Added click-to-focus to GTK+ Areas and documented that click-to-focus happens; also TODOs related to that.

area.go

@@ -80,6 +80,7 @@ type MouseEvent struct {
 
 	// If the event was generated by a mouse button being pressed, Down contains the ID of that button.
 	// Otherwise, Down contains 0.
+	// If Down contains nonzero, the Area will also receive keyboard focus.
 	Down		uint
 
 	// If the event was generated by a mouse button being released, Up contains the ID of that button.

area_unix.go

@@ -141,6 +141,8 @@ func finishMouseEvent(widget *C.GtkWidget, data C.gpointer, me MouseEvent, mb ui
 
 //export our_area_button_press_event_callback
 func our_area_button_press_event_callback(widget *C.GtkWidget, event *C.GdkEvent, data C.gpointer) C.gboolean {
+	// clicking doesn't automatically transfer keyboard focus; we must do so manually (thanks tristan in irc.gimp.net/#gtk+)
+	C.gtk_widget_grab_focus(widget)
 	e := (*C.GdkEventButton)(unsafe.Pointer(event))
 	me := MouseEvent{
 		// GDK button ID == our button ID

area_windows.go

@@ -622,7 +622,7 @@ func areaWndProc(s *sysData) func(hwnd _HWND, uMsg uint32, wParam _WPARAM, lPara
 			}
 			return defwndproc()
 		case _WM_MOUSEACTIVATE:
-			// register our window for keyboard input
+			// transfer keyboard focus to our Area on an activating click
 			// (see http://www.catch22.net/tuts/custom-controls)
 			r1, _, err := _setFocus.Call(uintptr(s.hwnd))
 			if r1 == 0 {		// failure

todo.md

@@ -38,7 +38,8 @@ super ultra important things:
 - resizing seems to be completely and totally broken in the Wayland backend
 	- TODO find out if this is a problem on the GTK+/Wayland side (no initial window-configure event?)
 - redrawing controls after a window resize on Windows does not work properly
-- clicking on Areas in GTK+ don't bring keyboard focus to them?
+- test click to keyboard focus for Areas on Mac OS X
+- make sure Areas get keyboard focus when clicking outside the actual Area space on all platforms
 - make sure keyboard events on numpad off on all platforms don't switch between controls
 - on Windows, Shift+(num pad key) triggers the shifted key code when num lock is off; will need to reorder key code tests on all platforms to fix this
 - pressing global keycodes (including kwin's zoom in/out) when running the keyboard test in wine causes the Area to lose keyboard focus; this doesn't happen on the GTK+ version (fix the Windows version to behave like the GTK+ version)