[core] Add API to control prefetching tiles beyond the current zoom level

9 files changed, 22 insertions, 6 deletions

diff --git a/include/mbgl/map/map.hpp b/include/mbgl/map/map.hpp
index ac0a398d25..300ec15126 100644
--- a/include/mbgl/map/map.hpp
+++ b/include/mbgl/map/map.hpp
@@ -115,6 +115,8 @@ public:
     // default `delta` is 4.
     void setPrefetchZoomDelta(uint8_t delta);
     uint8_t getPrefetchZoomDelta() const;
+    void setPrefetchParentTiles(bool enable);
+    bool getPrefetchParentTiles() const;
 
     // Debug
     void setDebug(MapDebugOptions);
diff --git a/src/mbgl/algorithm/update_renderables.hpp b/src/mbgl/algorithm/update_renderables.hpp
index 57cd4f41ec..608c0a99bc 100644
--- a/src/mbgl/algorithm/update_renderables.hpp
+++ b/src/mbgl/algorithm/update_renderables.hpp
@@ -20,7 +20,8 @@ void updateRenderables(GetTileFn getTile,
                        RenderTileFn renderTile,
                        const IdealTileIDs& idealTileIDs,
                        const Range<uint8_t>& zoomRange,
-                       const uint8_t dataTileZoom) {
+                       const uint8_t dataTileZoom,
+                       const bool prefetchParentTiles) {
     std::unordered_set<OverscaledTileID> checked;
     bool covered;
     int32_t overscaledZ;
@@ -81,7 +82,7 @@ void updateRenderables(GetTileFn getTile,
                 }
             }
 
-            if (!covered) {
+            if (!covered && prefetchParentTiles) {
                 // We couldn't find child tiles that entirely cover the ideal tile.
                 for (overscaledZ = dataTileZoom - 1; overscaledZ >= zoomRange.min; --overscaledZ) {
                     const auto parentDataTileID = idealDataTileID.scaledTo(overscaledZ);
diff --git a/src/mbgl/map/map.cpp b/src/mbgl/map/map.cpp
index 649e0e321e..b1e06e6db5 100644
--- a/src/mbgl/map/map.cpp
+++ b/src/mbgl/map/map.cpp
@@ -452,6 +452,14 @@ uint8_t Map::getPrefetchZoomDelta() const {
     return impl->prefetchZoomDelta;
 }
 
+void Map::setPrefetchParentTiles(bool enable) {
+    impl->prefetchParentTiles = enable;
+}
+
+bool Map::getPrefetchParentTiles() const {
+    return impl->prefetchParentTiles;
+}
+
 bool Map::isFullyLoaded() const {
     return impl->style->impl->isLoaded() && impl->rendererFullyLoaded;
 }
diff --git a/src/mbgl/map/map_impl.cpp b/src/mbgl/map/map_impl.cpp
index ea55dfd1a8..ee25e17d96 100644
--- a/src/mbgl/map/map_impl.cpp
+++ b/src/mbgl/map/map_impl.cpp
@@ -65,6 +65,7 @@ void Map::Impl::onUpdate() {
         annotationManager,
         fileSource,
         prefetchZoomDelta,
+        prefetchParentTiles,
         bool(stillImageRequest),
         crossSourceCollisions
     };
diff --git a/src/mbgl/map/map_impl.hpp b/src/mbgl/map/map_impl.hpp
index 416662f9e5..42b5420968 100644
--- a/src/mbgl/map/map_impl.hpp
+++ b/src/mbgl/map/map_impl.hpp
@@ -70,6 +70,7 @@ public:
     bool cameraMutated = false;
 
     uint8_t prefetchZoomDelta = util::DEFAULT_PREFETCH_ZOOM_DELTA;
+    bool prefetchParentTiles = true;
 
     bool loading = false;
     bool rendererFullyLoaded;
diff --git a/src/mbgl/renderer/render_orchestrator.cpp b/src/mbgl/renderer/render_orchestrator.cpp
index 983bc09485..a41df00aa2 100644
--- a/src/mbgl/renderer/render_orchestrator.cpp
+++ b/src/mbgl/renderer/render_orchestrator.cpp
@@ -159,7 +159,8 @@ std::unique_ptr<RenderTree> RenderOrchestrator::createRenderTree(const UpdatePar
         updateParameters.annotationManager,
         *imageManager,
         *glyphManager,
-        updateParameters.prefetchZoomDelta
+        updateParameters.prefetchZoomDelta,
+        updateParameters.prefetchParentTiles
     };
 
     glyphManager->setURL(updateParameters.glyphURL);
diff --git a/src/mbgl/renderer/tile_parameters.hpp b/src/mbgl/renderer/tile_parameters.hpp
index 6a2deee35c..a095154ff5 100644
--- a/src/mbgl/renderer/tile_parameters.hpp
+++ b/src/mbgl/renderer/tile_parameters.hpp
@@ -23,6 +23,7 @@ public:
     ImageManager& imageManager;
     GlyphManager& glyphManager;
     const uint8_t prefetchZoomDelta;
+    const bool prefetchParentTiles;
 };
 
 } // namespace mbgl
diff --git a/src/mbgl/renderer/tile_pyramid.cpp b/src/mbgl/renderer/tile_pyramid.cpp
index 54e0b1eb26..07a066b4ba 100644
--- a/src/mbgl/renderer/tile_pyramid.cpp
+++ b/src/mbgl/renderer/tile_pyramid.cpp
@@ -170,11 +170,11 @@ void TilePyramid::update(const std::vector<Immutable<style::LayerProperties>>& l
 
     if (!panTiles.empty()) {
         algorithm::updateRenderables(getTileFn, createTileFn, retainTileFn,
-                [](const UnwrappedTileID&, Tile&) {}, panTiles, zoomRange, panZoom);
+                [](const UnwrappedTileID&, Tile&) {}, panTiles, zoomRange, panZoom, parameters.prefetchParentTiles);
     }
 
     algorithm::updateRenderables(getTileFn, createTileFn, retainTileFn, renderTileFn,
-                                 idealTiles, zoomRange, tileZoom);
+                                 idealTiles, zoomRange, tileZoom, parameters.prefetchParentTiles);
     
     for (auto previouslyRenderedTile : previouslyRenderedTiles) {
         Tile& tile = previouslyRenderedTile.second;
diff --git a/src/mbgl/renderer/update_parameters.hpp b/src/mbgl/renderer/update_parameters.hpp
index b7aee9b572..ddf4316ce3 100644
--- a/src/mbgl/renderer/update_parameters.hpp
+++ b/src/mbgl/renderer/update_parameters.hpp
@@ -37,7 +37,8 @@ public:
     std::shared_ptr<FileSource> fileSource;
 
     const uint8_t prefetchZoomDelta;
-    
+    const bool prefetchParentTiles;
+
     // For still image requests, render requested
     const bool stillImageRequest;