X11: in HandleDNDposition() we never recursed through all children

The bug was that it only checked for the immediate children of
the toplevel window. It never recursed through all levels of
children finding the correct child the mouse cursor is over.
This is now fixed.

This also allows embedded frames or forms to work with DND.

1 files changed, 24 insertions, 12 deletions

diff --git a/src/corelib/x11/fpg_x11.pas b/src/corelib/x11/fpg_x11.pas
index 0209af14..37c2b507 100644
--- a/src/corelib/x11/fpg_x11.pas
+++ b/src/corelib/x11/fpg_x11.pas
@@ -1021,6 +1021,13 @@ var
   Msg: TXEvent;
   dx, dy, dx2, dy2: cint;
   child: TWindow;
+  prevchild: TWindow;
+
+  ret_root: TfpgWinHandle;
+  ret_child: TfpgWinHandle;
+  root_x, root_y: integer;
+  child_x, child_y: integer;
+
   s: string;
   i: integer;
   lTargetWinHandle: TWindow;
@@ -1050,25 +1057,30 @@ begin
   writeln('  x_root: ', x_root, '  y_root: ', y_root);
   {$ENDIF}
 
-  // query to see if we accept to be drop target
+  // Find window under cursor, and position of cursor inside that window
   XTranslateCoordinates(FDisplay, XDefaultRootWindow(FDisplay), ATopLevelWindow.WinHandle,
-      x_root, y_root, @dx, @dy, @child);
-
-  {$IFDEF DNDDEBUG}
-  writeln(Format('x:%d  y:%d  child:%d', [dx, dy, child]));
-  {$ENDIF}
-
-  if child <> 0 then
+      x_root, y_root, @dx, @dy, @ret_child);
+  child := ret_child;
+  prevchild := ATopLevelWindow.WinHandle;
+  while ret_child <> 0 do   // If we have chidren, iterate until we reach the top most child
   begin
-    w := FindWindowByHandle(child);
+    child :=  ret_child;
     dx2 := dx;
     dy2 := dy;
-    XTranslateCoordinates(FDisplay, ATopLevelWindow.WinHandle, w.WinHandle,
-        dx2, dy2, @dx, @dy, @child);
-  end
+    XTranslateCoordinates(FDisplay, prevchild, child,
+        dx2, dy2, @dx, @dy, @ret_child);
+    prevchild := child;
+  end;
+
+  if child <> 0 then
+    w := FindWindowByHandle(child)
   else
     w := ATopLevelWindow;
 
+  {$IFDEF DNDDEBUG}
+  writeln(Format('x:%d  y:%d  child:%d (%x)', [dx, dy, w.WinHandle, w.WinHandle]));
+  {$ENDIF}
+
   if Assigned(w) then
   begin
     lTargetWinHandle := w.WinHandle;