Draft: NEED HELP: Canvas scale prerender

The goal of this MR is scale current canvas to the next zoom position making "instant" previews while finish drawing.

Currently it store files to disk for debug that slow. You need a complex draw to see better and in a big screen with small tile size and debug mode for test in badest position and take time to compare results visualy.

Working except a gap when zoom is not from canvas center, I try to fix in a try/carch but finaly get desesperarted, so I leave for other to finish.