D3 Examples - Triangle to Rectangle Decomposition

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<!DOCTYPE html>
<style>
​
circle {
  cursor: move;
  fill: #fff;
  stroke: #000; 
  stroke-width: 1px;
}
​
circle.active {
  stroke: #000;
  stroke-width: 2px;
}
​
path.subject {
  fill: none;
  stroke: rgba(0, 0, 0, 0.3);
  stroke-width: 2px;
}
​
path.canonicalRectangle {
  fill: none;
  stroke: rgba(0, 0, 240, 1);
  stroke-width: 2px;
}
​
path.canonicalSquare {
  fill: none;
  fill: rgba(240, 0, 0, 0.1);
  stroke-dasharray: 5, 5;
  stroke: rgba(240, 0, 0, 1);
  stroke-width: 2px;
}
​
</style>
<svg width="960" height="960"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="https://d3js.org/d3-array.v1.min.js"></script>
<script src="https://d3js.org/d3-polygon.v1.min.js"></script>
<script src="https://npmcdn.com/earcut@2.1.1/dist/earcut.min.js"></script>
<script src="scissors.debug.js"></script>
<script>
​
var svg = d3.select("svg"),
    width = svg.attr("width"),
    height = svg.attr("height");
​
var color = d3.scaleOrdinal(d3.schemeCategory20);
​
// Counter-clockwise orientation.
var subject = [[width / 2, height / 5],
            [width / 5, 3 * height / 5],
            [3 * width / 5, 3 * height / 5]];
​
var subjectPolygon = svg.append("path")
    .datum(subject)
    .attr("class", "subject");
​
// Control points for the subject polygon.
var circle = svg.selectAll("circle")
  .data(subject);
​
var origin = [0, 0];
​
circle.enter()
  .append("circle")
    .attr("r", 9)
    .attr("cx", function(d) { return d[0]; })
    .attr("cy", function(d) { return d[1]; })
    .call(d3.drag()
        .on("start", dragstarted)
        .on("drag", dragged)
        .on("end", dragended));
​
update();
​
// Redraw polygons in response to control point movement.
function update() {
  let sideLength = Math.sqrt(Math.abs(d3.polygonArea(subject))),
      canonicalRectangle = scissors.triangle2Rectangle(subject),
      canonicalSquare = scissors.rectangle2Rectangle(canonicalRectangle, sideLength);
      
  // Ensure subject polygon has counter-clockwise orientation.
  if (!ccw(subject)) subject.reverse();
​
  subjectPolygon.attr("d", function(d) { return "M" + d.join("L") + "Z"; });
​
  svg.selectAll(".canonicalRectangle").remove();
  svg.selectAll(".canonicalSquare").remove();
​
  rectangle = svg.selectAll(".canonicalRectangle")
    .data(canonicalRectangle); // Key on Object reference.
  
  rectangle.enter().insert("path")
      .attr("class", "canonicalRectangle")
      .attr("d", function(d) { return "M" + d.join("L") + "Z"; });
​
​
  square = svg.selectAll(".canonicalSquare")
    .data(canonicalSquare); // Key on Object reference.
  
  square.enter().insert("path")
      .attr("fill", function(d, i) { return color(i); })
      .attr("class", "canonicalSquare")
      .attr("d", function(d) { return "M" + d.join("L") + "Z"; });
​
  // Circles drawn on top of all other SVG elements.
  d3.selectAll("circle").raise();
}
​
function dragstarted(d) {
  d3.select(this).classed("active", true);
}
​
function dragged(d) {
  d3.select(this)
      .attr("cx", d[0] = d3.event.x)
      .attr("cy", d[1] = d3.event.y)
  update();
}
​
function dragended(d, i) {
  d3.select(this).classed("active", false);
}
​
function polygonClone(polygon) {
  var cloned = [],
      i,
      n;
​
  for (i = 0, n = polygon.length; i < n; i++) {
    cloned.push([polygon[i][0], polygon[i][1]]);
  }
​
  return cloned;
}
​
// Returns true of the given polygon has counter-clockwise orientation.
function ccw(polygon) {
  function polygonInside(p, a, b) {
    return (b[0] - a[0]) * (p[1] - a[1]) < (b[1] - a[1]) * (p[0] - a[0]);
  }
​
  return polygonInside(d3.polygonCentroid(polygon), polygon[0], polygon[1]);
}
​
</script>
​
    