iOS dev eliminates memory crashes when exporting 1.2-gigapixel images using mmap

A developer building Mozary, an iOS photo mosaic app, solved persistent out-of-memory crashes that occurred when exporting extremely large images on iPhone. The core problem was that a 1.2-gigapixel canvas requires roughly 4.8 GB of uncompressed RAM, far exceeding iOS memory limits that typically terminate apps well below that threshold. The fix involved backing the drawing canvas with a memory-mapped file using mmap, so pixel data pages out to disk instead of consuming RAM. A CGImage is then wrapped around the same memory mapping via CGDataProvider and streamed directly to a JPEG file, avoiding the costly makeImage() copy entirely. With this approach, RAM usage during export dropped from approximately 4.8 GB to a few dozen megabytes regardless of output size.