commit 02754e43ceb2d1d7a20b706c90d5aa9b2f6a95ad
Author:     ManoloFLTK <41016272+ManoloFLTK@users.noreply.github.com>
AuthorDate: Wed Nov 17 14:58:45 2021 +0100
Commit:     ManoloFLTK <41016272+ManoloFLTK@users.noreply.github.com>
CommitDate: Wed Nov 17 15:00:21 2021 +0100

    Fix Fl_Window::decorated_w() in some X11 situations.

 src/drivers/X11/Fl_X11_Window_Driver.cxx | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git src/drivers/X11/Fl_X11_Window_Driver.cxx src/drivers/X11/Fl_X11_Window_Driver.cxx
index ab15f27..5dea0fb 100644
--- src/drivers/X11/Fl_X11_Window_Driver.cxx
+++ src/drivers/X11/Fl_X11_Window_Driver.cxx
@@ -159,6 +159,15 @@ void Fl_X11_Window_Driver::decorated_win_size(int &w, int &h)
   if (status == 0 || root == parent) return;
   XWindowAttributes attributes;
   XGetWindowAttributes(fl_display, parent, &attributes);
+  // sometimes, very wide window borders are reported
+  // ignore them all:
+  XWindowAttributes w_attributes;
+  XGetWindowAttributes(fl_display, Fl_X::i(win)->xid, &w_attributes);
+  if (attributes.width - w_attributes.width >= 20) {
+    attributes.height -= (attributes.width - w_attributes.width);
+    attributes.width = w_attributes.width;
+  }
+  
   int nscreen = screen_num();
   float s = Fl::screen_driver()->scale(nscreen);
   w = attributes.width / s;