Try to avoid resetting/recreating cairo structures more often than necessary.

src/Fl_Cairo.cxx

@@ -39,9 +39,9 @@
     Creates transparently a cairo_surface_t object.
     gc is an HDC context in  WIN32, a CGContext* in Quartz, a display on X11
  */
-cairo_surface_t * cairo_create_surface(void * gc, int W, int H) {
+cairo_surface_t * cairo_create_surface(void * gc, Window w, int W, int H) {
 # if defined(USE_X11)
-    return cairo_xlib_surface_create(fl_display, fl_window, fl_visual->visual, W, H);
+    return cairo_xlib_surface_create(fl_display, w, fl_visual->visual, W, H);
 # elif   defined(WIN32)
     return cairo_win32_surface_create((HDC) gc);
 # elif defined(__APPLE_QUARTZ__)
@@ -53,31 +53,49 @@ cairo_surface_t * cairo_create_surface(void * gc, int W, int H) {
 
 cairo_surface_t *fl_cairo_surface;
 cairo_t *fl_cairo_context;
+static Window real_xid;
+static int W, H;
 
 cairo_t * 
 Fl::cairo_make_current(Fl_Window* wi) {
     if (!wi) return NULL; // Precondition
 
+    Window w = wi->i->other_xid ? wi->i->other_xid : wi->i->xid;
+
+    if ( ( fl_cairo_context && fl_cairo_context == wi->i->cc ) &&
+         w && w == real_xid && 
+         wi->w() == W && wi->h() == H )
+        /* already current */
+        return wi->i->cc;
+
+    real_xid = w;
+    W = wi->w();
+    H = wi->h();
+
+    if ( wi->i->cs )
+    {
+        cairo_xlib_surface_set_drawable( wi->i->cs, w, wi->w(), wi->h() );
+        cairo_destroy( wi->i->cc );
+        wi->i->cc = 0;
+    }
+    else
+    {
+        wi->i->cs = cairo_create_surface(fl_gc, w, wi->w(), wi->h());
+    }
+
     if ( ! wi->i->cc )
     {
         /* set this window's context to be the current one */
-        wi->i->cs = cairo_create_surface(fl_gc, wi->w(), wi->h());
         wi->i->cc = cairo_create( wi->i->cs );
-//        cairo_surface_destroy( s );
     }
 
     fl_cairo_surface = wi->i->cs;
     fl_cairo_context = wi->i->cc;
 
+    printf( "NTK: cairo_make_current()\n" );
     return wi->i->cc;
 }
 
-void
-Fl::cairo_set_drawable ( Fl_Window *wi )
-{
-    cairo_xlib_surface_set_drawable( wi->i->cs, fl_window, wi->w(), wi->h() );
-}
-
 #endif // FLTK_HAVE_CAIRO
 
 //

src/Fl_Double_Window.cxx

@@ -308,6 +308,7 @@ void Fl_Double_Window::flush(int eraseoverlay) {
     //make_current(); // make sure fl_gc is non-zero
   Fl_X *myi = Fl_X::i(this);
   if (!myi->other_xid) {
+
 #if defined(USE_X11) || defined(WIN32)
     myi->other_xid = fl_create_offscreen(w(), h());
     clear_damage(FL_DAMAGE_ALL);
@@ -316,8 +317,14 @@ void Fl_Double_Window::flush(int eraseoverlay) {
       myi->other_xid = fl_create_offscreen(w(), h());
       clear_damage(FL_DAMAGE_ALL);
     }
+
+
 #else
 # error unsupported platform
+#endif
+
+#if FLTK_HAVE_CAIRO
+    Fl::cairo_make_current( this );
 #endif
   }
 
@@ -346,9 +353,7 @@ void Fl_Double_Window::flush(int eraseoverlay) {
     }
 #else // X:
     fl_window = myi->other_xid;
-#if FLTK_HAVE_CAIRO
-    Fl::cairo_set_drawable( this );
-#endif
+    
     fl_clip_region(myi->region);
 
     draw();
@@ -359,10 +364,6 @@ void Fl_Double_Window::flush(int eraseoverlay) {
 
     fl_window = myi->xid;
 
-#if FLTK_HAVE_CAIRO
-    Fl::cairo_set_drawable( this );
-#endif
-
     fl_clip_region(myi->region);
 
 #endif
@@ -394,6 +395,7 @@ void Fl_Double_Window::hide() {
   Fl_X* myi = Fl_X::i(this);
   if (myi && myi->other_xid) {
       fl_delete_offscreen(myi->other_xid);
+      myi->other_xid = 0;
   }
   Fl_Window::hide();
 }