proc_raster_copy

Copies one raster tile into another, cell for cell, apron included.

proc.raster runs it for its channel set's checkpoints, restores and clears, and for Raster:copy(). A checkpoint is a copy of every live channel tile taken as the state after a stack index, so an edit to an op after that index restores the copy instead of re-running the ops up to it. A clear is the same copy with a zeroed tile as the source. Raster:copy() duplicates every layer's tiles so a mutating op leaves the original untouched.

dst's length decides how many cells are copied, so the two tiles must be the same shape.

It reads src and writes dst, one thread per cell, apron included, 64 to a workgroup.