Support for GUI scaling: add API to get/set the scaling factor value.

Also, define an FLTK event triggered when the scaling is changed and an option
to disable the transient window showing the new scaling factor.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@13011 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

7 files changed, 61 insertions, 9 deletions

diff --git a/FL/Enumerations.H b/FL/Enumerations.H
index 2a1908f8e..68b38f242 100644
--- a/FL/Enumerations.H
+++ b/FL/Enumerations.H
@@ -403,8 +403,9 @@ enum Fl_Event {	// events
       The Fl::event_dy() method can be used to find magnification amount,
       Fl::event_x() and Fl::event_y() are set as well.
      */
-  FL_ZOOM_GESTURE	= 26
-
+  FL_ZOOM_GESTURE	= 26,
+  /** A zoom event (crtl-/+/-/0/) was processed */
+  FL_ZOOM_EVENT = 27
 // DEV NOTE: Keep this list in sync with FL/names.h
 };
 
diff --git a/FL/Fl.H b/FL/Fl.H
index 6bb1f7447..1075c3831 100644
--- a/FL/Fl.H
+++ b/FL/Fl.H
@@ -252,6 +252,10 @@ public:
      /// if the GTK library is available on the platform (linux/unix only).
      /// When switched off, GTK file dialogs aren't used even if the GTK library is available.
     OPTION_FNFC_USES_GTK,
+    /// When switched on (default), the library shows in a transient yellow window the zoom factor
+    /// value.
+    /// When switched off, no such window gets displayed.
+    OPTION_SHOW_SCALING,
       // don't change this, leave it always as the last element
       /// For internal use only.
     OPTION_LAST
@@ -989,7 +993,15 @@ int main() {
 
 
 /** \defgroup  fl_screen  Screen functions
-	fl global screen functions declared in <FL/Fl.H>
+	fl global screen functions declared in <FL/Fl.H>.
+ FLTK supports high-DPI screens using a screen scaling factor.
+ The scaling factor value can be changed by typing ctrl-/+/-/0/
+ (cmd-/+/-/0/ under MacOS). FLTK sends the FL_ZOOM_EVENT when the
+ factor value is changed, to which a callback can be associated with Fl::add_handler().
+ By default, FLTK also displays the new scaling factor value in a yellow, transient window.
+ This can be changed with Fl::option(OPTION_SHOW_SCALING, 0).
+ The scaling factor value is programmatically get and set with the Fl::screen_scale() functions.
+ 
      @{ */
   static int x(); // via screen driver
   static int y(); // via screen driver
@@ -1009,6 +1021,9 @@ int main() {
   static void screen_work_area(int &X, int &Y, int &W, int &H, int n); // via screen driver
   static void screen_work_area(int &X, int &Y, int &W, int &H); // via screen driver
   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();
+
 /**   @} */
 
 
diff --git a/FL/Fl_Graphics_Driver.H b/FL/Fl_Graphics_Driver.H
index 3057d127e..d21576a6a 100644
--- a/FL/Fl_Graphics_Driver.H
+++ b/FL/Fl_Graphics_Driver.H
@@ -158,8 +158,6 @@ public:
   } driver_feature;
 
 protected:
-  /** Sets the current value of the scaling factor */
-  virtual void scale(float f) { scale_ = f; }
   int fl_clip_state_number; ///< For internal use by FLTK
   static const matrix m0; ///< For internal use by FLTK
   Fl_Font font_; ///< current font
@@ -256,6 +254,8 @@ public:
   static Fl_Graphics_Driver &default_driver();
   /** Current scale factor between FLTK and drawing units: drawing = FLTK * scale() */
   float scale() { return scale_; }
+  /** Sets the current value of the scaling factor */
+  virtual void scale(float f) { scale_ = f; }
   /** Return whether the graphics driver can do alpha blending */
   virtual char can_do_alpha_blending() { return 0; }
   // --- implementation is in src/fl_rect.cxx which includes src/drivers/xxx/Fl_xxx_Graphics_Driver_rect.cxx
diff --git a/FL/names.h b/FL/names.h
index 46525d600..7b4700fbe 100644
--- a/FL/names.h
+++ b/FL/names.h
@@ -69,7 +69,7 @@ const char * const fl_eventnames[] =
   "FL_SCREEN_CONFIGURATION_CHANGED",
   "FL_FULLSCREEN",
   "FL_ZOOM_GESTURE",
-  "FL_EVENT_27", // not yet defined, just in case it /will/ be defined ...
+  "FL_ZOOM_EVENT",
   "FL_EVENT_28", // not yet defined, just in case it /will/ be defined ...
   "FL_EVENT_29", // not yet defined, just in case it /will/ be defined ...
   "FL_EVENT_30"  // not yet defined, just in case it /will/ be defined ...
diff --git a/src/Fl.cxx b/src/Fl.cxx
index 3a682c039..8d99d679e 100644
--- a/src/Fl.cxx
+++ b/src/Fl.cxx
@@ -16,6 +16,10 @@
 //     http://www.fltk.org/str.php
 //
 
+/** \file
+ Implementation of the member functions of class Fl.
+ */
+
 #include "config_lib.h"
 
 #include <FL/Fl.H>
@@ -1860,8 +1864,11 @@ bool Fl::option(Fl_Option opt)
       options_[OPTION_DND_TEXT] = tmp;
       opt_prefs.get("ShowTooltips", tmp, 1);                    // default: on
       options_[OPTION_SHOW_TOOLTIPS] = tmp;
-      opt_prefs.get("FNFCUsesGTK", tmp, 1);                    // default: on
+      opt_prefs.get("FNFCUsesGTK", tmp, 1);                     // default: on
       options_[OPTION_FNFC_USES_GTK] = tmp;
+      
+      opt_prefs.get("ShowZoomFactor", tmp, 1);                  // default: on
+      options_[OPTION_SHOW_SCALING] = tmp;
     }
     { // next, check the user preferences
       // override system options only, if the option is set ( >= 0 )
@@ -1881,6 +1888,9 @@ bool Fl::option(Fl_Option opt)
       if (tmp >= 0) options_[OPTION_SHOW_TOOLTIPS] = tmp;
       opt_prefs.get("FNFCUsesGTK", tmp, -1);
       if (tmp >= 0) options_[OPTION_FNFC_USES_GTK] = tmp;
+      
+      opt_prefs.get("ShowZoomFactor", tmp, -1);
+      if (tmp >= 0) options_[OPTION_SHOW_SCALING] = tmp;
     }
     { // now, if the developer has registered this app, we could as for per-application preferences
     }
@@ -2058,6 +2068,11 @@ void Fl::disable_im()
   Fl::screen_driver()->disable_im();
 }
 
+/**
+ Opens the display.
+ Automatically called by the library when the first window is show()'n.
+ Does nothing if the display is already open.
+ */
 void fl_open_display()
 {
   Fl::screen_driver()->open_display();
@@ -2110,6 +2125,24 @@ float Fl::screen_scale(int n) {
   return Fl::screen_driver()->scale(n);
 }
 
+/** Set the value of the GUI scaling factor for screen number \p n.
+Call this function before the fist window is show()'n and after
+a call to fl_open_display() to set the application's initial scaling factor value. */
+void Fl::screen_scale(int n, float factor) {
+  Fl::screen_driver()->scale(n, factor);
+  Fl_Graphics_Driver::default_driver().scale(factor);
+}
+
+/**
+  See if scaling factors are supported by this platform.
+ \return 0 if scaling factors are not supported by this platform,
+ 1 if a single scaling factor value is shared by all screens, 2 if each screen
+ can have its own scaling factor value.
+  \see Fl::screen_scale(int)
+ */
+int Fl::screen_scaling_supported() {
+  return Fl::screen_driver()->rescalable();
+}
 
 // Pointers you can use to change FLTK to another language.
 // Note: Similar pointers are defined in FL/fl_ask.H and src/fl_ask.cxx
diff --git a/src/Fl_Screen_Driver.cxx b/src/Fl_Screen_Driver.cxx
index d04db7094..9c0857972 100644
--- a/src/Fl_Screen_Driver.cxx
+++ b/src/Fl_Screen_Driver.cxx
@@ -336,7 +336,9 @@ static void del_transient_window(void *data) {
 }
 
 void Fl_Screen_Driver::transient_scale_display(float f, int nscreen)
-{ // transiently show the new scaling value using a shaped window
+{
+  if (!Fl::option(Fl::OPTION_SHOW_SCALING)) return;
+  // transiently show the new scaling value using a shaped window
   int w = 150;
   // draw a white rounded box on black background
   Fl_Screen_Driver *d = Fl::screen_driver();
@@ -427,6 +429,7 @@ int Fl_Screen_Driver::scale_handler(int event)
     screen_dr->rescale_all_windows_from_screen(screen, f*initial_scale);
     Fl_Screen_Driver::transient_scale_display(f, screen);
     screen_dr->init_workarea();
+    Fl::handle(FL_ZOOM_EVENT, NULL);
     return 1;
   }
   return 0;
diff --git a/src/Fl_cocoa.mm b/src/Fl_cocoa.mm
index e2ad85728..1371d7a67 100644
--- a/src/Fl_cocoa.mm
+++ b/src/Fl_cocoa.mm
@@ -2146,7 +2146,7 @@ static FLTextInputContext* fltextinputcontext_instance = nil;
   fl_lock_function();
   FLWindow *cw = (FLWindow*)[self window];
   Fl_Window *window = [cw getFl_Window];
-  float scale = fl_graphics_driver->scale();
+  float scale = Fl::screen_driver()->scale(0);
   if ( !window->parent() && window->border() && fabs(rect.size.height - window->h() * scale) > 5. ) { // this happens with tabbed windows
         window->resize([cw frame].origin.x/scale,
                        (main_screen_height - ([cw frame].origin.y + rect.size.height))/scale,