[whatwg] Supporting scrollTop and scrollLeft on the Canvas element
chuck at jumis.com
Tue Jan 31 14:35:45 PST 2012
Floating a proposal here:
I'd like to see scrollTop and scrollLeft supported for the Canvas
element. They would simply fire an onscroll event on the element, and do
Many Canvas UIs use only one visible canvas layer, or otherwise, one
main canvas layer.
It'd be quite handy to be able to use the scrollTop and scrollLeft
setters, and as an author, hook into canvas.onscroll to identify when
updates ought to be painted.
Currently, authors can create a large canvas, and place it in a div:
<div style="overflow: hidden">
<canvas>This can is larger than the div</canvas>
It would be great to be able to respond to scroll events, such as
Element.scrollIntoViewIfNeeded and/or ctx.scrollPathIntoView,
and simplify the model in the future.
<canvas onscroll="repaint(scrollLeft,scrollTop)">This canvas is the same
size as the div and responds to onscroll</canvas>
The values for scrollLeft and scrollTop would be in css pixels, as they
are for other elements, and when set, they would trigger an onscroll
event, as usual.
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