[whatwg] windowToCanvas()

Tab Atkins Jr. jackalmage at gmail.com
Wed Aug 31 14:12:00 PDT 2011

On Wed, Aug 31, 2011 at 10:52 AM, David Geary
<david.mark.geary at gmail.com> wrote:
> In a previous email titled ‘Should Paths be First Class Citizens’, I briefly
> discussed this code snippet:
> context.canvas.onmousedown = function (e) {
>   var loc = windowToCanvas(context.canvas, e);
>   polygons.forEach( function (polygon) {  // polygons is an array of
> polygon objects
>      polygon.createPath();  // my polygons have a createPath() method
>      if (context.isPointInPath(loc.x, loc.y)) {
>         alert('mouse clicked in polygon');
>      }
>   });
> }
> I implemented the windowToCanvas() myself. That methods’s not too difficult
> to implement after you know how to do it properly, but it’s not very
> straightforward to implement if you are new to web development.
> Would it make sense to add such a method to the Canvas specification?

I assume this just translates window-relative coordinates to
element-relative coordinates.  Yes, that sort of thing is useful, but
it's nothing to do with canvas specifically - it would be useful for
every element if it were easier to do that sort of thing.


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