diff --git a/index.php b/index.php
index 13ac4da..57ac9ce 100644
--- a/index.php
+++ b/index.php
@@ -133,8 +133,8 @@
                     };
 
                     function draw(e) {
-                        var posX = (e.clientX - crect.left) * canvas.width / crect.width - 1;
-                        var posY = (e.clientY - crect.top) * canvas.height / crect.height - 1;
+                        var posX = e.offsetX * canvas.width / crect.width - 1;
+                        var posY = e.offsetY * canvas.height / crect.height - 1;
 
                         console.log(posX + " " + posY);