TRANMAP

A TRANMAP is a WAD lump originating from the Boom source port for supporting translucency on objects, supplementing the partial invisibility effect used in Doom and Doom II. It is a precalculated lookup table similar to COLORMAP, but maps each color against each other color, rather than against specific luminosity levels. It is 65536 bytes (256×256) and determines what each translucent foreground color changes to when shown in front of another color. Each color is multiplied by the user's translucency percentage and then blended with all other colors in the palette in turn. The result of each computation is matched to the closest color in the palette and is stored in a way that allows a simple array index to be computed from the foreground and background colors while drawing graphics.

It is comparable to the TINTTAB lump used in Heretic and Hexen.

Customization
TRANMAPs are created by using a base map. This reference TRANMAP is opened in a image editor of the user's choice (any editor that supports layers will do) to create a new layer with the same color bars from the base TRANMAP in it. Either copy and paste, or duplicate the layer. Then, you rotate it 90 degrees counter-clockwise and set its opacity to the amount of translucency that is needed. Changing the brightness or coloring of the horizontal bars will affect what's behind the midtexture, and changing the vertical bars in the transparent layer will affect the transparent midtexture itself.

The resultant new TRANMAP needs to be imported into a WAD with whatever lump name that is desired, and either use the Save As Doom Flat menu item in XWE, or use SLADE3 to convert it into the correct format. To use it in a map, tag all the lines you want to make translucent, but do not set special 260 (translucent line) on them. Put a line in a dummy sector somewhere that has special 260 and that sector tag, with the TRANMAP lump's name as its middle texture.

TRANMAPs can also be created using, a tool from the Boom Editing Utilities suite to turn a file made by Boom into a  file that can be included as a custom translucency lump. Because of this, new effects can be achieved with a tweaked TRANMAP, such as:
 * Additive blending
 * Grayscaling effects
 * Color inversion
 * Hue-shifting

Limitations
TRANMAP based effects carry impressive results, but are limited to 8 bit software rendering. based ports cannot render these effects accurately, and can only deliver a approximation of the end results.

Supported ports

 * Boom
 * Doom Retro
 * Eternity Engine
 * LsdlDoom
 * MBF
 * PrBoom
 * PrBoom+
 * SMMU
 * WinMBF
 * Woof
 * ZDoom
 * Partially supports the TRANMAP lump, but does not support custom effects