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Re: [pointerevents] Add OS image dragging to non-normative reasons for pointercancel

From: Brenton Simpson via GitHub <sysbot+gh@w3.org>
Date: Thu, 11 May 2017 23:10:20 +0000
To: public-pointer-events@w3.org
Message-ID: <issue_comment.created-300940957-1494544219-sysbot+gh@w3.org>
Hmmm…  I was afraid `downEvent.preventDefault()` would suppress `pointermove`, but it doesn't seem to.

Still, when `pointerdown` fires, I don't know enough about the user intent yet to know if I should cancel.  By the time I do, [it's too late](https://codepen.io/appsforartists/pen/zwWMKe0).  Calling `downEvent.preventDefault()` after I have measured that the cursor has moved far enough to know I should be dragging doesn't stop `click` or `scroll` from firing.

What if there is a clickable element, like a `<button>`, in the draggable container?  I would want the user to be able to click on it if they don't move their cursor but to drag the container if they do.  Similarly, imagine a carousel that pans left/right.  If the user drags left/right, my JS event listener ought to drag the carousel to show the next image.  If the user drags up/down, the page ought to scroll (the browser default).  In `pointerdown`, I don't have enough information to know if I should prevent the default behavior.

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Received on Thursday, 11 May 2017 23:10:28 UTC

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