function legend({
color,
title,
tickSize = 6,
width = 320,
height = 44 + tickSize,
marginTop = 18,
marginRight = 0,
marginBottom = 16 + tickSize,
marginLeft = 0,
ticks = width / 64,
tickFormat,
tickValues,
invert,
inline
} = {}) {
const svg = d3
.create("svg")
.attr("width", width)
.attr("height", height)
.attr("viewBox", [0, 0, width, height])
.style("overflow", "visible")
.style("display", d => {
if (inline) {
return "inline";
} else {
return "block";
}
});
let tickAdjust = g =>
g.selectAll(".tick line").attr("y1", marginTop + marginBottom - height);
let x;
if (color.interpolate) {
const n = Math.min(color.domain().length, color.range().length);
x = color
.copy()
.rangeRound(
d3.quantize(d3.interpolate(marginLeft, width - marginRight), n)
);
svg
.append("image")
.attr("x", marginLeft)
.attr("y", marginTop)
.attr("width", width - marginLeft - marginRight)
.attr("height", height - marginTop - marginBottom)
.attr("preserveAspectRatio", "none")
.attr(
"xlink:href",
ramp(
color.copy().domain(d3.quantize(d3.interpolate(0, 1), n)),
255,
invert
).toDataURL()
);
}
// Sequential
else if (color.interpolator) {
x = Object.assign(
color
.copy()
.interpolator(d3.interpolateRound(marginLeft, width - marginRight)),
{
range() {
return [marginLeft, width - marginRight];
}
}
);
svg
.append("image")
.attr("x", marginLeft)
.attr("y", marginTop)
.attr("width", width - marginLeft - marginRight)
.attr("height", height - marginTop - marginBottom)
.attr("preserveAspectRatio", "none")
.attr("xlink:href", ramp(color.interpolator(), 256, invert).toDataURL());
// scaleSequentialQuantile doesn’t implement ticks or tickFormat.
if (!x.ticks) {
if (tickValues === undefined) {
const n = Math.round(ticks + 1);
tickValues = d3
.range(n)
.map(i => d3.quantile(color.domain(), i / (n - 1)));
}
if (typeof tickFormat !== "function") {
tickFormat = d3.format(tickFormat === undefined ? ",f" : tickFormat);
}
}
}
// Threshold
else if (color.invertExtent) {
const thresholds = color.thresholds
? color.thresholds() // scaleQuantize
: color.quantiles
? color.quantiles() // scaleQuantile
: color.domain(); // scaleThreshold
const thresholdFormat =
tickFormat === undefined
? d => d
: typeof tickFormat === "string"
? d3.format(tickFormat)
: tickFormat;
x = d3
.scaleLinear()
.domain([-1, color.range().length - 1])
.rangeRound([marginLeft, width - marginRight]);
svg
.append("g")
.selectAll("rect")
.data(color.range())
.join("rect")
.attr("x", (d, i) => x(i - 1))
.attr("y", marginTop)
.attr("width", (d, i) => x(i) - x(i - 1))
.attr("height", height - marginTop - marginBottom)
.attr("fill", d => d);
tickValues = d3.range(thresholds.length);
tickFormat = i => thresholdFormat(thresholds[i], i);
}
// Ordinal
else {
x = d3
.scaleBand()
.domain(color.domain())
.rangeRound([marginLeft, width - marginRight]);
svg
.append("g")
.selectAll("rect")
.data(color.domain())
.join("rect")
.attr("x", x)
.attr("y", marginTop)
.attr("width", Math.max(0, x.bandwidth() - 1))
.attr("height", height - marginTop - marginBottom)
.attr("fill", color);
tickAdjust = () => {};
}
svg
.append("g")
.attr("transform", `translate(0,${height - marginBottom})`)
.call(
d3
.axisBottom(x)
.ticks(ticks, typeof tickFormat === "string" ? tickFormat : undefined)
.tickFormat(typeof tickFormat === "function" ? tickFormat : undefined)
.tickSize(tickSize)
.tickValues(tickValues)
)
.call(tickAdjust)
.call(g => g.select(".domain").remove())
.call(g =>
g
.append("text")
.attr("x", marginLeft)
.attr("y", marginTop + marginBottom - height - 6)
.attr("fill", "currentColor")
.attr("text-anchor", "start")
.attr("font-weight", "bold")
.text(title)
);
return svg.node();
}