Update Fl::keyboard_screen_scaling()

- make the internal variable static
- make it callable after fl_open_display()
- document that it's currently only usable to switch scaling off

FL/Fl.H

@@ -3,17 +3,17 @@
 //
 // Main header file for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2018 by Bill Spitzak and others.
+// Copyright 1998-2020 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
 // file is missing or damaged, see the license at:
 //
-//     http://www.fltk.org/COPYING.php
+//     https://www.fltk.org/COPYING.php
 //
 // Please report all bugs and problems on the following page:
 //
-//     http://www.fltk.org/str.php
+//     https://www.fltk.org/str.php
 //
 
 /** \file
@@ -1037,7 +1037,7 @@ int main() {
   static float screen_scale(int n); // via screen driver
   static void screen_scale(int n, float factor); // via screen driver
   static int screen_scaling_supported();
-  static void keyboard_screen_scaling(int);
+  static void keyboard_screen_scaling(int value);
 
 /**   @} */
 

src/Fl.cxx

@@ -3,17 +3,17 @@
 //
 // Main event handling code for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 1998-2018 by Bill Spitzak and others.
+// Copyright 1998-2020 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
 // file is missing or damaged, see the license at:
 //
-//     http://www.fltk.org/COPYING.php
+//     https://www.fltk.org/COPYING.php
 //
 // Please report all bugs and problems on the following page:
 //
-//     http://www.fltk.org/str.php
+//     https://www.fltk.org/str.php
 //
 
 /** \file
@@ -2155,11 +2155,20 @@ int Fl::screen_scaling_supported() {
 }
 
 /** Controls the possibility to scale all windows by ctrl/+/-/0/ or cmd/+/-/0/.
- This function must be called before fl_open_display() runs to be effective.
- \param value 0 to stop recognition of ctrl/+/-/0/ (or cmd/+/-/0/ under macOS) keys as window scaling.
- */
+
+  This function \b should be called before fl_open_display() runs.
+  If it is not called, the default is to handle these keys for
+  window scaling.
+
+  \note This function can currently only be used to switch the internal
+    handler \b off, i.e. \p value must be 0 (zero) - all other values
+    result in undefined behavior and are reserved for future extension.
+
+  \param value 0 to stop recognition of ctrl/+/-/0/ (or cmd/+/-/0/ under macOS)
+    keys as window scaling.
+*/
 void Fl::keyboard_screen_scaling(int value) {
-  Fl::screen_driver()->keyboard_screen_scaling = value;
+  Fl_Screen_Driver::keyboard_screen_scaling = value;
 }
 
 // Pointers you can use to change FLTK to another language.

src/Fl_Screen_Driver.H

@@ -3,17 +3,17 @@
 //
 // All screen related calls in a driver style class.
 //
-// Copyright 1998-2018 by Bill Spitzak and others.
+// Copyright 1998-2020 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
 // file is missing or damaged, see the license at:
 //
-//     http://www.fltk.org/COPYING.php
+//     https://www.fltk.org/COPYING.php
 //
 // Please report all bugs and problems on the following page:
 //
-//     http://www.fltk.org/str.php
+//     https://www.fltk.org/str.php
 //
 
 /**
@@ -63,10 +63,10 @@ protected:
 
   int num_screens;
   static  float fl_intersection(int x1, int y1, int w1, int h1,
-                                      int x2, int y2, int w2, int h2);
+				int x2, int y2, int w2, int h2);
 
 public:
-  bool keyboard_screen_scaling; // true means ctrl/+/-/0/ resize windows
+  static int keyboard_screen_scaling; // true means ctrl/+/-/0/ resize windows
   static char bg_set;
   static char bg2_set;
   static char fg_set;

src/Fl_Screen_Driver.cxx

@@ -37,9 +37,10 @@ char Fl_Screen_Driver::bg_set = 0;
 char Fl_Screen_Driver::bg2_set = 0;
 char Fl_Screen_Driver::fg_set = 0;
 
+int Fl_Screen_Driver::keyboard_screen_scaling = 1;
 
 Fl_Screen_Driver::Fl_Screen_Driver() :
-num_screens(-1), text_editor_extra_key_bindings(NULL), keyboard_screen_scaling(true)
+num_screens(-1), text_editor_extra_key_bindings(NULL)
 {
 }
 
@@ -397,6 +398,7 @@ void Fl_Screen_Driver::transient_scale_display(float f, int nscreen)
 // respond to Ctrl-'+' and Ctrl-'-' and Ctrl-'0' (Ctrl-'=' is same as Ctrl-'+') by rescaling all windows
 int Fl_Screen_Driver::scale_handler(int event)
 {
+  if (!keyboard_screen_scaling) return 0;
   if ( event != FL_SHORTCUT || (!Fl::event_command()) ) return 0;
   int key = Fl::event_key() & ~(FL_SHIFT+FL_COMMAND);
   if (key == '=' || key == '-' || key == '+' || key == '0' || key == 0xE0/* for '0' on Fr keyboard */) {
@@ -471,7 +473,8 @@ void Fl_Screen_Driver::open_display()
     been_here = true;
     if (rescalable()) {
       use_startup_scale_factor();
-      if (keyboard_screen_scaling) Fl::add_handler(Fl_Screen_Driver::scale_handler);
+      if (keyboard_screen_scaling)
+	Fl::add_handler(Fl_Screen_Driver::scale_handler);
       int mx, my;
       int ns = Fl::screen_driver()->get_mouse(mx, my);
       Fl_Graphics_Driver::default_driver().scale(scale(ns));