xform can be NULL when setting the identity.

dlls/gdi/dc.c

@@ -1217,7 +1217,7 @@ BOOL WINAPI ModifyWorldTransform( HDC hdc, const XFORM *xform,
 
     /* Check for illegal parameters */
     if (!dc) return FALSE;
-    if (!xform) goto done;
+    if (!xform && iMode != MWT_IDENTITY) goto done;
 
     /* Check that graphics mode is GM_ADVANCED */
     if (dc->GraphicsMode!=GM_ADVANCED) goto done;

dlls/gdi/tests/.cvsignore

@@ -4,6 +4,7 @@ brush.ok
 clipping.ok
 gdiobj.ok
 generated.ok
+mapping.ok
 metafile.ok
 palette.ok
 testlist.c

dlls/gdi/tests/Makefile.in

@@ -11,6 +11,7 @@ CTESTS = \
 	clipping.c \
 	gdiobj.c \
 	generated.c \
+	mapping.c \
 	metafile.c \
 	palette.c
 

dlls/gdi/tests/mapping.c

+/*
+ * Unit tests for mapping functions
+ *
+ * Copyright (c) 2005 Huw Davies
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <assert.h>
+#include <stdio.h>
+#include <math.h>
+
+#include "wine/test.h"
+#include "winbase.h"
+#include "wingdi.h"
+#include "winuser.h"
+#include "winerror.h"
+
+
+void test_modify_world_transform(void)
+{
+    HDC hdc = GetDC(0);
+    int ret;
+
+    ret = SetGraphicsMode(hdc, GM_ADVANCED);
+    if(!ret) /* running in win9x so quit */
+    {
+        ReleaseDC(0, hdc);
+        return;
+    }
+
+    ret = ModifyWorldTransform(hdc, NULL, MWT_IDENTITY);
+    ok(ret, "ret = %d\n", ret);
+
+    ret = ModifyWorldTransform(hdc, NULL, MWT_LEFTMULTIPLY);
+    ok(!ret, "ret = %d\n", ret);
+
+    ret = ModifyWorldTransform(hdc, NULL, MWT_RIGHTMULTIPLY);
+    ok(!ret, "ret = %d\n", ret);
+
+    ReleaseDC(0, hdc);
+}
+
+START_TEST(mapping)
+{
+    test_modify_world_transform();
+}