From 4ca4e5d6cae11418bb4ef26a382d2a649ebd46f6 Mon Sep 17 00:00:00 2001
From: narzoul <narzoul@users.noreply.github.com>
Date: Sun, 21 Jun 2020 13:42:49 +0200
Subject: [PATCH] Fixed overlap detection in Blitter

Fixes graphics corruption in TalesWeaver (issue #72).
---
 DDrawCompat/DDraw/Blitter.cpp | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/DDrawCompat/DDraw/Blitter.cpp b/DDrawCompat/DDraw/Blitter.cpp
index 16af97f..9db6b05 100644
--- a/DDrawCompat/DDraw/Blitter.cpp
+++ b/DDrawCompat/DDraw/Blitter.cpp
@@ -516,6 +516,20 @@ namespace
 		srcRect.bottom += srcRect.top;
 		srcRect.right += srcRect.left;
 
+		LONG rowError = 0;
+		if (src < dst)
+		{
+			rowError = (dstRect.right - srcRect.left > static_cast<LONG>(pitch)) ? 1 : 0;
+		}
+		else
+		{
+			rowError = (srcRect.right - dstRect.left > static_cast<LONG>(pitch)) ? -1 : 0;
+		}
+		srcRect.left += rowError * pitch;
+		srcRect.right += rowError * pitch;
+		srcRect.top -= rowError;
+		srcRect.bottom -= rowError;
+
 		RECT r = {};
 		if (!IntersectRect(&r, &dstRect, &srcRect))
 		{