1.202 class theme_colour

A theme_colour is a colour whose name describes its role rather than its value, for example ui_window_background or syntax_comment. It is derived from another colour, which is the name of another theme colour or a system colour (sys_*), or a colour object. The xpce user interface and the development tools refer to theme colours, either directly or by name, so they follow the selected theme when its colours change:

?- new(_, theme_colour(my_highlight, khaki1)),
   send(new(P, picture), open),
   send(P, display, new(B, box(100, 100))),
   send(B, fill, my_highlight).
?- new(_, theme_colour(my_highlight, khaki4)),
   send(@display_manager, colours_changed).

The RGB value is computed when it is needed, by following theme_colour<-derived_from through other theme colours until an ordinary colour is found. Changing what any theme colour is derived from, or reloading the system colours, resets the RGB value of all theme colours, so each is resolved again on its next use. Theme colours may therefore refer to each other in any order and a theme colour may be created before the colour it refers to. A cycle or an unknown colour name prints a warning and resolves to grey50.

Theme colours are locked and never garbage collected. They are never returned when looking up a colour from its RGB values (see colour<-lookup), because their value changes. All theme colours are in the chain @theme_colours.

xpce defines a number of theme colours itself, the ui_* colours for the basic user interface elements and the ansi_* colours of the terminal. They are created when the class is initialised. Their values in the default light theme are in the hash table @theme_colour_defaults. Themes are managed by the Prolog library library(pce_theme). See the section Themes of the XPCE User Guide.

See also

- class colour
- display_manager->colours_changed
- display_manager->system_colours_changed

1.202.1 Instance variables

theme_colour <- derived_from: name|colour

The colour this colour is derived from. This is not called value because colour<-value is the value of the HSV model. Either a colour name, which may be the name of another theme colour, or a colour object. The name #RRGGBB specifies an RGB value.

1.202.2 Send methods

theme_colour ->initialise: name=name, derived_from=name|colour, summary=[string]*

Create a theme colour with the given name, derived from the given colour. The colour is added to @colours and @theme_colours and locked. Its colour<-rgba is @default until it is resolved. If a theme colour with this name exists, theme_colour<-lookup returns it after setting theme_colour->derived_from.

theme_colour ->derived_from: name|colour

Change the colour this colour is derived from. If it differs, the RGB value of all theme colours is reset, so they are resolved again on their next use. This does not redraw anything: use display_manager ->colours_changed after changing theme colours.

theme_colour ->unlink:

Remove the colour from @theme_colours and @colours.

1.202.3 Get methods

theme_colour <-lookup: name=name, derived_from=name|colour, summary=[string]* -> theme_colour

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