From b95f2b699d99d63f68376c6e80a2e441c1ee39be Mon Sep 17 00:00:00 2001
From: Vadim Zeitlin <vadim@wxwidgets.org>
Date: Tue, 28 Jun 2022 22:50:24 +0200
Subject: [PATCH] Clarify that wxDC::CopyAttributes() doesn't copy scaling
 factor

Also show an example of setting the scaling factor in wxMemoryDC
documentation.
---
 interface/wx/dc.h       |  3 +++
 interface/wx/dcmemory.h | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/interface/wx/dc.h b/interface/wx/dc.h
index 52a9905206..09b5015897 100644
--- a/interface/wx/dc.h
+++ b/interface/wx/dc.h
@@ -1500,6 +1500,9 @@ public:
             - Background brush
             - Layout direction
 
+        Note that the scaling factor is not considered to be an attribute of
+        wxDC and is @e not copied by this function.
+
         @param dc
             A valid (i.e. its IsOk() must return @true) source device context.
      */
diff --git a/interface/wx/dcmemory.h b/interface/wx/dcmemory.h
index d7c4dfa3f9..b30bd19ee6 100644
--- a/interface/wx/dcmemory.h
+++ b/interface/wx/dcmemory.h
@@ -38,6 +38,25 @@
 
     This happens automatically when wxMemoryDC object goes out of scope.
 
+    Note that the scaling factor of the bitmap determines the scaling factor
+    used by this device context, so when using a memory device context as a
+    back buffer for a window, you should typically create the bitmap using the
+    same scale factor as used by the window, e.g.
+    @code
+    void MyWindow::OnPaint(wxPaintEvent&)
+    {
+        wxBitmap bmp;
+        bmp.CreateWithDIPSize(GetClientSize(), GetDPIScaleFactor());
+        {
+            wxMemoryDC memdc(bmp);
+            ... use memdc to draw on the bitmap ...
+        }
+
+        wxPaintDC dc(this);
+        dc.DrawBitmap(bmp, wxPoint(0, 0));
+    }
+    @endcode
+
     @library{wxcore}
     @category{dc}