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STR #3392

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STR #3392

Application:FLTK Library
Status:5 - New
Priority:1 - Request for Enhancement, e.g. asking for a feature
Scope:3 - Applies to all machines and operating systems
Subsystem:Core Library
Summary:Fl::set_font() limited to italic and bold fonts
Created By:djcj
Assigned To:Unassigned
Fix Version:Unassigned
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#1 manolo
06:29 Jul 31, 2017

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#1 djcj
10:58 Jul 28, 2017
from fl_font_xft.cxx:

    switch (*name++) {
    case 'I': slant = XFT_SLANT_ITALIC; break; // italic
    case 'P': slant = XFT_SLANT_ITALIC;        // bold-italic (falls-through)
    case 'B': weight = XFT_WEIGHT_BOLD; break; // bold
    case ' ': break;                           // regular
    default: name--;                           // no prefix, restore name

Light, medium, demi-bold, oblique and black are not supported:


#2 manolo
06:34 Jul 31, 2017
Could you, please, test with the attached medium.patch
and report whether you get what you want?

With it, you should see all your black, medium, light and
demi bold fonts. Oblique fonts should be already
visible, but they are called italic by FLTK.

Notice that the patch is against FLTK branch 1.4,
because that's where new developments of FLTK are targetted.
#3 djcj
09:27 Jul 31, 2017
Is it really a good idea to hard-code it that way? Isn't it better to let the user set the slant and weight as parameters?  
#4 manolo
01:11 Aug 01, 2017
The goal of this patch is only to obtain for the X11+XFT
platform the same behaviour as with other platforms
(X11 + PANGO, MSWindows, Mac OS).

There, Fl::set_fonts() detects all fonts available on the
system, and this includes black, medium, light, demibold
fonts. Oblique fonts are most often treated as Italic.
With the patch, these fonts also are given distinct names
under XFT.

There are 2 alternative ways to use any of these fonts:
1) call Fl::set_fonts() and then fl_font(fnum, size) where
fnum is the corresponding Fl_Font;
2) assign an adequate Fl_Font to the desired font identified
by its name, for example:
   Fl::set_font(FL_FREE_FONT, "Arial Black");
   fl_font(FL_FREE_FONT, size);

Fl::set_fonts() arranges first the predefined fonts (courier,
times,...) and then all other fonts in alphabetical order.
Since font style names (medium, light, italic, black, bold,...)
mostly appear at the end of font names, it is simple to detect
group of font names that differ only by style and to treat
them as a font family.
#5 djcj
09:45 Aug 01, 2017
I'm trying:

Fl::set_font(FL_FREE_FONT, "Ubuntu Light Italic");
fl_font(FL_FREE_FONT, 14);

But I get: error: ‘fl_font’ was not declared in this scope
#6 manolo
12:45 Aug 01, 2017
To call fl_font() you have to #include <FL/fl_draw.H>

The Fl::set_font() function expects an FLTK-style font name,
which means italic font names begin by I, bold by B, bold-italic by P,
and others by space. The initial space can be ommited.

So you can do:
Fl::set_cont(FL_FREE_FONT, " Ubuntu Light"); // normal variant
Fl::set_font(FL_FREE_FONT + 1, "IUbuntu Light"); // italic variant

To wrap up: replace final "italic" by initial "I",
final "bold" by initial "B", final "bold italic" by initial "P",
and for everything else, use the font name as given by the
test/fonts program prefixed by a space.

The patch makes test/fonts list font names not seen without it,
those with light, black, medium, demi-bold styles.
#7 djcj
05:01 Aug 03, 2017
Okay, Fl::set_font(FL_FREE_FONT, " Ubuntu") will set the Ubuntu font as intended.
However sung Fl::set_font(FL_FREE_FONT, " Ubuntu Light") results in the font looking the same, but Ubuntu Light should be much thinner. Also, what's actually the reason behind using fl_font(FL_FREE_FONT, 14) ?
#8 manolo
01:40 Aug 07, 2017
Here is the purpose of these two calls:
  Fl::set_font(FL_FREE_FONT, " Ubuntu");
This assigns the 'Ubuntu' font to FLTK's font index number FL_FREE_FONT.

  fl_font(FL_FREE_FONT, 14);
This makes the font with index FL_FREE_FONT and with size 14 current.
All further text drawings will be done with that font.

You must call the fl_font() function to determine what font
will be used to draw text.
#9 manolo
09:28 Aug 07, 2017
@djcj: I suggest you run the test/fonts program
from the series of FLTK examples of source code.
Please apply the patch first, then build, and then
run test/fonts.

With this program you can visualize all fonts
detected by FLTK on your system, and select any to
draw the text located in the top window panel.

In my hands, and with Ubuntu, "Ubuntu Light"
is visibly lighter than "Ubuntu".

The fonts used by test/fonts are usable by any other
FLTK-based program, with the Fl::set_font()
and fl_font() calls explained at comments above.
CAVEAT: font names shown by the test/fonts program
and those accepted by Fl::set_font() slightly differ,
as detailed in comment #6 above. Pay also attention
to lower/uppercase letters in font names.

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