6 files changed, 31 insertions, 0 deletions
diff --git a/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.H b/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.H
index 29ae7570e..d825e6580 100644
--- a/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.H
+++ b/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.H
@@ -94,6 +94,8 @@ public:
   virtual void enable_im();
   virtual void disable_im();
   virtual void open_display();
+  // --- compute dimensions of an Fl_Offscreen
+  virtual void offscreen_size(Fl_Offscreen o, int &width, int &height);
 };
 
 
diff --git a/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx b/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx
index 71a64292d..8856f8cfe 100644
--- a/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx
+++ b/src/drivers/Cocoa/Fl_Cocoa_Screen_Driver.cxx
@@ -400,6 +400,12 @@ int Fl_Cocoa_Screen_Driver::input_widget_handle_key(int key, unsigned mods, unsi
   return -1;
 }
 
+void Fl_Cocoa_Screen_Driver::offscreen_size(Fl_Offscreen off, int &width, int &height)
+{
+  width = CGBitmapContextGetWidth(off);
+  height = CGBitmapContextGetHeight(off);
+}
+
 //
 // End of "$Id$".
 //
diff --git a/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.H b/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.H
index 80529138f..5c016ce73 100644
--- a/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.H
+++ b/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.H
@@ -77,6 +77,7 @@ public:
   virtual void enable_im();
   virtual void disable_im();
   virtual void open_display();
+  virtual void offscreen_size(Fl_Offscreen off, int &width, int &height);
 };
 
 
diff --git a/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.cxx b/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.cxx
index 6c3e99dca..2b1f65e0a 100644
--- a/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.cxx
+++ b/src/drivers/WinAPI/Fl_WinAPI_Screen_Driver.cxx
@@ -638,6 +638,15 @@ float Fl_WinAPI_Screen_Driver::desktop_scaling_factor() {
   return scaling;
 }
 
+void Fl_WinAPI_Screen_Driver::offscreen_size(Fl_Offscreen off, int &width, int &height)
+{
+  BITMAP bitmap;
+  if ( GetObject(off, sizeof(BITMAP), &bitmap) ) {
+    width = bitmap.bmWidth;
+    height = bitmap.bmHeight;
+  }
+}
+
 //
 // End of "$Id$".
 //
diff --git a/src/drivers/X11/Fl_X11_Screen_Driver.H b/src/drivers/X11/Fl_X11_Screen_Driver.H
index 8f3638718..2be26a1ee 100644
--- a/src/drivers/X11/Fl_X11_Screen_Driver.H
+++ b/src/drivers/X11/Fl_X11_Screen_Driver.H
@@ -87,6 +87,8 @@ public:
   virtual void disable_im();
   virtual void open_display();
   virtual void close_display();
+  // --- compute dimensions of an Fl_Offscreen
+  virtual void offscreen_size(Fl_Offscreen o, int &width, int &height);
 };
 
 
diff --git a/src/drivers/X11/Fl_X11_Screen_Driver.cxx b/src/drivers/X11/Fl_X11_Screen_Driver.cxx
index d28859949..7095ea948 100644
--- a/src/drivers/X11/Fl_X11_Screen_Driver.cxx
+++ b/src/drivers/X11/Fl_X11_Screen_Driver.cxx
@@ -1143,6 +1143,17 @@ Fl_RGB_Image *Fl_X11_Screen_Driver::read_win_rectangle(uchar *p, int X, int Y, i
   return rgb;
 }
 
+
+void Fl_X11_Screen_Driver::offscreen_size(Fl_Offscreen off, int &width, int &height)
+{
+  int px, py;
+  unsigned w, h, b, d;
+  Window root;
+  XGetGeometry(fl_display, off, &root, &px, &py, &w, &h, &b, &d);
+  width = (int)w;
+  height = (int)h;
+}
+
 //
 // End of "$Id$".
 //