Clipping region doesn't resize to canvas size

import QtQuick 2.0

Canvas {
    id: canvas

    height: 200
    width: 200

    onPaint: {
        var ctx = canvas.getContext('2d')

        ctx.clearRect(0, 0, width, height)

        ctx.save()

        ctx.beginPath();
        ctx.rect(0, 0, width/2, height/2);
        ctx.strokeStyle = "red";
        ctx.stroke();
        ctx.clip();

        ctx.fillStyle = "blue"
        ctx.fillRect(0, 0, width, height);

        ctx.restore()
    }
}