Modify the graphics state. Only the specified values will be modified.
This method will normally be called using the named-argument conventions
of XPCE:
...,
send(Gr, graphics_state, pen := 2, colour := red),
...
It is not allowed to return from graphical->_redraw_area
with a modified state. Therefore redraw-methods that modify the state
should normally use graphical->save_graphics_state
and graphical->restore_graphics_state.
Here is a typical example, drawing a thicker line.
'_redraw_area'(MyGr, Area:area) :->
send(MyGr, save_graphics_state),
send(MyGr, graphics_state, pen := 2),
send(MyGr, draw_line, 0,0,100,100),
send(MyGr, restore_graphics_state).
NOTE: It is generally advised to paint graphical
objects that require the same graphics state together. So, if you need
to paint alternating thick and thin lines, first draw all thick lines
and then all thin lines instead of switching the state between each
line.
