Space Dog's Retro-Map Tutorial
Explaination of Skin Mapping for Newbies
Every model has a set of coordinates, usually referred to as the "skin mapping", that maps a skin to the model's surface. Since no two models have the same skin mapping, skins for one model cannot be used on another.
Explaination of Retro-Map
Simply put, Retro-Map takes your skins made for an old skin mapping and rearranges the pixels to create a new skins for a different skin mapping. There are several reasons you'd want to do this: First of all, there's the simple fact that everyone makes mistakes. You may decide after finishing a skin that the skin waste is way to high, or that the layout of the skin is less than optimal, and when that happens, you'd rather not have to completely start a skin from scratch. Another reason is that you may want to use a photograph as your skin, and you need to rearrange it to fit a pre-existing skin mapping.
How It Works
Open a copy of the model with the old skin mapping in NST. Let's assume you want to Retro-Map the entire mesh, so click "Mapping->Select All", then click "Mapping->Export". Enter a file name (in this tutorial we'll call the file "oldmapping.nmp") and save.
Now open the model with the new skin mapping. Click "Mapping->Select All" again, then click "Mapping->Retro-Map". A pop-up file dialog will appear. Find the skin you want to retro-map and double-click. Next, a second file dialog will appear, and this time you'll want to find "oldmapping.nmp" and double-click. That's it. The retro-mapped skin should appear before your very eyes.
"Black Edge" Phenomenon
As some of you already know, NST isn't exactly perfect when it comes the edges of your skin mapping, and the Retro-Map feature is no exception. When retro-mapping, NST will drop some pixels that lie on the very edges of your skin mapping. Since skinners usually us a black background for their skins, the result is usually a series of black triangles that line the edges of your model in Quake 2 software mode, and definite black seams on your model in OpenGL mode. You will have to compensate for this problem by filling in the missing pixels.
Double Your Skin Size, Double Your Fun
Retro-Map doesn't do any blending of pixels, so if a sizable area of a skin is retro-mapped to a relatively small area in the new skin, you'll get a sort of non-mipmapped glittery effect that looks especially bad if the area had a lot of detail. One way to fix this is to double the scale of everything (doubling the skin size for both skin mappings as well as doubling the size of the skin), performing the Retro-Map at the increased scale, then shrinking the resulting skin down to the original size. It should be noted, however, that this process is labor intensive and often unnecessary.
You Ought To Be In Pictures
Say you want to Retro-Map a photograph to fit the skin mapping for your model. Create a skin mapping that matches the layout on the photograph and export it to an NMP file. (DO NOT SAVE THE MODEL!) Then load up your model with the original skin mapping and Retro-Map the photograph using the NMP file you just saved. Easy as cake!
Showing Your True Color
"Oh, no!", you cry. "I work on my skins in 24-bit color and then reduce them to the Quake 2 pallette, and NST only supports 256 colors! How do I retro-map my beautiful true color images???"
Okay, so maybe you're not thinking that. However, there are some situations you'll want to do this, especially if you're developing a model for both Q2 and Quake III Arena formats at the same time. Here's the solution: First, get a copy of Paint Shop Pro 5.01. (Note: You may be able to do the following with another graphics editor, such as Photoshop. You'll have to check the features of your software.) Load up your image, break it up into Red, Green and Blue channels, and save each channel as a 256 color PCX or BMP file. Since NST supports any 256 pallette rather than just the Q2 pallette, you can retro-map the three images one at a time, then recombine the channels in Paint Shop Pro once you're done. For best results, you may want to combine this with the scale doubling technique I mentioned earlier.