Use FC_SIZE (point size) instead of FC_PIXEL_SIZE for cairo/Xft font rendering

[sporteka2]

Mlterm uses FC_PIXEL_SIZE for fontconfig font size in cairo and Xft type engines. This means the fontsize config value is interpreted as absolute pixels, ignoring the system DPI setting (Xft.dpi).

Other terminal emulators (gnome-terminal, wezterm, alacritty) use FC_SIZE (point size), which makes fonts scale correctly with the display DPI. This causes mlterm's font to appear at a different physical size than other terminals when Xft.dpi is set to a non-default value.

For example, on a system with Xft.dpi: 307:

• gnome-terminal with "DejaVu Sans Mono 10" (10pt) renders at ~43px: 10 * 307 / 72
• mlterm with fontsize=10 renders at 10px (tiny)
• mlterm with fontsize=43 renders at 43px but column widths may be wrong

The fix is to change fc_size_type from FC_PIXEL_SIZE to FC_SIZE in uitoolkit/libtype/ui_font_ft.c. See the get_fc_col_width() function which already handles both modes correctly with DPI-based calculations for FC_SIZE.

Proposed change:

-static const char *fc_size_type = FC_PIXEL_SIZE;
+static const char *fc_size_type = FC_SIZE;

[arakiken]

Thanks.
--point option enables FC_SIZE even now, but are you suggesting changing the default value of the --point option from false to true?
Let me give that some thought.

[sporteka2]

Yes, changing the default of --point to true would be the right approach. Without it, fontsize is interpreted as pixels (FC_PIXEL_SIZE), so on high-DPI displays (e.g. Xft.dpi=307), the user must manually calculate the correct pixel value to match the point size used by other terminals.

I tested this on a system with Xft.dpi=307 (physical DPI 96). With --point=true and fontsize=10, fontconfig uses its default DPI (75) instead of Xft.dpi, resulting in 10×75/72≈10px rendering. GNOME Terminal reads Xft.dpi and passes it to fontconfig, so the same "DejaVu Sans Mono 10" renders at 10×307/72≈43px.

It would also help if mlterm could read Xft.dpi and pass it via FC_DPI to fontconfig when --point is enabled, so that the point-to-pixel conversion uses the correct system DPI rather than fontconfig's hardcoded default of 75.

[sporteka2]

The main issue is not about changing the default of --point. The problem is that mlterm doesn't respect system font settings automatically.

Other terminals (gnome-terminal, wezterm, kitty) read Xft.dpi and use it for point-to-pixel conversion. They also respect the system monospace font configured in the desktop environment (e.g. org.cinnamon.desktop.interface monospace-font-name). When a user sets their font in system settings, all terminals pick it up automatically.

mlterm currently requires manual configuration in ~/.mlterm/main and ~/.mlterm/font to match what other terminals do out of the box. On a system with Xft.dpi=307, mlterm with --point and fontsize=10 renders at ~10px because fontconfig uses its default DPI (75) instead of Xft.dpi.

The request is: make mlterm read Xft.dpi from X resources and pass it to fontconfig via FC_DPI when --point is enabled, so that the font size matches other terminals without any manual DPI or fontsize tweaking.

[arakiken]

Thanks.
I fixed it. -> 04fc42b
Note that the --point option remains false by default.