Is there bucket rendering in Corona?
--- This article applies to pre-1.4 versions of Corona. Bucket rendering has been removed since then and replaced with proper adaptivity in progressive mode. ---
Yes. You can enable it by going to Render Setup > Performance > Performance Settings and under "Basic configuration" section changing "Render engine" from "Progressive" to "Bucket". After switching, the "Bucket Render Engine" rollout will appear providing additional settings. The bucket engine works exactly the same as progressive, but it has simple adaptivity implemented, which means that it will perform best in scenes with large, uniform areas (such as walls).
Bucket rendering settings:
"Samples per iter" - the number of AA samples per pixel used by each bucket during 1 pass - in terms of quality, it is an equivalent of passes in progressive mode (bucket: 32 samples per iter, 1 pass = progressive: 32 passes; bucket: 32 samples per iter, 2 passes = progressive: 64 passes, etc).
"Passes" - each pass is finished after the buckets sample all available pixels.
"Adaptive thresh" - this setting determines whether neighboring pixels will receive samples during the next pass, or not. Higher values = faster rendering, lower quality; lower values = slower rendering, higher quality; extreme values will make adaptivity inefficient.