max width, label, swatches

Author: Fil

README.md

@@ -261,7 +261,35 @@ Plot automatically generates axes for position scales. You can configure these a
 * *scale*.**labelAnchor** - the label anchor: *top*, *right*, *bottom*, *left*, or *center*
 * *scale*.**labelOffset** - the label position offset (in pixels; default 0, typically for facet axes)
 
-Plot does not currently generate a legend for the *color*, *radius*, or *opacity* scales, but when it does, we expect that some of the above options will also be used to configure legends. Top-level options are also supported as shorthand: **grid** (for *x* and *y* only; see [facet.grid](#facet-options)), **inset**, **round**, **align**, and **padding**.
+
+Plot can generate a color legend:
+
+* *color*.**legend** - a function that is passed the color scale and the color options, and returns a color legend that will be inserted at the top of the figure.
+
+If *color.legend* is true, a default color legend is created, with swatches for categorical and ordinal scales, and a ramp for continuous scales.
+
+The color swatches can be configured with the following options:
+* *color*.**columns** - the number of swatches per row
+* *color*.**format** - a format function for the labels
+* *color*.**swatchSize** - the size of the swatch (if square)
+* *color*.**swatchWidth** - the swatches’ width
+* *color*.**swatchHeight** - the swatches’ height 
+* *color*.**marginLeft** - the legend’s left margin
+
+The continuous color legends can be configured with the following options:
+* *color*.**label** - the scale’s label
+* *color*.**tickSize** - the tick size
+* *color*.**width** - the legend’s width
+* *color*.**height** - the legend’s height
+* *color*.**marginTop** - the legend’s top margin
+* *color*.**marginRight** - the legend’s right margin
+* *color*.**marginBottom** - the legend’s bottom margin
+* *color*.**marginLeft** - the legend’s left margin
+* *color*.**ticks** - number of ticks
+* *color*.**tickFormat** - a format function for the legend’s ticks
+* *color*.**tickValues** - the legend’s tick values
+
+Plot does not currently generate a legend for the *radius*, or *opacity* scales, but when it does, we expect that some of the above options will also be used to configure legends. Top-level options are also supported as shorthand: **grid** (for *x* and *y* only; see [facet.grid](#facet-options)), **inset**, **round**, **align**, and **padding**.
 
 ### Color options
 

package.json

@@ -32,6 +32,7 @@
   "devDependencies": {
     "@rollup/plugin-json": "^4.1.0",
     "@rollup/plugin-node-resolve": "^11.2.1",
+    "canvas": "^2.8.0",
     "clean-css": "^5.1.1",
     "eslint": "^7.12.1",
     "esm": "^3.2.25",

src/figure.js

@@ -0,0 +1,23 @@
+
+// Wrap the plot in a figure with a caption, if desired.
+export function figureWrap(svg, caption, legends) {
+  if (caption == null && legends.length === 0) return svg;
+  const figure = document.createElement("figure");
+  if (legends.length > 0) {
+    const figlegends = document.createElement("div");
+    figlegends.className = "legends";
+    figure.appendChild(figlegends);
+    for (const l of legends) {
+      if (l instanceof Node) {
+        figlegends.appendChild(l);
+      }
+    }
+  }
+  figure.appendChild(svg);
+  if (caption != null) {
+    const figcaption = document.createElement("figcaption");
+    figcaption.appendChild(caption instanceof Node ? caption : document.createTextNode(caption));
+    figure.appendChild(figcaption);
+  }
+  return figure;
+}

src/legends.js

@@ -0,0 +1,16 @@
+import {colorLegend} from "./legends/color.js";
+
+export function createLegends(descriptors, dimensions) {
+  const legends = [];
+  
+  for (let key in descriptors) {
+    let {legend, ...options} = descriptors[key];
+    if (key === "color" && legend === true) legend = colorLegend;
+    if (typeof legend === "function") {
+      const l = legend(options, dimensions);
+      if (l instanceof Node) legends.push(l);
+    }
+  }
+  
+  return legends;
+}

src/legends/color.js

@@ -0,0 +1,160 @@
+import {swatches} from "./swatches.js";
+import {scale} from "../scales.js";
+import {create, scaleLinear, quantize, interpolate, interpolateRound, quantile, range, format, scaleBand, axisBottom} from "d3";
+
+export function colorLegend({width, ...options}, {width: maxWidth}) {
+  switch(options.type) {
+    case "ordinal":
+    case "categorical":
+      return swatches(scale(options), options);
+  }
+  return legend(scale(options), {
+    width: width !== undefined ? width : Math.min(240, maxWidth),
+    ...options
+  });
+}
+
+function legend(color, {
+  label,
+  tickSize = 6,
+  width = 240, 
+  height = 44 + tickSize,
+  marginTop = 18,
+  marginRight = 0,
+  marginBottom = 16 + tickSize,
+  marginLeft = 0,
+  ticks = width / 64,
+  tickFormat,
+  tickValues
+} = {}) {
+  const svg = create("svg")
+      .attr("width", width)
+      .attr("height", height)
+      .attr("viewBox", [0, 0, width, height])
+      .style("overflow", "visible")
+      .style("display", "block");
+
+  let tickAdjust = g => g.selectAll(".tick line").attr("y1", marginTop + marginBottom - height);
+  let x;
+
+  // Continuous
+  if (color.interpolate) {
+    const n = Math.min(color.domain().length, color.range().length);
+
+    x = color.copy().rangeRound(quantize(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(quantize(interpolate(0, 1), n))).toDataURL());
+  }
+
+  // Sequential
+  else if (color.interpolator) {
+    x = Object.assign(color.copy()
+        .interpolator(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()).toDataURL());
+
+    // scaleSequentialQuantile doesn’t implement ticks or tickFormat.
+    if (!x.ticks) {
+      if (tickValues === undefined) {
+        const n = Math.round(ticks + 1);
+        tickValues = range(n).map(i => quantile(color.domain(), i / (n - 1)));
+      }
+      if (typeof tickFormat !== "function") {
+        tickFormat = 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" ? format(tickFormat)
+        : tickFormat;
+
+    x = 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 = range(thresholds.length);
+    tickFormat = i => thresholdFormat(thresholds[i], i);
+  }
+
+  // Ordinal
+  else {
+    x = 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(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(label === undefined ? () => {}
+      : g => g.append("text")
+        .attr("x", marginLeft)
+        .attr("y", marginTop + marginBottom - height - 6)
+        .attr("fill", "currentColor")
+        .attr("text-anchor", "start")
+        .attr("font-weight", "bold")
+        .attr("class", "label")
+        .text(label));
+
+  return svg.node();
+}
+
+function ramp(color, n = 256) {
+  const canvas = create("canvas").attr("width", n).attr("height", 1).node();
+  const context = canvas.getContext("2d");
+  for (let i = 0; i < n; ++i) {
+    context.fillStyle = color(i / (n - 1));
+    context.fillRect(i, 0, 1, 1);
+  }
+  return canvas;
+}

src/legends/swatches.js

@@ -0,0 +1,43 @@
+import {create} from "d3";
+
+export function swatches(color, {
+  columns = null,
+  format = x => x,
+  swatchSize = 15,
+  swatchWidth = swatchSize,
+  swatchHeight = swatchSize,
+  marginLeft = 0
+} = {}) {
+  const swatches = create("div")
+    .classed("swatches", true)
+    .attr("style", `--marginLeft: ${+marginLeft}px; --swatchWidth: ${+swatchWidth}px; --swatchHeight: ${+swatchHeight}px`);
+
+  if (columns !== null) {
+    const elems = swatches.append("div")
+      .style("columns", columns);
+    for (const value of color.domain()) {
+      const d = elems.append("div").classed("swatch-item", true);
+      d.append("div")
+        .classed("swatch-block", true)
+        .style("background", color(value));
+      const label = format(value);
+      d.append("div")
+        .classed("swatch-label", true)
+        .text(label)
+        .attr("title", label.replace(/["&]/g, entity));
+    }
+  } else {
+    swatches
+      .selectAll()
+      .data(color.domain())
+      .join("span")
+      .classed("swatch", true)
+      .style("--color", color)
+      .text(format);
+  }
+  return swatches.node();
+}
+
+function entity(character) {
+  return `&#${character.charCodeAt(0).toString()};`;
+}

src/plot.js

@@ -3,6 +3,8 @@ import {Axes, autoAxisTicks, autoAxisLabels, autoScaleLabel} from "./axes.js";
 import {facets} from "./facet.js";
 import {values} from "./mark.js";
 import {Scales, autoScaleRange, exposeScales} from "./scales.js";
+import {figureWrap} from "./figure.js";
+import {createLegends} from "./legends.js";
 import {offset} from "./style.js";
 
 export function plot(options = {}) {
@@ -91,7 +93,11 @@ export function plot(options = {}) {
     if (node != null) svg.appendChild(node);
   }
 
-  return exposeScales(wrap(svg, {caption}), scaleDescriptors);
+  const descriptors = exposeScales(scaleDescriptors);
+  const legends = createLegends(descriptors, dimensions);
+  const figure = figureWrap(svg, caption, legends);
+  figure.scales = descriptors;
+  return figure;
 }
 
 function Dimensions(
@@ -140,14 +146,3 @@ function autoHeight({y, fy, fx}) {
   const ny = y ? (y.family === "ordinal" ? y.scale.domain().length : Math.max(7, 17 / nfy)) : 1;
   return !!(y || fy) * Math.max(1, Math.min(60, ny * nfy)) * 20 + !!fx * 30 + 60;
 }
-
-// Wrap the plot in a figure with a caption, if desired.
-function wrap(svg, {caption} = {}) {
-  if (caption == null) return svg;
-  const figure = document.createElement("figure");
-  figure.appendChild(svg);
-  const figcaption = document.createElement("figcaption");
-  figcaption.appendChild(caption instanceof Node ? caption : document.createTextNode(caption));
-  figure.appendChild(figcaption);
-  return figure;
-}

src/scales.js

@@ -78,7 +78,7 @@ function Scale(key, channels = [], options = {}) {
 }
 
 export function scale(options) {
-  return Scale(undefined, undefined, options).scale;
+  return Scale(options.key, undefined, options).scale;
 }
 
 function inferScaleType(key, channels, {type, domain, range}) {
@@ -112,16 +112,16 @@ function asOrdinalType(key, type = "categorical") {
   return registry.get(key) === position ? "point" : type;
 }
 
-export function exposeScales(figure, scaleDescriptors) {
-  const scales = figure.scales = {};
+export function exposeScales(scaleDescriptors) {
+  const scales = {};
   for (const key in scaleDescriptors) {
     let cache;
     Object.defineProperty(scales, key, {
       enumerable: true,
       get: () => cache = cache || exposeScale(scaleDescriptors[key])
     });
   }
-  return figure;
+  return scales;
 }
 
 function exposeScale({scale, ...options}) {