[core] Avoid GeoJSON source flickering on style transitions

platform/android/CHANGELOG.md

@@ -6,6 +6,7 @@ Mapbox welcomes participation and contributions from everyone.  If you'd like to
 
 ### Bug fixes
  - Fixed the rendering bug caused by redundant pending requests for already requested images [#15864](https://github.com/mapbox/mapbox-gl-native/pull/15864)
+ - Fixed Geo JSON source flickering on style transition [#15907](https://github.com/mapbox/mapbox-gl-native/pull/15907)
 
 ### Performance improvements
  - Enable incremental vacuum for the offline database in order to make data removal requests faster and to avoid the excessive disk space usage (creating a backup file on VACUUM call) [#15837](https://github.com/mapbox/mapbox-gl-native/pull/15837)

platform/ios/CHANGELOG.md

@@ -10,6 +10,7 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
 ### Bug fixes
 * Fixed the rendering bug caused by redundant pending requests for already requested images [#15864](https://github.com/mapbox/mapbox-gl-native/pull/15864)
 * Enable incremental vacuum for the offline database in order to make data removal requests faster and to avoid the excessive disk space usage (creating a backup file on VACUUM call). ([#15837](https://github.com/mapbox/mapbox-gl-native/pull/15837))
+* Fixed Geo JSON source flickering on style transition. ([#15907](https://github.com/mapbox/mapbox-gl-native/pull/15907))
 
 ## 5.5.0
 

src/mbgl/renderer/sources/render_geojson_source.cpp

@@ -85,26 +85,27 @@ void RenderGeoJSONSource::update(Immutable<style::Source::Impl> baseImpl_,
     enabled = needsRendering;
 
     auto data_ = impl().getData().lock();
+    if (!data_) {
+        // In Continuous mode, keep the existing tiles if the new data_ is not
+        // yet available, thus providing smart style transitions without flickering.
+        // In other modes, allow clearing the tile pyramid first, before the early
+        // return in order to avoid render tests being flaky.
+        if (parameters.mode != MapMode::Continuous) tilePyramid.clearAll();
+        return;
+    }
 
     if (data.lock() != data_) {
         data = data_;
         tilePyramid.reduceMemoryUse();
-
-        if (data_) {
-            const uint8_t maxZ = impl().getZoomRange().max;
-            for (const auto& pair : tilePyramid.getTiles()) {
-                if (pair.first.canonical.z <= maxZ) {
-                    static_cast<GeoJSONTile*>(pair.second.get())->updateData(data_->getTile(pair.first.canonical), needsRelayout);
-                }
+        const uint8_t maxZ = impl().getZoomRange().max;
+        for (const auto& pair : tilePyramid.getTiles()) {
+            if (pair.first.canonical.z <= maxZ) {
+                static_cast<GeoJSONTile*>(pair.second.get())
+                    ->updateData(data_->getTile(pair.first.canonical), needsRelayout);
             }
         }
     }
 
-    if (!data_) {
-        tilePyramid.clearAll();
-        return;
-    }
-
     tilePyramid.update(layers,
                        needsRendering,
                        needsRelayout,