function drawGrid() {
    var w = gridCanvas.width;
    var h = gridCanvas.height;

    gridContext.clearRect(0, 0, w, h);

    gridContext.beginPath();
    gridContext.strokeStyle = "#999999";
    gridContext.lineWidth = 0.3;

    var x = distanceBetweenLines;
    while(x <= w) {
        gridContext.moveTo(x, 0);
        gridContext.lineTo(x, h);
        x += distanceBetweenLines;
    }

    var y = distanceBetweenLines;
    while(y <= h) {
        gridContext.moveTo(0, y);
        gridContext.lineTo(w, y);
        y += distanceBetweenLines;
    }

    gridContext.stroke();
}