Extract code into hasMultipleOuterRings()

Author: zstadler

src/expression/evaluation_context.ts

@@ -2,7 +2,7 @@ import {Color} from './values';
 import type {FormattedSection} from './types/formatted';
 import type {GlobalProperties, Feature, FeatureState} from './index';
 import {ICanonicalTileID} from '../tiles_and_coordinates';
-import {calculateSignedArea} from '../util/classify_rings';
+import {hasMultipleOuterRings} from '../util/classify_rings';
 
 const geometryTypes = ['Unknown', 'Point', 'LineString', 'Polygon'];
 const simpleGeometryType = {
@@ -63,18 +63,10 @@ class EvaluationContext {
         if (geometryType !== 'Polygon') {
             return `Multi${geometryType}`;
         }
-        // Following https://github.com/mapbox/vector-tile-js/blob/77851380b63b07fd0af3d5a3f144cc86fb39fdd1/lib/vectortilefeature.js#L197
-        for (let i = 0, ccw; i < len; i++) {
-            const area = calculateSignedArea(geom[i]);
-            if (area === 0) continue;
-            if (ccw === undefined) {
-                ccw = area < 0;
-            } else if (ccw === area < 0) {
-                // Same direction as the first ring -> a second outer ring
-                return 'MultiPolygon';
-            }
+        if (hasMultipleOuterRings(geom)) {
+            return 'MultiPolygon';
         }
-        return geometryType;
+        return 'Polygon';
     }
 
     geometry() {

src/util/classify_rings.ts

@@ -60,7 +60,7 @@ function compareAreas(a: {area: number}, b: {area: number}) {
  * @param ring - Exterior or interior ring
  * @returns Signed area
  */
-export function calculateSignedArea(ring: Point2D[]): number {
+function calculateSignedArea(ring: Point2D[]): number {
     let sum = 0;
     for (let i = 0, len = ring.length, j = len - 1, p1, p2; i < len; j = i++) {
         p1 = ring[i];
@@ -69,3 +69,27 @@ export function calculateSignedArea(ring: Point2D[]): number {
     }
     return sum;
 }
+
+/**
+ * Returns if there are multiple outer rings.
+ * The first ring is a outer ring. Its direction, cw or ccw, defines the direction of outer rings.
+ *
+ * @param rings - List of rings
+ * @returns Are there multiple outer rings
+ */
+export function hasMultipleOuterRings(rings: Point2D[][]): boolean {
+    // Following https://github.com/mapbox/vector-tile-js/blob/77851380b63b07fd0af3d5a3f144cc86fb39fdd1/lib/vectortilefeature.js#L197
+    const len = rings.length;
+    for (let i = 0, direction; i < len; i++) {
+        const area = calculateSignedArea(rings[i]);
+        if (area === 0) continue;
+        if (direction === undefined) {
+            // Keep the direction of the first ring
+            direction = area < 0;
+        } else if (direction === area < 0) {
+            // Same direction as the first ring -> a second outer ring
+            return true;
+        }
+    }
+    return false;
+}