Don't use FL_DAMAGE_CHILD optimization because it's incompatible with transparency.

src/Fl.cxx

@@ -1675,8 +1675,14 @@ void Fl_Widget::damage(uchar fl, int X, int Y, int W, int H) {
     wi->damage_ |= fl;
     wi = wi->parent();
     if (!wi) return;
-    fl = FL_DAMAGE_CHILD;
+    /* we use FL_DAMAGE_EXPOSE now because of alpha blending and FL_NO_BOX and frames... */
+    fl = FL_DAMAGE_EXPOSE;
   }
+
+  fl = FL_DAMAGE_CHILD;
+
+  /* at this point 'wi' is the window */
+
   Fl_X* i = Fl_X::i((Fl_Window*)wi);
   if (!i) return; // window not mapped, so ignore it
 

src/Fl_Group.cxx

@@ -725,24 +725,25 @@ void Fl_Group::draw_children() {
 		 h() - Fl::box_dh(box()));
   }
 
-  if (damage() & ~FL_DAMAGE_CHILD) { // redraw the entire thing:
+//  if (damage() & ~FL_DAMAGE_CHILD) { // redraw the entire thing:
+//  if ( damage() & FL_DAMAGE_ALL ) {
     for (int i=children_; i--;) {
       Fl_Widget& o = **a++;
       draw_child(o);
       draw_outside_label(o);
     }
-  } else {	// only redraw the children that need it:
-    for (int i=children_; i--;) update_child(**a++);
-  }
+  /* } else {	// only redraw the children that need it: */
+  /*   for (int i=children_; i--;) update_child(**a++); */
+  /* } */
 
   if (clip_children()) fl_pop_clip();
 }
 
 void Fl_Group::draw() {
-  if (damage() & ~FL_DAMAGE_CHILD) { // redraw the entire thing:
+//  if (damage() & ~FL_DAMAGE_CHILD) { // redraw the entire thing:
     draw_box();
     draw_label();
-  }
+//  }
   draw_children();
 }
 

src/Fl_Window.cxx

@@ -106,10 +106,11 @@ void Fl_Window::draw() {
   //  - we draw the box with x=0 and y=0 instead of x() and y()
   //  - we don't draw a label
 
-  if (damage() & ~FL_DAMAGE_CHILD) {	 // draw the entire thing
-    draw_box(box(),0,0,w(),h(),color()); // draw box with x/y = 0
-  }
-  draw_children();
+//    if (damage() & ~FL_DAMAGE_CHILD) {	 // draw the entire thing
+    /* always draw the box because the children may be transparent */
+        draw_box(box(),0,0,w(),h(),color()); // draw box with x/y = 0
+//    }
+    draw_children();
 
   if (fl_gc && !parent() && resizable() && (!size_range_set || minh!=maxh || minw!=maxw)) {
     int dx = Fl::box_dw(box())-Fl::box_dx(box());