[core] Only run placement for first layer per SymbolBucket

Native version of mapbox/mapbox-gl-js#6548.
Port of mapbox/mapbox-gl-js#6550.
Prevents symbols that share the same layout properties from colliding against each other.

Bump GL JS pin to get regression test.
Rename "bucketName" -> "bucketLeaderID" to make it clearer what it represents.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/mbgl/text/cross_tile_symbol_index.cpp b/src/mbgl/text/cross_tile_symbol_index.cpp
index 01a4a02b4e..b0c3511ce3 100644
--- a/src/mbgl/text/cross_tile_symbol_index.cpp
+++ b/src/mbgl/text/cross_tile_symbol_index.cpp
@@ -153,6 +153,10 @@ bool CrossTileSymbolIndex::addLayer(RenderSymbolLayer& symbolLayer) {
         auto bucket = renderTile.tile.getBucket(*symbolLayer.baseImpl);
         assert(dynamic_cast<SymbolBucket*>(bucket));
         SymbolBucket& symbolBucket = *reinterpret_cast<SymbolBucket*>(bucket);
+        if (symbolBucket.bucketLeaderID != symbolLayer.getID()) {
+            // Only add this layer if it's the "group leader" for the bucket
+            continue;
+        }
 
         if (!symbolBucket.bucketInstanceId) {
             symbolBucket.bucketInstanceId = ++maxBucketInstanceId;