在D3定向力图中改变箭头标记的方向

Question

我正在尝试在每个链接中插入一个箭头标记。但是我想改变箭头的方向，让它们面向每个链接的另一端。

以下是代码：

    svg.append("svg:defs").selectAll("marker")
        .data(["end"])      // Different link/path types can be defined here
      .enter().append("svg:marker")
        .attr("id", "end")    // This section adds in the arrows
        .attr("viewBox", "0 -5 10 10")
        .attr("refX", 15)
        .attr("refY", -1.5)
        .attr("markerWidth", 6)
        .attr("markerHeight", 6)
        .attr("orient", 180)
      .append("svg:path")
        .attr("d", "M0,-5L10,0L0,5");

    // add the links and the arrows
    var pg = svg.append("svg:g").selectAll("path")
        .data(force.links())
      .enter().append("g");

    var path = pg.append("path")
        .attr("class", "link")
        .attr("marker-end", "url(#end)")

怎么可能？

我试图更改.attr("marker-end", "url(#end)");

代表.attr("marker-end", "url(#start)");

然后标记就消失了。我想知道的另一件事是代码的哪一部分定义了链接的曲率以及如何改变它。

谢谢。

Answer 1

您应该查看标记的"orient"属性：https://www.w3.org/TR/svg-markers/#OrientAttribute

在您的情况下：.attr("orient", "auto-start-reverse")或.attr("orient", 180)会起作用。

可以在这篇文章中找到一个例子：Display an arrow head in the middle of D3 force layout link

关于曲率，相关部分是

dr = Math.sqrt(dx * dx + dy * dy);

作为dr，半径变大，会有更多的曲线。

Answer 2

svg.select("defs").append("marker")
    .attr("id", "start")
    .attr("viewBox", "0 -5 10 10")
    .attr("refX", -5)
    .attr("refY", 0)
    .attr("markerWidth", 6)
    .attr("markerHeight", 6)    
    .attr("orient", "auto")
    .append("path")
    .attr("d", "M0,0L10,-5L10,5");

var path = svg.append("svg:g").selectAll("path")
    .data(force.links())
    .enter().append("svg:path")
    .attr("class", "link")
    .attr("marker-start", "url(#start)")
    .attr("marker-end", "url(#end)");

var links= [
  {
    "source": "Harry",
    "target": "Sally",
    "value": 1.2
  },
  {
    "source": "Harry",
    "target": "Mario",
    "value": 1.3
  },
  {
    "source": "Sarah",
    "target": "Alice",
    "value": 0.2
  },
  {
    "source": "Eveie",
    "target": "Alice",
    "value": 0.5
  },
  {
    "source": "Peter",
    "target": "Alice",
    "value": 1.6
  },
  {
    "source": "Mario",
    "target": "Alice",
    "value": 0.4
  },
  {
    "source": "James",
    "target": "Alice",
    "value": 0.6
  },
  {
    "source": "Harry",
    "target": "Carol",
    "value": 0.7
  },
  {
    "source": "Harry",
    "target": "Nicky",
    "value": 0.8
  },
  {
    "source": "Bobby",
    "target": "Frank",
    "value": 0.8
  },
  {
    "source": "Alice",
    "target": "Mario",
    "value": 0.7
  },
  {
    "source": "Harry",
    "target": "Lynne",
    "value": 0.5
  },
  {
    "source": "Sarah",
    "target": "James",
    "value": 1.9
  },
  {
    "source": "Roger",
    "target": "James",
    "value": 1.1
  },
  {
    "source": "Maddy",
    "target": "James",
    "value": 0.3
  },
  {
    "source": "Sonny",
    "target": "Roger",
    "value": 0.5
  },
  {
    "source": "James",
    "target": "Roger",
    "value": 1.5
  },
  {
    "source": "Alice",
    "target": "Peter",
    "value": 1.1
  },
  {
    "source": "Johan",
    "target": "Peter",
    "value": 1.6
  },
  {
    "source": "Alice",
    "target": "Eveie",
    "value": 0.5
  },
  {
    "source": "Harry",
    "target": "Eveie",
    "value": 0.1
  }
];

var nodes = {};

// Compute the distinct nodes from the links.
links.forEach(function(link) {
    link.source = nodes[link.source] || 
        (nodes[link.source] = {name: link.source});
    link.target = nodes[link.target] || 
        (nodes[link.target] = {name: link.target});
    link.value = +link.value;
});

var width = 960,
    height = 500;

var force = d3.layout.force()
    .nodes(d3.values(nodes))
    .links(links)
    .size([width, height])
    .linkDistance(60)
    .charge(-300)
    .on("tick", tick)
    .start();

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

// build the arrow.
svg.append("svg:defs").selectAll("marker")
    .data(["end"])      // Different link/path types can be defined here
  .enter().append("svg:marker")    // This section adds in the arrows
    .attr("id", String)
    .attr("viewBox", "0 -5 10 10")
    .attr("refX", 15)
    .attr("refY", -1.5)
    .attr("markerWidth", 6)
    .attr("markerHeight", 6)
    .attr("orient", "auto")
  .append("svg:path")
    .attr("d", "M0,-5L10,0L0,5");

svg.select("defs").append("marker")
    .attr("id", "start")
    .attr("viewBox", "0 -5 10 10")
    .attr("refX", -5)
    .attr("refY", 0)
    .attr("markerWidth", 6)
    .attr("markerHeight", 6)    
    .attr("orient", "auto")
    .append("path")
    .attr("d", "M0,0L10,-5L10,5");

// add the links and the arrows
var path = svg.append("svg:g").selectAll("path")
    .data(force.links())
    .enter().append("svg:path")
    .attr("class", "link")
    .attr("marker-start", "url(#start)")
    .attr("marker-end", "url(#end)");

// define the nodes
var node = svg.selectAll(".node")
    .data(force.nodes())
  .enter().append("g")
    .attr("class", "node")
    .call(force.drag);

// add the nodes
node.append("circle")
    .attr("r", 5);

// add the text 
node.append("text")
    .attr("x", 12)
    .attr("dy", ".35em")
    .text(function(d) { return d.name; });

// add the curvy lines
function tick() {
    path.attr("d", function(d) {
        var dx = d.target.x - d.source.x,
            dy = d.target.y - d.source.y,
            dr = Math.sqrt(dx * dx + dy * dy);
        return "M" + 
            d.source.x + "," + 
            d.source.y + "A" + 
            dr + "," + dr + " 0 0,1 " + 
            d.target.x + "," + 
            d.target.y;
    });

    node
        .attr("transform", function(d) { 
  	    return "translate(" + d.x + "," + d.y + ")"; });
}

path.link {
  fill: none;
  stroke: #666;
  stroke-width: 1.5px;
}

circle {
  fill: #ccc;
  stroke: #fff;
  stroke-width: 1.5px;
}

text {
  fill: #000;
  font: 10px sans-serif;
  pointer-events: none;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>