diff --git a/effects.cpp b/effects.cpp
index 3c527b495d..2f5c87d897 100644
--- a/effects.cpp
+++ b/effects.cpp
@@ -55,7 +55,7 @@ Matrix operator*( const Matrix& m1, const Matrix& m2 )
             for( int k = 0;
                  k < 4;
                  ++k )
-                s += m1.m[ i ][ k ]  * m2.m[ k ][ j ];
+                s += m1.m[ k ][ j ]  * m2.m[ i ][ k ];
             r.m[ i ][ j ] = s;
             }
     return r;
@@ -102,6 +102,24 @@ bool Matrix::isOnlyTranslate() const
         && m[ 3 ][ 3 ] == 1;
     }
 
+QPoint Matrix::transform( const QPoint& p ) const
+    {
+    int vec[ 4 ] = { p.x(), p.y(), 0, 1 };
+    int res[ 4 ];
+    for( int i = 0;
+         i < 4;
+         ++i )
+        {
+        double s = 0;
+        for( int j = 0;
+             j < 4;
+             ++j )
+            s += m[ i ][ j ] * vec[ j ];
+        res[ i ] = int( s );
+        }
+    return QPoint( res[ 0 ], res[ 1 ] );
+    }
+
 //****************************************
 // Effect
 //****************************************
diff --git a/effects.h b/effects.h
index 6997c5d226..92bdb91a03 100644
--- a/effects.h
+++ b/effects.h
@@ -13,8 +13,9 @@ License. See the file "COPYING" for the exact licensing terms.
 #ifndef KWIN_EFFECTS_H
 #define KWIN_EFFECTS_H
 
-#include <QMap>
-#include <QTimer>
+#include <qmap.h>
+#include <qpoint.h>
+#include <qtimer.h>
 
 namespace KWinInternal
 {
@@ -32,6 +33,7 @@ class Matrix
         double xTranslate() const;
         double yTranslate() const;
         double zTranslate() const;
+        QPoint transform( const QPoint& p ) const;
         double m[ 4 ][ 4 ];
     };