Collecting rendering statistics in Libvob

There are several reasons to want rendering statistics: to adjust complexity parameters at run-time, or (currently most importantly) to load high-resolution mipmap levels of the currently most prominent textures.

The requirements for the latter application are more stringent; specifically, the statistics have to be pushed from the activated collectors on the C++ side to the Java side to avoid having to explicitly poll each collector.


When statistics get collected, a way to 1) ignore (zero) them, and 2) call callbacks for them.

We only need one central (static) handling point for now, but implementing more in the future should be trivial..



The main difficulty in implementing the push of data is to ensure that the Java objects will be garbage corrected. Because the Java garbage collector cannot know that a global reference inside the C++ arena depends only on a given Java object (i.e. when the Java proxy of a C++ renderable is deleted, the C++ renderable gets deleted).

Thus, there must be a weak reference in the chain from the C++ object to the callback. It's probably easiest to do this on the java side.

Collection point

In order to make the pushing of triggered statistics possible after the rendering has finished, there needs to be a C++ queue containing pointers to all activated statistics.

When statistics are inserted into a statistics-collecting object, the object should check if it has been inserted to the activated statistics queue. If not, it should insert itself.

Implementation details

On the C++ side, the implementation is according to the following UML diagram:

Vob.Stats.Collector Vob.Stats.Collector renderstatistics_cxx

On the Java side, the class GL.TexAccum is the center: creating it with an object implementing the GL.StatsCallback interface allows pushing, using weak references.