feat: Add a map.corners() utility function

src/map.js

@@ -1440,6 +1440,27 @@ var map = function (arg) {
     return m_this;
   };
 
+  /**
+   * Get the corners of the map.  Since the map can be rotated, this is
+   * necessarily not the same as the overall bounds, which is the orthogonal
+   * bounding box.
+   *
+   * @param {string|geo.transform|null} [gcs] `undefined` to use the interface
+   *    gcs, `null` to use the map gcs, or any other transform.  If setting the
+   *    bounds, they are converted from this gcs to the map projection.  The
+   *    returned bounds are converted from the map projection to this gcs.
+   * @returns {geo.geoPosition[]} The corners of the map in the order
+   *    upper-left, upper-right, lower-right, lower-left.
+   */
+  this.corners = function (gcs) {
+    return [
+      m_this.displayToGcs({x: 0, y: 0}, gcs),
+      m_this.displayToGcs({x: m_width, y: 0}, gcs),
+      m_this.displayToGcs({x: m_width, y: m_height}, gcs),
+      m_this.displayToGcs({x: 0, y: m_height}, gcs)
+    ];
+  };
+
   /**
    * Get the center zoom level necessary to display the given bounds.
    *

src/markerFeature.js

@@ -228,7 +228,7 @@ var markerFeature = function (arg) {
     // Find markers inside the bounding box
     idx = m_rangeTree.range(min.x, min.y, max.x, max.y);
 
-    idx.sort((a, b) => a - b);
+    idx = Uint32Array.from(idx).sort();
     // Filter by circular region
     idx.forEach(function (i) {
       var d = data[i],
@@ -353,16 +353,20 @@ var markerFeature = function (arg) {
     };
     // Find markers inside the bounding box.  Only these could be in the polygon
     idx = m_rangeTree.range(min.x, min.y, max.x, max.y);
-    // sort by index
-    idx.sort((a, b) => a - b);
+    /* sort by index.  This had been
+     *  idx.sort((a, b) => a - b);
+     * but this requires continual casting from int to str and back, so using
+     * a Uint32Array is faster, though potentially limits the maximum number of
+     * markers. */
+    idx = Uint32Array.from(idx).sort();
     // filter markers within the polygon
     idx.forEach(function (i) {
       var d = data[i];
       let p = m_this.position()(d, i);
-      let rad = radius(data[i], i),
-          swz = scaleWithZoom(data[i], i);
-      const so = strokeOffset(data[i], i),
-          s = swz ? strokeWidth(data[i], i) : 0;
+      let rad = radius(d, i),
+          swz = scaleWithZoom(d, i);
+      const so = strokeOffset(d, i),
+          s = swz ? strokeWidth(d, i) : 0;
       let ris = radiusIncludesStroke(d, i);
       ris = ris === undefined ? true : ris;
       const rwos = ris ? rad + s * (so - 1) / 2 : rad;  // radius without stroke

src/pointFeature.js

@@ -329,7 +329,7 @@ var pointFeature = function (arg) {
     // Find points inside the bounding box
     idx = m_rangeTree.range(min.x, min.y, max.x, max.y);
 
-    idx.sort((a, b) => a - b);
+    idx = Uint32Array.from(idx).sort();
     // Filter by circular region
     idx.forEach(function (i) {
       var d = data[i],
@@ -434,7 +434,7 @@ var pointFeature = function (arg) {
     // Find points inside the bounding box.  Only these could be in the polygon
     idx = m_rangeTree.range(min.x, min.y, max.x, max.y);
     // sort by index
-    idx.sort((a, b) => a - b);
+    idx = Uint32Array.from(idx).sort();
     // filter points within the polygon
     idx.forEach(function (i) {
       var d = data[i],

tests/cases/map.js

@@ -266,6 +266,8 @@ describe('geo.core.map', function () {
         bottom: -128 * units,
         width: 256 * units,
         height: 256 * units})).toBe(true);
+      expect(closeToEqual(m.corners()[0], {x: -180, y: 85.05}));
+      expect(closeToEqual(m.corners(null)[0], {x: -128 * units, y: 128 * units}));
       m.ingcs('EPSG:3857');
       expect(m.ingcs()).toBe('EPSG:3857');
       expect(closeToEqual(m.bounds(), {