G6 provides multiple built-in edge types, including line, polyline, quadratic (quadratic Bézier curve edge), cubic (cubic Bézier curve edge), cubic-horizontal, cubic-vertical, and more. These built-in edges can meet most basic scenario requirements.

However, in actual projects, you may encounter requirements that these basic edges cannot satisfy. In such cases, you need to create custom edges. Don't worry, it's simpler than you think!

Before Starting: Understanding the Basic Components of an Edge

In G6, a complete edge typically consists of the following parts:

• key: The main graphic of the edge, representing the primary shape of the edge, such as straight lines, polylines, etc.
• label: Text label, usually used to display the name or description of the edge
• arrow: Arrow, used to indicate the direction of the edge
• halo: Graphic displaying halo effects around the main graphic

Ways to Create Custom Edges Choose the Right Approach

There are two main ways to create custom edges:

1. Inherit from Existing Edge Types Recommended

This is the most commonly used approach. You can choose to inherit from one of the following types:

• BaseEdge - The most basic edge class, providing core edge functionality
• Line - Straight line edge
• Polyline - Polyline edge
• Quadratic - Quadratic Bézier curve edge
• Cubic - Cubic Bézier curve edge
• CubicVertical - Vertical cubic Bézier curve edge
• CubicHorizontal - Horizontal cubic Bézier curve edge

Why choose this approach?

• 📌 Less code: Reuse existing edge properties and methods, only focus on new functionality
• 📌 Fast development: Suitable for most project requirements, quickly achieve business goals
• 📌 Easy maintenance: Clear code structure, clear inheritance relationships

2. Build from Scratch Based on G Graphics System Advanced Usage

If existing edge types don't meet your requirements, you can create edges from scratch based on G's underlying graphics system.

Why choose this approach?

• 📌 Maximum freedom: Complete control over every detail of the edge, achieving any complex effects
• 📌 Special requirements: Highly customized scenarios that existing edge types cannot satisfy
• 📌 Performance optimization: Performance optimization for specific scenarios

Create Your First Custom Edge in Three Steps

Let's start with the most basic BaseEdge to implement a custom straight line edge:

import { Graph, register, BaseEdge, ExtensionCategory } from '@antv/g6';

class MyLineEdge extends BaseEdge {
  getKeyStyle(attributes) {
    return { ...super.getKeyStyle(attributes), lineWidth: 2, stroke: '#A4D3EE' };
  }

  getKeyPath(attributes) {
    const { sourceNode, targetNode } = this;
    const [x1, y1] = sourceNode.getPosition();
    const [x2, y2] = targetNode.getPosition();

    return [
      ['M', x1, y1],
      ['L', x2, y2],
    ];
  }
}

register(ExtensionCategory.EDGE, 'my-line-edge', MyLineEdge);

const graph = new Graph({
  container: 'container',
  height: 200,
  data: {
    nodes: [
      { id: 'node1', style: { x: 100, y: 50 } },
      { id: 'node2', style: { x: 300, y: 120 } },
    ],
    edges: [{ source: 'node1', target: 'node2' }],
  },
  node: {
    style: {
      fill: '#7FFFD4',
      stroke: '#5CACEE',
      lineWidth: 2,
    },
  },
  edge: {
    type: 'my-line-edge',
    style: {
      zIndex: 3,
    },
  },
});

graph.render();

Step 1: Write Custom Edge Class

import { BaseEdge } from '@antv/g6';
import type { BaseEdgeStyleProps } from '@antv/g6';

class MyLineEdge extends BaseEdge {
  // Define edge style, can add or override default styles
  protected getKeyStyle(attributes: Required<BaseEdgeStyleProps>) {
    // Call parent class method to get basic style, then add custom styles
    return { ...super.getKeyStyle(attributes), lineWidth: 2, stroke: '#A4D3EE' };
  }

  // Implement abstract method: define edge path
  // This is an abstract method of BaseEdge, all subclasses must implement it
  protected getKeyPath(attributes) {
    // Get source node and target node
    const { sourceNode, targetNode } = this;

    // Get node position coordinates
    const [x1, y1] = sourceNode.getPosition();
    const [x2, y2] = targetNode.getPosition();

    // Return SVG path array, defining a straight line from start to end
    return [
      ['M', x1, y1],
      ['L', x2, y2],
    ];
  }
}

Step 2: Register Custom Edge

Use the register method to register the edge type so that G6 can recognize your custom edge:

import { ExtensionCategory } from '@antv/g6';

register(ExtensionCategory.EDGE, 'my-line-edge', MyLineEdge);

The register method requires three parameters:

• Extension category: ExtensionCategory.EDGE indicates this is an edge type
• Type name: my-line-edge is the name we give to this custom edge, which will be used in configuration later
• Class definition: MyLineEdge is the edge class we just created

Step 3: Apply Custom Edge

In the graph configuration, use our custom edge by setting edge.type:

const graph = new Graph({
  container: 'container',
  data: {
    nodes: [
      { id: 'node1', style: { x: 100, y: 100 } },
      { id: 'node2', style: { x: 300, y: 150 } },
    ],
    edges: [{ source: 'node1', target: 'node2' }],
  },
  node: {
    style: {
      fill: '#7FFFD4',
      stroke: '#5CACEE',
      lineWidth: 2,
    },
  },
  edge: {
    type: 'my-line-edge',
    style: {
      zIndex: 3,
    },
  },
});

graph.render();

🎉 Congratulations! You have created your first custom edge.

Going Further: Understanding the Principles of Edge Rendering

Atomic Graphics

G6 nodes are drawn using atomic graphic units provided by the G graphics system. Here are common graphic elements and their uses:

For more atomic graphics and detailed properties, please refer to Element - Shape (Optional)

All these graphics can be dynamically created or updated through upsert(), automatically managing graphic state and lifecycle.

Element Base Class

Before starting to customize elements, you need to understand some important properties and methods in G6 element base classes:

Properties

Methods

upsert(name, Ctor, style, container, hooks): Graphic Creation/Update

When creating custom elements, you will frequently use the upsert method. It's short for "update or insert", responsible for adding or updating graphics in elements:

upsert(key: string, Ctor: { new (...args: any[]): DisplayObject }, style: Record<string, any>, container: DisplayObject);

For example, inserting a purple circle at a fixed position:

this.upsert(
  'element-key', // Unique identifier of the element
  'circle', // Graphic type, such as 'rect', 'circle', etc.
  { x: 100, y: 100, fill: '#a975f3' }, // Style configuration object
  container, // Parent container
);

Why use upsert instead of directly creating graphics through container.appendChild()? Because:

1. Better performance: When state changes or data updates, it intelligently reuses existing graphics instead of deleting and rebuilding, greatly improving rendering performance
2. Simpler code: No need to manually check if elements exist
3. Easy management: All graphics created through upsert are recorded in the node's shapeMap, you can easily get them through this.getShape(key)

render(attributes, container): Main Entry Point for Rendering Edges

Every custom edge class must implement the render(attributes, container) method, which defines how the edge is "drawn". You can use various atomic graphics here to compose the structure you want.

render(style: Record<string, any>, container: Group): void;

getShape(name): Get Created Graphics

Sometimes, you need to modify the properties of a sub-graphic after creation, or make sub-graphics interact with each other. In this case, the getShape method can help you get any graphic previously created through upsert:

⚠️ Note: The order of graphics is important. If graphic B depends on the position of graphic A, you must ensure A is created first

Element Conventions

• Use Conventional Properties

Currently conventional element properties include:

• Get element size through this.getSize()

• Get edge start and end points through const [sourcePoint, targetPoint] = this.getEndpoints(attributes, false) (simple mode - doesn't consider node shape, directly returns node center or nearest port center position)

• Get edge start and end points through const [sourcePoint, targetPoint] = this.getEndpoints(attributes) (optimized mode - default is true, considers node shape, returns connection points on node boundary)

• Use Paired getXxxStyle and drawXxxShape Methods for Graphic Drawing

getXxxStyle is used to get graphic styles, drawXxxShape is used to draw graphics. Graphics created this way support automatic animation execution.

Where Xxx is the camelCase form of the key passed when calling the upsert method.

• Access Graph Context through this.context

Lifecycle Hooks

The following lifecycle hook functions are provided, which you can override in custom edges to execute specific logic at key moments:

State Response

One of the most powerful aspects of G6 element design is the ability to separate "state response" from "rendering logic".

You can define styles for each state in edge configuration:

edge: {
  type: 'custom-edge',
  style: { stroke: '#eee' },
  state: {
    selected: {
      stroke: '#f00',
    },
    hover: {
      lineWidth: 3,
      stroke: '#1890ff',
    },
  },
}

Method to switch states:

graph.setElementState(edgeId, ['selected']);

This state will be passed to the render() method's attributes, and the merged result by the internal system will be automatically applied to the graphics.

You can also customize rendering logic based on state:

protected getKeyStyle(attributes: Required<BaseEdgeStyleProps>) {
  const style = super.getKeyStyle(attributes);

  // Adjust style based on state
  if (attributes.states?.includes('selected')) {
    return {
      ...style,
      stroke: '#1890ff',
      lineWidth: 2,
      shadowColor: 'rgba(24,144,255,0.2)',
      shadowBlur: 15,
    };
  }

  return style;
}

From Simple to Complex

Custom Path Polyline Edge

import { Graph, register, BaseEdge, ExtensionCategory } from '@antv/g6';

class MyPolylineEdge extends BaseEdge {
  getKeyPath(attributes) {
    const [sourcePoint, targetPoint] = this.getEndpoints(attributes);

    return [
      ['M', sourcePoint[0], sourcePoint[1]],
      ['L', targetPoint[0] / 2 + (1 / 2) * sourcePoint[0], sourcePoint[1]],
      ['L', targetPoint[0] / 2 + (1 / 2) * sourcePoint[0], targetPoint[1]],
      ['L', targetPoint[0], targetPoint[1]],
    ];
  }
}

register(ExtensionCategory.EDGE, 'my-polyline-edge', MyPolylineEdge);

const graph = new Graph({
  container: 'container',
  height: 200,
  data: {
    nodes: [
      { id: 'node-0', style: { x: 100, y: 50, ports: [{ key: 'right', placement: [1, 0.5] }] } },
      { id: 'node-1', style: { x: 250, y: 150, ports: [{ key: 'left', placement: [0, 0.5] }] } },
    ],
    edges: [{ source: 'node-0', target: 'node-1' }],
  },
  edge: {
    type: 'my-polyline-edge',
    style: {
      startArrow: true,
      endArrow: true,
      stroke: '#F6BD16',
    },
  },
  behaviors: ['drag-element'],
});

graph.render();

Additional Labels

import { Graph, Line, register, BaseEdge, ExtensionCategory, subStyleProps } from '@antv/g6';

class LabelEdge extends Line {
  render(attributes, container) {
    super.render(attributes);
    this.drawEndLabel(attributes, container, 'start');
    this.drawEndLabel(attributes, container, 'end');
  }

  drawEndLabel(attributes, container, type) {
    const key = type === 'start' ? 'startLabel' : 'endLabel';
    const [x, y] = this.getEndpoints(attributes)[type === 'start' ? 0 : 1];

    const fontStyle = {
      x,
      y,
      dx: type === 'start' ? 15 : -15,
      fontSize: 16,
      fill: 'gray',
      textBaseline: 'middle',
      textAlign: type,
    };
    const style = subStyleProps(attributes, key);
    const text = style.text;
    this.upsert(`label-${type}`, 'text', text ? { ...fontStyle, ...style } : false, container);
  }
}

register(ExtensionCategory.EDGE, 'extra-label-edge', LabelEdge);

const graph = new Graph({
  container: 'container',
  height: 200,
  data: {
    nodes: [
      { id: 'node-0', style: { x: 100, y: 100 } },
      { id: 'node-1', style: { x: 300, y: 100 } },
    ],
    edges: [{ source: 'node-0', target: 'node-1' }],
  },
  edge: {
    type: 'extra-label-edge',
    style: {
      startArrow: true,
      endArrow: true,
      stroke: '#F6BD16',
      startLabelText: 'start',
      endLabelText: 'end',
    },
  },
  behaviors: ['drag-element'],
});

graph.render();