Fix Child Windows under Wayland are clipped on resizing … (#987)

FL/Fl_Window.H

@@ -625,6 +625,9 @@ public:
   static char show_next_window_iconic() {
     return show_next_window_iconic_;
   }
+  
+  void allow_expand_outside_parent();
+  
 };
 
 #endif

src/Fl_Window.cxx

@@ -977,3 +977,11 @@ void Fl_Window::is_maximized_(bool b) {
   if (b) set_flag(MAXIMIZED);
   else clear_flag(MAXIMIZED);
 }
+
+/** Allow this subwindow to expand outside the area of its parent window.
+ This is presently implemented only for the Wayland platform to help support window docking.
+ \since 1.4.0
+*/
+void Fl_Window::allow_expand_outside_parent() {
+  if (parent()) pWindowDriver->allow_expand_outside_parent();
+}

src/Fl_Window_Driver.H

@@ -207,6 +207,7 @@ public:
   static void scroll_to_selected_item(Fl_Window *);
 
   virtual fl_uintptr_t os_id() { return 0; }
+  virtual void allow_expand_outside_parent() {}
 };
 
 #endif // FL_WINDOW_DRIVER_H

src/drivers/Wayland/Fl_Wayland_Window_Driver.H

@@ -56,6 +56,7 @@ private:
     Fl_Image* shape_; ///<  shape image
     cairo_pattern_t *mask_pattern_;
   } *shape_data_;
+  bool can_expand_outside_parent_; // specially to allow window docking (#987)
   cairo_rectangle_int_t *subRect_;   // makes sure subwindow remains inside its parent window
   static bool in_flush_; // useful for progressive window drawing
   Fl_Cursor standard_cursor_; // window's standard custom kind
@@ -143,6 +144,7 @@ public:
   static bool new_popup; // to support tall menu buttons
   bool process_menu_or_tooltip(struct wld_window *);
   static Fl_Window *previous_floatingtitle; // to support floating menuwindow w/ title
+  void allow_expand_outside_parent() FL_OVERRIDE { can_expand_outside_parent_ = true; }
 };
 
 

src/drivers/Wayland/Fl_Wayland_Window_Driver.cxx

@@ -70,6 +70,7 @@ Fl_Wayland_Window_Driver::Fl_Wayland_Window_Driver(Fl_Window *win) : Fl_Window_D
   gl_start_support_ = NULL;
   subRect_ = NULL;
   is_popup_window_ = false;
+  can_expand_outside_parent_ = false;
 }
 
 
@@ -1889,7 +1890,7 @@ static bool crect_equal(cairo_rectangle_int_t *to, cairo_rectangle_int_t *with)
 
 
 void Fl_Wayland_Window_Driver::checkSubwindowFrame() {
-  if (!pWindow->parent()) return;
+  if (!pWindow->parent() || can_expand_outside_parent_) return;
   // make sure this subwindow doesn't leak out of its parent window
   Fl_Window *from = pWindow, *parent;
   cairo_rectangle_int_t full = {0, 0, pWindow->w(), pWindow->h()}; // full subwindow area