[whatwg] Canvas textBaseline 'middle' conflicting definition

Dirk Schulze dschulze at adobe.com
Mon Mar 31 14:08:26 PDT 2014

On Mar 31, 2014, at 5:06 PM, Justin Novosad <junov at google.com> wrote:

> Wow, that is confusing. How can this be fixed without breaking existing web content? Are browsers currently compliant with the canvas spec, or do they implement the CSS definition of middle?

WebKit uses the definition for Canvas. It looks like David Hyatt implemented it in WebKit for Canvas following the Canvas spec a couple of years ago. Therefore, I assume it is the same for Blink. Didn’t check Gecko.

WebKit and Blink both implement 'alignment-baseline' following the definition in SVG as well. Very unfortunate the confusion.


> On Sun, Mar 30, 2014 at 3:11 PM, Dirk Schulze <dschulze at adobe.com> wrote:
> Hi,
> Canvas let you set alignment baselines with the textBaseline attribute [1].
> One of the baseline values is ‘middle’. The description of the ‘middle’ baseline seems to be in conflict with the definition for the alignment-baseline property in CSS[2].
> Canvas: The middle of the em square
> CSS: [..] it may be computed using 1/2 the "x-height”
> What Canvas uses as middle is described as ‘center’ in CSS. Is there a way that we can change the naming and/or definition of ‘middle’ in Canvas?
> Greetings,
> Dirk
> [1] http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-textbaseline
> [2] http://www.w3.org/TR/SVG11/text.html#TextAlignmentProperties

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