1.200 class theme_font

A theme_font is a font whose name describes its role rather than its appearance. The font aliases, such as normal, bold and tt, are theme fonts. A theme font is derived from another font and copies its family, style, weight and points. Unlike other fonts, a theme font is not shared with the fonts that have the same properties: normal and font(sans, normal, 12) are different objects. Changing the font a theme font is derived from changes the theme font in place, so everything that uses it follows:

?- send(new(P, picture), open),
   send(P, display, text('Hello world', left, normal)).
?- get(@pce, convert, normal, font, F),
   send(F, derived_from, font(serif, italic, 20)),
   send(@display_manager, fonts_changed).

Theme fonts are created from the class variables font.system_fonts and font.user_fonts when the first font is used. Changing these class variables and sending display_manager->fonts_changed updates the theme fonts. Theme fonts are in the hash table @font_aliases, which maps their name to the theme font, and in the chain @theme_fonts. They are protected, so they are never garbage collected.

A theme font may be derived from another theme font. It then takes the font the other theme font is derived from at that moment: it does not follow later changes to the other theme font. Methods that create a new font from a theme font, such as font<-rescale, create an ordinary font.

The class variable editor saves a theme font by its name. Its font items have a button to select a theme font.

See also

- class font
- class theme_colour
- display_manager->fonts_changed

1.200.1 Instance variables

theme_font <- name: name

Name of the font, e.g., normal. This is the key in @font_aliases.

theme_font <- derived_from: font

The font this font copies its family, style, weight and points from. This is never a theme font.

theme_font <-> summary: string*

Description of the role of this font.

1.200.2 Send methods

theme_font ->initialise: name=name, derived_from=font, summary=[string]*

Create a theme font with the given name, derived from the given font. The font is added to @font_aliases and @theme_fonts. If a theme font with this name exists, theme_font<-lookup returns it after setting theme_font->derived_from.

theme_font ->derived_from: font

Change the font this font is derived from. If it differs, the theme font copies its family, style, weight and points and drops its window system font and metrics, so they are computed again on the next use. This does not update the windows: use display_manager->fonts_changed after changing theme fonts.

theme_font ->unlink:

Remove the font from @theme_fonts and @font_aliases.

1.200.3 Get methods

theme_font <-lookup: name=name, derived_from=font, summary=[string]* -> theme_font

If a theme font with this name exists, update it using theme_font->derived_from and return it. This makes creating a theme font again a way to change it.