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The SIDEDEF Resource

by Matthew S. Fell

 

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 The SIDEDEF's function

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A SIDEDEF is a definition of what wall texture(s) to draw along a LINEDEF, and a group of SIDEDEFs outline the space of a SECTOR. There will be one SIDEDEF for a line that borders only one sector (and it must be the right side, as noted elsewhere). It is not necessary to define what would be seen from the other side of that line because the player can't go there. The DOOM player can only go (or see) where there is a SECTOR.

 

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 SIDEDEF structure

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The following table outlines the structure of each SIDEDEF's 30-byte record:

The structure of the SIDEDEF
Offset	Size	Purpose
0	short	X-offset for pasting the appropriate wall texture onto the wall's "space": positive offset moves into the texture, so the left portion gets cut off (# of columns off left side = offset). Negative offset moves texture farther right, in the wall's space.
2	short	Y-offset: analogous to the X-offset put applied to the vertical displacement of the wall textures.
4	8-byte string	"Upper" texture name: the part above the juncture with a lower ceiling of an adjacent sector.
12	8-byte string	"Lower" texture name: the part below a juncture with a higher-floored adjacent sector.
20	8-byte string	"Middle" texture name: the regular part of the wall. Also known as "Normal" or "Full" texture.
28	short	Number of the sector that this SIDEDEF faces or helps to surround.

 

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 Using Textures

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As already noted, the main role of the SIDEDEF is to tell the game engine how to render the view of the line of the SIDEDEF when viewed from the side to which it is attached. This it does by notifying which wall textures to display in which areas of the wall.

Texture Names

The texture names in the SIDEDEF structure are from the TEXTURE1/2 resources. The names of wall patches in the directory (between P_START and P_END) are not used directly, they are referenced through the PNAMES lump.

In addition, "-" may be used instead of a texture name: this means "no texture"--in other words, transparent.

Texture tiling

If a wall is wider than the texture to be pasted onto it, then the texture is tiled horizontally. A 64-wide texture will be pasted at 0, 64, 128, etc., unless an X-offset changes this. If the wall is taller than the texture, than the texture is tiled vertically, with one very important difference: it starts new tiles only at 128, 256, 384, etc. So if the texture is less than 128 high, there will be junk filling the undefined areas, and it looks ugly. This is sometimes called the "Tutti Frutti" effect.

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For more information about using textures, see the Understanding Textures: What needs painting? pages of The WADster's Guide.

 

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