[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, 2 insertions, 0 deletions

diff --git a/src/mbgl/renderer/paint_parameters.hpp b/src/mbgl/renderer/paint_parameters.hpp
index 60f5af4e9a..8d9a57955f 100644
--- a/src/mbgl/renderer/paint_parameters.hpp
+++ b/src/mbgl/renderer/paint_parameters.hpp
@@ -74,6 +74,8 @@ public:
     uint32_t currentLayer;
     float depthRangeSize;
     const float depthEpsilon = 1.0f / (1 << 16);
+    
+    float symbolFadeChange;
 };
 
 } // namespace mbgl