Thread Subject: Re: Allen's proposal for a newsection oncontent

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From: Sean Hayes
Date: Tue, Apr 03 2007 9:10 AM

1) even if DirectDraw is used, can't the AT sample the screen at the point
the letter is drawn and determine the color?

No, That's hardly practical; DirectX redraws to the screen at 50Hz (at minimum, usually considerably more); in principle the colour can change at every refresh. Most of this happens on the graphics card, so you would need to snoop the graphics card output buffer, which even if possible would kill performance. Furthermore you specify DirectX output in terms of movement of triangle vertices in a large output space, this is then interpolated in the output pipeline; you would then need to do an inverse mapping back from the intersecting triangles to figure out which letter belonged to which triangles - it would be a performance tar pit to try and do this.

Sean Hayes
Standards and Policy Team
Corporate Accessiblity Group
Microsoft
Phone:
mob +44 7977 455002
office +44 117 9719730

From: = EMAIL ADDRESS REMOVED = [mailto: = EMAIL ADDRESS REMOVED = ] On Behalf Of David Poehlman
Sent: 03 April 2007 15:59
To: TEITAC Web/Software Subcommittee
Subject: Re: [teitac-websoftware] Allen's proposal for a newsection oncontent

One danger in this I see. If we allow direct draw, we run the risk of not being able to take advantage of future possibilities. Also, don't you know? Braille comes in colors.



On Apr 3, 2007, at 10:53 AM, Gregg Vanderheiden wrote:

Following up for clarification:


Peter Korn Wrote:
Gregg Vanderheiden writes:


On the first point, (i.e. color values of the forground text and
background) I still am not sure I understand the benefit. If the
content is rendered to the screen the AT can always get the color
values. But from discussions in our other group it was my
understanding that there are no AT that can deal with presenting the
millions of colors to people in a way that they can understand.

This is a bad assumption. Content rendered via DirectDraw or some other
mechanism allowing applications to communicate directly to video memory
frame buffers may not such that "AT can always get the color values".
Nor in a requirement about content should we assume a content render is
involved. If I am converting this document to Braille or DAISY or some
other format, all I have to go on is the format. If the information I
need for accessibility isn't clearly present in the format, I won't be
able (and shouldn't be required) to run a particular content rendering
application and observe what it does in order to figure out what is
going on.

<end of Peter Korn Clip>


1) even if DirectDraw is used, can't the AT sample the screen at the point
the letter is drawn and determine the color?

2) if converting the document to braille, then wouldn't the other provision
which states that 'all information presented in color is also presented in
another way' meet your needs?


I am just trying to avoid
a) requiring information that AT won't use or the user can't use if
presented to them (like one of 4 million color codes).
b) having two clauses that solve the same problem.


Thanks.






Gregg
-- ------------------------------
Gregg C Vanderheiden Ph.D.

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