javascript - D3.js 向前和向后补间到特定点

Question

我刚刚开始在 D3 中使用补间，一开始看起来很简单，但现在我正在努力在当前的代码中实现这一目标:

• 补间到特定点，例如:从 0,0 到 lineData[4]
• 从 lineData[4] 补间回到点 0,0

(可能使用按钮来控制)

这是我目前的代码:https://jsfiddle.net/uozko2bw/2/

//The data for our line
var lineData = [ 
{ "x": 1,   "y": 5},  { "x": 20,  "y": 20},
{ "x": 40,  "y": 10}, { "x": 60,  "y": 40},
{ "x": 80,  "y": 5},  { "x": 100, "y": 60}];

var lineFunction = d3.line()
 .x(function(d) { return d.x; })
 .y(function(d) { return d.y; })
 .curve(d3.curveCardinal);

//The SVG Container
var svgContainer = d3.select("body").append("svg")
    .attr("width", 200)
    .attr("height", 200);

//The line SVG Path we draw
var lineGraph = svgContainer.append("path")
 .attr("d", lineFunction(lineData))
 .attr("stroke", "blue")
 .attr("stroke-width", 2)              
 .attr("fill", "none");

 var circle = svgContainer.append("circle")
  .attr("r", 5)
  .attr("transform", "translate(" + lineData[0].x + "," + lineData[0].y + 
 ")");

 transition();

 function transition() {
  circle.transition()
  .duration(10000)
  .attrTween("transform", translateAlong(lineGraph.node()))
  .each("end", transition);
 }

 function translateAlong(path) {
 var l = path.getTotalLength();

 return function(d, i, a) {
   return function(t) {
     var p = path.getPointAtLength(t * l);
     return "translate(" + p.x + "," + p.y + ")";
   };
 };
}

Answer 1

interpolator 中的t通常从 0 到 1:

The returned interpolator will then be invoked for each frame of the transition, in order, being passed the eased time t, typically in the range [0, 1].

因此，您可以简单地调用另一个插值器，其中 t 从 1 变为 0:

var p = path.getPointAtLength((1-t) * l);

这是演示:

//The data for our line
 var lineData = [ 
 	{ "x": 1,   "y": 5},  { "x": 20,  "y": 20},
   { "x": 40,  "y": 10}, { "x": 60,  "y": 40},
   { "x": 80,  "y": 5},  { "x": 100, "y": 60}];

var lineFunction = d3.line()
     .x(function(d) { return d.x; })
     .y(function(d) { return d.y; })
     .curve(d3.curveCardinal);

//The SVG Container
var svgContainer = d3.select("body").append("svg")
		.attr("width", 200)
		.attr("height", 200);

//The line SVG Path we draw
var lineGraph = svgContainer.append("path")
     .attr("d", lineFunction(lineData))
     .attr("stroke", "blue")
     .attr("stroke-width", 2)              
     .attr("fill", "none");

var circle = svgContainer.append("circle")
    .attr("r", 5)
    .attr("transform", "translate(" + lineData[0].x + "," + lineData[0].y + ")");

transition();

/*
svgContainer.on("click", function() {
    transition();
});*/

function transition() {
  circle.transition()
      .duration(10000)
      .attrTween("transform", translateAlong(lineGraph.node()))
      .on("end", transition2);
}

function transition2() {
  circle.transition()
      .duration(10000)
      .attrTween("transform", translateAlong2(lineGraph.node()));
}

function translateAlong(path) {
  var l = path.getTotalLength();
  
  return function(d, i, a) {
    return function(t) {
      var p = path.getPointAtLength(t * l);
      return "translate(" + p.x + "," + p.y + ")";
    };
  };
}

function translateAlong2(path) {
  var l = path.getTotalLength();
  
  return function(d, i, a) {
    return function(t) {
      var p = path.getPointAtLength((1-t) * l);
      return "translate(" + p.x + "," + p.y + ")";
    };
  };
}

<script src="https://d3js.org/d3.v4.min.js"></script>

PS:在 D3 v4 中，是 .on("end"...，而不是 each("end"...。

PPS:我的解决方案中有很多重复。我会给你做干作业。