bugThe FreeType Project - Bugs: bug #55080, Clarification of subpixel rsb/lsb...

 
 

bug #55080: Clarification of subpixel rsb/lsb deltas

Submitted by:  Sylvain <slvn>
Submitted on:  Fri 23 Nov 2018 09:05:19 PM UTC  
 
Severity:  3 - Normal Item Group:  None
Status:  None Privacy:  Public
Assigned to:  None Open/Closed:  Open
Planned Release:  None

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Thu 06 Dec 2018 09:42:00 PM UTC, comment #3: 
Alexei Podtelezhnikov <podtelez>
Project Member
Sun 25 Nov 2018 10:24:37 AM UTC, comment #2: 

Ok!

Just something I see which seem to confirm ftcommon is better:

with current ftcommon/ftstring:

- If I render "iiiiii" with hinting light + subpixel, and I just make the size decrease. The global string width always goes decreasing.

If I modify ftstring to refer to freetype.h, and I just make the size decrease.
The global string width doesn't always decrease. It decreases, then can increase, then go decreasing again.

Sylvain <slvn>
Sun 25 Nov 2018 03:44:35 AM UTC, comment #1: 

IMHO, neither is correct. The (less wrong) expression in ftcommon.c   assumes that the distance between the edge stems is not altered by hinting. I do not think that this is true.

If indeed we only consider light hinting that does not move anything in x-direction, than truly the advance rounding delta is stored in rsb_delta and it needs to be subtracted. In the light mode lsb_delta is zero by definition.

Let's wait for Werner's arguments.

Alexei Podtelezhnikov <podtelez>
Project Member
Fri 23 Nov 2018 09:05:19 PM UTC, original submission:  

In subpixel mode:

freetype.h advices to add: rsb_delta - lsb_delta
whereas ftcommon.c is doing:  lsb_delta - rsb_delta

http://git.savannah.gnu.org/cgit/freetype/freetype2.git/tree/include/freetype/freetype.h#n1839

http://git.savannah.gnu.org/cgit/freetype/freetype2-demos.git/tree/src/ftcommon.c#n1389

Sylvain <slvn>

 

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