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.
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.
Both bugs can happen if a widget doesn't have an associated window()
or in similar situations. These fixes returns NULL to prevent crashes.
Bugs observed in special test scenarios, not real-life programs.
It's not necessary to call wl_subsurface_place_above() because
"A new sub-surface is initially added as the top-most in the stack of its siblings and parent."
This is a partial fix of issue #525 that reproduces under Wayland the "unofficial",
X11-specific way to cancel a Dnd operation by calling Fl::pushed(0).
It turns out it's necessary to memorize 2 event serial numbers :
- serial changed at each pointer and key event;
- pointer_enter_serial changed when pointer enters a surface
because this one and not any other is needed for exact cursor changes
by wl_pointer_set_cursor() in do_set_cursor().
The d-n-d target window is now always the top-level window even if the
mouse is over a subwindow. That's what all other platforms do.
Global var fl_dnd_target_surface memorise what's the current d-n-d target
surface and follows changes from top-window to subwindows.
