Transforms and Vertices
The egg syntax defines all transforms, including joint transforms, relative to the parent node only. When the animation is played, Panda accumulates the transforms for each joint.
Although joints are defined using a local transform, vertices are defined in an egg file using global coordinates, which is irrespective of transforms appearing within the egg file. This means when Panda loads the egg file is loaded, the vertex coordinates given in the egg file must be pre-transformed by the appropriate inverse matrix to compensate.
Custom .egg Readers/Writers
When writing an importer or exporter for panda, you have two choices.
One option is to use the panda runtime library, which includes code
for reading, parsing, storing, and emitting Egg files. This approach
can save you a great deal of effort. However, it does require that you link
with the panda runtime system, which may be inconvenient if you wish
to distribute a small, standalone file translator.
If you decide to use the panda runtime system, the classes you will need to
use are defined in the
panda3d.egg module, such as
so forth. Like all panda classes, these are documented in the API reference manual.
The other alternative is to parse/generate the Egg file entirely by yourself.
In this case, you will need to read the
syntax documentation for egg files. This documentation is part of the source code on GitHub. The file format is human-readable, and fairly straightforward.
If you are writing a program to generate Egg files, either approach is equally good. However, if you are writing a program to parse Egg files, we do recommend using the panda runtime library, rather than writing your own parser, for the simple reason that it is difficult to write a parser that accepts all valid Egg files. Also, the Egg syntax might be extended from time to time, and relying on the runtime library to parse the Egg syntax will ensure that your program continues to parse future Egg files.