app: add GimpChunkIterator
Factor out the region-chunking logic of GimpProjection into a new GimpChunkIterator type, providing a generic mechanism for iterating over a cairo region in discrete chunks. The iterator doesn't perform any processing itself, but rather dispenses rectangular chunks, which the user then processes. Iteration is broken into intervals, the duration of which is configurable. Each iteration begins with a call to gimp_chunk_iterator_next(), after which gimp_chunk_iterator_get_rect() should be called in succession to fetch a rectangle to process, until it returns FALSE, which marks the end of the iteration. Updates to the UI should take place in the interval between iterations, but not during an iteration. The iterator dynamically adjusts the chunk size according to processing speed, in order to match the target iteration interval. The iterator can be given a priority rectangle, which is processed before the rest of the region. It can also be given a representative tile rectangle, defining a regular tile grid; dispensed chunks are aligned to the tile grid as much as possible.
Showing with 520 additions and 0 deletions