3a898db363
Split thumbnail job in 2 passes. First pass will render visible images and second part renders set of "guaranteed" equally spaced images. When viewing larger amount of strips, it is likely that only 1 or 2 images will be rendered in first pass, while in second pass it is up to 30 images. This results (seemingly) in 3x better performance, but zooming before set of guaranteed images is done will be slightly more inaccurate.