[core] Switch from background to foreground placement

 - Background placement code now just generates static symbol buffers
 - Don't render GeometryTiles until their symbols are loaded. This is necessary for the CrossTileSymbolIndex to successfully prevent flicker.
 - SymbolInstances are transferred to SymbolBucket for use on foreground during collision detection
 - Symbols are sorted on foreground by sorting their index buffer but leaving vertex buffers intact (only works within one segment)
 - Vertical glyphs are generated at same time as horizontal glyphs. `reprojectLineLabels` chooses which one to use at render time and hides the other.
 - Icons are now always represented with a single collision box, even if they're placed along a line (this means their rotation alignment may be wrong, but the approach of representing them with multiple collision boxes wasn't very accurate either).
 - Generate vertices for new debug collision boxes and collision circles
 - Only add symbols within tile boundaries (reduces work, avoids double-draw)
 - Update symbol_projection.cpp to support line label projection calls from CollisionIndex.

1 files changed, 3 insertions, 4 deletions

diff --git a/src/mbgl/tile/tile.hpp b/src/mbgl/tile/tile.hpp
index 8be7c4d862..65a497aaae 100644
--- a/src/mbgl/tile/tile.hpp
+++ b/src/mbgl/tile/tile.hpp
@@ -23,7 +23,6 @@ namespace mbgl {
 class DebugBucket;
 class TransformState;
 class TileObserver;
-class PlacementConfig;
 class RenderLayer;
 class RenderedQueryOptions;
 class SourceQueryOptions;
@@ -47,7 +46,7 @@ public:
     virtual void upload(gl::Context&) = 0;
     virtual Bucket* getBucket(const style::Layer::Impl&) const = 0;
 
-    virtual void setPlacementConfig(const PlacementConfig&) {}
+    virtual void setShowCollisionBoxes(const bool) {}
     virtual void setLayers(const std::vector<Immutable<style::Layer::Impl>>&) {}
     virtual void setMask(TileMask&&) {}
 
@@ -92,6 +91,8 @@ public:
     bool isComplete() const {
         return loaded && !pending;
     }
+    
+    virtual void resetCrossTileIDs() {};
 
     void dumpDebugLogs() const;
 
@@ -101,8 +102,6 @@ public:
 
     // Contains the tile ID string for painting debug information.
     std::unique_ptr<DebugBucket> debugBucket;
-    
-    virtual float yStretch() const { return 1.0f; }
 
 protected:
     bool triedOptional = false;