STR #3321

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STR #3321

Application:FLTK Library
Status:5 - New
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:Unassigned
Fix Version:Unassigned
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#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
 
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