Smoothed Fisheye (d3-fisheye)

Move the mouse to change the focal point of the fisheye. The left side of the grid shows fisheye with smoothing which is implemented in this plugin https://github.com/duaneatat/d3-fisheye and described here https://observablehq.com/@duaneatat/smoothed-fisheye - The right side is the sarkar-brown fisheye effect which has the abrupt discontinuity at the edge of the fisheye effect.

<!DOCTYPE html>
<meta charset="utf-8" />
<style>
  .background {
    fill: none;
    pointer-events: all;
  }

path {
    fill: none;
    stroke: #333;
  }
</style>
<body>
  <script src="//d3js.org/d3.v3.min.js"></script>
  <script src="fisheye-deprecated.js"></script>
  <script src="d3-fisheye.js"></script>
  <script>
    var width = 960,
      height = 500,
      xStepsBig = d3.range(10, width, 20),
      yStepsBig = d3.range(10, height, 20),
      xStepsSmall = d3.range(0, width + 4, 4),
      yStepsSmall = d3.range(0, height + 4, 4);

const points = [];
    for (var i = 0; i < 100; i++) {
      points.push({ x: Math.random() * width, y: Math.random() * height });
    }

var fisheye = d3Fisheye
      .radial()
      .radius(120)
      .distortion(5)
      .smoothingRatio(0.5);
    var fisheyeDeprecated = d3fisheyeDeprecated
      .circular()
      .radius(100)
      .distortion(5);

var line = d3.svg.line();

var svg = d3
      .select('body')
      .append('svg')
      .attr('width', width)
      .attr('height', height)
      .append('g')
      .attr('transform', 'translate(-.5,-.5)');

svg
      .append('rect')
      .attr('class', 'background')
      .attr('width', width)
      .attr('height', height);

const pointsSelection = svg
      .selectAll('dot')
      .data(points)
      .enter()
      .append('circle')
      .attr('r', 5)
      .attr('cx', function(d) {
        return d.x;
      })
      .attr('cy', function(d) {
        return d.y;
      });

svg
      .selectAll('.x')
      .data(xStepsBig)
      .enter()
      .append('path')
      .attr('class', 'x')
      .datum(function(x) {
        return yStepsSmall.map(function(y) {
          return [x, y];
        });
      });

svg
      .selectAll('.y')
      .data(yStepsBig)
      .enter()
      .append('path')
      .attr('class', 'y')
      .datum(function(y) {
        return xStepsSmall.map(function(x) {
          return [x, y];
        });
      });

var path = svg.selectAll('path').attr('d', line);

svg.on('mousemove', function() {
      const mouse = d3.mouse(this);
      fisheye.focus(mouse);
      fisheyeDeprecated.focus(mouse);
      pointsSelection
        .each(d => {
          if (mouse[0] > 500) {
            d.fisheye = fisheyeDeprecated(d);
          } else {
            d.fisheye = fisheye([d.x, d.y]);
          }
        })
        .attr('cx', function(d) {
          if (mouse[0] > 500) {
            return d.fisheye.x;
          } else {
            return d.fisheye[0];
          }
        })
        .attr('cy', function(d) {
          if (mouse[0] > 500) {
            return d.fisheye.y;
          } else {
            return d.fisheye[1];
          }
        });
      path.attr('d', function(d) {
        return line(
          d.map(tuple => {
            if (mouse[0] > 500) {
              const point = fisheyeDeprecated({ x: tuple[0], y: tuple[1] });
              return [point.x, point.y];
            } else {
              return fisheye(tuple);
            }
          })
        );
      });
    });
  </script>
</body>

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