jstopo深蓝科技风拓扑，自定义拖拽生成。
html
<canvas
ref="canvas"
@drop="drop($event)"
@dragover="allowDrop($event)"
@mousemove="onMouseMove"
@mouseup="onMouseUp"
@contextmenu.prevent="()=>{}"
@mousewheel="onMouseWheel"
@mousedown="onMouseDown">
</canvas>
