To convert models to Panda from GMax, you must first convert models to .X format, and then load them into Panda as .X files, or convert them further using x2egg and/or egg2bam.
There is a fair amount of work involved in setting up the GMax-to-X converter, but once it is set up the conversion process is reportedly very easy.
There are several plug-ins required to export .X files from gmax:
1. First download the ‘Gmax gamepack SDK’ found at this link: FlightSimulator exporter plugin. Size is about 15Mb. Although only 3 files are actually needed, they are not available as separate downloads, so unfortunately you’ll need to download the whole thing.
2. Next, download programs 'MDLCommander' and 'Middleman'.
3. After download, you’ll see that the 'fs2004_sdk-gmax-setup' is an exe. If you install it in the default gmax directory, you’ll end up with a lot of extra stuff that you don’t need. So create a new folder somewhere on your hard drive and install it there.
4. When done, open the folder, go to gamepacks > fs2004 > plugins. And copy all 3 files: 'FSModelExp.dle', 'makemdl.exe' and 'makemdl.parts.xml' to your main ../gmax/plugins folder.
5. You need to rename two of the files. Right click on 'makemdl.exe' and rename it to to 'mkmdl.exe'. Then right click on 'makemdl.parts.xml' and rename it to 'mkmdl.parts.xml' (without the quotes).
6. Next, unzip 'MDLCommander.zip'. Then copy 'mdlcommander.exe' to your main ../gmax/plugins folder. This file also needs to be renamed. Right click on 'mdlcommander.exe' and rename it to 'makem.exe'.
7. Finally, unzip 'Middleman13beta3.zip'. Then copy 'makemdl.exe' to your main ../gmax/plugins folder. That’s it, you’re done!
To convert your gmax model to .X format: Go to ‘File > Export’ and select ‘Flightsim Aircraft Object (.MDL) from the file type dropdown. Type in a filename and click Save. The Middleman dialog window should now appear. Click the ‘Options’ tab and check ‘SaveXFile’ (this saves the x file) and ‘nocompile’ (this tells mdlcommander to only create an .X file not mdl/bgl). Then click the GO button.
After a few seconds the dialog will close and your newly exported .X model should be in the directory where you saved it to.
Bugs in the Process
The GMax converter writes slightly nonstandard .X files; it writes the name "TextureFileName" instead of "TextureFilename" for each texture reference. It may also generate hyphens in identifiers. Both of these can confuse the X file parser in Panda3D version 1.0.4 and earlier (this will be fixed in a future release of Panda). In the meantime, the temporary workaround is to edit the .X file by hand to rename these strings to the correct case and remove hyphens.