[core] Add setMaxOverscaleFactorForParentTiles

13 files changed, 92 insertions, 14 deletions

diff --git a/include/mbgl/style/source.hpp b/include/mbgl/style/source.hpp
index 622c2e42ff..32b15bdf47 100644
--- a/include/mbgl/style/source.hpp
+++ b/include/mbgl/style/source.hpp
@@ -75,6 +75,20 @@ public:
     virtual void loadDescription(FileSource&) = 0;
     void setPrefetchZoomDelta(optional<uint8_t> delta) noexcept;
     optional<uint8_t> getPrefetchZoomDelta() const noexcept;
+
+    // Sets a limit for how much a parent tile can be overscaled.
+    //
+    // When a set of tiles for a current zoom level is being rendered and some of the
+    // ideal tiles that cover the screen are not yet loaded, parent tile could be
+    // used instead. This might introduce unwanted rendering side-effects, especially
+    // for raster tiles that are overscaled multiple times.
+    //
+    // For example, an overscale factor of 3 would mean that on zoom level 3, the
+    // minimum zoom level of a parent tile that could be used in place of an ideal
+    // tile during rendering would be zoom 0. By default, no limit is set, so any
+    // parent tile may be used.
+    void setMaxOverscaleFactorForParentTiles(optional<uint8_t> overscaleFactor) noexcept;
+    optional<uint8_t> getMaxOverscaleFactorForParentTiles() const noexcept;
     void dumpDebugLogs() const;
 
     virtual bool supportsLayerType(const mbgl::style::LayerTypeInfo*) const = 0;
diff --git a/src/mbgl/algorithm/update_renderables.hpp b/src/mbgl/algorithm/update_renderables.hpp
index 57cd4f41ec..316ada8269 100644
--- a/src/mbgl/algorithm/update_renderables.hpp
+++ b/src/mbgl/algorithm/update_renderables.hpp
@@ -2,6 +2,7 @@
 
 #include <mbgl/tile/tile_id.hpp>
 #include <mbgl/tile/tile_necessity.hpp>
+#include <mbgl/util/optional.hpp>
 #include <mbgl/util/range.hpp>
 
 #include <unordered_set>
@@ -20,7 +21,8 @@ void updateRenderables(GetTileFn getTile,
                        RenderTileFn renderTile,
                        const IdealTileIDs& idealTileIDs,
                        const Range<uint8_t>& zoomRange,
-                       const uint8_t dataTileZoom) {
+                       const uint8_t dataTileZoom,
+                       const optional<uint8_t>& maxParentOverscaleFactor = nullopt) {
     std::unordered_set<OverscaledTileID> checked;
     bool covered;
     int32_t overscaledZ;
@@ -86,6 +88,11 @@ void updateRenderables(GetTileFn getTile,
                 for (overscaledZ = dataTileZoom - 1; overscaledZ >= zoomRange.min; --overscaledZ) {
                     const auto parentDataTileID = idealDataTileID.scaledTo(overscaledZ);
 
+                    // Request / render parent tile only if it's overscale factor is less than defined maximum.
+                    if (maxParentOverscaleFactor && (dataTileZoom - overscaledZ) > *maxParentOverscaleFactor) {
+                        break;
+                    }
+
                     if (checked.find(parentDataTileID) != checked.end()) {
                         // Break parent tile ascent, this route has been checked by another child
                         // tile before.
diff --git a/src/mbgl/annotation/render_annotation_source.cpp b/src/mbgl/annotation/render_annotation_source.cpp
index 85665961d3..b03b7662d8 100644
--- a/src/mbgl/annotation/render_annotation_source.cpp
+++ b/src/mbgl/annotation/render_annotation_source.cpp
@@ -40,7 +40,8 @@ void RenderAnnotationSource::update(Immutable<style::Source::Impl> baseImpl_,
         {0, 16},
         optional<LatLngBounds>{},
         [&](const OverscaledTileID& tileID) { return std::make_unique<AnnotationTile>(tileID, parameters); },
-        baseImpl->getPrefetchZoomDelta());
+        baseImpl->getPrefetchZoomDelta(),
+        baseImpl->getMaxOverscaleFactorForParentTiles());
 }
 
 std::unordered_map<std::string, std::vector<Feature>>
diff --git a/src/mbgl/renderer/sources/render_custom_geometry_source.cpp b/src/mbgl/renderer/sources/render_custom_geometry_source.cpp
index a54802b21b..ecb74b6503 100644
--- a/src/mbgl/renderer/sources/render_custom_geometry_source.cpp
+++ b/src/mbgl/renderer/sources/render_custom_geometry_source.cpp
@@ -53,7 +53,8 @@ void RenderCustomGeometrySource::update(Immutable<style::Source::Impl> baseImpl_
             return std::make_unique<CustomGeometryTile>(
                 tileID, impl().id, parameters, impl().getTileOptions(), *tileLoader);
         },
-        baseImpl->getPrefetchZoomDelta());
+        baseImpl->getPrefetchZoomDelta(),
+        baseImpl->getMaxOverscaleFactorForParentTiles());
 }
 
 } // namespace mbgl
diff --git a/src/mbgl/renderer/sources/render_geojson_source.cpp b/src/mbgl/renderer/sources/render_geojson_source.cpp
index 490abe8a6b..4083a96500 100644
--- a/src/mbgl/renderer/sources/render_geojson_source.cpp
+++ b/src/mbgl/renderer/sources/render_geojson_source.cpp
@@ -118,7 +118,8 @@ void RenderGeoJSONSource::update(Immutable<style::Source::Impl> baseImpl_,
         [&, data_](const OverscaledTileID& tileID) {
             return std::make_unique<GeoJSONTile>(tileID, impl().id, parameters, data_);
         },
-        baseImpl->getPrefetchZoomDelta());
+        baseImpl->getPrefetchZoomDelta(),
+        baseImpl->getMaxOverscaleFactorForParentTiles());
 }
 
 mapbox::util::variant<Value, FeatureCollection>
diff --git a/src/mbgl/renderer/sources/render_raster_dem_source.cpp b/src/mbgl/renderer/sources/render_raster_dem_source.cpp
index 953484f6c6..9b2345f8e0 100644
--- a/src/mbgl/renderer/sources/render_raster_dem_source.cpp
+++ b/src/mbgl/renderer/sources/render_raster_dem_source.cpp
@@ -37,7 +37,8 @@ void RenderRasterDEMSource::updateInternal(const Tileset& tileset,
         tileset.zoomRange,
         tileset.bounds,
         [&](const OverscaledTileID& tileID) { return std::make_unique<RasterDEMTile>(tileID, parameters, tileset); },
-        baseImpl->getPrefetchZoomDelta());
+        baseImpl->getPrefetchZoomDelta(),
+        baseImpl->getMaxOverscaleFactorForParentTiles());
     algorithm::updateTileMasks(tilePyramid.getRenderedTiles());
 }
 
diff --git a/src/mbgl/renderer/sources/render_raster_source.cpp b/src/mbgl/renderer/sources/render_raster_source.cpp
index 7ef7b26459..f759623cdd 100644
--- a/src/mbgl/renderer/sources/render_raster_source.cpp
+++ b/src/mbgl/renderer/sources/render_raster_source.cpp
@@ -35,7 +35,8 @@ void RenderRasterSource::updateInternal(const Tileset& tileset,
         tileset.zoomRange,
         tileset.bounds,
         [&](const OverscaledTileID& tileID) { return std::make_unique<RasterTile>(tileID, parameters, tileset); },
-        baseImpl->getPrefetchZoomDelta());
+        baseImpl->getPrefetchZoomDelta(),
+        baseImpl->getMaxOverscaleFactorForParentTiles());
     algorithm::updateTileMasks(tilePyramid.getRenderedTiles());
 }
 
diff --git a/src/mbgl/renderer/sources/render_vector_source.cpp b/src/mbgl/renderer/sources/render_vector_source.cpp
index 324599d45d..3ac16a136f 100644
--- a/src/mbgl/renderer/sources/render_vector_source.cpp
+++ b/src/mbgl/renderer/sources/render_vector_source.cpp
@@ -33,7 +33,8 @@ void RenderVectorSource::updateInternal(const Tileset& tileset,
         [&](const OverscaledTileID& tileID) {
             return std::make_unique<VectorTile>(tileID, baseImpl->id, parameters, tileset);
         },
-        baseImpl->getPrefetchZoomDelta());
+        baseImpl->getPrefetchZoomDelta(),
+        baseImpl->getMaxOverscaleFactorForParentTiles());
 }
 
 } // namespace mbgl
diff --git a/src/mbgl/renderer/tile_pyramid.cpp b/src/mbgl/renderer/tile_pyramid.cpp
index f7f02f5582..c456bf6e24 100644
--- a/src/mbgl/renderer/tile_pyramid.cpp
+++ b/src/mbgl/renderer/tile_pyramid.cpp
@@ -58,7 +58,8 @@ void TilePyramid::update(const std::vector<Immutable<style::LayerProperties>>& l
                          const Range<uint8_t> zoomRange,
                          optional<LatLngBounds> bounds,
                          std::function<std::unique_ptr<Tile>(const OverscaledTileID&)> createTile,
-                         optional<uint8_t> sourcePrefetchZoomDelta) {
+                         const optional<uint8_t>& sourcePrefetchZoomDelta,
+                         const optional<uint8_t>& maxParentTileOverscaleFactor) {
     // If we need a relayout, abandon any cached tiles; they're now stale.
     if (needsRelayout) {
         cache.clear();
@@ -177,13 +178,26 @@ void TilePyramid::update(const std::vector<Immutable<style::LayerProperties>>& l
     renderedTiles.clear();
 
     if (!panTiles.empty()) {
-        algorithm::updateRenderables(getTileFn, createTileFn, retainTileFn,
-                [](const UnwrappedTileID&, Tile&) {}, panTiles, zoomRange, panZoom);
+        algorithm::updateRenderables(
+            getTileFn,
+            createTileFn,
+            retainTileFn,
+            [](const UnwrappedTileID&, Tile&) {},
+            panTiles,
+            zoomRange,
+            panZoom,
+            maxParentTileOverscaleFactor);
     }
 
-    algorithm::updateRenderables(getTileFn, createTileFn, retainTileFn, renderTileFn,
-                                 idealTiles, zoomRange, tileZoom);
-    
+    algorithm::updateRenderables(getTileFn,
+                                 createTileFn,
+                                 retainTileFn,
+                                 renderTileFn,
+                                 idealTiles,
+                                 zoomRange,
+                                 tileZoom,
+                                 maxParentTileOverscaleFactor);
+
     for (auto previouslyRenderedTile : previouslyRenderedTiles) {
         Tile& tile = previouslyRenderedTile.second;
         tile.markRenderedPreviously();
diff --git a/src/mbgl/renderer/tile_pyramid.hpp b/src/mbgl/renderer/tile_pyramid.hpp
index 5f2bfd1ea9..7dd2ab5341 100644
--- a/src/mbgl/renderer/tile_pyramid.hpp
+++ b/src/mbgl/renderer/tile_pyramid.hpp
@@ -42,7 +42,8 @@ public:
                 Range<uint8_t> zoomRange,
                 optional<LatLngBounds> bounds,
                 std::function<std::unique_ptr<Tile>(const OverscaledTileID&)> createTile,
-                optional<uint8_t> sourcePrefetchZoomDelta);
+                const optional<uint8_t>& sourcePrefetchZoomDelta,
+                const optional<uint8_t>& maxParentTileOverscaleFactor);
 
     const std::map<UnwrappedTileID, std::reference_wrapper<Tile>>& getRenderedTiles() const { return renderedTiles; }
     Tile* getTile(const OverscaledTileID&);
diff --git a/src/mbgl/style/source.cpp b/src/mbgl/style/source.cpp
index 644a31dace..51a3c80089 100644
--- a/src/mbgl/style/source.cpp
+++ b/src/mbgl/style/source.cpp
@@ -43,6 +43,18 @@ optional<uint8_t> Source::getPrefetchZoomDelta() const noexcept {
     return baseImpl->getPrefetchZoomDelta();
 }
 
+void Source::setMaxOverscaleFactorForParentTiles(optional<uint8_t> overscaleFactor) noexcept {
+    if (getMaxOverscaleFactorForParentTiles() == overscaleFactor) return;
+    auto newImpl = createMutable();
+    newImpl->setMaxOverscaleFactorForParentTiles(std::move(overscaleFactor));
+    baseImpl = std::move(newImpl);
+    observer->onSourceChanged(*this);
+}
+
+optional<uint8_t> Source::getMaxOverscaleFactorForParentTiles() const noexcept {
+    return baseImpl->getMaxOverscaleFactorForParentTiles();
+}
+
 void Source::dumpDebugLogs() const {
     Log::Info(Event::General, "Source::id: %s", getID().c_str());
     Log::Info(Event::General, "Source::loaded: %d", loaded);
diff --git a/src/mbgl/style/source_impl.cpp b/src/mbgl/style/source_impl.cpp
index 7f6f633eda..98433a8c86 100644
--- a/src/mbgl/style/source_impl.cpp
+++ b/src/mbgl/style/source_impl.cpp
@@ -1,8 +1,19 @@
 #include <mbgl/style/source_impl.hpp>
+#include <mbgl/util/constants.hpp>
+#include <mbgl/util/logging.hpp>
 
 namespace mbgl {
 namespace style {
 
+namespace {
+void WarnIfOverscaleFactorCapsPrefetchDelta(const optional<uint8_t>& overscale, const optional<uint8_t>& prefetch) {
+    const uint8_t prefetchDelta = std::max<uint8_t>(util::DEFAULT_PREFETCH_ZOOM_DELTA, prefetch.value_or(0u));
+    if (overscale && *overscale < prefetchDelta) {
+        Log::Warning(Event::Style, "Parent tile overscale factor will cap prefetch delta to %d", int(*overscale));
+    }
+}
+} // namespace
+
 Source::Impl::Impl(SourceType type_, std::string id_)
     : type(type_),
       id(std::move(id_)) {
@@ -10,11 +21,21 @@ Source::Impl::Impl(SourceType type_, std::string id_)
 
 void Source::Impl::setPrefetchZoomDelta(optional<uint8_t> delta) noexcept {
     prefetchZoomDelta = std::move(delta);
+    WarnIfOverscaleFactorCapsPrefetchDelta(maxOverscaleFactor, prefetchZoomDelta);
 }
 
 optional<uint8_t> Source::Impl::getPrefetchZoomDelta() const noexcept {
     return prefetchZoomDelta;
 }
 
+void Source::Impl::setMaxOverscaleFactorForParentTiles(optional<uint8_t> overscaleFactor) noexcept {
+    maxOverscaleFactor = std::move(overscaleFactor);
+    WarnIfOverscaleFactorCapsPrefetchDelta(maxOverscaleFactor, prefetchZoomDelta);
+}
+
+optional<uint8_t> Source::Impl::getMaxOverscaleFactorForParentTiles() const noexcept {
+    return maxOverscaleFactor;
+}
+
 } // namespace style
 } // namespace mbgl
diff --git a/src/mbgl/style/source_impl.hpp b/src/mbgl/style/source_impl.hpp
index d2c5d54d10..af8435537a 100644
--- a/src/mbgl/style/source_impl.hpp
+++ b/src/mbgl/style/source_impl.hpp
@@ -22,10 +22,13 @@ public:
     virtual optional<std::string> getAttribution() const = 0;
     void setPrefetchZoomDelta(optional<uint8_t> delta) noexcept;
     optional<uint8_t> getPrefetchZoomDelta() const noexcept;
+    void setMaxOverscaleFactorForParentTiles(optional<uint8_t> overscaleFactor) noexcept;
+    optional<uint8_t> getMaxOverscaleFactorForParentTiles() const noexcept;
 
     const SourceType type;
     const std::string id;
     optional<uint8_t> prefetchZoomDelta;
+    optional<uint8_t> maxOverscaleFactor;
 
 protected:
     Impl(SourceType, std::string);