[core] fix cutoff cross-tile labels in MapMode::Tile

Increase the CollisionIndex's padding so that more of a tile's data gets
considered when checking for collisions. This should fix clipped
variable placement text labels.

3 files changed, 8 insertions, 4 deletions

diff --git a/src/mbgl/text/collision_index.cpp b/src/mbgl/text/collision_index.cpp
index c83b117b9a..30502ff7c0 100644
--- a/src/mbgl/text/collision_index.cpp
+++ b/src/mbgl/text/collision_index.cpp
@@ -22,10 +22,13 @@ namespace mbgl {
 // the viewport for collision detection so that the bulk of the changes
 // occur offscreen. Making this constant greater increases label
 // stability, but it's expensive.
-static const float viewportPadding = 100;
+static const float viewportPaddingDefault = 100;
+// Viewport padding must be much larger for static tiles to avoid clipped labels.
+static const float viewportPaddingForStaticTiles = 1024;
 
-CollisionIndex::CollisionIndex(const TransformState& transformState_)
+CollisionIndex::CollisionIndex(const TransformState& transformState_, const MapMode& mapMode)
     : transformState(transformState_)
+    , viewportPadding(mapMode == MapMode::Tile ? viewportPaddingForStaticTiles : viewportPaddingDefault)
     , collisionGrid(transformState.getSize().width + 2 * viewportPadding, transformState.getSize().height + 2 * viewportPadding, 25)
     , ignoredGrid(transformState.getSize().width + 2 * viewportPadding, transformState.getSize().height + 2 * viewportPadding, 25)
     , screenRightBoundary(transformState.getSize().width + viewportPadding)
diff --git a/src/mbgl/text/collision_index.hpp b/src/mbgl/text/collision_index.hpp
index 4e8a2fdb62..abd2c8eef6 100644
--- a/src/mbgl/text/collision_index.hpp
+++ b/src/mbgl/text/collision_index.hpp
@@ -20,7 +20,7 @@ class CollisionIndex {
 public:
     using CollisionGrid = GridIndex<IndexedSubfeature>;
 
-    explicit CollisionIndex(const TransformState&);
+    explicit CollisionIndex(const TransformState&, const MapMode&);
 
     std::pair<bool,bool> placeFeature(const CollisionFeature& feature,
                                       Point<float> shift,
@@ -72,6 +72,7 @@ private:
 
     const TransformState transformState;
 
+    const float viewportPadding;
     CollisionGrid collisionGrid;
     CollisionGrid ignoredGrid;
     
diff --git a/src/mbgl/text/placement.cpp b/src/mbgl/text/placement.cpp
index ecc8f93032..7964ad24c7 100644
--- a/src/mbgl/text/placement.cpp
+++ b/src/mbgl/text/placement.cpp
@@ -95,7 +95,7 @@ Placement::Placement(const TransformState& state_,
                      style::TransitionOptions transitionOptions_,
                      const bool crossSourceCollisions,
                      optional<Immutable<Placement>> prevPlacement_)
-    : collisionIndex(state_),
+    : collisionIndex(state_, mapMode_),
       mapMode(mapMode_),
       transitionOptions(std::move(transitionOptions_)),
       placementZoom(state_.getZoom()),