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Linguica

[Vanilla Level Editing] Lesson 5: The Low-Down on Textures

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LESSON 5: THE LOW-DOWN ON TEXTURES

So far in this tutorial you have used a number of floor, ceiling, and wall textures to paint the “hard surfaces” of your WAD. You have seen that while it may be easy to specify their use, making them look right is not always so simple.

This room provides you with the full low-down on DOOM textures. You will see and use textures that act as more than mere paint. You will also be shown something of the full richness of the texture palette that has been provided by the designers at id Software.

In addition, the rules for applying textures will be discussed in full, along with the consequences of transgressing those rules. By the time you complete this room, you will know how to apply textures to any of your WAD’s surfaces and have them look just right.

This room also leads you on three WAD Sorties, building on the WADs produced in previous rooms. During these sorties, you will see something of DOOM’s great outdoors, with the addition of a courtyard to your WAD. At long last, you will also be shown how to cure the problems of texture alignment which have been plaguing your WAD throughout the last few Sorties.

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CEILING AND FLOOR TEXTURES

Your first introduction to textures in this mission was as tiles for ceilings and floors. These ceiling and floor textures make a good topic with which to begin a full survey of DOOM textures.

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FLATS

These simple, square, graphical textures are often termed floor and ceiling flats or tiles to distinguish them from the more complex wall textures that you will encounter later in this room. The DOOM game engine will allow flats to be applied interchangeably to floors or ceilings. You may find, how-ever, that not all textures will look equally good on both surfaces — and some may look downright odd if used inappropriately.

As they are all of a standard size, DOOM’s graphical engine applies flats in a standard way to floor and ceiling surfaces. A flat’s exact position is determined from the map’s X,Y coordinate grid: Flats are always placed starting at a coordinate that is a multiple of 64.

As well as being positioned firmly on this grid, tiles are always oriented the same way, along a north-south axis. The flat’s first texel (the texel from its top left corner when viewed as in Figure 5.1) is copied to the appropriate surface at the starting coordinate. Subsequent texels are transferred to adjacent locations to the east (working across the graphic) and south (working down the graphic). If the same texture is applied to both the floor and ceiling of a sector, these two surfaces will appear as mirror images of each other. Each texel on the ceiling will be the same color as the texel on the floor directly below it.

Because they are locked to the coordinate system in the manner just described, floors and ceilings have their patterns rendered with no reference to walls or other map elements (except that these textures are clipped by their sector boundaries, of course). This methodology ensures that adjacent sectors having the same floor or ceiling heights can have their textures connected smoothly across the boundary between them, whatever the shape or orientation of that boundary. It also means that if the designer is not careful, walls may cut blithely across features in the ceiling or floor textures, making them look odd. Remember the abortive attempt to use the CEIL3_6 texture in the southwestern room of your WAD, back in WAD Sortie 4?

Note that the only way of changing the way that floor and ceiling textures line up with your sector boundaries is to reposition your map lines to make them clip the flats differently. The flats themselves cannot be moved or rotated.

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SEEING THE SKY

The previous room taught you that walls can be assigned a transparent texture (or have texture omitted, depending upon how you care to think of it) to allow sectors beyond them to be visible through them. You are possibly wondering whether there is an equivalent transparent texture for ceilings, one that will enable the player to see out to the sky and the rest of the outside world. After all, you have seen something like this in DOOM, haven’t you?

The answers are “Yes” and “What outside world?” DOOM is capable of displaying the sky and distant mountains and such, but don’t think that such “outside” elements exist anywhere on your map (or anywhere else, for that matter).

When you want your players to see sky, the ceiling texture to use goes by the name of F_SKY1. As its name suggests, this texture provides you with something rather more special than transparent paint — it provides you with sky. This shouldn’t surprise you. After all, what use would transparent paint be on the ceiling? There is nothing beyond the ceiling to see, only void. And, as you will find out shortly, that is not a pretty sight.

If you try to preview F_SKY1, however, you may be a little surprised by what you see.



“Where is the sky?” you may ask. “And how could they get it all into a 64×64 tile anyway? It surely wouldn’t work! Are you sure about this?” I can see that I’m going to have to convince you.

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WAD SORTIE 6: ADDING AN OUTDOOR SECTOR

This WAD Sortie will extend your existing WAD by leading you through the steps needed for the addition of an outdoor courtyard area.

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BREAKING OUT

Start by adding just three new lines to the south wall of the southwest room, as shown in Figure 5.3. These will eventually form the exit from the southwest room to the new courtyard.

The short ends of the rectangle are about 56 units long. The long dimension isn’t critical, but don’t make it too long; 360 units is fine.

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DEFINING THE COURTYARD

Now draw the additional lines shown. These lines will form the courtyard’s enclosing walls. Apply the BROWN1 texture to them.



Don’t worry about the precise size or shape of this area (but don’t encroach too far to the West: I have other things planned for there), just make it match the basic form shown.

If you always build your sectors sequentially in this way, working out from existing sectors, GZDB has something to build from (a neighboring sector) and will assign more useful values to the various attributes by copying them from the adjacent sector.

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TAKING THE ROOF OFF

Now, right click on the new sector and edit the sky to be F_SKY1. The floor texture MFLR8_1, inherited from the inner rooms, is rather inappropriate for a courtyard, so I suggest you change it while you’re here. I think you’ll find that FLAT1_1 fits the bill nicely. And because it’s a bright sunny day in the land of DOOM, why not take the lighting level up to 255? Then save the file as D2WAD6.WAD and try it out.

Now do you believe me? I know the transition between sky and building doesn’t look right yet, but you will have a chance to fix that in a moment. For now, I just wanted you to see the sky.

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FAKING THE GREAT OUTDOORS

Now that you have seen the reality of F_SKY1, you need to know how to use it. There are a number of aspects of this particular texture that can be confusing, so I’ll set you straight on these first.

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SOURCES OF CONFUSION WITH DOOM SKIES

You have already observed the principal confusing aspect: the absence of the flat itself from the list of ceiling textures. The reason that there is no ceiling flat for this texture is the obvious one: A realistic and believable rendering of the sky could not be obtained by tiling a 64×64 graphic. Not surprisingly, therefore, DOOM doesn’t use one. (Quite what it is that you see when previewing F_SKY1 remains something of a mystery — probably a dummy entry in the flats table to keep the graphics engine happy.)

To add to the confusion, the sky textures (for, as you will see, there are more than one) can be found lurking amongst the wall textures. Preview the wall texture called SKY1 and you will see the sky graphic used in your last WAD. Wall textures SKY2 and SKY3 should look familiar, too.

(Remember, you will need to be in Linedefs Mode to preview wall textures in GZDB.)

This leads me to the final point of confusion: the fact that there are three separate graphics for portraying the sky, but only one ceiling texture name for obtaining them.

All of this confusion can be cleared up by realizing that F_SKY1 is not a texture at all. It is a special name, used to trigger a different ceiling-painting technique. To utilize it properly, you need to understand how it works.

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HOW IT ALL WORKS

This is how the process operates. When the game engine comes to paint a ceiling marked as F_SKY1, it checks first to see what the current episode is (or level, in DOOM II). From this information, the engine decides which sky texture to use. SKY1 is used for Episode 1, SKY2 for Episode 2, and SKY3 for Episode 3. (DOOM II spreads the three sky textures out over its 30-odd levels in a similar manner.) You, therefore, can only choose which of the three sky textures you want to appear in your WAD by choosing the episode (or level) that your map appears in.

Having located the appropriate texture (stored amongst the wall textures), the graphical engine pastes this into the ceiling space of the appropriate sector. Rather than performing the graphical transformations necessary to create the normal ceiling perspective, however, the texture is pasted onto the screen area, pixel for pixel, starting at the top of the screen and working down (clipped, of course, by any other textured surfaces in view at the time). The player’s viewing direction is used to determine the horizontal screen displacement of the graphic so that the sky (and any associated distant vista) appears to rotate correctly as the player turns. No other scaling is ever performed on this graphic, thus giving it the appearance of being at an infinite distance from the player at all times.

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USING THE SKY TEXTURE EFFECTIVELY

Once this process is properly understood, use of the F_SKY1 texture becomes a fairly simple and straightforward matter. Look back at your sample outdoor area. If you ignore the details of the sky graphic and imagine ceiling tiles placed over the area that it occupies, you should be able to see quite easily that the sky does indeed act as a replacement for the ceiling, in that it occupies precisely the same area as tiles would. Notice how the plane of the “outdoor ceiling” runs continuously into the ceiling of the adjacent “indoor” area. It does so because the ceiling heights are the same in all three of the sectors in view.

To create an illusion that the “building” the player has just left has height beyond its ceiling, as a real building would have, the outdoor sector must have its ceiling raised. Why? To make the sky higher. This will create an upper texture in the step down from this higher sky to the ceiling of the adjacent indoor sector. By using a pattern appropriate to the outside surface of the building as the texture for this step down, you can create the upper facade of the building. Used with care, this can produce reasonably realistic-looking buildings. It does need care, however, because this facade is just like those of a Western movie-set: flat, with nothing of substance behind it. Allow the player too close to its edges and it will be seen around, giving the trick away.

Another useful characteristic of the F_SKY1 painting technique is that the sky texture used is always rendered at a constant brightness, regardless of the brightness level specified for the sector. This allows the use of variations in lighting level in outdoor sectors to simulate areas of shade without making the sky look odd as a consequence. However, the inability to apply sloping shadow areas to walls can limit the usefulness of this, as you will see shortly.

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USING THE SKY TEXTURE IN OTHER PLACES

F_SKY1 can be applied to the floor, but, not surprisingly, it produces an odd effect there. Remember that the display position of a texture applied as F_SKY1 is always reckoned from the top of the screen. Being 128 pixels high, it will need to repeat before it reaches the space set aside for it on the floor. The result is generally somewhat less than attractive and never realistic — the effect does bear experimentation, however.

Similarly, any of the SKY textures can be applied to walls, where they will look and act like any other wall texture. They will not behave as if they had been painted as sky; they will simply look like a picture of the sky painted on the walls — which, of course, is what they will be.

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WAD SORTIE 7: IMPROVING THE OUTDOOR SECTOR

If you would like to start up GZDB again, I will show you how to improve the appearance of the outer courtyard by applying some of these techniques.

You have learned that to create the appearance of a building adjoining the courtyard, the ceiling of the outdoor sector needs to be raised. If the ceiling of the entire courtyard area were to be raised, however, it would also have the effect of raising all of the enclosing walls, as they are formed by the bounding lines of this sector. I would like these walls to stay the height they currently are: any higher and this space will start to feel cramped and the walls would look artificially high. To achieve the desired effect, the current single courtyard sector needs to be divided up into various new sectors, each responsible for different sections of the outer walls. This will enable the heights of these wall sections to be varied independently of each other.

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PRESERVING THE EXISTING WALL HEIGHTS

The walls along the western and southern boundaries are fine as they are: to prevent them from being changed when the main sector’s ceiling is raised, they need to be placed in a sector of their own. To achieve that, you will need to add some more lines to your map.

Start at the vertex in the northwestern corner of the courtyard. Draw a line from this vertex at an angle of about 135 until you are a little way, 80 units or so, from the western wall. Add lines sufficient to mark off an area of the courtyard sector that contains all of its western and southern walls. The exact shape is unimportant, but aim to keep the new area fairly thin so as to consume as little of the main courtyard sector as possible. End the drawing at the vertex in the southeastern corner of the courtyard. Leave enough room at this southeastern vertex for additional lines to be added to permit similar treatment of the eastern walls later.

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BUILDING THE FACADE

Now that you've preserved a strip near the western/southern wall, take the ceiling of the main courtyard sector up to 216.

Thinking about this particular sector, it is probably worth lowering the floor a touch, in order to make the change in floor pattern between the indoor and outdoor areas more natural. Therefore, take the floor down to –16. This, of course, changes the sector’s elevation relative to the other outdoor sector to its west and south, so you will need to reduce that sector’s floor to match. In turn, this modification will alter the apparent wall heights that these changes were designed to preserve, so be sure to bring the outer sector’s ceiling down by 16 units, as well, to 144.

Finally, to complete the facade of the building, apply BROWN1 to both essential textures of the line shared by the courtyard and the gap through the wall.

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UPPER TEXTURES BETWEEN F_SKY1 SECTORS

You may be worrying about some other texture locations that you know to be essential and to which you have, as yet, applied no texture: the upper textures of the eastern side of the lines dividing your two courtyard sectors. You may be wondering just how these areas can be dealt with. After all, you don’t want to see any textures here — they would seem to be hanging in thin air, wouldn’t they? And yet, you have been taught that such textures are essential. If you inspect these lines now, you will see that GZDB thinks so, too — it has warning signs for their upper texture slots. But what can be put there that won’t look odd?

The answer is that it doesn’t matter what you put there — DOOM won’t use it anyway! Another change in the painting technique invoked by the use of the F_SKY1 texture is that upper textures between adjacent sectors with F_SKY1 specified for their ceilings will not be painted. This enables the designer to vary the ceiling heights of outdoor sectors in order to alter the heights of surrounding walls and still have the sky effect work correctly.

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MODIFYING THE EASTERN WALL

This might be a good point to save your WAD. Call it D2WAD7.WAD. Before trying it out, though, it is worth making a few more changes.

The modifications you have just made should have created a raised wall to the north of the outside courtyard, while keeping the western and southern walls as they were. The eastern wall has not been given its own sector, however, so this will now be at the same height as the “building” to the North. In my opinion, it would be better to have this wall closer in height to the other outer walls, so this eastern area needs to be split away from the main courtyard sector, too. You could introduce a little visual interest to the courtyard by varying the wall’s texture as well; one of the vine textures would go well here. Vines tend to look a bit odd growing out of paving-stones, though, so while you’re adding a sector to bring the walls down, why not put it to use by letting it create a border to the paving?

Separate the eastern wall from the main courtyard by making another new sector. Start at the extreme southeast vertex and draw a series of lines parallel to and about 32 units away from the lines that mark out the eastern wall of the courtyard. These should connect to the existing lines at the south and north ends of the eastern wall. The short lines that connect the new series of lines to the existing ones will need to run at an angle of about 45° to the others in order not to cross or connect to other lines. It is imperative that your new sector takes none but the eastern walls away from existing sectors, otherwise the desired height effects will be spoiled.

When the new sector is defined, set the floor height of the new thin sector to –20. (The vine border should be a little lower than the stone of the courtyard, don’t you think?) A ceiling height of 108 will bring the walls down, as desired.

Set the floor texture to FLAT10 — this seems suited to the task of providing something for a vine to grow in — and the ceiling to F_SKY1. Reduce the lighting to 144. (This vine is going to be in the shade of the wall.)

Now that you have finished adjusting the sector attributes, apply the BROVINE2 texture to the main texture slot of the courtyard’s eastern wall sections.

Save the WAD as D2WAD7A.WAD before going on.

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ADDING AN AREA OF SHADE

The final modification to make to this WAD before trying out your handiwork is to add an area of shade to the courtyard.

The eastern vine border has already been set to a lower brightness level than the rest of the courtyard. Leaving the shade coincident with this border will create a somewhat artificial appearance, though, so it is worth adding another sector to extend the shade some way over the paving to make it more credible.

The new sector should start and finish at the same vertices as the previous one: the southern and northern ends of the eastern wall. Again, start drawing at the extreme southeast vertex. The rest of the lines should run parallel to the eastern wall, somewhere to the west of the western edge of the vine-border sector. Remember that you are drawing the shadow line that would be produced by the sun if it were due east and quite high in the sky. The following image shows the final arrangement of lines you are aiming for.



After successfully drawing the new lines, change your new sector’s floor to FLAT1_1 (the ceiling should already be F_SKY1) and its floor and ceiling heights to –16 and 216, respectively, to match the main courtyard sector. Leave its brightness at 144.

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FIXING THE INTERCONNECTION

Finally, reduce the ceiling of the interconnection between indoors and out to a height of 128. This will create an essential texture inside the room. Apply STONE3 to that texture, to match its neighbors. You might also want to change the interconnection’s ceiling texture, as lights will look a bit odd here. You should find that CEIL5_2 is OK. Finally, save the WAD as D2WAD7B.WAD and try it out.

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REVIEWING YOUR HANDIWORK

Head straight out to inspect your courtyard. In passing, you may notice that, unlike your previous opening in a wall, the one out to the courtyard has ended up looking OK from inside the building. When viewed from the outside, though, texture alignment isn’t too good around the opening. Apart from that, everything else should look fine. (Well, maybe the shady area isn’t perfect, but it’s about as good as DOOM allows.)

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WALL TEXTURES REVISITED

Having seen how floors and ceilings are painted, the intricate details of how textures make it on to the walls will now be revealed.

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THE DIFFERENCES BETWEEN WALL AND CEILING TEXTURES

You have seen that ceiling and floor flats are all the same size: 64 x 64 pixels. If you care to preview a few wall textures, however, you will quickly see that wall textures vary widely in size, both in their horizontal and their vertical dimensions. The familiar STONE2 is 128 pixels square; STEP1 is just 32 wide by 8 pixels high; BROVINE2 is a comparatively massive 256 by 128 pixels, while LITE4 is 16 x 128.

The differences between flats and wall textures go beyond variation in size, however. To optimize the use of space in the main WAD file (where all of these textures are stored), wall textures are sometimes broken down into a series of common graphical patches. The textures themselves are then created as an assemblage of these smaller patches. In this way, a large number of different wall textures can be created by careful repetition, juxtaposition, and overlapping of a surprisingly small number of graphical elements.

The patches themselves can be virtually any size, although the final texture height must not exceed 128 pixels. Some wall textures are made up of just a single large patch (CEMENT1, for instance), while others, such as LITE3, are produced from many repetitions of the same small patch. This multi-patch characteristic of some wall textures can limit their use, as you will see shortly.

The final main difference between flats and wall textures is that it is possible for wall textures to have transparent areas within them. The previous room introduced you to the notion of the transparent texture, which provides completely see-through lines on your map. That, of course, is not any special texture but an absence of texture altogether. You will find, though, that there are wall textures that, in effect, use a transparent paint to produce holes through which a player can see. Preview the texture MIDGRATE to see an example of these see-through textures.

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SUMMARY OF TYPES OF WALL TEXTURE

In summary, then, the textures that can be applied to a line’s various texture slots may be:

  • The transparent texture (really no texture at all): Nothing is rendered here, except the view beyond the line.
  • A solid texture: The texture completely covers the specified area.
  • A see-through texture: The texture has holes in it through which the view beyond the line is rendered.
There are a couple of other special effects of which wall textures are capable; you will learn more of these towards the end of this lesson.

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THE CONSEQUENCES OF OMITTING ESSENTIAL TEXTURES

So far, you have been told that essential textures are so named because they block a player’s view of the void. You have been warned that to allow a player to view the void is to court mishap and disaster. It is time that you were told the true extent of the dangers inherent in viewing the void.

MISSING ESSENTIAL UPPERS/LOWERS

You have already seen the effect of omitting essential upper textures: DOOM fills the gap with ceiling texture from the adjacent sector. This will produce visual confusion, as you will remember from one of your early WADs. Other than that, though, the result is not serious — indeed, if you hunt around, you will find that id Software has missed quite a few from their own WADs.

The effect of a missing lower is similar: the adjacent sector’s floor appears to be at the level of the current sector’s — until the player reaches it, whereupon the step up comes as a surprise!

MISSING ESSENTIAL MAIN TEXTURE

The effect of a transparent main texture on a single-sided line is much more disastrous — it results in what is known as the Hall of Mirrors (HOM) effect. Rather than leaving the line’s space empty, the graphical engine fills it with copies of various other parts of the current view, producing a flickering display of seeming reflections, reminiscent of the fairground amusement from which the effect derives its name. It is extremely distracting for the player to encounter the Hall of Mirrors effect in a WAD. It cannot be used to any constructive effect and most players will simply see it as a fault (which, of course, it is).

Avoid this effect by making sure you never omit any essential main textures.

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SEE-THROUGH TEXTURES

See-through textures used as essential wall textures produce another type of fault known as the Tutti-Frutti effect. The solid parts of the texture are shown correctly, but the gaps through which the player can normally see are filled with pixels of random color. This can sometimes be put to decorative use in a WAD, but mostly it just looks wrong. The effect is best avoided by ensuring that all essential textures are covered by completely solid coloring.

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TEXTURE PLACEMENT

Now that you know more about the nature of wall textures and what happens if they are missed off your lines, the precise details of the process whereby the paint is applied to the walls can be considered.

The mechanism that the DOOM engine uses for the placement of wall textures is as follows. First, the main texture name is consulted and the appropriate set of component patches are assembled into the graphic to be used. What happens with that graphic depends on the setting of the line’s two-sided flag. The single-sided line is the simpler case and will be examined first.

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PAINTING SINGLE-SIDED LINES

Because a single-sided line lies at a single sector’s boundary with only void beyond it, such lines can only ever possess a main texture. DOOM renders a single-sided line onscreen by pasting the graphic for its main texture into the upper left corner of its space, at the point where this space meets the ceiling. The pattern is repeatedly applied, like tiles, horizontally and vertically until the entire wall space, from left to right and ceiling to floor, is covered. The following illustrates this process schematically for the simple graphical pattern shown at the left of the figure.



This process may sound straightforward but, in fact, it only works correctly with textures of the right size: the graphic must be either precisely 128 pixels tall, or tall enough to fill the space without vertical repetition. This is because the DOOM engine only gets its vertical repetitions correct if they occur at 128-pixel intervals. The use of graphics that need to be repeated at intervals other than 128 pixels leads to small gaps in the rendering. These fill with multi-colored graphical noise, aka more Tutti-Frutti. You should ensure that you use textures that are 128 pixels high on single-sided walls, or textures that are at least as tall as the wall space into which they will be painted.

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PAINTING TWO-SIDED LINES

The graphics engine handles two-sided lines in a different manner. The painting starts in the usual way with the main texture. If none is given, the space is left clear, as you have seen; otherwise, the specified graphic is applied, as a tile, in the top left-hand corner of the main texture space. Note that this will only be at the ceiling if no upper texture is required on this side of the line. The main texture pattern is repeated horizontally, just as with single-sided lines, but it is not repeated down the vertical dimension of the wall. This may leave a horizontal strip of the wall unpainted. This strip will be treated as transparent (which is perfectly okay on a two-sided main texture, remember).

After considering the main texture, DOOM then paints a two-sided line’s other textures as necessary. The lower texture is painted in the same manner as the main texture of a single-sided line. The painting starts at the top left corner of the lower texture space and repeats horizontally and vertically until the space is filled.

The upper texture is painted in a similar manner, with the exception that here the pattern is painted first at the bottom left corner of the upper texture. The graphic is repeated horizontally to the right, as usual, and vertically upwards until the space is filled.

The following illustrates schematically DOOM’s default method of painting a two-sided line’s (potentially) three textures.



Once again, if vertical repetitions are needed to fill the space of the upper and lower textures, these will only occur correctly when the appropriate graphics are precisely 128 pixels tall.

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SPECIAL TREATMENT OF TWO-SIDED LINE MAIN TEXTURES

You need to be aware that DOOM gives special consideration to the main texture of a two-sided line. Remember that these lines, by definition, connect adjacent sectors. They therefore represent an interconnection between one space and another; as such, one would ordinarily expect these main textures to be transparent. If they carry a texture at all, it is most likely to be one of the see-through textures of the grid and grating variety.

Because this space is not really part of a wall, any pattern which occupies this area is rendered on the screen not by the usual wall-painting part of the game engine, but by that part which is responsible for the handling of Things. Now, this area of the graphics engine knows nothing about vertical tiling (monsters don’t normally stand on each other’s shoulders!) It consequently won’t produce any — although it will repeat the patterns horizontally as needed. This usually causes no problems, as the majority of grid and fencing textures would look strange if tiled vertically.

More significantly, however, because the graphics associated with Things are always single-patch pictures (called sprites), this part of the graphics engine cannot cope with wall textures that consist of complex, overlaid patches. It will handle single-patch wall textures (which is what all of the see-through textures are) and textures that, when assembled, have all of their patches placed side-by-side horizontally and without overlap. Other arrangements of patches cannot be used.

If you use a texture that is made up of overlapping patches, or patches that are arranged vertically, as the main texture of a two-sided line, a serious error will occur. Whenever it is asked to display such a texture, DOOM will pour weird streams of color down from the offending wall-space, often to the bottom of the screen. At the same time, the PC will slow to a crawl. This is known as the Medusa effect (so-named because the player sees snakes and is turned to stone!). Medusa makes the WAD unplayable while the offending space is in view. To eliminate it, you need to ensure that the main textures of your two-sided lines are all either transparent, or do not consist of vertically positioned or overlapping patches.

This restriction does not apply to upper or lower textures, because these are always handled by the wall-painting part of the engine.

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