From 83ca3c4ef27c644754e9696913f263d09c232172 Mon Sep 17 00:00:00 2001
From: Richard Reznicek <richard.reznicek@mail.de>
Date: Sat, 13 Jun 2020 10:11:22 +0200
Subject: [PATCH] Fix flickering when resizing MDI parent frame in wxMSW

The wxMDIParentFrame::Create() function simply called
wxApp::GetRegisteredClassName(wxT("wxMDIFrame")) without providing
apropriate flags parameter depending on the presence/absence of the
wxFULL_REPAINT_ON_RESIZE flag in style. Thus, the MDI parent frame was
always created using the window class with the CS_HREDRAW | CS_VREDRAW
style flags set. Choosing the appropriate value for the flags parameter
of the wxApp::GetRegisteredClassName() function (like in the
wxWindowMSW::GetMSWClassName() function) fixes the flicker issue. The
wxApp::GetRegisteredClassName() call in wxMDIChildFrame::Create()
is adapted as well just for the sake of consistency.

See #18213.

Closes https://github.com/wxWidgets/wxWidgets/pull/1892
---
 src/msw/mdi.cpp | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/src/msw/mdi.cpp b/src/msw/mdi.cpp
index 3d555e24cf..479e878f8b 100644
--- a/src/msw/mdi.cpp
+++ b/src/msw/mdi.cpp
@@ -198,7 +198,11 @@ bool wxMDIParentFrame::Create(wxWindow *parent,
   msflags &= ~WS_VSCROLL;
   msflags &= ~WS_HSCROLL;
 
-  if ( !wxWindow::MSWCreate(wxApp::GetRegisteredClassName(wxT("wxMDIFrame")),
+  if ( !wxWindow::MSWCreate(wxApp::GetRegisteredClassName(
+                                    wxT("wxMDIFrame"), -1, 0,
+                                    (style & wxFULL_REPAINT_ON_RESIZE) ? wxApp::RegClass_Default
+                                                                       : wxApp::RegClass_ReturnNR
+                                   ),
                             title.t_str(),
                             pos, size,
                             msflags,
@@ -842,10 +846,11 @@ bool wxMDIChildFrame::Create(wxMDIParentFrame *parent,
 
   MDICREATESTRUCT mcs;
 
-  wxString className =
-      wxApp::GetRegisteredClassName(wxT("wxMDIChildFrame"), COLOR_WINDOW);
-  if ( !(style & wxFULL_REPAINT_ON_RESIZE) )
-      className += wxApp::GetNoRedrawClassSuffix();
+  wxString className = wxApp::GetRegisteredClassName(
+                               wxT("wxMDIChildFrame"), COLOR_WINDOW, 0,
+                               (style & wxFULL_REPAINT_ON_RESIZE) ? wxApp::RegClass_Default
+                                                                  : wxApp::RegClass_ReturnNR
+                              );
 
   mcs.szClass = className.t_str();
   mcs.szTitle = title.t_str();