This is partially a RFC type of patch because it's somewhat related on
the interface and such topics are always controversial.
The idea of this patch is to make watch-pixels-dry process less boring,
especially when doing GPU rendering where tiles are big and takes forever
to sample, without giving any feedback to artists when the tile will be
Current visualization is using rather funny idea of drawing progress
combined with the tile corner visualization: instead of drawing cross
in the corner we draw a side from a corner, clockwise, and it length
matches tile progress. So when tile becomes closer to a fully sampled
tile rectangle gets "more" closed.
While the interface part is a subject for discussion, the underlying
statistics part report part of the change could go in IMO.
We might also find a good way to visualize tile progress when using