Fix for STR#3475: X11 platform, re-use current screen scaling factor when processing a screen reconfiguration event.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@12939 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

FL/Fl_Screen_Driver.H

@@ -170,7 +170,7 @@ public:
   static int scale_handler(int event);
   virtual void init_workarea() {}
   virtual float desktop_scale_factor() {return 1;}
-  void use_startup_scale_factor();
+  float use_startup_scale_factor();
   enum APP_SCALING_CAPABILITY {
     NO_APP_SCALING = 0, ///< The platform does not support rescaling.
     SYSTEMWIDE_APP_SCALING, ///< The platform supports rescaling with the same factor for all screens.

src/Fl_Screen_Driver.cxx

@@ -295,7 +295,7 @@ int Fl_Screen_Driver::input_widget_handle_key(int key, unsigned mods, unsigned s
 void Fl_Screen_Driver::rescale_all_windows_from_screen(int screen, float f)
 {
   float old_f = this->scale(screen);
-  if (f == old_f) return;
+  //if (f == old_f) return;
   this->scale(screen, f);
   Fl_Graphics_Driver *d = Fl_Display_Device::display_device()->driver();
   d->scale(f);
@@ -428,7 +428,7 @@ int Fl_Screen_Driver::scale_handler(int event)
 
 
 // use the startup time scaling value
-void Fl_Screen_Driver::use_startup_scale_factor()
+float Fl_Screen_Driver::use_startup_scale_factor()
 {
   float factor;
   char *p = 0;
@@ -441,9 +441,7 @@ void Fl_Screen_Driver::use_startup_scale_factor()
   else {
     factor = desktop_scale_factor();
   }
-  if (factor) {
+  return factor;
-    for (int i = 0; i < screen_count(); i++)  scale(i, factor);
-  }
 }
 
 
@@ -455,7 +453,8 @@ void Fl_Screen_Driver::open_display()
     been_here = true;
     screen_count(); // initialize, but ignore return value
     if (rescalable()) {
-      use_startup_scale_factor();
+      float factor = use_startup_scale_factor();
+      for (int i = 0; i < screen_count(); i++)  scale(i, factor);
       Fl::add_handler(Fl_Screen_Driver::scale_handler);
       int mx, my;
       int ns = Fl::screen_driver()->get_mouse(mx, my);

src/Fl_x.cxx

@@ -1220,6 +1220,51 @@ static KeySym fl_KeycodeToKeysym(Display *d, KeyCode k, unsigned i) {
   return XKeycodeToKeysym(d, k, i);
 }
 
+#if USE_XRANDR
+static void react_to_screen_reconfiguration() {
+#if USE_XFT
+  // memorize previous screen sizes and scales
+  int old_count = Fl::screen_count();
+  int (*sizes)[4] =  new int[old_count][4];
+  float *scales = new float[old_count];
+  for (int screen = 0; screen < old_count; screen++) {
+    Fl::screen_xywh(sizes[screen][0], sizes[screen][1], sizes[screen][2], sizes[screen][3], screen);
+    scales[screen] = Fl::screen_scale(screen);
+  }
+#endif // USE_XFT
+  Fl::call_screen_init(); // compute new screen sizes
+#if USE_XFT
+  // detect whether screen sizes were unchanged
+  bool nochange = (old_count == Fl::screen_count());
+  if (nochange) {
+    for (int screen = 0; screen < old_count; screen++) {
+      int X,Y,W,H;
+      Fl::screen_xywh(X,Y,W,H, screen);
+      X /= scales[screen];
+      Y /= scales[screen];
+      W /= scales[screen];
+      H /= scales[screen];
+      if (X != sizes[screen][0] || Y != sizes[screen][1] || W != sizes[screen][2] || H != sizes[screen][3]) {
+        nochange = false;
+        break;
+      }
+    }
+  }
+  delete[] sizes;
+  if (nochange) { // screen sizes did not change: re-use previous screen scale values
+    for (int screen = 0; screen < old_count; screen++)
+      Fl::screen_driver()->scale(screen, scales[screen]);
+  } else {
+    float factor = Fl::screen_driver()->use_startup_scale_factor();
+    for (int screen = 0; screen < Fl::screen_count(); screen++)
+      Fl::screen_driver()->rescale_all_windows_from_screen(screen, factor);
+  }
+  delete[] scales;
+#endif // USE_XFT
+}
+#endif // USE_XRANDR
+
+
 int fl_handle(const XEvent& thisevent)
 {
   XEvent xevent = thisevent;
@@ -1251,12 +1296,7 @@ int fl_handle(const XEvent& thisevent)
 #if USE_XRANDR  
   if( XRRUpdateConfiguration_f && xevent.type == randrEventBase + RRScreenChangeNotify) {
     XRRUpdateConfiguration_f(&xevent);
-    Fl::call_screen_init();
+    react_to_screen_reconfiguration();
-#if USE_XFT
-    float factor = Fl::screen_driver()->desktop_scale_factor();
-    for (int screen = 0; screen <= Fl::screen_count(); screen++)
-      Fl::screen_driver()->rescale_all_windows_from_screen(screen, factor);
-#endif // USE_XFT
     Fl::handle(FL_SCREEN_CONFIGURATION_CHANGED, NULL);
   }
 #endif // USE_XRANDR