Fonts

Tk's label widget allows you to change the font used to display text via the font configuration option. The canvas and text widgets, covered in the following chapters, also allow you to specify fonts. Other themed widgets that display text may not have a font configuration option, but their fonts can be changed using styles.

We'll cover styles in detail later. In essence, they replace the old way of tweaking multiple configuration options on individual widgets. Instead, fonts, colors, and other settings that control appearance can be bundled together in a style. That style can then be applied to multiple widgets. It's akin to the difference between hardcoding display-oriented markup inside HTML pages vs. using CSS to keep display-specific information separate.

As with many things in Tk, the default fonts are usually a good choice. If you need to make changes, this section shows you the best way to do so, using named fonts. Tk includes named fonts suitable for use in all different components of your user interface. They take into account the conventions of the specific platform you're running on. You can also specify your own fonts when you need additional flexibility.

The font command reference provides full details on specifying fonts, as well as other font-related operations.

Many older Tk programs hardcoded fonts, using either the "family size style" format we'll see below, X11 font names, or the older and more arcane X11 font specification strings. These applications looked increasingly dated as platforms evolved. Worse, fonts were often specified on a per-widget basis, leaving font decisions spread throughout the code. Named fonts, particularly the standard fonts that Tk provides, are a far better solution. Reviewing and updating font decisions is an easy and important change to make in any existing applications.

Standard Fonts

Each platform defines specific fonts that should be used for standard user interface elements. Tk encapsulates many of these decisions into a standard set of named fonts. They are available on all platforms, though the exact font used will vary. This helps abstract away platform differences. Of course, the standard widgets use these named fonts. The predefined fonts are:

TkDefaultFont : Default for items not otherwise specified.

TkTextFont : Used for entry widgets, listboxes, etc.

TkFixedFont : A standard fixed-width font.

TkMenuFont : The font used for menu items.

TkHeadingFont : Font for column headings in lists and tables.

TkCaptionFont : A font for window and dialog caption bars.

TkSmallCaptionFont: A smaller caption font for tool dialogs.

TkIconFont : A font for icon captions.

TkTooltipFont : A font for tooltips.

Platform-Specific Fonts

Tk provides additional named fonts to help you comply with less common situations on specific platforms. Individual platform guidelines detail how and where these fonts should be used. These fonts are only defined on specific platforms. You'll need to take that into account if your application is portable across platforms.

Tk on X11 recognizes any valid X11 font name (see, e.g., the xlsfonts command). However, these can vary with the operating system, installed software, and the configuration of the individual machine. There is no guarantee that a font available on your X11 system has been installed on any other X11 system.

On Windows, Tk provides named fonts for all the fonts that can be set in the "Display" Control Panel. It recognizes the following font names: system, ansi, device, systemfixed, ansifixed, and oemfixed.

On macOS, the Apple Human Interface Guidelines (HIG) specifies a number of additional fonts. Tk recognizes the following names: systemSystemFont, systemSmallSystemFont, systemApplicationFont, systemViewsFont, systemMenuItemFont, systemMenuItemCmdKeyFont, systemPushButtonFont, systemAlertHeaderFont, systemMiniSystemFont, systemDetailEmphasizedSystemFont, systemEmphasizedSystemFont, systemSmallEmphasizedSystemFont, systemLabelFont, systemMenuTitleFont, systemMenuItemMarkFont, systemWindowTitleFont, systemUtilityWindowTitleFont, systemToolbarFont, and systemDetailSystemFont.

Working with Named Fonts

Tk provides several operations that help you work with named fonts. You can start by getting a list of all the currently defined named fonts.

#![allow(unused)]
fn main() {
println!( "{:#?}", tk.font_names()? );
}

You can find out the actual system font represented by an abstract named font. This consists of the family (e.g., Times or Helvetica), the size (in points if positive, in pixels if negative), the weight (normal or bold), the slant (roman or italic), and boolean attributes for underline and overstrike. You can find out the font's metrics (how tall characters in the font can be and whether it is monospaced), and even measure how many pixels wide a piece of text rendered in the font would be.

#![allow(unused)]
fn main() {
println!( "{:#?}", tk.font_actual_get_all( Font::<()>::Name( "TkTextFont" ))? );
// e.g. -family .AppleSystemUIFont -size 13 -weight normal -slant roman -underline 0 -overstrike 0

println!( "{:#?}", tk.font_metrics_get_all( Font::<()>::Name( "TkTextFont" ))? );
// e.g. -ascent 13 -descent 3 -linespace 16 -fixed 0

println!( "{:#?}", tk.font_measure( Font::<()>::Name( "TkTextFont" ), "The quick brown fox" )? );
// e.g. 124
}
}

You can also create your own fonts, which can then be used exactly like the predefined ones. To do so, choose a name for the font and specify its font attributes as above.

#![allow(unused)]
fn main() {
tk.font_create( "AppHighlightFont", -family("Helvetica") -size(12) -weight("bold") )?;
root.add_ttk_label( "l" -text("Attention!") -font("AppHighlightFont") )?
    .grid(())?;
}
}

The family attribute specifies the font family. Tk ensures the names Courier, Times, and Helvetica are available, though they may be mapped to an appropriate monospaced, serif, or sans-serif font). Other fonts installed on your system can be used, but the usual caveats about portability apply. You can get the names of all available families with:

#![allow(unused)]
fn main() {
println!( "{:#?}", tk.font_families()? );
}

Run Example

cargo run --example fonts