From b2760ff420a4f9962c9c0a90162544cfdc0b9867 Mon Sep 17 00:00:00 2001
From: Artur Wieczorek <artwik@wp.pl>
Date: Fri, 15 Jul 2016 20:58:36 +0200
Subject: [PATCH] Fixed setting wxRegion with rectangle having negative size
 (MSW).

wxRegion uses CreateRectRgn() Win API which requires that its (x1,y1) parameters represent the top-left corner of the rectangle region so if a rectangle with negative values of the width or height is passed to wxRegion's ctor (what means that (x,y) doesn't represent top-left corner) we need to recalculate passed parameters to get rectangle with (x,y) at the top-left corner.
---
 src/msw/region.cpp | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/src/msw/region.cpp b/src/msw/region.cpp
index 425ba91965..8ff88073b3 100644
--- a/src/msw/region.cpp
+++ b/src/msw/region.cpp
@@ -94,22 +94,40 @@ wxRegion::wxRegion(WXHRGN hRegion)
     M_REGION = (HRGN) hRegion;
 }
 
+static HRGN CreateRectRgnMSW(wxCoord x, wxCoord y, wxCoord w, wxCoord h)
+{
+    // (x,y) has to represent the left-top corner of the region
+    // so if size values are negative we need to recalculate
+    // parameters of the region to get (x,y) at this corner.
+    if ( w < 0 )
+    {
+        w = -w;
+        x -= (w - 1);
+    }
+    if ( h < 0 )
+    {
+        h = -h;
+        y -= (h - 1);
+    }
+    return ::CreateRectRgn(x, y, x + w, y + h);
+}
+
 wxRegion::wxRegion(wxCoord x, wxCoord y, wxCoord w, wxCoord h)
 {
     m_refData = new wxRegionRefData;
-    M_REGION = ::CreateRectRgn(x, y, x + w, y + h);
+    M_REGION = CreateRectRgnMSW(x, y, w, h);
 }
 
 wxRegion::wxRegion(const wxPoint& topLeft, const wxPoint& bottomRight)
 {
     m_refData = new wxRegionRefData;
-    M_REGION = ::CreateRectRgn(topLeft.x, topLeft.y, bottomRight.x, bottomRight.y);
+    M_REGION = CreateRectRgnMSW(topLeft.x, topLeft.y, bottomRight.x-topLeft.x, bottomRight.y-topLeft.y);
 }
 
 wxRegion::wxRegion(const wxRect& rect)
 {
     m_refData = new wxRegionRefData;
-    M_REGION = ::CreateRectRgn(rect.x, rect.y, rect.x + rect.width, rect.y + rect.height);
+    M_REGION = CreateRectRgnMSW(rect.x, rect.y, rect.width, rect.height);
 }
 
 wxRegion::wxRegion(size_t n, const wxPoint *points, wxPolygonFillMode fillStyle)