[core] Simplify and fix sprite atlas coordinate calculations

* Always return image metrics exclusive of padding
* Work with integer coordinates whenever possible
* Eliminate redundant SpriteAtlasElement members
* Fix asymmetric re-padding in getIconQuad when pixelRatio != 1
* Add explanatory comments

3 files changed, 10 insertions, 5 deletions

diff --git a/src/mbgl/tile/geometry_tile.cpp b/src/mbgl/tile/geometry_tile.cpp
index 8f14a9c8aa..e3c4e7bf3b 100644
--- a/src/mbgl/tile/geometry_tile.cpp
+++ b/src/mbgl/tile/geometry_tile.cpp
@@ -40,7 +40,8 @@ GeometryTile::GeometryTile(const OverscaledTileID& id_,
              ActorRef<GeometryTile>(*this, mailbox),
              id_,
              obsolete,
-             parameters.mode),
+             parameters.mode,
+             parameters.pixelRatio),
       glyphAtlas(glyphAtlas_),
       spriteAtlas(spriteAtlas_),
       placementThrottler(Milliseconds(300), [this] { invokePlacement(); }) {
diff --git a/src/mbgl/tile/geometry_tile_worker.cpp b/src/mbgl/tile/geometry_tile_worker.cpp
index 1d683b3a11..3fd6bb47f0 100644
--- a/src/mbgl/tile/geometry_tile_worker.cpp
+++ b/src/mbgl/tile/geometry_tile_worker.cpp
@@ -26,12 +26,14 @@ GeometryTileWorker::GeometryTileWorker(ActorRef<GeometryTileWorker> self_,
                                        ActorRef<GeometryTile> parent_,
                                        OverscaledTileID id_,
                                        const std::atomic<bool>& obsolete_,
-                                       const MapMode mode_)
+                                       const MapMode mode_,
+                                       const float pixelRatio_)
     : self(std::move(self_)),
       parent(std::move(parent_)),
       id(std::move(id_)),
       obsolete(obsolete_),
-      mode(mode_) {
+      mode(mode_),
+      pixelRatio(pixelRatio_) {
 }
 
 GeometryTileWorker::~GeometryTileWorker() = default;
@@ -275,7 +277,7 @@ void GeometryTileWorker::redoLayout() {
     std::unordered_map<std::string, std::unique_ptr<SymbolLayout>> symbolLayoutMap;
     std::unordered_map<std::string, std::shared_ptr<Bucket>> buckets;
     auto featureIndex = std::make_unique<FeatureIndex>();
-    BucketParameters parameters { id, mode };
+    BucketParameters parameters { id, mode, pixelRatio };
 
     GlyphDependencies glyphDependencies;
     IconDependencies iconDependencies;
diff --git a/src/mbgl/tile/geometry_tile_worker.hpp b/src/mbgl/tile/geometry_tile_worker.hpp
index 0d4cba04b3..3a15763a82 100644
--- a/src/mbgl/tile/geometry_tile_worker.hpp
+++ b/src/mbgl/tile/geometry_tile_worker.hpp
@@ -31,7 +31,8 @@ public:
                        ActorRef<GeometryTile> parent,
                        OverscaledTileID,
                        const std::atomic<bool>&,
-                       const MapMode);
+                       const MapMode,
+                       const float pixelRatio);
     ~GeometryTileWorker();
 
     void setLayers(std::vector<Immutable<style::Layer::Impl>>, uint64_t correlationID);
@@ -61,6 +62,7 @@ private:
     const OverscaledTileID id;
     const std::atomic<bool>& obsolete;
     const MapMode mode;
+    const float pixelRatio;
 
     enum State {
         Idle,