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I am trying to draw a rectangle polyline over a canvas containing a color image, then (via way of a mouse drag move event) remove that rectangle polyline with it's original points and redraw as a new rectangle polyline using the new x,y co-ordinates. Code below paints with or without "xor", my problem is it will not erase when using the same points, happy for any help - Thanks - Andy UniSession.AddJS('var context=fMain.cArea._cc_; '+ 'var polyln = ['+s+']; '+ 'var shape = polyln.slice(0); '+ '{ '+ ' context.globalAlpha = 1; '+ ' context.globalCompositeOperation = ''xor''; '+ ' context.lineWidth = 1; '+ ' context.strokeStyle = "'+LineColourStr+'"; '+ ' context.moveTo(shape.shift(), shape.shift()); '+ ' while(shape.length) '+ ' { '+ ' context.lineTo(shape.shift(), shape.shift()); '+ ' } '+ ' context.stroke(); '+ ' context.globalCompositeOperation = ''source-over''; '+ ' context.globalAlpha = 1; '+ '}; ' );