The problem to fix is that the arrow drawn by draw_arrow1() in src/fl_symbols.cxx
displays a faint clear line between the stem and head of the arrow with the Cairo
graphics driver.
This occurs because draw_arrow1() draws the arrow in 2 steps (a rectangle +
a triangle) and the Cairo driver is configured to use antialiasing when filling
polygons. The antialiasing produces the faint line between stem and head.
Why does draw_arrow1() draw a rectangle + a triangle rather than a
7-vertex polygon? That's because the X11 graphics driver fails with its polygon-
drawing function when the polygon is also rotated: the polygon is drawn
empty.
We want to keep using antialiasing under Cairo for polygons because
the result is better with non horizontal/vertical polygon edges.
This implementation changes function draw_arrow1() which draws
the arrow as a 7-vertex filled polygon except when the graphics driver
returns false for its virtual member function can_fill_non_convex_polygon().
In that situation, draw_arrow1() draws, as before, a rectangle + a triangle.
The new, virtual member function can_fill_non_convex_polygon() returns
true except for the X11 graphics driver. Therefore, draw_arrow1() is effectively
unchanged under the X11 driver.
For a very simple test program see STR 3222, File 2:
https://www.fltk.org/strfiles/3222/value_slider.cxx
Known issues:
- range checking of the value box size is very limited
- resizing the widget does not change the value box size
- drawing issues are possible if the value box size and the widget
size are not compatible (e.g. value box too large)
Use the new standard arrow drawing methods (whose style depends on
the active scheme) for "arrows" used in Fl_Menu and Fl_Menu_Button.
To do: maybe we need some "fine tuning" of arrow sizes in some of
the modified widgets using the new "arrow drawing" methods.
The problem was that after a drag-n-drop within a window, text selection
by shift+arrow key stopped working.
Also, improves drag-n-drop within a window by leaving insertion point
at end of dragged text.
This removes the cause of this developer's message
# FIXME: This needs to be redesigned! Forcing GTK_FOUND to 0 (NO) is a bad
# FIXME: idea because there could be unwanted side effects. AlbrechtS
"Arrows" in widgets are those GUI elements mostly represented by
triangles pointing in a particular direction as in scrollbars,
choice widgets, some menus, valuators and Fl_Counter widgets.
The code has been simplified and standardized such that all these
GUI elements are drawn identically per FLTK scheme.
Widget authors no longer need to write code to calculate arrow sizes
and draw polygons etc.
Different schemes can and do implement different drawing functions.
Todo: see comments "FIXME_ARROW" in src/Fl_Menu_Button.cxx and
src/Fl_Menu.cxx
Selecting a text range programmatically would not sync
some variables with the actual selection. This also fixes
a crash bug in macOS when dragging text that was
selected by buffer()->select() only.
