do-unseen.red

Red [
	title:    "DO-UNSEEN mezzanine"
	purpose:  "Disable View redraws from triggering during given code evaluation"
	author:   @hiiamboris
	license:  BSD-3
	provides: do-unseen
	depends:  trap
	notes: {
		I'm using this in a *lot* of places, so it finally deserves a mezz status.

		Purpose is optimization. E.g. you wanna update 100 faces at once.
		Would you render the layout 100 times, or only once? DO-UNSEEN ensures the latter.
		After updating everything, call SHOW on the parent face that contains all updated faces and you're good.

		You cannot use non-local control flow within it, e.g. break from an outer loop
		(otherwise it would leave `auto-sync?` in a changed state)
	}
]

; #include %catchers.red

if object? :system/view [								;-- CLI programs skip this
	do-unseen: function [
		"Evaluate CODE with view/auto-sync?: off"
		code [block!]
	][
		old: get sync: 'system/view/auto-sync?
		set sync off
		also trap/catch code [error: thrown] (
			set sync old
			if error [do error]							;-- rethrow the error AFTER restoring auto-sync
		)
	]
]