Document Coordinate System intepretation

• From: Pierre-Anthony Lemieux <pal@sandflow.com>
• Date: Tue, 23 May 2017 21:50:35 -0700
• To: "public-tt@w3.org" <public-tt@w3.org>
• Message-ID: <CAF_7JxAPx76X5xZnCiYtxjCyAzg5XiCLXjxqssesodvw58fk6w@mail.gmail.com>

Hi Glenn et al.,

Before I continue filing issues on PR #321, I thought I would confirm
(or not) my summary understanding of the document coordinate system as
currently proposed.

- the coordinate system is in logical pixels
- the aspect ratio of each of the logical pixels is set by the value
of Pixel Aspect Ratio (PAR) of the root container
- the origin of the coordinate system is the top left corner of the
root container
- the positive x-axis points to the right edge of the root container,
while the positive y-axis points to the bottom edge of the root
contain
- the extent of the root container in this coordinate system is set
either by (a) tts:extent if specified in "px" or (b) arbitrarily by
the document processing context such that the ratio of the width
divided by the height is equal to the computed Storage Aspect Ratio
(SAR) of the root container

Thanks,

-- Pierre

Received on Wednesday, 24 May 2017 04:51:33 UTC