Disable automatically panning to elements that aren't entirely visible?

[CannibalKush]

Is your feature request related to a problem? Please describe.
I'm using some voodoo to pin the JS-draw canvas' viewport to the exact same place as the DOM's scroll.
This may or may not be a good idea, but the issue I'm experiencing is that, if I draw something on the edge of the viewport, then select it, my viewport pans so that that element is in the middle (breaking this pinning I'm trying to do).

Describe the solution you'd like
I'd like some way to disable this auto-pan behaviour.

Describe alternatives you've considered
I've looked through a bunch of the methods provided by the Editor and Viewport code, but I couldn't find anything that would disable this behavior.

I would be happy to learn that this is something that already exists!

[personalizedrefrigerator]

Here are some options:

1. Undo the last change to the viewport when it becomes invalid

I would suggest using editor.notifier for this, in a way similar to how js-draw internally enforces zoom limits:

js-draw/packages/js-draw/src/Editor.ts

Lines 443 to 470 in e11574b

	this.notifier.on(EditorEventType.ViewportChanged, (evt) => {
	if (evt.kind !== EditorEventType.ViewportChanged) return;
	const getZoom = (mat: Mat33) => mat.transformVec3(Vec2.unitX).length();
	const zoom = getZoom(evt.newTransform);
	if (zoom > this.settings.maxZoom || zoom < this.settings.minZoom) {
	const oldZoom = getZoom(evt.oldTransform);
	let resetTransform = Mat33.identity;
	if (oldZoom <= this.settings.maxZoom && oldZoom >= this.settings.minZoom) {
	resetTransform = evt.oldTransform;
	} else {
	// If 1x zoom isn't acceptable, try a zoom between the minimum and maximum.
	resetTransform = Mat33.scaling2D((this.settings.minZoom + this.settings.maxZoom) / 2);
	}
	this.viewport.resetTransform(resetTransform);
	} else if (!isFinite(zoom)) {
	// Recover from possible division-by-zero
	console.warn(
	`Non-finite zoom (${zoom}) detected. Resetting the viewport. This was likely caused by division by zero.`,
	);
	if (isFinite(getZoom(evt.oldTransform))) {
	this.viewport.resetTransform(evt.oldTransform);
	} else {
	this.viewport.resetTransform();
	}

Note that the logic above resets the zoom level to event.oldTransform in some cases where event.newTransform has an invalid zoom level. It may be possible to do something similar here.

Related documentation:

• Editor.viewport
• Editor.notifier

2. Make the DOM match js-draw's scroll

This solution would also use editor.notifier and would probably work like this:

• Add a listener for EditorEventType.ViewportChanged.
• If a valid viewport position,
  • Set document.body.style.transform to editor.viewport.canvasToScreenTransform.toCSSMatrix().
• Else,
  • Reset the transform to event.oldTransform (as in the first proposed solution)

[personalizedrefrigerator]

I've converted this to a discussion. Please let me know if the above solutions aren't sufficient.