Published unlisted
Edited
Dec 27, 2021
2 stars
Plot.plot({
[facet ? "facet" : "_disabled"]: {
data,
x: d => (d.x1 > d.x2) ? "left" : "right",
y: d => (d.y1 > d.y2) ? "down" : "up"
},
[facet ? "fy" : "_fy"]: { domain: ["up", "down"] },
marks: [
arrow(data, {
x1: "x1", x2: "x2", y1: "y1", y2: "y2", // mark coordinates
stroke: "value", // mark style
strokeWidth: 1.5, // global style
angle, arrowheadangle, arrowheadlen // plugin config
})
]})
mutable debug = ({})
function arrow() {
class Arrow extends Plot.Link {
constructor(_, opts) {
// initialize Plot.link normally
const R = super(...arguments);
// save the options, we'll use some of them
this.opts = opts; // 💡 shouldn't this be the general rule? we'd save this constructor step
}
render() {
const opts = this.opts;
// Let Plot.link create paths from data
const node = super.render(...arguments);
const lines = d3.select(node).attr("fill", "none").selectAll("path");
// get their properties and replace the paths' d:
lines.select(function() {
const [x1, y1, x2, y2] = this.getAttribute("d").split(/[ML,]/g).slice(1).map(Number);
this.setAttribute("d", getPath(x1, y1, x2, y2, opts));
});
return node;
}
}
return new Arrow(...arguments);
// TODO? write this as a relative tension rather than angle?
// (see https://observablehq.com/@mbostock/inequality-in-american-cities#arc)
function getPath(x1, y1, x2, y2, {angle = Math.PI/4, arrowheadlen = 10, arrowheadangle = 0.4}) {
const CLOCKWISE = +(+angle < 0);
const ANGLE = Math.abs(+angle);
const D = 1 / (2 * Math.tan(Math.max(1e-7, ANGLE / 2)));
// get the chord length between points
const dx = x2 - x1, dy = y2 - y1;
const h = Math.hypot(dy, dx);
// get the distance at which chord of height h subtends {angle} radians
const d = h * D;
// get the radius {r} of the circumscribed circle
const r = Math.hypot(d, h / 2);
// arrow head
const l = Math.min(arrowheadlen, h * 0.3), a = arrowheadangle;
const tangentAngle = Math.atan2(dy, dx)
+ (CLOCKWISE ? 1 : -1) * ANGLE / 2 * (1 - (l / r / Math.PI));
const x3 = x2 - l * Math.cos(tangentAngle + a), y3 = y2 - l * Math.sin(tangentAngle + a);
const x4 = x2 - l * Math.cos(tangentAngle - a), y4 = y2 - l * Math.sin(tangentAngle - a);
// build path string
return r < 1e5
? `M ${x1} ${y1} A ${r} ${r} 0 0 ${CLOCKWISE} ${x2} ${y2} L ${x3} ${y3} M ${x2} ${y2} L ${x4} ${y4}`
: `M ${x1} ${y1} L ${x2} ${y2} L ${x3} ${y3} M ${x2} ${y2} L ${x4} ${y4}`
}
}
data = Array.from({length: 30}, () => ({ x1: random(), x2: random() + random() + random(), y1: random(), y2: random(), value: Math.random() }))
random = d3.randomNormal()
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