[core] don't break ascent in the overscaled tile phase

We optimize our updateRenderable algorithm by breaking ascent when we've already checked a certain tile. So far, we've compared the UnwrappedTileIDs, but they don't include the overscale component. When ascending through overscaled tile IDs, we've stopped the ascent too early, when we should've kept the search going.

2 files changed, 54 insertions, 5 deletions

diff --git a/src/mbgl/algorithm/update_renderables.hpp b/src/mbgl/algorithm/update_renderables.hpp
index 5fbe0d943f..57cd4f41ec 100644
--- a/src/mbgl/algorithm/update_renderables.hpp
+++ b/src/mbgl/algorithm/update_renderables.hpp
@@ -21,7 +21,7 @@ void updateRenderables(GetTileFn getTile,
                        const IdealTileIDs& idealTileIDs,
                        const Range<uint8_t>& zoomRange,
                        const uint8_t dataTileZoom) {
-    std::unordered_set<UnwrappedTileID> checked;
+    std::unordered_set<OverscaledTileID> checked;
     bool covered;
     int32_t overscaledZ;
 
@@ -85,14 +85,13 @@ void updateRenderables(GetTileFn getTile,
                 // 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);
-                    const auto parentRenderTileID = parentDataTileID.toUnwrapped();
 
-                    if (checked.find(parentRenderTileID) != checked.end()) {
+                    if (checked.find(parentDataTileID) != checked.end()) {
                         // Break parent tile ascent, this route has been checked by another child
                         // tile before.
                         break;
                     } else {
-                        checked.emplace(parentRenderTileID);
+                        checked.emplace(parentDataTileID);
                     }
 
                     tile = getTile(parentDataTileID);
@@ -117,7 +116,7 @@ void updateRenderables(GetTileFn getTile,
                         parentIsLoaded = tile->isLoaded();
 
                         if (tile->isRenderable()) {
-                            renderTile(parentRenderTileID, *tile);
+                            renderTile(parentDataTileID.toUnwrapped(), *tile);
                             // Break parent tile ascent, since we found one.
                             break;
                         }
diff --git a/test/algorithm/update_renderables.test.cpp b/test/algorithm/update_renderables.test.cpp
index 7d6a0fcb13..e142758f29 100644
--- a/test/algorithm/update_renderables.test.cpp
+++ b/test/algorithm/update_renderables.test.cpp
@@ -1259,3 +1259,53 @@ TEST(UpdateRenderables, LoadRequiredIfIdealTileCantBeFound) {
               }),
               log);
 }
+
+// Tests overzooming a 0/0/0 tile to zoom level 4, when the maxzoom is 2.
+TEST(UpdateRenderables, LoadOverscaledMaxZoomTile) {
+    ActionLog log;
+    MockSource source;
+    auto getTileData = getTileDataFn(log, source.dataTiles);
+    auto createTileData = createTileDataFn(log, source.dataTiles);
+    auto retainTileData = retainTileDataFn(log);
+    auto renderTile = renderTileFn(log);
+
+    source.zoomRange.max = 2;
+    source.idealTiles.emplace(UnwrappedTileID{ 2, 0, 0 });
+
+    auto tile_4_2_0_0 = source.createTileData(OverscaledTileID{ 4, 0, { 2, 0, 0 } });
+    tile_4_2_0_0->renderable = false;
+    tile_4_2_0_0->triedOptional = true;
+    tile_4_2_0_0->loaded = true;
+
+    auto tile_3_2_0_0 = source.createTileData(OverscaledTileID{ 3, 0, { 2, 0, 0 } });
+    tile_3_2_0_0->renderable = false;
+    tile_3_2_0_0->triedOptional = true;
+    tile_3_2_0_0->loaded = true;
+
+    auto tile_2_2_0_0 = source.createTileData(OverscaledTileID{ 2, 0, { 2, 0, 0 } });
+    tile_2_2_0_0->renderable = false;
+    tile_2_2_0_0->triedOptional = true;
+    tile_2_2_0_0->loaded = true;
+
+    // Tile level 1 won't be overscaled.
+    auto tile_1_1_0_0 = source.createTileData(OverscaledTileID{ 1, 0, { 1, 0, 0 } });
+    tile_1_1_0_0->renderable = true;
+    tile_1_1_0_0->triedOptional = true;
+    tile_1_1_0_0->loaded = true;
+
+    algorithm::updateRenderables(getTileData, createTileData, retainTileData, renderTile,
+                                 source.idealTiles, source.zoomRange, 4);
+    EXPECT_EQ(ActionLog({
+                  GetTileDataAction{ { 4, 0, { 2, 0, 0 } }, Found },
+                  RetainTileDataAction{ { 4, 0, { 2, 0, 0 } }, TileNecessity::Required },
+                  GetTileDataAction{ { 5, 0, { 2, 0, 0 } }, NotFound },
+                  GetTileDataAction{ { 3, 0, { 2, 0, 0 } }, Found },
+                  RetainTileDataAction{ { 3, 0, { 2, 0, 0 } }, TileNecessity::Required },
+                  GetTileDataAction{ { 2, 0, { 2, 0, 0 } }, Found },
+                  RetainTileDataAction{ { 2, 0, { 2, 0, 0 } }, TileNecessity::Required },
+                  GetTileDataAction{ { 1, 0, { 1, 0, 0 } }, Found },
+                  RetainTileDataAction{ { 1, 0, { 1, 0, 0 } }, TileNecessity::Required },
+                  RenderTileAction{ { 1, 0, 0 }, *tile_1_1_0_0 },
+              }),
+              log);
+}