Option to make extruded polygon roofs flat

packages/Main/src/Converter/Feature2Mesh.js

@@ -606,6 +606,7 @@ function updateExtrudedPolygonBuffers(featureMesh, buffers, id) {
     style.setContext(context);
 
     const { vertices, colors, batchIds, indices } = buffers;
+    const { levelled_roofs } = style.fill;
 
     // geometry range
     const geometry = context.geometry;
@@ -620,6 +621,15 @@ function updateExtrudedPolygonBuffers(featureMesh, buffers, id) {
     const startTop = start + numVertices / 3;
     const endIn = startIn + count * 3;
 
+    let minAltitude = Infinity;
+    if (levelled_roofs) {
+        for (let i = startIn; i < endIn; i += 3) {
+            if (!vertices) { continue; }
+            context.setLocalCoordinatesFromArray(feature.vertices, i);
+            minAltitude = Math.min(minAltitude, style.fill.base_altitude);
+        }
+    }
+
     for (let i = startIn; i < endIn; i += 3) {
         const t = numVertices + i;
 
@@ -641,9 +651,15 @@ function updateExtrudedPolygonBuffers(featureMesh, buffers, id) {
                 .toArray(vertices, i);
 
             // populate top geometry buffers
-            topCoord.copy(up)
-                .multiplyScalar(extrusion_height).add(baseCoord)
-                .toArray(vertices, t);
+            if (levelled_roofs) {
+                topCoord.copy(up)
+                    .multiplyScalar(minAltitude - worldCoord.z + extrusion_height).add(localCoord)
+                    .toArray(vertices, t);
+            } else {
+                topCoord.copy(up)
+                    .multiplyScalar(extrusion_height).add(baseCoord)
+                    .toArray(vertices, t);
+            }
         }
 
         if (batchIds) {
@@ -874,7 +890,10 @@ export default {
                 style.addEventListener('style-property-changed', (event) => {
                     if (event.parameter === 'color') {
                         this._styleColorVersion++;
-                    } else if (event.parameter === 'extrusion_height' || event.parameter === 'base_altitude') {
+                    } else if (
+                        event.parameter === 'extrusion_height' ||
+                        event.parameter === 'base_altitude' ||
+                        event.parameter === 'levelled_roofs') {
                         this._stylePositionVersion++;
                     }
                 });

packages/Main/src/Core/Style.js

@@ -322,6 +322,10 @@ function _addIcon(icon, domElement, opt) {
  * then the altitude value is set to 0.
  * @property {number | Function} [fill.extrusion_height] - Only for {@link GeometryLayer} and if user sets it.
  * If defined, polygons will be extruded by the specified amount.
+ * @property {boolean} [fill.levelled_roofs=false] - Only for {@link GeometryLayer} with extrusion.
+ * When true, all roof vertices are placed at a uniform height equal to the polygon's minimum
+ * base altitude plus the extrusion height, producing flat-topped extrusions even over uneven
+ * terrain. Cannot be set to a function.
  * @property {object} stroke - Lines and polygons edges.
  * @property {string | Function | THREE.Color} stroke.color The color of the line. Can be any [valid
  * color string](https://developer.mozilla.org/en-US/docs/Web/CSS/color_value).
@@ -534,6 +538,21 @@ class Style extends EventDispatcher {
         defineStyleProperty(this, 'fill', 'pattern', params.pattern);
         defineStyleProperty(this, 'fill', 'base_altitude', params.base_altitude, baseAltitudeDefault);
 
+        // levelled_roofs is a raw boolean. No function evaluation or data-source fallback
+        this._levelledRoofs = params.levelled_roofs ?? false;
+        Object.defineProperty(this.fill, 'levelled_roofs', {
+            enumerable: true,
+            get: () => this._levelledRoofs,
+            set: (v) => {
+                this._levelledRoofs = Boolean(v);
+                this.dispatchEvent({
+                    type: 'style-property-changed',
+                    style: this,
+                    parameter: 'levelled_roofs',
+                });
+            },
+        });
+
         // define a special case for extrusion_height
         // to be able to know if user set it or not without calling the getter
         this._extrusionHeight = params.extrusion_height;