Determine the default height when the projection domain is set (#2102)

* Determine the default height when the projection domain is set

closes #2063

* Only scale if passed a width (height being always passed with width, there's no need to check both)
the case where width and height are undefined is when we are testing the projection's aspect ratio with a given domain

Note that the path in the SVG is broken (full of NaN) when projection.scale() === 0. This seems to be a secondary issue.

* adding the case where the projection is given by a {type: function, domain}

Author: Fil

src/dimensions.js

@@ -94,7 +94,8 @@ function autoHeight(
 ) {
   const nfy = fy ? fy.scale.domain().length : 1;
 
-  // If a projection is specified, use its natural aspect ratio (if known).
+  // If a projection is specified, compute an aspect ratio based on the domain,
+  // defaulting to the projection’s natural aspect ratio (if known).
   const ar = projectionAspectRatio(projection);
   if (ar) {
     const nfx = fx ? fx.scale.domain().length : 1;

src/projection.js

@@ -167,8 +167,10 @@ function scaleProjection(createProjection, kx, ky) {
       if (precision != null) projection.precision?.(precision);
       if (rotate != null) projection.rotate?.(rotate);
       if (typeof clip === "number") projection.clipAngle?.(clip);
-      projection.scale(Math.min(width / kx, height / ky));
-      projection.translate([width / 2, height / 2]);
+      if (width != null) {
+        projection.scale(Math.min(width / kx, height / ky));
+        projection.translate([width / 2, height / 2]);
+      }
       return projection;
     },
     aspectRatio: ky / kx
@@ -183,7 +185,7 @@ function conicProjection(createProjection, kx, ky) {
       const projection = type(options);
       if (parallels != null) {
         projection.parallels(parallels);
-        if (domain === undefined) {
+        if (domain === undefined && width != null) {
           projection.fitSize([width, height], {type: "Sphere"});
         }
       }
@@ -234,16 +236,25 @@ export function hasProjection({projection} = {}) {
   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 createProjection above!
+// When a projection is specified, we can use its 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 createProjection above!
 export function projectionAspectRatio(projection) {
   if (typeof projection?.stream === "function") return defaultAspectRatio;
-  if (isObject(projection)) projection = projection.type;
+  if (isObject(projection)) {
+    let domain, options;
+    ({domain, type: projection, ...options} = projection);
+    if (domain != null && projection != null) {
+      const type = typeof projection === "string" ? namedProjection(projection).type : projection;
+      const [[x0, y0], [x1, y1]] = geoPath(type({...options, width: 100, height: 100})).bounds(domain);
+      const r = (y1 - y0) / (x1 - x0);
+      return r && isFinite(r) ? (r < 0.2 ? 0.2 : r > 5 ? 5 : r) : defaultAspectRatio;
+    }
+  }
   if (projection == null) return;
   if (typeof projection !== "function") {
     const {aspectRatio} = namedProjection(projection);