How to avoid double drawn rectangulars , GWT, HTML5, Canvas

Hi, 

I created this peace of code:

canvas = Canvas.createIfSupported();

context = canvas.getContext2d();

canvas.setCoordinateSpaceWidth(WIDTH);

canvas.setCoordinateSpaceHeight(HEIGHT);

panel.add(canvas);

canvas.addTouchStartHandler(new TouchStartHandler() {

@Override

public void onTouchStart(TouchStartEvent event) {

JsArray<Touch> changedTouches = event.getChangedTouches();

if (changedTouches.length() > 0) {

context.beginPath();

int offsetLeft = canvas.getAbsoluteLeft();

int offsetTop = canvas.getAbsoluteTop();

context.fillRect(changedTouches.get(0).getPageX()

- offsetLeft, changedTouches.get(0).getPageY()

- offsetTop, 10, 10);

context.stroke();

}

// context.moveTo(changedTouches.get(0).getPageX() - offsetLeft,

// changedTouches.get(0).getPageY() - offsetTop);

event.preventDefault();

}

});

Problem is that every single touch generates two rectangulars on the screen? What is wrong with my code ?

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