sketch.paperjs test code

gistfile1.js

var values = {
    radius: 40,
    opacity: 1,
    color: 'red',
    animate: false
};

var components = {
    radius: {
        type: 'slider', label: 'Radius',
        min: 10, max: 100,
        step: 5
    },
    opacity: {
        type: 'slider', label: 'Opacity',
        min: 0, max: 1,
        step: 0.01
    },
    color: {
        type: 'list', label: 'Color',
        options: ['red', 'yellow', 'purple', 'green']
    },
    animate: {
        type: 'boolean', label: 'Animate'
    }
};

var palette = new Palette('My Palette', components, values);

function onMouseDrag(event) {
    var circle = new Path.Circle(event.point, values.radius);
    circle.fillColor = values.color;
    circle.opacity = values.opacity;
    if (values.animate) {
        var count = 0;
        var vector = new Point(1, 0);
        circle.onFrame = function(event) {
            if (count < 100) {
                circle.position += vector;
                circle.scale(1.005, 1.003);
            } else if (count < 200) {
                circle.position -= vector;
                circle.scale(1 / 1.005, 1 / 1.003);
            }
            count++;
        };
    }
}