From 922c2ab8bb6dc1cc2664f2572c9d62951178ff33 Mon Sep 17 00:00:00 2001
From: maxim <maxim@lazarus-ide.org>
Date: Thu, 28 May 2015 20:19:27 +0000
Subject: [PATCH] Merged revision(s) 49170 #8077f55310 from trunk: LCL-Win:
 Prevent flicker in TListbox. Issue #28146, patch from wp. ........

git-svn-id: branches/fixes_1_4@49198 -
---
 lcl/interfaces/win32/win32wsstdctrls.pp | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/lcl/interfaces/win32/win32wsstdctrls.pp b/lcl/interfaces/win32/win32wsstdctrls.pp
index 42e54761ec..d28d7462ad 100644
--- a/lcl/interfaces/win32/win32wsstdctrls.pp
+++ b/lcl/interfaces/win32/win32wsstdctrls.pp
@@ -583,6 +583,9 @@ var
   WindowInfo: PWin32WindowInfo;
   NCCreateParams: PNCCreateParams;
   LMessage: TLMessage;
+  Count: LResult;
+  Top: Integer;
+  ARect: TRect;
 begin
   case Msg of
     WM_NCCREATE:
@@ -609,6 +612,26 @@ begin
         LMessage.Result := 0;
         Exit(DeliverMessage(WindowInfo^.WinControl, LMessage));
       end;
+    WM_ERASEBKGND:
+      // Avoid unnecessary background paints to avoid flickering of the listbox
+      begin
+        WindowInfo := GetWin32WindowInfo(Window);
+        Count := SendMessage(Window, LB_GETCOUNT, 0, 0);
+        if Assigned(WindowInfo^.WinControl) and
+          (TCustomListBox(WindowInfo^.WinControl).Columns < 2) and
+          (Count <> LB_ERR) and (SendMessage(Window, LB_GETITEMRECT, Count - 1, Windows.LParam(@ARect)) <> LB_ERR) then
+        begin
+          Top := ARect.Bottom;
+          Windows.GetClientRect(Window, ARect);
+          ARect.Top := Top;
+          if not IsRectEmpty(ARect) then
+            Windows.FillRect(HDC(WParam), ARect, WindowInfo^.WinControl.Brush.Reference.Handle);
+          Result := 1;
+        end
+        else
+          Result := CallDefaultWindowProc(Window, Msg, WParam, LParam);
+        Exit;
+      end;
   end;
   // normal processing
   Result := WindowProc(Window, Msg, WParam, LParam);