Here’s the code. Everything prefixed with ‘RS’ is from Roassal. Alternatively, just look at where I use canvas. Keep in mind this is quick spaghetti code, and it includes the full solution for day 10 part 2.

day10p1vis: in
	| input starts canvas |
	
	canvas := RSCanvas new.
	input := CTNewArray2D
		fromArray: ((in copyWithRegex: '\n|\r' matchesReplacedWith: '') 
			collect: [ :v | v asString asInteger ] as: Array)
		width: (in lineNumber: 1) size.	
	
	input withIndexesDo: [ :x :y :val |
		canvas add: (RSLabel new size: 5; text: val; x: x * 12; y: y * 12) ].
	canvas signalUpdate.
	(canvas @ RSCanvasController) open.
	14 seconds wait.
	starts := (input contents indicesOf: 0) collect: [:v | input indexToCoord: v].
	
	d9heads := OrderedCollection new.
	^ starts sumNumbers: [ :s | | thead |
		canvas signalUpdate.
		0.08 seconds wait.
		d9heads removeAll.
		
		thead := RSBox new size: 12; position: s * 12; color: Color red translucent.
		canvas add: thead.
	
		self d9graphvis: input start: s dir: -1@0 canvas: canvas.
	]

d9graphvis: input start: start dir: dir canvas: canvas
	| next sum direc bounded bnext |
	
	bounded := [ :p | (p x between: 1 and: input width) 	and: [ p y between: 1 and: input height ] ].
	
	direc := dir.
	sum := 0.
	4 timesRepeat: [ 
		next := start + direc.
		bnext := RSBox new size: 12; position: next*12; color: Color blue translucent.
		canvas add: bnext.
		"canvas signalUpdate."
		"0.034 seconds wait."
		sum := sum + ((bounded value: next) ifTrue: [
			((input at: next) = 9 and: [(input at: start) = 8])
				ifTrue: [ bnext color: Color green translucent. 1 ]
				ifFalse: [ (input at: next) = ((input at: start) + 1)
					ifTrue: [ | t | 
						t :=  self d9graphvis: input start: next dir: direc canvas: canvas.
						t = 0 ifTrue: [ self canvasRemove: { bnext } canvas: canvas ].
						t ]
					ifFalse: [ self canvasRemove: { bnext } canvas: canvas. 0 ] 
				]
			]
		ifFalse: [ self canvasRemove: { bnext } canvas: canvas. 0 ]).
		direc := direc rightRotated.
		"canvas signalUpdate."
		"0.034 seconds wait."
	].

	^ sum.