Make Fl::display(const char *) active also for the Wayland platform.

src/Fl_System_Driver.H

@@ -91,8 +91,6 @@ public:
   virtual int single_arg(const char *) { return 0; }
   // implement if the system adds unwanted program argument pair(s)
   virtual int arg_and_value(const char * /*name*/, const char * /*value*/) { return 0; }
-  // implement to process the -display argument
-  virtual void display_arg(const char *) { }
   // default implementation should be enough
   virtual int XParseGeometry(const char* string, int* x, int* y, unsigned int* width, unsigned int* height);
   static void warning(const char* format, ...);

src/Fl_arg.cxx

@@ -21,6 +21,7 @@
 #include <FL/Fl_Window.H>
 #include "Fl_Window_Driver.H"
 #include "Fl_System_Driver.H"
+#include "Fl_Screen_Driver.H"
 #include <FL/Fl_Tooltip.H>
 #include <FL/filename.H>
 #include <FL/fl_draw.H>
@@ -172,7 +173,7 @@ int Fl::arg(int argc, char **argv, int &i) {
     geometry = v;
 
   } else if (fl_match(s, "display", 2)) {
-    Fl::system_driver()->display_arg(v);
+    Fl::screen_driver()->display(v);
 
   } else if (Fl::system_driver()->arg_and_value(s, v)) {
     // nothing to do

src/Fl_display.cxx

@@ -21,11 +21,10 @@
 #include "Fl_Screen_Driver.H"
 
 /**
- \brief Sets the X display to use for all windows.
+ Sets the X or Wayland display to use for all windows.
 
- Actually this just sets the environment variable $DISPLAY to the passed string,
- so this only works before you show() the first window or otherwise open the
- display.
+ This sets the environment variable $DISPLAY or $WAYLAND_DISPLAY to the passed string,
+ so this only works before you show() the first window or otherwise open the display.
 
  This does nothing on other platforms.
 */

src/drivers/Wayland/Fl_Wayland_Screen_Driver.H

@@ -148,6 +148,7 @@ public:
   virtual int get_mouse(int &x, int &y);
   virtual void open_display_platform();
   virtual void close_display();
+  virtual void display(const char *d);
   // --- compute dimensions of an Fl_Offscreen
   virtual void offscreen_size(Fl_Offscreen o, int &width, int &height);
   virtual int has_marked_text() const;

src/drivers/Wayland/Fl_Wayland_Screen_Driver.cxx

@@ -1492,6 +1492,12 @@ void Fl_Wayland_Screen_Driver::reset_spot() {
 }
 
 
+void Fl_Wayland_Screen_Driver::display(const char *d)
+{
+  if (d) ::setenv("WAYLAND_DISPLAY", d, 1);
+}
+
+
 struct wl_display *fl_wl_display() {
   if (!Fl_Wayland_Screen_Driver::wl_display || !Fl_Wayland_Screen_Driver::wl_registry) return NULL;
   return Fl_Wayland_Screen_Driver::wl_display;

src/drivers/X11/Fl_X11_System_Driver.H

@@ -28,7 +28,6 @@ public:
     key_table = NULL;
     key_table_size = 0;
   }
-  virtual void display_arg(const char *arg);
   virtual int XParseGeometry(const char*, int*, int*, unsigned int*, unsigned int*);
   // these 2 are in Fl_get_key.cxx
   virtual int event_key(int k);

src/drivers/X11/Fl_X11_System_Driver.cxx

@@ -70,10 +70,6 @@ extern "C" {
 #endif
 
 
-void Fl_X11_System_Driver::display_arg(const char *arg) {
-  Fl::display(arg);
-}
-
 int Fl_X11_System_Driver::XParseGeometry(const char* string, int* x, int* y,
                                          unsigned int* width, unsigned int* height) {
   return ::XParseGeometry(string, x, y, width, height);