If anyone wants the latest version of this script I've attached a zip to this post. The new script will import UV mapping now, as well as exporting it. This is very useful for quick customisation of existing models.
The zip also includes a basic Blender file (named !Base_file_for_importing.blend) that is already set up with lamps for most layers, so you can import different .3dp's to different layers and immediately be able to see what you're doing. This can be handy for model levels of detail, and for importing a locomotive and its tender to the same file.
The .blend also has a basic material and texture locked in, using settings that will automatically work well for RT3 skinning.
To play around with an existing model, just import all the relevant .3dp files one at a time (batch import is not possible yet). All the imported objects will not have a material and texture assigned yet, so just after import all components will be a basic grey in colour.
There is no need to create any new materials if you are only importing one model. To get the imported model looking like it does in the game, start by setting the loco or building body to the default material (it's called Base Material in the .blend, just to give it an obvious name). Now use the A key twice to select all objects, then use Shift+Right Click to make the loco body the active object. Next, use Ctrl+L to open a pop-up menu, and left click Materials in the menu options. All objects will now be set to the Base Material.
This base material will still be grey until you call in the model's A skin. Once all objects are set to the same material, go to the texture settings and scroll down to the image section. Left click the X button next to where it says Works_grey_base.png (clicking this unlinks the default packed file and unlocks the file browser).
Now open the file browser (Open button, of course) to find and select the model's .dds or .tga A skin. The model should now be skinned correctly.
To see how each component of the model maps to the skin you need to right click on a component to select it, change the view from Object mode to Edit mode, then hit the A key to select all vertices. The mapping for that component will now be visible in the UV editor window, beneath the main 3D window.
If you are only wanting to re-skin an existing model this is all you have to worry about. You don't have to concern yourself with the export side of things. You can just edit your skin image in Photoshop or whatever, and use the update button to update the view in Blender. This will give you a much faster skinning time than having to check it all in the game every time you make a small change.
If you want to customise the mesh for a model there are a few more tricks you need to know.
The script will still only export components that have UV mapping. Any components that do not have UV mapping will cause an error if you try to export them. Before exporting, make sure any components that lack UV mapping are not selected.
This new version of the script will only export selected objects. If you have one object that is your locomotive body and you want to export that, just right click it to select it before running the export script. The created .3dp will only contain the locomotive body.
If you have the loco body split down into several components (boiler, cab, whatever) but you want them all to be included in the finished .3dp, hold down Shift and right click every component you want to include, then run the export script.
After exporting you may need to check the attachment points in the resulting .3dp's. By default they are set to zero on all three axes. This is fine for loco and tender bodies, and for buildings, but will require manual hex editing for some other components (connecting rods, etc). That's not difficult to do. If anyone needs tips on how to do it, just ask.
