1250090 - Add width and height to CanvasRenderingContext2D

Status: RESOLVED INVALID

(Core :: Canvas: 2D, defect)

Description

[Xidorn Quan [:xidorn] UTC+10]

The HTML spec includes "width" and "height" attribute for CanvasRenderingContext2D to get the dimensions of the canvas. [1]

This would be useful because otherwise there is no efficient way to get the geometry inside the rAF loop. Some apps use clientWidth and clientHeight to get the width and height (e.g. MDN's pointerlock demo [2]), which hurts the performance because of triggering flush.

[1] https://html.spec.whatwg.org/multipage/scripting.html#2dcontext
[2] https://github.com/mdn/pointer-lock-demo/blob/3f6cfe118e5e2b205314680c69dd94f34978b8ed/app.js#L41

Comment 1

[Milan Sreckovic [:milan] (needinfo for best results)]

This is different from the width and height that we have today?  https://dxr.mozilla.org/mozilla-central/source/dom/canvas/CanvasRenderingContext2D.h#428

Comment 2

[Xidorn Quan [:xidorn] UTC+10]

Probably the same. We may just need to expose it in the WebIDL file.

Comment 3

[Vincent Liu[:vliu]]

(In reply to Xidorn Quan [:xidorn] (UTC+8) from comment #2)
> Probably the same. We may just need to expose it in the WebIDL file.

I can take this bug for the following things based on requirement.

Comment 4

[Vincent Liu[:vliu]]

I will assign this bug to Farmer because he is interested in looking into it

Comment 5

[Farmer Tseng[:fatseng](inactive)]

I can't find width and height attributes in CanvasRenderingContext2D spec. [1]
But found they are in htmlcanvaselement. [2]
Do ctx.canvas.width and ctx.canvas.height also hurt performance?


[1] https://html.spec.whatwg.org/multipage/scripting.html#2dcontext
[2] https://html.spec.whatwg.org/multipage/scripting.html#htmlcanvaselement

Comment 6

[Xidorn Quan [:xidorn] UTC+10]

It seems it is removed a while ago: https://github.com/whatwg/html/pull/1074

And yes, canvas.width / canvas.height should be the right way to go, which I wasn't aware of.