Switch to "one-phase" tile loading:

 - Don't render tiles that don't have a symbol layer
 - Remove unused tiles/bucket from the cross tile symbol index
 - Clear cached "crossTileIDs" from symbol buckets that are removed from the symbol index

5 files changed, 48 insertions, 11 deletions

diff --git a/src/mbgl/renderer/tile_pyramid.cpp b/src/mbgl/renderer/tile_pyramid.cpp
index 4acc67daa8..fae16c9ce6 100644
--- a/src/mbgl/renderer/tile_pyramid.cpp
+++ b/src/mbgl/renderer/tile_pyramid.cpp
@@ -119,6 +119,7 @@ void TilePyramid::update(const std::vector<Immutable<style::Layer::Impl>>& layer
     // use because they're still loading. In addition to that, we also need to retain all tiles that
     // we're actively using, e.g. as a replacement for tile that aren't loaded yet.
     std::set<OverscaledTileID> retain;
+    std::set<UnwrappedTileID> rendered;
 
     auto retainTileFn = [&](Tile& tile, TileNecessity necessity) -> void {
         if (retain.emplace(tile.id).second) {
@@ -149,6 +150,7 @@ void TilePyramid::update(const std::vector<Immutable<style::Layer::Impl>>& layer
     };
     auto renderTileFn = [&](const UnwrappedTileID& tileID, Tile& tile) {
         renderTiles.emplace_back(tileID, tile);
+        rendered.emplace(tileID);
     };
 
     renderTiles.clear();
@@ -176,6 +178,13 @@ void TilePyramid::update(const std::vector<Immutable<style::Layer::Impl>>& layer
         auto tilesIt = tiles.begin();
         auto retainIt = retain.begin();
         while (tilesIt != tiles.end()) {
+            auto renderedIt = rendered.find(tilesIt->first.toUnwrapped());
+            if (renderedIt == rendered.end()) {
+                // Since this tile isn't in the render set, crossTileIDs won't be kept
+                // updated by CrossTileSymbolIndex. We need to reset the stored crossTileIDs
+                // so they're not reused if/when this tile is re-added to the render set
+                tilesIt->second->resetCrossTileIDs();
+            }
             if (retainIt == retain.end() || tilesIt->first < *retainIt) {
                 if (!needsRelayout) {
                     tilesIt->second->setNecessity(TileNecessity::Optional);
diff --git a/src/mbgl/text/cross_tile_symbol_index.cpp b/src/mbgl/text/cross_tile_symbol_index.cpp
index 13771fcd9b..8655e45804 100644
--- a/src/mbgl/text/cross_tile_symbol_index.cpp
+++ b/src/mbgl/text/cross_tile_symbol_index.cpp
@@ -7,7 +7,7 @@
 namespace mbgl {
 
 
-TileLayerIndex::TileLayerIndex(OverscaledTileID coord_, std::vector<SymbolInstance>& symbolInstances, uint32_t bucketInstanceId_) 
+TileLayerIndex::TileLayerIndex(OverscaledTileID coord_, std::vector<SymbolInstance>& symbolInstances, uint32_t bucketInstanceId_)
     : coord(coord_), bucketInstanceId(bucketInstanceId_) {
         for (SymbolInstance& symbolInstance : symbolInstances) {
             indexedSymbolInstances[symbolInstance.key].emplace_back(symbolInstance.crossTileID, getScaledCoordinates(symbolInstance, coord));
@@ -28,11 +28,16 @@ void TileLayerIndex::findMatches(std::vector<SymbolInstance>& symbolInstances, c
     float tolerance = coord.canonical.z < newCoord.canonical.z ? 1 : std::pow(2, coord.canonical.z - newCoord.canonical.z);
 
     for (auto& symbolInstance : symbolInstances) {
-        // already has a match, skip
-        if (symbolInstance.crossTileID) continue;
+        if (symbolInstance.crossTileID) {
+            // already has a match, skip
+            continue;
+        }
 
         auto it = indexedSymbolInstances.find(symbolInstance.key);
-        if (it == indexedSymbolInstances.end()) continue;
+        if (it == indexedSymbolInstances.end()) {
+            // No symbol with this key in this bucket
+            continue;
+        }
 
         auto scaledSymbolCoord = getScaledCoordinates(symbolInstance, newCoord);
 
@@ -72,7 +77,9 @@ void CrossTileSymbolLayerIndex::addBucket(const OverscaledTileID& coord, SymbolB
         auto zoomIndexes = indexes.find(z);
         if (zoomIndexes != indexes.end()) {
             for (auto& childIndex : zoomIndexes->second) {
-                if (!childIndex.second.coord.isChildOf(coord)) continue;
+                if (!childIndex.second.coord.isChildOf(coord)) {
+                    continue;
+                }
                 childIndex.second.findMatches(bucket.symbolInstances, coord);
             }
         }
@@ -110,8 +117,7 @@ bool CrossTileSymbolLayerIndex::removeStaleBuckets(const std::unordered_set<uint
     bool tilesChanged = false;
     for (auto& zoomIndexes : indexes) {
         for (auto it = zoomIndexes.second.begin(); it != zoomIndexes.second.end();) {
-            // TODO remove false condition when pyramid flickering is fixed
-            if (false && !currentIDs.count(it->second.bucketInstanceId)) {
+            if (!currentIDs.count(it->second.bucketInstanceId)) {
                 it = zoomIndexes.second.erase(it);
                 tilesChanged = true;
             } else {
@@ -140,12 +146,17 @@ bool CrossTileSymbolIndex::addLayer(RenderSymbolLayer& symbolLayer) {
         assert(dynamic_cast<SymbolBucket*>(bucket));
         SymbolBucket& symbolBucket = *reinterpret_cast<SymbolBucket*>(bucket);
 
-        if (!symbolBucket.bucketInstanceId) symbolBucketsChanged = true;
+        if (!symbolBucket.bucketInstanceId) {
+            symbolBucketsChanged = true;
+        }
         layerIndex.addBucket(renderTile.tile.id, symbolBucket);
         currentBucketIDs.insert(symbolBucket.bucketInstanceId);
     }
 
-    if (layerIndex.removeStaleBuckets(currentBucketIDs)) symbolBucketsChanged = true;
+    if (layerIndex.removeStaleBuckets(currentBucketIDs)) {
+        symbolBucketsChanged = true;
+    }
     return symbolBucketsChanged;
 }
 } // namespace mbgl
+
diff --git a/src/mbgl/tile/geometry_tile.cpp b/src/mbgl/tile/geometry_tile.cpp
index e1a5c272f9..02f1e53093 100644
--- a/src/mbgl/tile/geometry_tile.cpp
+++ b/src/mbgl/tile/geometry_tile.cpp
@@ -125,8 +125,9 @@ void GeometryTile::setShowCollisionBoxes(const bool showCollisionBoxes_) {
 }
 
 void GeometryTile::onLayout(LayoutResult result, const uint64_t resultCorrelationID) {
-    loaded = true;
-    renderable = true;
+    // Don't mark ourselves loaded or renderable until the first successful placement
+    // TODO: Ideally we'd render this tile without symbols as long as this tile wasn't
+    //  replacing a tile at a different zoom that _did_ have symbols.
     (void)resultCorrelationID;
     nonSymbolBuckets = std::move(result.nonSymbolBuckets);
     featureIndex = std::move(result.featureIndex);
@@ -281,4 +282,16 @@ void GeometryTile::querySourceFeatures(
     }
 }
 
+void GeometryTile::resetCrossTileIDs() {
+    for (auto& bucket : symbolBuckets) {
+        SymbolBucket* symbolBucket = dynamic_cast<SymbolBucket*>(bucket.second.get());
+        if (symbolBucket && symbolBucket->bucketInstanceId) {
+            symbolBucket->bucketInstanceId = 0;
+            for (auto& symbolInstance : symbolBucket->symbolInstances) {
+                symbolInstance.crossTileID = 0;
+            }
+        }
+    }
+}
+
 } // namespace mbgl
diff --git a/src/mbgl/tile/geometry_tile.hpp b/src/mbgl/tile/geometry_tile.hpp
index 80f2f8c6d7..3f4b36984b 100644
--- a/src/mbgl/tile/geometry_tile.hpp
+++ b/src/mbgl/tile/geometry_tile.hpp
@@ -96,6 +96,8 @@ public:
 
     void onError(std::exception_ptr, uint64_t correlationID);
     
+    void resetCrossTileIDs() override;
+    
 protected:
     const GeometryTileData* getData() {
         return data.get();
diff --git a/src/mbgl/tile/tile.hpp b/src/mbgl/tile/tile.hpp
index 0aa2a1bcad..6c163c93bb 100644
--- a/src/mbgl/tile/tile.hpp
+++ b/src/mbgl/tile/tile.hpp
@@ -95,6 +95,8 @@ public:
     bool isComplete() const {
         return loaded && !pending;
     }
+    
+    virtual void resetCrossTileIDs() {};
 
     void dumpDebugLogs() const;