Themes
Just before the first window is shown, fltk calls the "theme"
function, which is used to initialize the styles to the user's and
programmer's preferences. This is a function pointer and it is set and
read with fltk::theme(x) and fltk::theme(). This function should set all the NamedStyle structures to the correct
values for the appearance selected by the user and operating system.
The return value is ignored but you should return true for future
compatability.
This pointer is declared as a "C" function to make it easier to
load the correct function by name from a plugin. Theme functions are
actually of the form
extern "C" bool fltk_theme(). A typedef of
fltk::Theme is provided.
By default this points at a C function called "fltk_theme" that in
turn calls the function fltk::system_theme(). You can "override" the
theme function and customize fltk's appearance in several ways:
- If fltk is dynamically linked (or statically linked on some Unix
systems, including Linux if -shared was given to the linker) a "theme
plugin" can be loaded. You can use the function fltk::load_plugin() to read such a plugin in a
portable way. The default fltk::args()
function does this.
- If fltk is statically linked (or in all cases on some Unix systems
such as Irix), your program can replace fltk_theme with it's own
definition at compile time. The one you supply will replace the one in
the fltk library.
- You can call fltk::theme(function) to set the function
directly.
Get or set the function that will be called when the theme is loaded.
(NYI) This string is maintained so that a theme plugin can look at it
and use it for any purpose it wants. fltk::args() will set this if the user gives the
"-scheme" switch. The default value is null.
Force the theme to be loaded. Calling this multiple times does nothing
(call reload_theme() if you want to make a
change to theme(). take effect). Normally fltk
calls this just before the first window is shown(). You can call this
earlier to make sure all the styles are correct, for instance if you
want to measure the size of labels, which depends on the font
selected.
If load_theme() has been called, this will
restore all the Style information back to the compiled-in default
values, and then call the theme() function again. This is useful if
theme() changes, or if external information that your theme uses changes.
If load_theme() has never been called this returns and does
nothing. This allows your code to change the themes several times
without wasting time before the first window is shown.
On Windows this is automatically called in response to a
WM_SYSCOLORCHANGE. On X the theme itself needs to set up some
event handler to call this, see the KDE theme source code for an example.
To implement "themes" the theme code needs to write a number of static
locations, primarily the default style of several classes. You
ususally only need to change a few styles to implement a theme. All
widgets inherit from the default style anything that they don't set
themselves.
The following functions are useful when writing a theme.
System-specific "theme". This is called by default by fltk, and if you
write a theme function you probably want to call it as well. On Window
it uses GetSysColor(), and it does similar things on other operating
systems to get the appearance to match the user's settings for other
software as much as possible.
Loads a shared object (DLL) in a portable way. name is a
complete filename and symbol is the name of some object in the
plugin.
If the plugin file successfully loads (or has already been loaded)
then a pointer to the given symbol is returned. If the plugin is not
found or the symbol is not in it then an appropriate error message is
printed on stderr and null is returned.
You can pass NULL as the symbol to indicate that
you just want to load the plugin. In this case a non-zero value is
returned if the plugin successfully loads, but you cannot use this
value for anything other than to test for success.
fltk::Widget::default_style
Provides all the defaults described above. This is the only style
that does not have a parent. Highlighting is disabled by default, to
turn it on you should set highlight color.
fltk::Style::find("input")
This style is used by fltk::Input, but a few other widgets directly refer
to it to draw imbedded text editing fields.
fltk::Style::find("output")
This style is used by fltk::Output, but a few other widgets directly
refer to it to draw imbedded display fields. Setting the color to
gray will simulate NeXTStep or other user interfaces where
interactivity is indicated by color.
fltk::Style::find("CheckButton")
Styles usually need to mess with the button_color and glyph function
here to get check marks correct.
fltk::Style::find("menu")
This style is used for the pop-up menu windows.
button_box is drawn around each item, and
selection_color is used to color the current one.
fltk::Style::find("item")
Menu items. If you use checkmarks in menus you will have to make
similar fixes to this as to CheckButton. Notice that the box drawn
around each item is chosen by "menu", not by this.
fltk::Style::find("Scrollbar")
Styles usually need to mess with the box, button_box, button_color,
and glyph function to get these to appear correctly.
fltk::Tooltip::default_style
The box and color of this controls the appearance of the tooltips.
This is always linked in, so you don't need find(). Tooltips also
have some other static fields to set the timeout and position, see the
fltk::Tooltip documentation.