Intersection of curves II

The underlying JavaScript code

   var board = JXG.JSXGraph.initBoard('jxgbox', {
        axis:true,
        boundingbox:[-5, 5, 5, -5]
    });

    var curve1 = board.create('curve', [
            [-3, 3, 0, -3],
            [3, 3, 0, 3]
        ],
        {strokeColor: 'black', fillColor: 'none', fillOpacity: 0.8});

    var curve2 = board.create('polygon', [[3, 4], [-4, 0], [-4, 4]],
            {strokeColor: 'blue', fillColor: 'red', fillOpacity: 0.3});

    var clip = board.create('curveintersection', [curve1, curve2], 
            {strokeWidth: 3, fillColor: 'yellow', fillOpacity: 0.6 });