Adaptive bounds calculation

src/geo/transform.js

@@ -2,7 +2,7 @@
 
 import LngLat from './lng_lat.js';
 import LngLatBounds from './lng_lat_bounds.js';
-import MercatorCoordinate, {mercatorXfromLng, mercatorYfromLat, mercatorZfromAltitude, latFromMercatorY, MAX_MERCATOR_LATITUDE, circumferenceAtLatitude} from './mercator_coordinate.js';
+import MercatorCoordinate, {mercatorXfromLng, mercatorYfromLat, mercatorZfromAltitude, lngFromMercatorX, latFromMercatorY, MAX_MERCATOR_LATITUDE, circumferenceAtLatitude} from './mercator_coordinate.js';
 import {getProjection} from './projection/index.js';
 import {tileAABB} from '../geo/projection/tile_transform.js';
 import Point from '@mapbox/point-geometry';
@@ -1344,7 +1344,60 @@ class Transform {
             new Point(Number.MAX_VALUE, Number.MAX_VALUE);
     }
 
+    _getGlobeBounds(): LngLatBounds {
+        const topLeft = new Point(this._edgeInsets.left, this._edgeInsets.top);
+        const topRight = new Point(this.width - this._edgeInsets.right, this._edgeInsets.top);
+        const bottomRight = new Point(this.width - this._edgeInsets.right, this.height - this._edgeInsets.bottom);
+        const bottomLeft = new Point(this._edgeInsets.left, this.height - this._edgeInsets.bottom);
+
+        const tl = this.pointCoordinate3D(topLeft);
+        const tr = this.pointCoordinate3D(topRight);
+        const br = this.pointCoordinate3D(bottomRight);
+        const bl = this.pointCoordinate3D(bottomLeft);
+
+        let minX = Math.min(tl.x, bl.x);
+        let maxX = Math.max(tr.x, br.x);
+        let minY = Math.min(tl.y, tr.y);
+        let maxY = Math.max(bl.y, br.y);
+
+        // we pick an error threshold for calculating the bbox that balances between performance and precision
+        const s = Math.pow(2, -this.zoom);
+        const maxErr = s / 16;
+
+        const processSegment = (ax, ay, bx, by) => {
+            const mx = (ax + bx) / 2;
+            const my = (ay + by) / 2;
+
+            const p = new Point(mx, my);
+            const pm = this.pointCoordinate3D(p);
+            const err = Math.max(0, minX - pm.x, minY - pm.y, pm.x - maxX, pm.y - maxY);
+
+            minX = Math.min(minX, pm.x);
+            maxX = Math.max(maxX, pm.x);
+            minY = Math.min(minY, pm.y);
+            maxY = Math.max(maxY, pm.y);
+
+            if (err > maxErr) {
+                processSegment(ax, ay, mx, my);
+                processSegment(mx, my, bx, by);
+            }
+        };
+
+        processSegment(topLeft.x, topLeft.y, topRight.x, topRight.y);
+        processSegment(topRight.x, topRight.y, bottomRight.x, bottomRight.y);
+        processSegment(bottomRight.x, bottomRight.y, bottomLeft.x, bottomLeft.y);
+        processSegment(bottomLeft.x, bottomLeft.y, topLeft.x, topLeft.y);
+
+        const sw = new LngLat(lngFromMercatorX(minX), latFromMercatorY(minY));
+        const ne = new LngLat(lngFromMercatorX(maxX), latFromMercatorY(maxY));
+        return new LngLatBounds(sw, ne);
+    }
+
     _getBounds(min: number, max: number): LngLatBounds {
+        if (this.projection.name === 'globe') {
+            return this._getGlobeBounds();
+        }
+
         const topLeft = new Point(this._edgeInsets.left, this._edgeInsets.top);
         const topRight = new Point(this.width - this._edgeInsets.right, this._edgeInsets.top);
         const bottomRight = new Point(this.width - this._edgeInsets.right, this.height - this._edgeInsets.bottom);

test/unit/ui/map.test.js

@@ -1426,6 +1426,27 @@ test('Map', (t) => {
             t.end();
         });
 
+        t.test('globe bounds', (t) => {
+            const map = createMap(t, {zoom: 0, skipCSSStub: true});
+            const mercatorBounds = map.getBounds();
+
+            t.same(
+                toFixed(mercatorBounds.toArray()),
+                toFixed([[ -70.3125000000, -57.3265212252, ], [ 70.3125000000, 57.3265212252]])
+            );
+
+            map.setProjection('globe');
+            t.stub(console, 'warn');
+            const globeBounds = map.getBounds();
+
+            t.same(
+                toFixed(globeBounds.toArray()),
+                toFixed([[ -73.8873304141, 73.8873304141, ], [ 73.8873304141, -73.8873304141]])
+            );
+
+            t.end();
+        });
+
         t.end();
 
         function toFixed(bounds) {