W3C home > Mailing lists > Public > public-houdini@w3.org > February 2015

Re: Font Metrics concerns

From: Alan Stearns <stearns@adobe.com>
Date: Sun, 8 Feb 2015 03:57:45 +0000
To: Chris Lilley <chris@w3.org>, Tab Atkins Jr. <jackalmage@gmail.com>
CC: "public-houdini@w3.org" <public-houdini@w3.org>, John Daggett <jdaggett@mozilla.com>, Bram Stein <stein@adobe.com>
Message-ID: <D0FD293B.23B6A%stearns@adobe.com>
On 2/8/15, 2:52 PM, "Chris Lilley" <chris@w3.org> wrote:

>Hello Tab,
>Sunday, February 8, 2015, 3:55:38 AM, you wrote:
>> On Sun, Feb 8, 2015 at 1:45 PM, Alan Stearns <stearns@adobe.com> wrote:
>>> The TextMetrics interface has attributes for some of these metrics in
>>> pixel units. This makes sense for the canvas measurements being made by
>>> that interface, but I’m thinking the font interface we’re designing
>>> be expressed in more abstract units. One possibility is to add a
>>> unitsPerEm attribute and express all the other metrics in those
>>> font-specific units. That’s probably the most natural thing to do for
>>> typographers. But I think it could also work to rationalize on a single
>>> unitsPerEm value or use an em percentage.
>> An em percentage is fine with me.  No need to indirect through some
>> variable amount of units.
>I think that people with a type background are going to want to use
>the units for their preferred font format (so 1000 or 2048, in
>practice) and will resent having to mentally convert to em percentage
>when they normally think in other units.
>So values in units, together with units-per-em (like the descriptor),
>is a better method for the intended audience. This can also be
>expressed as a percentage, for people who are comfortable with that.

I think this depends on how the values will be used. If every use ends up

metric/unitsPerEm * actualEmInPixels

Then giving the metrics in em percentage makes using the interface easier.



Received on Sunday, 8 February 2015 03:58:16 UTC

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