[Bug 27690] New: Problematic definition of TextMetrics.emHeightDescent

https://www.w3.org/Bugs/Public/show_bug.cgi?id=27690

            Bug ID: 27690
           Summary: Problematic definition of TextMetrics.emHeightDescent
           Product: HTML WG
           Version: unspecified
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: HTML Canvas 2D Context
          Assignee: jaymunro@microsoft.com
          Reporter: motiz88@gmail.com
        QA Contact: public-html-bugzilla@w3.org
                CC: mike@w3.org, public-html-admin@w3.org,
                    public-html-wg-issue-tracking@w3.org

Quoting the current spec and adding my own comments inline:

> emHeightDescent attribute
...
> positive numbers indicating that the given baseline is below the bottom of that em square

This breaks the following convention otherwise followed by all Ascent/Descent
attribute pairs:
Ascent = positive numbers indicating a distance going up
Descent = positive numbers indicating a distance going down
(Thus Ascent+Descent = Height in a sense)

I propose that emHeightDescent be brought in line with this convention.

> (Zero if the given baseline is the top of that em square.)
This was probably meant to say "bottom".

To give some context - I am the author of
https://github.com/motiz88/canvas-text-metrics-polyfill and actively working on
bringing conforming measureText implementations to Chrome and Firefox (Chrome
Canary has it, behind a flag and with some issues).

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Received on Wednesday, 24 December 2014 09:57:23 UTC