1 files changed, 75 insertions, 1 deletions
diff --git a/src/drivers/X11/Fl_X11_Window_Driver.cxx b/src/drivers/X11/Fl_X11_Window_Driver.cxx
index 0da90b246..2912169a9 100644
--- a/src/drivers/X11/Fl_X11_Window_Driver.cxx
+++ b/src/drivers/X11/Fl_X11_Window_Driver.cxx
@@ -19,11 +19,29 @@
 
 #include "../../config_lib.h"
 #include "Fl_X11_Window_Driver.H"
+#include <FL/fl_draw.H>
+#if USE_XDBE
+#include <X11/extensions/Xdbe.h>
+static int can_xdbe(); // forward
+
+// class to be used only if Xdbe is used
+class Fl_X11_Dbe_Window_Driver : public Fl_X11_Window_Driver {
+public:
+  Fl_X11_Dbe_Window_Driver(Fl_Window *w) : Fl_X11_Window_Driver(w) {}
+  virtual int double_flush(int eraseoverlay);
+  virtual void destroy_double_buffer();
+};
+#endif
 
 
 Fl_Window_Driver *Fl_Window_Driver::newWindowDriver(Fl_Window *w)
 {
-  return new Fl_X11_Window_Driver(w);
+#if USE_XDBE
+  if (can_xdbe()) // strictly necessary only for Fl_Double_Window, but does no harm for Fl_Window
+    return new Fl_X11_Dbe_Window_Driver(w);
+  else
+#endif
+    return new Fl_X11_Window_Driver(w);
 }
 
 
@@ -41,6 +59,62 @@ void Fl_X11_Window_Driver::take_focus()
       Fl_X::activate_window(xid);
 }
 
+#if USE_XDBE
+
+static int can_xdbe() { // whether the Xdbe extension is usable
+  static int tried;
+  static int use_xdbe = 0;
+  if (!tried) {
+    tried = 1;
+    int event_base, error_base;
+    if (!XdbeQueryExtension(fl_display, &event_base, &error_base)) return 0;
+    Drawable root = RootWindow(fl_display,fl_screen);
+    int numscreens = 1;
+    XdbeScreenVisualInfo *a = XdbeGetVisualInfo(fl_display,&root,&numscreens);
+    if (!a) return 0;
+    for (int j = 0; j < a->count; j++) {
+      if (a->visinfo[j].visual == fl_visual->visualid) {
+        use_xdbe = 1; break;
+      }
+    }
+    XdbeFreeVisualInfo(a);
+  }
+  return use_xdbe;
+}
+
+int Fl_X11_Dbe_Window_Driver::double_flush(int eraseoverlay) {
+    if (!other_xid) {
+      other_xid = XdbeAllocateBackBufferName(fl_display, xid, XdbeCopied);
+      backbuffer_bad = 1;
+      w->clear_damage(FL_DAMAGE_ALL);
+    }
+    if (backbuffer_bad || eraseoverlay) {
+      // Make sure we do a complete redraw...
+      if (region) {XDestroyRegion(region); region = 0;}
+      w->clear_damage(FL_DAMAGE_ALL);
+      backbuffer_bad = 0;
+    }
+    // Redraw as needed...
+    if (w->damage()) {
+      fl_clip_region(region); region = 0;
+      fl_window = other_xid;
+      draw();
+      fl_window = xid;
+    }
+    // Copy contents of back buffer to window...
+    XdbeSwapInfo s;
+    s.swap_window = xid;
+    s.swap_action = XdbeCopied;
+    XdbeSwapBuffers(fl_display, &s, 1);
+    return 1;
+}
+
+void Fl_X11_Dbe_Window_Driver::destroy_double_buffer() {
+    XdbeDeallocateBackBufferName(fl_display, other_xid);
+  other_xid = 0;
+}
+
+#endif // USE_XDBE
 
 //
 // End of "$Id$".