ISSUE-318: Hypothetical Render Model glyph copy assumes no sub-pixel positioning

HRM glyph copy assumes no sub-pixel positioning

Hypothetical Render Model glyph copy assumes no sub-pixel positioning

State:

CLOSED

Product:

TTML IMSC 1.0

Raised by:

Nigel Megitt

Opened on:

2014-05-22

Description:

IMSC 1 FPWD includes in the Hypothetical Render Model a test for how two glyphs can be considered identical for buffer copying purposes. This does not take into account sub-pixel positioning of anti-aliased text, which would result in different per-pixel buffer values for a glyph that would otherwise be considered identical using the current criteria.

For presentation devices that layout text using sub-pixel accuracy and render glyphs with anti-aliasing this test of identity will fail resulting in wrongly painted glyphs.

I propose that an extra criterion is added to the glyph identity test that the post-layout sub-pixel offset relative to the pixel grid, horizontally and vertically, is identical.

[1] https://dvcs.w3.org/hg/ttml/raw-file/ea1a92310a27/ttml-ww-profiles/ttml-ww-profiles.html#paint-text

Related Actions Items:

No related actions

Related emails:

1. {minutes} TTWG Meeting 2015-10-29 (from nigel.megitt@bbc.co.uk on 2015-10-29)
2. {minutes} TTWG Meeting 5/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-05)
3. RE: {agenda} TTWG Meeting 5/6/2014 (from mdolan@newtbt.com on 2014-06-04)
4. {agenda} TTWG Meeting 5/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-04)
5. Re: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0] (from glenn@skynav.com on 2014-05-29)
6. {agenda} TTWG Meeting 29/5/2014 (from nigel.megitt@bbc.co.uk on 2014-05-28)
7. Re: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-27)
8. Re: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0] (from glenn@skynav.com on 2014-05-24)
9. Re: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-23)
10. Re: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0] (from pal@sandflow.com on 2014-05-23)
11. Re: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-23)
12. RE: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0] (from mdolan@newtbt.com on 2014-05-23)
13. Re: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-23)
14. RE: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0] (from mdolan@newtbt.com on 2014-05-22)
15. Re: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0] (from nigel.megitt@bbc.co.uk on 2014-05-22)
16. RE: ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0] (from mdolan@newtbt.com on 2014-05-22)
17. ISSUE-318 (HRM glyph copy assumes no sub-pixel positioning): Hypothetical Render Model glyph copy assumes no sub-pixel positioning [TTML IMSC 1.0] (from sysbot+tracker@w3.org on 2014-05-22)

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