STR #3321

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STR #3321

Application:FLTK Library
Status:2 - Closed w/o Resolution
Priority:3 - Moderate, e.g. unable to compile the software
Scope:2 - Specific to an operating system
Subsystem:X11
Summary:[X11/Xft] Overlapping lines (font rendering problems)
Version:1.3.3
Created By:michaelbaeuerle
Assigned To:AlbrechtS
Fix Version:Unassigned
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Trouble Report Files:

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Trouble Report Comments:


Name/Time/Date Text top right image
 
#1 michaelbaeuerle
08:16 Jul 25, 2016
On some systems in the Fl_Text_Editor widget it seems that the lines
overlap by one pixel. If the text contains '_' (underscore) characters
they are not visible with the default font size.

Setting the font size much larger from the application works as
workaround (and proves that the invisible characters are really there).

The reason for this behaviour seems to be the font hinting of Xft.
Setting the X ressources as follows solves the problem:
|
| Xft.antialias: true
| Xft.hinting: true
| Xft.autohint: false
| Xft.hintstyle: hintfull

This X ressources should make the problem visible on systems that work
correctly by default:
|
| Xft.antialias: true
| Xft.hinting: true
| Xft.autohint: false
| Xft.hintstyle: hintslight
                 ^^^^^^^^^^
I found this notice that GNOME modifies this setup:
<https://wiki.archlinux.org/index.php/Font_Configuration#Hintstyle>
so whether the problem occurs should not depend on the operating
system but on the desktop environment used.


How to reproduce:
- Operating system should not matter but must use X11
- Ressources set in the X-Server as listed above
- FLTK compiled to use X11 and Xft
- Test program for Fl_Text_Editor is sufficient
- Type some text that contain '_' (underscore) characters
 
 
#2 AlbrechtS
04:34 Jun 02, 2021
I tried to reproduce this w/o success on Linux Mint 20 (based on Ubuntu 20.04 LTS) using FLTK 1.4 (Git) and either bare Xft or Pango. I could always see the underscores.

I looked around to figure out which kind of hinting applies to my system but I'm not a Linux expert and I'm mostly using the default setup. Do you know of any function/program that can show me the active font hinting type, or can you give clear advice how (in which file) to edit what you described "This X ressources should make the problem visible on systems that work correctly by default"?

FTR: I looked around in /etc/fonts and I can only find:

/etc/fonts/conf.d/10-hinting-slight.conf:8:  <description>Set hintslight to hintstyle</description>
/etc/fonts/conf.d/10-hinting-slight.conf:17:    <edit name="hintstyle" mode="append"><const>hintslight</const></edit>

which seems to indicate that on my system "hintslight" is active despite the fact that the fonts are shown correctly.

Two questions:

(1) Does this STR still apply, i.e. does it still require any actions?

(2) If yes, what could we do? Is there a way to change this setting on the fly in FLTK applications, or what are your suggestions?

Note: if these questions are not answered or if there is no sensible suggestion within a reasonable time (7-14 days) I'll have to close this STR.
 
 
#3 AlbrechtS
11:09 Jun 14, 2021
Warning: this STR will be closed on June 16 if there's no further reply...  
 
#4 michaelbaeuerle
00:57 Jun 16, 2021
I am busy at the moment.
If you can give me some more time, I will test it again.
 
 
#5 AlbrechtS
02:20 Jun 16, 2021
OK, I'll wait for your feedback...  
 
#6 AlbrechtS
03:20 Jun 16, 2021
Michael, this is unrelated to this STR but ...

Could you please take a look at our GitHub Issue #238:
"scandir_posix.c readentry should check for ENOENT"

https://github.com/fltk/fltk/issues/238

The code in question was written by you. Every comment to the issue would be appreciated. TIA.
 
 
#7 AlbrechtS
09:54 Jul 01, 2021
Michael, any progress with testing ?  
 
#8 michaelbaeuerle
08:44 Jul 02, 2021
Today I have tested FLTK 1.3.6 with many different configurations for Xft.
Some of them have displayed the text so ugly that it was nearly unreadable.
But I found no configuration that renders the underscores invisible anymore.

Likely the behaviour depends on the font in use, and my machine today has a different set of fonts installed.

I remember the problem on machines that display multiple underscores with no visiable space between the characters.
My test machine displays multiple underscores with clearly visible spaces between the characters, therefore it does not use the font that showed the problem at that time.

If nobody else have seen similar problems, I think this STR can be closed without resolution.
 
 
#9 AlbrechtS
14:14 Jul 02, 2021
Thanks. Closing ...  
bottom left image   bottom right image

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