From 7555fb02d290f5dc9bcb28cdd4628258b6630d91 Mon Sep 17 00:00:00 2001
From: narzoul <narzoul@users.noreply.github.com>
Date: Sat, 23 Jan 2016 20:40:01 +0100
Subject: [PATCH] Fixed scrollbars not updating when scrolling

The nonclient area is now also invalidated when scrolling.
Added similar handling for WM_MOUSEWHEEL messages.
---
 DDrawCompat/CompatGdiWinProc.cpp | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/DDrawCompat/CompatGdiWinProc.cpp b/DDrawCompat/CompatGdiWinProc.cpp
index 54ac958..1cda7dd 100644
--- a/DDrawCompat/CompatGdiWinProc.cpp
+++ b/DDrawCompat/CompatGdiWinProc.cpp
@@ -10,7 +10,8 @@
 namespace
 {
 	void eraseBackground(HWND hwnd, HDC dc);
-	void ncPaint(HWND wnd);
+	void ncPaint(HWND hwnd);
+	void updateScrolledWindow(HWND hwnd);
 
 	LRESULT CALLBACK callWndRetProc(int nCode, WPARAM wParam, LPARAM lParam)
 	{
@@ -37,7 +38,7 @@ namespace
 			}
 			else if (WM_VSCROLL == ret->message || WM_HSCROLL == ret->message)
 			{
-				InvalidateRect(ret->hwnd, nullptr, TRUE);
+				updateScrolledWindow(ret->hwnd);
 			}
 		}
 
@@ -58,6 +59,20 @@ namespace
 		}
 	}
 
+	LRESULT CALLBACK mouseProc(int nCode, WPARAM wParam, LPARAM lParam)
+	{
+		if (HC_ACTION == nCode)
+		{
+			auto mhs = reinterpret_cast<MOUSEHOOKSTRUCT*>(lParam);
+			if (WM_MOUSEWHEEL == wParam)
+			{
+				updateScrolledWindow(mhs->hwnd);
+			}
+		}
+
+		return CallNextHookEx(nullptr, nCode, wParam, lParam);
+	}
+
 	void ncPaint(HWND hwnd)
 	{
 		if (!CompatGdi::beginGdiRendering())
@@ -88,6 +103,11 @@ namespace
 		ReleaseDC(hwnd, windowDc);
 		CompatGdi::endGdiRendering();
 	}
+
+	void updateScrolledWindow(HWND hwnd)
+	{
+		RedrawWindow(hwnd, nullptr, nullptr, RDW_ERASE | RDW_FRAME | RDW_INVALIDATE);
+	}
 }
 
 namespace CompatGdiWinProc
@@ -96,5 +116,6 @@ namespace CompatGdiWinProc
 	{
 		const DWORD threadId = GetCurrentThreadId();
 		SetWindowsHookEx(WH_CALLWNDPROCRET, callWndRetProc, nullptr, threadId);
+		SetWindowsHookEx(WH_MOUSE, &mouseProc, nullptr, threadId);
 	}
 }