itch.io

Thanks for the comment! About the images, they are indeed very big in memory, 1024x1024 pixels, so 1MB each. On disk they are compressed with lz4. That makes them less than half the size. There is a cache for loaded/decompressed images and least-recently-used ones are dropped when the memory is getting full.

The rendering is optimized by interpolating in blocks. UVs are calculated every 16x8 pixels. View ray direction to equirectangular UV using fixed-point atan2 (approximation with small cache) and acos (look-up-table).