openslide/openslide — pull request #87 by bgilbert (2012-02-17 17:37:17+00:00)
Title: MIRAX: Avoid subtiling if there are no overlaps or position map

Slides exported from the Pannoramic viewer have no overlaps or position map, but we are still needlessly processing subtiles for the higher layers. Worse, we assume `CameraImageDivisionsPerSide` == 1 for these slides, so we are processing 16x as many subtiles as we would on the original slide.

For such slides, do not impose a lower bound on the number of tiles per layer, and do not subtile. When checking for active camera positions, we now need to accept a tile when any of its constituent positions are active.

On my system, this patch reduces the time to read layer 8 on an exported version of `CMU-1` from 250 ms to 10 ms.