derive x & y scale domains from geometry (#1468)

* derive x & y scale domains from geometry

* follow-up: derive x & y scale domains from geometry (#1663)

* fix pending issues and add tests

* optimize and comment

* move hasProjection

---------

Co-authored-by: Mike Bostock <mbostock@gmail.com>

---------

Co-authored-by: Philippe Rivière <fil@rezo.net>

Author: mbostock

src/dimensions.js

@@ -38,7 +38,7 @@ export function createDimensions(scales, marks, options = {}) {
   // specified explicitly, adjust the automatic height accordingly.
   let {
     width = 640,
-    height = autoHeight(scales, marks, options, {
+    height = autoHeight(scales, options, {
       width,
       marginTopDefault,
       marginRightDefault,
@@ -89,14 +89,13 @@ export function createDimensions(scales, marks, options = {}) {
 
 function autoHeight(
   {x, y, fy, fx},
-  marks,
   {projection, aspectRatio},
   {width, marginTopDefault, marginRightDefault, marginBottomDefault, marginLeftDefault}
 ) {
   const nfy = fy ? fy.scale.domain().length : 1;
 
   // If a projection is specified, use its natural aspect ratio (if known).
-  const ar = projectionAspectRatio(projection, marks);
+  const ar = projectionAspectRatio(projection);
   if (ar) {
     const nfx = fx ? fx.scale.domain().length : 1;
     const far = ((1.1 * nfy - 0.1) / (1.1 * nfx - 0.1)) * ar; // 0.1 is default facet padding

src/marks/geo.js

@@ -22,7 +22,7 @@ export class Geo extends Mark {
     super(
       data,
       {
-        geometry: {value: options.geometry},
+        geometry: {value: options.geometry, scale: "projection"},
         r: {value: vr, scale: "r", filter: positive, optional: true}
       },
       withDefaultSort(options),

src/plot.js

@@ -10,7 +10,7 @@ import {axisFx, axisFy, axisX, axisY, gridFx, gridFy, gridX, gridY} from "./mark
 import {frame} from "./marks/frame.js";
 import {tip} from "./marks/tip.js";
 import {arrayify, isColor, isIterable, isNone, isScaleOptions, map, yes, maybeIntervalTransform} from "./options.js";
-import {createProjection} from "./projection.js";
+import {createProjection, getGeometryChannels, hasProjection} from "./projection.js";
 import {createScales, createScaleFunctions, autoScaleRange, exposeScales} from "./scales.js";
 import {innerDimensions, outerDimensions} from "./scales.js";
 import {position, registry as scaleRegistry} from "./scales/index.js";
@@ -48,8 +48,8 @@ export function plot(options = {}) {
 
   // Compute a Map from scale name to an array of associated channels.
   const channelsByScale = new Map();
-  if (topFacetState) addScaleChannels(channelsByScale, [topFacetState]);
-  addScaleChannels(channelsByScale, facetStateByMark);
+  if (topFacetState) addScaleChannels(channelsByScale, [topFacetState], options);
+  addScaleChannels(channelsByScale, facetStateByMark, options);
 
   // Add implicit axis marks. Because this happens after faceting (because it
   // depends on whether faceting is present), we must initialize the facet state
@@ -139,7 +139,7 @@ export function plot(options = {}) {
   }
 
   // Initalize the scales and dimensions.
-  const scaleDescriptors = createScales(addScaleChannels(channelsByScale, stateByMark), options);
+  const scaleDescriptors = createScales(addScaleChannels(channelsByScale, stateByMark, options), options);
   const scales = createScaleFunctions(scaleDescriptors);
   const dimensions = createDimensions(scaleDescriptors, marks, options);
 
@@ -217,8 +217,8 @@ export function plot(options = {}) {
   // reinitialization. Preserve existing scale labels, if any.
   if (newByScale.size) {
     const newChannelsByScale = new Map();
-    addScaleChannels(newChannelsByScale, stateByMark, (key) => newByScale.has(key));
-    addScaleChannels(channelsByScale, stateByMark, (key) => newByScale.has(key));
+    addScaleChannels(newChannelsByScale, stateByMark, options, (key) => newByScale.has(key));
+    addScaleChannels(channelsByScale, stateByMark, options, (key) => newByScale.has(key));
     const newScaleDescriptors = inheritScaleLabels(createScales(newChannelsByScale, options), scaleDescriptors);
     const newScales = createScaleFunctions(newScaleDescriptors);
     Object.assign(scaleDescriptors, newScaleDescriptors);
@@ -410,21 +410,40 @@ function inferChannelScales(channels) {
   }
 }
 
-function addScaleChannels(channelsByScale, stateByMark, filter = yes) {
+function addScaleChannels(channelsByScale, stateByMark, options, filter = yes) {
   for (const {channels} of stateByMark.values()) {
     for (const name in channels) {
       const channel = channels[name];
       const {scale} = channel;
       if (scale != null && filter(scale)) {
-        const scaleChannels = channelsByScale.get(scale);
-        if (scaleChannels !== undefined) scaleChannels.push(channel);
-        else channelsByScale.set(scale, [channel]);
+        // Geo marks affect the default x and y domains if there is no
+        // projection. Skip this (as an optimization) when a projection is
+        // specified, or when the domains for x and y are specified.
+        if (scale === "projection") {
+          if (!hasProjection(options)) {
+            const gx = options.x?.domain === undefined;
+            const gy = options.y?.domain === undefined;
+            if (gx || gy) {
+              const [x, y] = getGeometryChannels(channel);
+              if (gx) addScaleChannel(channelsByScale, "x", x);
+              if (gy) addScaleChannel(channelsByScale, "y", y);
+            }
+          }
+        } else {
+          addScaleChannel(channelsByScale, scale, channel);
+        }
       }
     }
   }
   return channelsByScale;
 }
 
+function addScaleChannel(channelsByScale, scale, channel) {
+  const scaleChannels = channelsByScale.get(scale);
+  if (scaleChannels !== undefined) scaleChannels.push(channel);
+  else channelsByScale.set(scale, [channel]);
+}
+
 // Returns the facet groups, and possibly fx and fy channels, associated with
 // the top-level facet option {data, x, y}.
 function maybeTopFacet(facet, options) {
@@ -518,8 +537,8 @@ function inferAxes(marks, channelsByScale, options) {
   } = options;
 
   // Disable axes if the corresponding scale is not present.
-  if (projection || (!isScaleOptions(x) && !hasScaleChannel("x", marks))) xAxis = xGrid = null;
-  if (projection || (!isScaleOptions(y) && !hasScaleChannel("y", marks))) yAxis = yGrid = null;
+  if (projection || (!isScaleOptions(x) && !hasPositionChannel("x", marks))) xAxis = xGrid = null;
+  if (projection || (!isScaleOptions(y) && !hasPositionChannel("y", marks))) yAxis = yGrid = null;
   if (!channelsByScale.has("fx")) fxAxis = fxGrid = null;
   if (!channelsByScale.has("fy")) fyAxis = fyGrid = null;
 
@@ -647,10 +666,11 @@ function hasAxis(marks, k) {
   return marks.some((m) => m.ariaLabel?.startsWith(prefix));
 }
 
-function hasScaleChannel(k, marks) {
+function hasPositionChannel(k, marks) {
   for (const mark of marks) {
     for (const key in mark.channels) {
-      if (mark.channels[key].scale === k) {
+      const {scale} = mark.channels[key];
+      if (scale === k || scale === "projection") {
         return true;
       }
     }

src/projection.js

@@ -14,6 +14,7 @@ import {
   geoOrthographic,
   geoPath,
   geoStereographic,
+  geoStream,
   geoTransform,
   geoTransverseMercator
 } from "d3";
@@ -222,17 +223,28 @@ export function project(cx, cy, values, projection) {
   }
 }
 
+// Returns true if a projection was specified. This should match the logic of
+// createProjection above, and is called before we construct the projection.
+// (Though note that we ignore the edge case where the projection initializer
+// may return null.)
+export function hasProjection({projection} = {}) {
+  if (projection == null) return false;
+  if (typeof projection.stream === "function") return true;
+  if (isObject(projection)) projection = projection.type;
+  return projection != null;
+}
+
 // When a named projection is specified, we can use its natural aspect ratio to
 // determine a good value for the projection’s height based on the desired
 // width. When we don’t have a way to know, the golden ratio is our best guess.
 // Due to a circular dependency (we need to know the height before we can
 // construct the projection), we have to test the raw projection option rather
 // than the materialized projection; therefore we must be extremely careful that
-// the logic of this function exactly matches Projection above!
-export function projectionAspectRatio(projection, marks) {
+// the logic of this function exactly matches createProjection above!
+export function projectionAspectRatio(projection) {
   if (typeof projection?.stream === "function") return defaultAspectRatio;
   if (isObject(projection)) projection = projection.type;
-  if (projection == null) return hasGeometry(marks) ? defaultAspectRatio : undefined;
+  if (projection == null) return;
   if (typeof projection !== "function") {
     const {aspectRatio} = namedProjection(projection);
     if (aspectRatio) return aspectRatio;
@@ -254,7 +266,22 @@ export function applyPosition(channels, scales, {projection}) {
   return position;
 }
 
-function hasGeometry(marks) {
-  for (const mark of marks) if (mark.channels.geometry) return true;
-  return false;
+export function getGeometryChannels(channel) {
+  const X = [];
+  const Y = [];
+  const x = {scale: "x", value: X};
+  const y = {scale: "y", value: Y};
+  const sink = {
+    point(x, y) {
+      X.push(x);
+      Y.push(y);
+    },
+    lineStart() {},
+    lineEnd() {},
+    polygonStart() {},
+    polygonEnd() {},
+    sphere() {}
+  };
+  for (const object of channel.value) geoStream(object, sink);
+  return [x, y];
 }

src/scales/index.js

@@ -22,6 +22,9 @@ export const opacity = Symbol("opacity");
 // Symbol scales have a default range of categorical symbols.
 export const symbol = Symbol("symbol");
 
+// There isn’t really a projection scale; this represents x and y for geometry.
+export const projection = Symbol("projection");
+
 // TODO Rather than hard-coding the list of known scale names, collect the names
 // and categories for each plot specification, so that custom marks can register
 // custom scales.
@@ -34,5 +37,6 @@ export const registry = new Map([
   ["color", color],
   ["opacity", opacity],
   ["symbol", symbol],
-  ["length", length]
+  ["length", length],
+  ["projection", projection]
 ]);