How to draw a custom triangle in renderItem in Apache Echarts

I want to draw custom triangle using renderItem method:

series: [
                    {
                        ....
                        type: 'custom',
                        renderItem: renderGanttItem,
                        ....
                    }
                ]

I see some build in functions how to draw rectangle in customer render item method. There are some good examples for it. But I could not find good examples how to draw some triangles. Maybe it is better to use some 'polygon'? Or maybe there are some other opportunities.

var rectNormal = clipRectByRect(params, {
                x: x,
                y: y,
                width: barLength,
                height: barHeight
            });
            return {
                type: 'group',
                children: [
                    {
                        type: 'rect',
                        ignore: !rectNormal,
                        shape: rectNormal,
                        style: api.style()
                    }
                ]
            };
        }

        function clipRectByRect(params, rect) {
            return echarts.graphic.clipRectByRect(rect, {
                x: params.coordSys.x,
                y: params.coordSys.y,
                width: params.coordSys.width,
                height: params.coordSys.height
            });
        }

How to draw a triangle? I need something like this