Everyone else uses it, so that means you should do it too!

Oh, and while you're at it, why not start smoking. Everyone does that too, so that has to mean it's good! (Bleh)

Eh, well, ACS shouldn't be too hard to learn if you know FraggleScript.. and if you'd rather not use ZDoom there's some really neat things you can do in Boom compatible ports by just plopping a voodoo player on a conveyor belt with some linedefs that trigger actions and such.

I'm sure there's a way to fix this 'slimetrails' problem in Legacy though (I have no idea what a slimetrail is, but meh).

[Graf Zahl]

AgentSpork said:

I'm sure there's a way to fix this 'slimetrails' problem in Legacy though (I have no idea what a slimetrail is, but meh).

Lee Killough's comments from the MBF source:

// Slime trails are inherent to Doom's coordinate system -- i.e. there is
// nothing that a node builder can do to prevent slime trails ALL of the time,
// because it's a product of the integer coordinate system, and just because
// two lines pass through exact integer coordinates, doesn't necessarily mean
// that they will intersect at integer coordinates. Thus we must allow for
// fractional coordinates if we are to be able to split segs with node lines,
// as a node builder must do when creating a BSP tree.

//
// A wad file does not allow fractional coordinates, so node builders are out
// of luck except that they can try to limit the number of splits (they might
// also be able to detect the degree of roundoff error and try to avoid splits
// with a high degree of roundoff error). But we can use fractional coordinates
// here, inside the engine. It's like the difference between square inches and
// square miles, in terms of granularity.
//

Slimetrails (aka. Firelines) become visible as parts of the ceiling and floor extending toward the center of the screen from top and bottom.

Boom and its derivates try to minimize the effect by projecting the offending vertices back onto the line they belong to.
Legacy does not so you'll see all those nice slimetrails in their full glory. :P

[SirBardCat]

Well at least now I know how they work, and what causes them so that in the future I can try to limit them. Maybe I can fix 'em in what I've got done so far, but it's gonna mean alot of line dragging. :|

[Piezo]

There is a nodebuilder that is specific for that very problem, particularly for Doom Legacy's openGL mode. I don't remember what it is called, but I read about it in the newdoom forums. I know someone that I recommended it to after playing his map he was working on and showing him where his walls were missing in openGL mode, and he must have found it and used it because later he sent me the map and I couldn't find any missing textures.

[Graf Zahl]

Piezo said:

There is a nodebuilder that is specific for that very problem, particularly for Doom Legacy's openGL mode. I don't remember what it is called, but I read about it in the newdoom forums. I know someone that I recommended it to after playing his map he was working on and showing him where his walls were missing in openGL mode, and he must have found it and used it because later he sent me the map and I couldn't find any missing textures.

That's Zennode. But it is still limited by the WAD format. The slimetrail issue is not a flaw in a node builder, it is a precision limitation in the level data. No node builder can get around it at all times.
The missing texture issue in Legacy's OpenGL mode is just a result of an utterly crappy rendering algorithm. I have absolutely no idea how that was possible in the first place but the Legacy team's reasoning just can't be correct because if it was true the level shouldn't render properly in software mode, too.
But AFAIK the OpenGL renderer in Legacy is being completely rewritten so hopefully this issue is soon history.