The arrows going from left to right marked "SKY" and "Wall texture" are possible lines of sight, and the associated text explains what will be painted at the position where the arrow hit. In this case there is a one-sided line between sector 2 and the void space. On this line the normal texture is painted as wall texture up until the height of the ceiling in sector 2. This is normally used to lower the outer walls in an outside area. The upper texture on a sector with SKY ceiling will never be painted. instead what is painted depends on what is on the other side of the sector where the line of sight hit. In this case where the LOS hit void space, the F_SKY texture is painted.
If you want to have a more solid looking wall, where you can see the
top of the wall, you can raise the floor height of sector 2 to be
equal to the ceiling height, and you will have a wall, where the top
of the wall is painted in the floor height of sector 2. (If the wall
is low enough for you to see the top.
Rule 2
This is the rule that is used to create the SKY
door special effect:
Here the floor heights of all the sectors 1, 2 and 3 should be equal.
(If you don't need it you can remove sector 3 and end up with a
configuration that's almost equal to the one in rule
1, except that you can't see the floor of sector 2 when the floor
heights of sector 1 and 2 are equal.
Rule 3
This shows that normally the upper part of a SKY sector is simply
transparent. Even though YOU can see through the upper part of a SKY
sector it doesn't mean that the monsters can. It's also impossible for
both players and monsters to walk or
shoot through the upper part of a sector. This gives some interesting
possibilities: how about putting a few of the really big monsters in
sector 3. When the player enters sector 1 he will see these monsters,
but they can't see the player. At the same time it's impossible for
both the player and the monsters to shoot each other, but that doesn't
mean that the player isn't going to try...
Rule 4
This is pretty much the same as rule 3.
This shows that the upper part of a SKY sector is transparent
independently of the height of sector 2. (Take care if the
floor heights of sector 1 or three are higher - see illegal
configuration 2).
The main difference between this and rule 3 is
that here the sound will propagate through the gap in sector 2, and if
the ceiling is high enough it will be possible to pass from sector 1
to sector 3.
Illegal SKY sector configurations
If you're building an area using the F_SKY texture, and you suddenly
get a HOM (Hall Of Mirror) error in your WAD, you should look for the
following problems:
This is one of the two exceptions to the general rule that the upper part of a SKY sector is transparent. If you see this configuration from sector 3 towards sector 1, you will see a normal SKY door, but seen from sector 1 the DOOM engine get confused because a line of sight isn't supposed to be able to pass through the linedef between sector 2 and sector 3.
This can be corrected by making the floor of sector 3 a little lower
(Sector 2 becomes transparent by rule 3),
or by creating a small extra sector between sector 1 and 2, with the
same floor height as sector 2 (F_SKY will be painted above sector 2 by
rule 2).
Illegal configuration 2
This illegal configuration is actually much like the previous one:
Here the problem is the same as in the first illegal configuration. It should be impossible for a line of sight to pass from sector 2 to 3. This confuses the DOOM engine so much that it doesn't know what to paint, and the result is HOM.
I don't really know what you're trying to build if you have a
configuration like this, so I really can't give you good instructions
as to how to correct this. If you ever find that this is a source of a
problem I suggest you mail
me. (Be prepared that I will ask you to explain exactly what you
are trying to achieve).
2. The SKY Door
All the sectors should have the SKY ceiling texture. Sectors 1, 3, 4 and 5 should have the same (normal)
floor and ceiling heights, while sector 2 has set the ceiling height to be equal to the floor height (and both equal
to the floor height of the other sectors). Sector 2 is the door sector, and it can be triggered like any other door.
Make sure that the sectors 3 and 4 are not large enough for the player
to get caught in them!
This works because of rule 2.
3. The SKY Window
Sector 1 is the room in which the player can walk around. Sector 2 is the window frame. Here the ceiling should be lower than the ceiling in sector 1. The floor of sector 2 will be the height of the window. To make sure that the SKY viewed through the window doesn't tile, you will have to set this quite high. Sector 3 is the "outside" part of the window. The ceiling texture here should be F_SKY, while the floor texture is still the same as in sector 2. Both ceiling and floor heights are the same in sector 2 and 3. Sector 4 on the other hand is the SKY door from before. Here both the ceiling and floor heights are set to be equal to the floor heights of the sectors 2 and 3. The ceiling texture of sector 4 should of course also be F_SKY. Sector 3 is needed so that you are in a "all SKY" area when you apply rule 2.
Note that if sector 2 is so high that it's impossible to see the floor, you can create the window like this:
The floor and ceiling heights/textures should of course be set just like in the first example.
4. The SKY at floor special effect
Apply F_SKY to the floor of sector 2, and a "non-SKY" texture to the
floor of sector 1. That should create the F_SKY at floor special effect.
5. SKY Everywhere
However it's possible to hide the thin sector completely simply by making it lower than the middle sector, so that it's out of sight. The effect is created like this:
All sectors should have ceiling texture F_SKY. Sector 1 should have floor texture F_SKY, and sector 2 and 3 can have any floor texture except F_SKY. Make sector 2 as thin as possible, and set the floor height of sector 1 to be 0. Now apply a floor height of -128 to the sectors 2 and 3. That should place them well out of sight, and set the ceiling height of sector 3 to be equal to the floor height, to create the F_SKY on the wall effect. Now you should have a room where you can see nothing but SKY!
This effect can be seen in spcial1b.zip
(73K). You can find the SKY everywhere room by going through the
two SKY doors to the north east. (I've put a small triangle of floor
texture in front of the door, so that you can see where it is in case
you need to get out again...).
The general way of creating a building smaller than the
walls in a courtyard, is to surround the building by a sector with
F_SKY texture and a lower ceiling height. This should paint SKY above
the building (above the ceiling height of the surrounding sector).
When you're surrounding the inner building with a lower SKY sector,
you should use rule 1 or rule 2
If the courtyard walls are so high that they should be visible over
the building, there will of course be painted SKY over the small
building. To avoid this you should make the smaller building inside
the courtyard just big enough to avoid this, or make the surrounding
courtyard walls smaller.
However it is possible to create the illusion that you can actually
see over a building without the SKY texture appearing over it. To do
this you have to maintain F_SKY as the ceiling texture (which means
no ceiling inside). To give the illusion that the ceiling is still
there, you create one using 2-sided textures like the STEPTOP in a
square pattern where you want the ceiling to be. This is demonstrated
in see_over.zip (4K) by Alden Bates (abates@central.co.nz).
All the dashed lines are internal lines in sector 1.
(Both sidedefs point to sector 1). Sector 1 is the main room. Set the
floor height to be 0 and the ceiling height as high as you want it.
Now apply the STEPTOP texture to the normal on both sides of all the dashed lines,
and make them lower unpegged. This should make the texture stick to
the floor. Then apply a Y-offset of say 80 or lower (make your own
experiments) so that the STEPTOP textures are painted above the
player. This will look as if there is a special kind of ceiling above.
(It might even look better than some of the original DOOM ceilings).
You can also experiment by making your own 2-sided textures for the
ceiling. (Maybe it's a good idea to use a texture higher than 16
units, as this makes it easier to avoid holes in the roof)
The Non-repeating Sky is a way to provide a unique sky background
throughout a 360 degree of view. The normal background sky, which is a
single-patch 256x128 texture, repeats every 90 degrees. By redefining the
appropriate SKY texture with a multi-patch texture, the sky can repeat every
180 degrees, or simply not repeat at all. The following table details the
requirements.
6. Low buildings in Courtyard
Construction of the effect
Create the following configuration:
6. Non Repeating SKY
This effect is used in trinity2.zip
(310K) by Steve McCrea (sm@eng.cam.ac.uk), Simon Wall and Elias
Papavassilopoulos. The non repeating F_SKY effect was originally an
idea by Olivier Montanuy (Olivier.Montanuy@ens.fr).
Number of patches Total texture size View
1 256 x 128 repeats every 90 degrees
2 512 x 128 repeats every 180 degrees
3 768 x 128 repeats every 270 degrees
4 1024 x 128 does not repeat