This commit fixes " "drawing an fl_pie() with dimension 1x1".
But it does not change "drawing fl_line() with begin position = end position does not show"
because the same behaviour is observed with Windows and macOS.
This commit allows to switch between FL_DOUBLE / FL_SINGLE modes
in widget-containing GL3 windows.
Demo program examples/OpenGL3test is modified to show FLTK widgets
even if the platform does not support OpenGL 3.
Under non-macOS platforms, the key is to call glUseProgram(0); after having used OpenGL 3
which allows to then use OpenGL 1 and draw FLTK widgets over the OpenGL3 scene.
Under macOS, this is impossible because macOS GL3 contexts are not compatible
with GL1. The solution implemented here is to create an additional Fl_Gl_Window
placed above and sized as the GL3-based window, to give it a non opaque,
GL1-based context, and to put the FLTK widgets in that additional window.
Function fl_read_image() obliges to keep a minimal use of global variable fl_window
also under the Wayland platform, even if its type (Window) makes little sense for
the hybrid library because it has its X11 value (given by X11/X.h) which is not
meaningful for the Wayland leg of the hybrid platform.
Virtual member function Fl_Surface_Device::as_image_surface() becomes useless.
1) add Wayland code that prevent subwindows from leaking outside their parent.
This does not cover GL subwindows.
2) add macOS code that prevent GL subwindows from leaking outside their parent.
This fixes issue #494 for the macOS platform.
N.B.: Wayland GL subwindows are not prevented from leaking because no solution
that would not require any change in client applications was found. Code that
would cover Wayland GL subwindows but would require client applications to always
use the FL_ALPHA flag is included in this commit in commented out form.
The old code would allocate memory on FL_KEYDOWN and FL_KEYUP events
and never free the latter.
The fix is to allocate memory only on FL_KEYDOWN events which will
be free'd later as intended.
Also fix two unrelated whitespace errors.
The problem is that the app sometimes stops after closing a file dialog window.
It results in fact from a bug in function draw_title_bar of libdecor-gtk.c that erroneously
calls libdecor_frame_set_max_content_size(). This bug is being proposed to be fixed
by a MR to libdecor.
But moving the libdecor_frame_set_min/max_content_size() calls after the capability changes
hides the bug, and the problem with file dialog doesn't show.
