Bug 42660 – mousedown in canvas should not trigger selection in document

• Component: WebCore Misc.
• Status: NEW

[Tony Gentilcore]

1. Open http://alteredqualia.com/canvasmol/
2. Click down on the rotating molecule
3. With the mouse button depressed, drag outside of the molecule to another point on the page

Notice that text in the page becomes selected.

There are a lot of cool HTML5 canvas demos that show off capabilities equivalent to flash. However, when interacting with them, I always get really annoyed by the fact that I frequently accidentally select other text/elements on the page. This doesn't seem to happen for plugins.

Rather than swallowing the events like plugins do, I think a reasonable heuristic would be to simply disallow selection if the selection begins inside of a canvas. But the mouseup/mousemove events would still go to the rest of the page in every other way. Thoughts?

[Erik Arvidsson]

This is easy. All we need to do is to make canStartSelection return false for HTMLCanvasElement.

The question is if we want to do this?

[Ojan Vafai]

My first reaction was that the current behavior is correct and that web developers can cancel mousedown if they don't want to perform a selection. But all the elements I can think of the are atomic (img, input type=radio, button, etc) the way canvas is don't allow starting selections. So, I think it makes sense to make canvas the same. FWIW, not selectioning also matches Firefox.

[Evan Jones]

Created attachment 101819 [details]
test case: click and drag or double click the canvas; compare to img

Double clicks cause the same "unexpected" behaviour: It causes the text following the <canvas> to be selected, whereas an <img> element does not do the same (attaching a stupid test case for this).