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vid-tutorial-async-event-loops.r

rebol [ file: %vid-tutorial-async-event-loops.r title: "async event loop tutorial" author: Maxim Olivier-Adlhoch purpose: {Show how to do async event handling with processing loops.} date: 2012-11-09 ] processing-active?: false slice: 0.01 ; change this to change default speed. cycle-colors: func [][ processing-active?: true ; set this to false to tell loop to break direction: 'down color: random white percent: 1 ; always start with full color forever [ switch direction [ up [ percent: percent + slice if percent >= 1 [direction: 'down] ] down [ percent: percent - slice if percent <= 0.5 [direction: 'up] ] ] clr-bx/color: color * percent show clr-bx unless processing-active? [ break none ] wait 0.01 ; adding a small delay in the wait slows down ; processing enough that it should ; bring back cpu usage to marginal values. ;------ ; the following is ESSENTIAL, otherwise, rebol remains alive, ; and loops as background task with no GUI. if empty? system/view/screen-face/pane [quit] ] ] view/new layout [ across clr-bx: box return pad 20x0 btn "start" [processing-active?: false wait 0 cycle-colors] btn "stop" [processing-active?: false] at 120x20 scroller 20x100 [ slice: 0.001 + (value * 0.05) ] ] random/seed 3 cycle-colors do-events quit
halt ;; to terminate script if DO'ne from webpage