trees

<!DOCTYPE html>
<meta charset="utf-8">
<style>
</style>

/*
Influenced by Miguel Ferreira:
https://codepen.io/MigFerreira/pen/RPZpgd

The original tree generation code is theirs.

I simplified some of the branch generation code and then added
code to allow for the animation.
*/

// Tree configuration
var branches = [];
var seed = {i: 0, x1: 480, y1: 700, x2: 480, y2: 425, a: 0, l: 75, d:0, children: []}; // a = angle, l = length, d = depth
var child_angle = 0.6; // Angle delta, all child branches will angle between 0 - 0.6 radians away from the parent angle
var child_length = 0.85; // Length delta (factor), all child branches will be 0.85 the length of the parent
var maxDepth = 10;

// Recursively create the tree
function create_branch(b) {
  branches.push(b);

if (b.d === maxDepth)
    return;

// two branches, flip the i from -1 to 1 to handle "left and right" branches
  for(var i = -1; i < 2; i = i + 2) {
    var ang = b.a + (Math.random() * child_angle * i);
    var newB = {
      i: branches.length,
      x1: b.x2,
      y1: b.y2,
      x2: b.x2 + (b.l * child_length) * Math.sin( ang ),
      y2: b.y2 - (b.l * child_length) * Math.cos( ang ),
      a: ang,
      orig_a: ang, // for book-keeping in animation
      animating: false,
      animate_counter: 0,
      l: b.l * child_length,
      d: b.d + 1,
      children: []
    };
    b.children.push(newB.i)
    create_branch(newB);
  }
}

function draw() {
  var color = d3.scale.linear()
      .domain([0, maxDepth])
      .range(["sienna","darkolivegreen"]);

d3.select('svg').selectAll('line')
    .data(branches)
  .enter()
    .append('line')
    .attr('id', function(d) { return "branch" + d.i; })
    .attr('x1', function(d) { return d.x1; })
    .attr('y1', function(d) { return d.y1; })
    .attr('x2', function(d) { return d.x2; })
    .attr('y2', function(d) { return d.y2; })
    .style('stroke-width', function(d) { return parseInt((maxDepth - d.d + 2) * .5) + 'px'; })
    .style('stroke', function(d) { return color(d.d); });
}

function animate() {
  // this runs every second,
  // every 10 seconds, stop triggering new animations for 10 seconds to allow things to settle
  // this ends up giving the perception of "breezes"
  animationCounter += 1;
  if(animationCounter == 20) { animationCounter = 0; }
  else if(animationCounter % 20 > 10) { return };

branches.forEach(function(branch) {
    if(branch.animating == false && Math.random() < (branch.d / 500.0)) {
      branch.animating = true;
      moveBranch(branch);
    }
  });
}

function moveBranch(branch) {
  modifier = branch.d / 15;
  branch.a = branch.orig_a + (Math.random() * modifier - (modifier/2.0));
  branch.x2 = branch.x1 + branch.l * Math.sin( branch.a );
  branch.y2 = branch.y1 - branch.l * Math.cos( branch.a );

// This is probably "bad" d3 with regards to the data selection,
  // it might even be easier to do this in jQuery or vanilla JS,
  // the one benefit is to take advantage of d3 duration/ease animation functionality.
  d3.select("#branch" + branch.i)
    .data([branch])
    .transition()
    .duration(3000)
    .ease('linear')
    .attr('x1', function(d) { return d.x1; })
    .attr('y1', function(d) { return d.y1; })
    .attr('x2', function(d) { return d.x2; })
    .attr('y2', function(d) { return d.y2; })
    .each('end', function(d) {
      if(d.animating == true) {
        if(d.animate_counter < 3) { // keep "swaying" for 3 more frames
          d.animate_counter += 1;
          moveBranch(d);
        } else {
          d.animating = false;
          d.animate_counter = 0;
        }
      }
    });

// make the children move
  branch.children.forEach(function(childIdx) {
    var currChild = branches[childIdx];
    currChild.x1 = branch.x2;
    currChild.y1 = branch.y2;
    moveBranch(currChild);
  });
}

create_branch(seed);
draw();

var animationCounter = 0;
setInterval(animate, 1000);

</script>

https://d3js.org/d3.v3.min.js