Fix enabling terrain while transitioning (#6266)

* Fix adding terrain while transitioning

* cleanup

* changelog

* add browser test

* increase timeout for windows

* replace non-functional integration test with working unit test for setting terrain during easeTo()

* Fix changelog (merge error)

---------

Co-authored-by: Birk Skyum <[email protected]>
Co-authored-by: Harel M <[email protected]>

Author: 3 people

CHANGELOG.md

@@ -10,6 +10,7 @@
 ### 🐞 Bug fixes
 - Prevent original input style JSON from being mutated by `Style.set*` methods ([#6216](https://github.com/maplibre/maplibre-gl-js/pull/6216))
 - Fix evaluating `global-state` in paint properties with other subexpressions ([#6048](https://github.com/maplibre/maplibre-gl-js/issues/6048))
+- Fix enabling terrain while transitioning [#6011](https://github.com/maplibre/maplibre-gl-js/issues/6011)
 
 ## 5.6.2
 

src/ui/camera.test.ts

@@ -1258,6 +1258,27 @@ describe('easeTo', () => {
 
         expect(spy.mock.calls.find(c => 'done' in c[0])).toBeTruthy();
     });
+
+    test('terrain set during easeTo', () => {
+        const camera = createCamera();
+        const stubNow = vi.spyOn(browser, 'now');
+
+        stubNow.mockImplementation(() => 0);
+
+        camera.easeTo({bearing: 97, duration: 500});
+        
+        stubNow.mockImplementation(() => 100);
+        camera.simulateFrame();
+
+        const terrain = {getMinTileElevationForLngLatZoom: () => 0,
+            getElevationForLngLatZoom: () => 0};
+        camera.terrain = terrain as any;
+
+        stubNow.mockImplementation(() => 500);
+        camera.simulateFrame();
+
+        expect(camera.getBearing()).toEqual(97);
+    });
 });
 
 describe('flyTo', () => {

src/ui/camera.ts

@@ -1187,6 +1187,11 @@ export abstract class Camera extends Evented {
     }
 
     _updateElevation(k: number) {
+
+        if (this._elevationStart === undefined || this._elevationCenter === undefined) {
+            this._prepareElevation(this.transform.center);
+        }
+
         this.transform.setMinElevationForCurrentTile(this.terrain.getMinTileElevationForLngLatZoom(this._elevationCenter, this.transform.tileZoom));
         const elevation = this.terrain.getElevationForLngLatZoom(this._elevationCenter, this.transform.tileZoom);
         // target terrain updated during flight, slowly move camera to new height