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Configure the Items	2

There are Node and Edge two types of items in a graph. In the last chapter, we rendered the Tutorial Demo with items with rough styles. Now, we are going to beautify the items while introducing the properties of the items.

Figure 1 The Tutorial Demo with cofigured items.

Basic Concept

Graph Item

There are Node and Edge two types of items in a graph. Several Built-in Nodes and Built-in Edges are provided by G6. The main difference between different types of items is their Graphics Shape. For example, a node's graphics type can be a circle, a rect, an image, or others.

Properties of Item

The properties of an item can be be divided into two categories:

Style Property style: Corresponds to the style in Canvas. When the State of an item is changed, the style can be updated. It is an object named style;
Other Property: Such as graphics type, id, they are a kind of properties that will not be changed when the State of the item is changed.

For example, When you change the state 'hover' or 'click' to true for a node A, only the style properties of A can be updated, e.g. fill, stroke, and so on. The other properties such as type can not be changed. To update the other properties, configure A by graph.updateItem manually.

Data Structure

The data structure of a node:

{
	id: 'node0',          // Unique id of the node
  type: 'circle',      // The type of graphics shape of the node
  size: 40,             // The size
  label: 'node0'        // The label
  visible: true,        // Controls the visible of the node when first render. false means hide the item. All the items are visible by default
  labelCfg: {           // The configurations for the label
    positions: 'center',// The relative position of the label
    style: {            // The style properties of the label
      fontSize: 12,     // The font size of the label
      // ...            // Other style properties of the label
    }
  }
  // ...,               // Other properties of the node
  style: {              // The object of style properties of the node
    fill: '#000',       // The filling color
    stroke: '#888',     // The stroke color
    // ...              // Other styleattribtues of the node
  }
}

The data structure of an edge is similar to node, but two more properties source and target in addition, representing the id of the source node and the id of the target node respectively.

We can refine the visual requirements in figure 1 of Tutorial Demo into:

Visual Effect:
- R1: Set the color for stroke and filling for nodes with fill and stroke;
- R2: Set the color for the label with labelCfg;
- R3: Set the opacity and color for edges with opacity，stroke;
- R4: Set the direction of the label with labelCfg;
Map the data to visual channels:
- R5: Configure the type of nodes with type according to the property class in node data;
- R6: Configure the line widht of edges with lineWidth according to the property weight in edge data.

Configure the Properties

To satisfy different scenario, G6 provides 7 ways to configure the properties for items. Here we will only introduce two of them:

Configure the global properties when instantiating a Graph;
Configure the properties for different items in their data.

1. Configure the Global Properties When Instantiating a Graph

Applicable Scene: Unify the configurations for all the nodes or edges.
Usage: Configure it with two configurations of graph:

defaultNode: The Style Property and Other Properties in the default state;
defaultEdge: The Style Property and Other Properties in the default state.

⚠️Attention: It is a way of unified global configuration, which does not distinguish the nodes with different properties (e.g. class and weight) in their data. That is to say, only R1, R2, R3, and R4 can be satisfied now:

Figure 2 Tutorial Demo with items configured by global configurations.

Configure the defaultNode and defaultEdge for graph to achieve the expected effect:

const graph = new G6.Graph({
  // ...                   // Other configurations of the graph
  // The style properties and other properties for all the nodes in the default state
  defaultNode: {
    size: 30, // The size of nodes
    // ...                 // The other properties
    // The style properties of nodes
    style: {
      fill: 'steelblue', // The filling color of nodes
      stroke: '#666', // The stroke color of nodes
      lineWidth: 1, // The line width of the stroke of nodes
    },
    // The properties for label of nodes
    labelCfg: {
      // The style properties for the label
      style: {
        fill: '#fff', // The color of the text
      },
    },
  },
  // The style properties and other properties for all the edges in the default state
  defaultEdge: {
    // ...                 // The other properties
    // The style properties of edges
    style: {
      opacity: 0.6, // The opacity of edges
      stroke: 'grey', // The color of the edges
    },
    // The properties for label of edges
    labelCfg: {
      autoRotate: true, // Whether to rotate the label according to the edges
    },
  },
});

2. Configure the Properties in Data

Applicable Scene: By this way, you can configure different items according to their properties in data.
Thus, the R5 and R6 can be satisfied now.
Usage: Write the properties into each item data, or traverse the data to assign the properties. Here we show assigning the attrbiutes into data by traversing:

const nodes = remoteData.nodes;
nodes.forEach((node) => {
  if (!node.style) {
    node.style = {};
  }
  switch (
    node.class // Configure the graphics type of nodes according to their class
  ) {
    case 'c0': {
      node.type = 'circle'; // The graphics type is circle when class = 'c0'
      break;
    }
    case 'c1': {
      node.type = 'rect'; // The graphics type is rect when class = 'c1'
      node.size = [35, 20]; // The node size when class = 'c1'
      break;
    }
    case 'c2': {
      node.type = 'ellipse'; // The graphics type is ellipse when class = 'c2'
      node.size = [35, 20]; // The node size when class = 'c2'
      break;
    }
  }
});

graph.data(remoteData);

The result:

Figure 3

From figure 3, we find some nodes are rendered as rects, some are ellipses. We also set the size to override the size in global configuration. The size is an array when the node is a rect or an ellipse. We did not set the size for circle node, so size: 30 in global configuration will still take effect for circle node. That is to say, configuring items by writing into data has higher priority than global configurations.

We further set the line widths for edges according to their weight:

// const nodes = ...

// Traverse the egdes data
const edges = remoteData.edges;
edges.forEach((edge) => {
  if (!edge.style) {
    edge.style = {};
  }
  edge.style.lineWidth = edge.weight; // Mapping the weight in data to lineWidth
});

graph.data(remoteData);