Speed up converter texture packing with Cython

[heinezen]

Required skills: Cython

Difficulty: Medium

Animation frames from AoE2 graphics files are packed into a texture atlas by the openage converter. We use bin packing to find the optimal arrangement (= smallest atlas dimensions) of the frames in the atlas. Bin packing becomes computationally intensive if a lot of frames are packed (looking at you Definitive Edition), so we want to optimize the algorithm as much as possible.

The goal of this issue is to speed up the bin packing implemented here using Cython. The most important methods to cythonize are pack() and factor(), since they are responsible for the packing logic. Ideally, these functions should contain as little Python overhead as possible.

Additional optimization might be possible such as:

• [ ] Currently pack() gets passed a list of frame objects, but technically only width, height and index of a frame are needed.
• [ ] Most of the games have a fixed number of frames per animation (e.g. 50 frames for a unit animation in AoC). These could be hardcoded as lookups into factor()
• [ ] texture_merge.pyx, the function initiating the binpacking, could also use optimization for merging the individual frames into the atlas using the packer settings.

You can test your changes with the singlefile media converter.

Further Reading

• Binpack code
• Converter architecture
• Converter workflow