draw a ChainShape

Camera camera = new OrthographicCamera();
InputAdapter paint = new InputAdapter() {

    private boolean drawing;
    private FloatArray coords = new FloatArray();
    private Vector3 tmp = new Vector3();

    @Override
    public boolean keyTyped(char character) {
        switch(character) {
        case 'c':
            if(drawing) // drawing was enabled, so this will disable it and create the ChainShape
                createChainShape();
            drawing = !drawing; // toggle
            return true;
        default:
            return false;
        }
    }

    @Override
    public boolean touchDragged(int screenX, int screenY, int pointer) {
        if(drawing) {
            tmp.x = screenX;
            tmp.y = screenY;
            camera.unproject(tmp);
            coords.add(tmp.x);
            coords.add(tmp.y);
            return true;
        }
        return false;
    }

    public ChainShape createChainShape() {
        ChainShape shape = new ChainShape();
        coords.shrink(); // reduce inner array to make sure it's not longer than needed
        shape.createChain(coords.items);
        return shape;
    }

};