React-konva double connected objects with arrow

Question

I'm trying to expand the Connected Objects demo by allowing two nodes (shapes of Circle class) to be double referenced (A connects to B with Arrow1 and B connects to A with Arrow2). I work with react-konva package.

I have implemented a demo on Code Sandbox with some basic functionality.

On line 5, 6 you'll find the Nodes info, on line 21 there exists a high-order component that creates the Arrow based on the start Node and end Node position.

In the default example, the arrows are working as expected. If you try to set the value of redNode.x to 300 the arrows overlap. The same happens when blueNode.x is equal to -100. This has something to do with the way I calculate the arrows (I suspect the equations on line 38).

Also note that as redNode.x moves to value 300, the two arrows approach each other (this happens on other values too), which is something I do not want to happen. I expect the arrows to have the same shape when the two nodes change position and not to overlap or approach each other. Unfortunately, my lack of mathematics does not help me solve the problem. I also tried to create a custom shape using quadraticCurveTo method without success.

Thanks in advance for the help. I appreciate all the solutions.

score 3 · Accepted Answer · answered Aug 26 '19 at 00:40

There are many ways to make curved lines. Here is my attempt to make it better:

import React from "react";
import ReactDOM from "react-dom";
import { Stage, Layer, Circle, Arrow, Text } from "react-konva";

const BLUE_DEFAULTS = {
  x: 100,
  y: 100,
  fill: "blue",
  width: 30,
  height: 30,
  draggable: true
};

const RED_DEFAULTS = {
  x: 100,
  y: 300,
  fill: "red",
  width: 30,
  height: 30,
  draggable: true
};

const Edge = ({ node1, node2 }) => {
  const dx = node1.x - node2.x;
  const dy = node1.y - node2.y;
  let angle = Math.atan2(-dy, dx);

  const radius = 20;
  const curvePower = 30;

  const arrowStart = {
    x: node2.x + -radius * Math.cos(angle + Math.PI),
    y: node2.y + radius * Math.sin(angle + Math.PI)
  };

  const arrowEnd = {
    x: node1.x + -radius * Math.cos(angle),
    y: node1.y + radius * Math.sin(angle)
  };

  const arrowCurve = {
    x:
      (arrowStart.x + arrowEnd.x) / 2 +
      curvePower * Math.cos(angle + Math.PI / 2),
    y:
      (arrowStart.y + arrowEnd.y) / 2 +
      curvePower * Math.sin(angle - Math.PI / 2)
  };

  return (
    <Arrow
      tension={0.2}
      points={[
        arrowStart.x,
        arrowStart.y,
        arrowCurve.x,
        arrowCurve.y,
        arrowEnd.x,
        arrowEnd.y
      ]}
      stroke="#000"
      fill="#000"
      strokeWidth={3}
      pointerWidth={6}
    />
  );
};

const App = () => {
  const [blueNode, updateBlueNode] = React.useState(BLUE_DEFAULTS);
  const [redNode, updateRedNode] = React.useState(RED_DEFAULTS);

  return (
    <Stage width={window.innerWidth} height={window.innerHeight}>
      <Layer>
        <Text text="Drag any node to see connections change" />
        <Edge node1={blueNode} node2={redNode} />
        <Edge node1={redNode} node2={blueNode} />
        <Circle
          {...blueNode}
          onDragMove={e => {
            updateBlueNode({ ...blueNode, ...e.target.position() });
          }}
        />
        <Circle
          {...redNode}
          onDragMove={e => {
            updateRedNode({ ...redNode, ...e.target.position() });
          }}
        />
      </Layer>
    </Stage>
  );
};

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);

Demo: https://codesandbox.io/s/react-konva-double-connected-objects-m5g22

This is superb! I want to ask you how you learned to calculate those formulas. This has something to do with trigonometry but can you suggest me some books for beginners? Something like "practical trigonometry for html canvas". It's a good idea for a blog post too! — Charles Nikolopoulos, Aug 27 '19 at 11:32
I don't know any books (probably there are some). But the book/post idea is cool, will take into account for me. Just have to learn "boring" math. — lavrton, Aug 27 '19 at 16:21

React-konva double connected objects with arrow

1 Answers1