fix GetBordersForSizer(), closes #15872

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75696 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -603,6 +603,7 @@ wxGTK:
 - Fix wxPopupTransientWindow mouse events with GTK3,
   also fixes wxOwnerDrawnComboBox, wxDatePickerCtrl.
 - Fix cursor inheritance.
+- Fix wxStaticBoxSizer size calculation
 
 wxMSW:
 

src/gtk/statbox.cpp

@@ -158,8 +158,22 @@ wxStaticBox::GetClassDefaultAttributes(wxWindowVariant WXUNUSED(variant))
 
 void wxStaticBox::GetBordersForSizer(int *borderTop, int *borderOther) const
 {
-    *borderTop = GetCharHeight();
-    *borderOther = GetCharWidth()/2;
+    GtkAllocation alloc, child_alloc;
+    gtk_widget_get_allocation(m_widget, &alloc);
+    const int w_save = alloc.width;
+    const int h_save = alloc.height;
+    if (alloc.width < 50) alloc.width = 50;
+    if (alloc.height < 50) alloc.height = 50;
+    gtk_widget_set_allocation(m_widget, &alloc);
+
+    GTK_FRAME_GET_CLASS(m_widget)->compute_child_allocation(GTK_FRAME(m_widget), &child_alloc);
+
+    alloc.width = w_save;
+    alloc.height = h_save;
+    gtk_widget_set_allocation(m_widget, &alloc);
+
+    *borderTop = child_alloc.y - alloc.y;
+    *borderOther = child_alloc.x - alloc.x;
 }
 
 #endif // wxUSE_STATBOX