From 88a39aa6f8fa6ce766e099eb9e63ce5625953963 Mon Sep 17 00:00:00 2001
From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Mon, 6 Nov 2023 22:44:54 +0100
Subject: [PATCH] Implement wxEVT_DPI_CHANGED generation for wxGTK

Just check if the scale factor has changed when getting a "configure"
event for a TLW as we're guaranteed to get one when the scale factor
does change, according to GTK documentation (and it does seem to work).

Closes #19290.
---
 include/wx/gtk/toplevel.h |  5 +++++
 interface/wx/event.h      |  3 +++
 src/gtk/toplevel.cpp      | 25 +++++++++++++++++++++++++
 3 files changed, 33 insertions(+)

diff --git a/include/wx/gtk/toplevel.h b/include/wx/gtk/toplevel.h
index f35562777d..9aff64dd21 100644
--- a/include/wx/gtk/toplevel.h
+++ b/include/wx/gtk/toplevel.h
@@ -190,6 +190,11 @@ private:
 
     bool m_updateDecorSize;
     bool m_deferShowAllowed;
+
+#ifdef __WXGTK3__
+    // last known scale factor value
+    double m_scaleFactor;
+#endif // __WXGTK3__
 };
 
 #endif // _WX_GTK_TOPLEVEL_H_
diff --git a/interface/wx/event.h b/interface/wx/event.h
index f781f0223e..1096d48f12 100644
--- a/interface/wx/event.h
+++ b/interface/wx/event.h
@@ -3439,6 +3439,9 @@ public:
     <a href="https://docs.microsoft.com/en-us/windows/desktop/sbscs/application-manifests">"Application Manifests" documentation</a>
     for more details).
 
+    This event is generated by wxGTK when using GTK 3.10 or later and only
+    since wxWidgets version 3.3.0.
+
     @beginEventTable{wxDPIChangedEvent}
     @event{EVT_DPI_CHANGED(func)}
         Process a @c wxEVT_DPI_CHANGED event.
diff --git a/src/gtk/toplevel.cpp b/src/gtk/toplevel.cpp
index 13b1857c6b..590dd7543f 100644
--- a/src/gtk/toplevel.cpp
+++ b/src/gtk/toplevel.cpp
@@ -339,6 +339,21 @@ gtk_frame_configure_callback( GtkWidget*,
 
 void wxTopLevelWindowGTK::GTKConfigureEvent(int x, int y)
 {
+#ifdef __WXGTK3__
+    // First of all check if our DPI has changed.
+    const auto newScaleFactor = GetContentScaleFactor();
+    if ( newScaleFactor != m_scaleFactor )
+    {
+        const auto oldScaleFactor = m_scaleFactor;
+
+        // It seems safer to change it before generating the events to avoid
+        // any chance of reentrancy.
+        m_scaleFactor = newScaleFactor;
+
+        WXNotifyDPIChange(oldScaleFactor, newScaleFactor);
+    }
+#endif // __WXGTK3__
+
     wxPoint point;
 #ifdef GDK_WINDOWING_X11
     if (gs_decorCacheValid)
@@ -709,6 +724,16 @@ bool wxTopLevelWindowGTK::Create( wxWindow *parent,
         g_object_ref(m_widget);
     }
 
+#ifdef __WXGTK3__
+    // This value may be incorrect as here it's just set to the scale factor of
+    // the primary monitor because the widget is not realized yet, but it's
+    // better than setting it to 1, as chances are that the window will be
+    // created on the primary monitor or, maybe, the other monitors use the
+    // same scale factor anyhow. And if this isn't the case, we will set it to
+    // the correct value when we get "configure-event" from GTK later.
+    m_scaleFactor = GetContentScaleFactor();
+#endif // __WXGTK3__
+
     wxWindow *topParent = wxGetTopLevelParent(m_parent);
     if (topParent && (((GTK_IS_WINDOW(topParent->m_widget)) &&
                        (GetExtraStyle() & wxTOPLEVEL_EX_DIALOG)) ||