"Kick" only when the current tile is renderable

CHANGES.md

@@ -20,6 +20,7 @@
 - Fixed a raster overlay bug that could cause unnecessary upsampling with failed or missing overlay tiles.
 - Fixed a bug in  `SubtreeFileReader::loadBinary` that prevented valid subtrees from loading if they did not contain binary data.
 - Fixed a bug in the `Tileset` selection algorithm that could cause detail to disappear during load in some cases.
+- Improved the "kicking" mechanism in the tileset selection algorithm. The new criteria allows holes in a `Tileset`, when they do occur, to be filled with loaded tiles more incrementally.
 
 ### v0.42.0 - 2024-12-02
 

Cesium3DTilesSelection/src/Tileset.cpp

@@ -1430,7 +1430,16 @@ Tileset::TraversalDetails Tileset::_visitTile(
       lastFrameSelectionResult == TileSelectionState::Result::Rendered &&
       pRenderContent && pRenderContent->getLodTransitionFadePercentage() < 1.0f;
 
-  if (kickDueToNonReadyDescendant || kickDueToTileFadingIn) {
+  // Only kick the descendants of this tile if it is renderable, or if we've
+  // exceeded the loadingDescendantLimit. It's pointless to kick the descendants
+  // of a tile that is not yet loaded, because it means we will still have a
+  // hole, and quite possibly a bigger one.
+  bool wantToKick = kickDueToNonReadyDescendant || kickDueToTileFadingIn;
+  bool willKick = wantToKick && (traversalDetails.notYetRenderableCount >
+                                     this->_options.loadingDescendantLimit ||
+                                 tile.isRenderable());
+
+  if (willKick) {
     // Kick all descendants out of the render list and render this tile instead
     // Continue to load them though!
     queuedForLoad = _kickDescendantsAndRenderTile(

Cesium3DTilesSelection/test/TestTilesetSelectionAlgorithm.cpp

@@ -563,31 +563,32 @@ TEST_CASE("Test additive refinement") {
   SECTION("Load external tilesets") {
     ViewState viewState = zoomToTileset(tileset);
 
-    // 1st frame. Root will get rendered first and 5 of its children are loading
-    // since they meet sse
+    // 1st frame. Root, its child, and its four grandchildren will all be
+    // rendered because they meet SSE, even though they're not loaded yet.
     {
       ViewUpdateResult result = tileset.updateView({viewState});
 
-      // root is rendered first
+      const std::vector<Tile*>& ttr = result.tilesToRenderThisFrame;
+      REQUIRE(ttr.size() == 7);
+
       REQUIRE(root->getState() == TileLoadState::Done);
       REQUIRE(!doesTileMeetSSE(viewState, *root, tileset));
       REQUIRE(root->getChildren().size() == 1);
+      REQUIRE(std::find(ttr.begin(), ttr.end(), pTilesetJson) != ttr.end());
+      REQUIRE(std::find(ttr.begin(), ttr.end(), root) != ttr.end());
 
-      // root's children don't have content loading right now, so only root get
-      // rendered
       const Tile& parentB3DM = root->getChildren().front();
       REQUIRE(parentB3DM.getState() == TileLoadState::ContentLoading);
       REQUIRE(!doesTileMeetSSE(viewState, parentB3DM, tileset));
       REQUIRE(parentB3DM.getChildren().size() == 4);
+      REQUIRE(std::find(ttr.begin(), ttr.end(), &parentB3DM) != ttr.end());
 
       for (const Tile& child : parentB3DM.getChildren()) {
         REQUIRE(child.getState() == TileLoadState::ContentLoading);
         REQUIRE(doesTileMeetSSE(viewState, child, tileset));
+        REQUIRE(std::find(ttr.begin(), ttr.end(), &child) != ttr.end());
       }
 
-      REQUIRE(result.tilesToRenderThisFrame.size() == 1);
-      REQUIRE(result.tilesToRenderThisFrame.front() == pTilesetJson);
-
       REQUIRE(result.tilesFadingOut.size() == 0);
 
       REQUIRE(result.tilesVisited == 7);
@@ -600,20 +601,26 @@ TEST_CASE("Test additive refinement") {
     {
       ViewUpdateResult result = tileset.updateView({viewState});
 
-      // root is rendered first
+      const std::vector<Tile*>& ttr = result.tilesToRenderThisFrame;
+      REQUIRE(ttr.size() == 8);
+
+      // root is done loading and rendered.
       REQUIRE(root->getState() == TileLoadState::Done);
       REQUIRE(!doesTileMeetSSE(viewState, *root, tileset));
       REQUIRE(root->getChildren().size() == 1);
+      REQUIRE(std::find(ttr.begin(), ttr.end(), root) != ttr.end());
 
-      // root's children don't have content loading right now, so only root get
-      // rendered
+      // root's child is done loading and rendered, too.
       const Tile& parentB3DM = root->getChildren().front();
       REQUIRE(parentB3DM.getState() == TileLoadState::Done);
       REQUIRE(!doesTileMeetSSE(viewState, parentB3DM, tileset));
       REQUIRE(parentB3DM.getChildren().size() == 4);
+      REQUIRE(std::find(ttr.begin(), ttr.end(), &parentB3DM) != ttr.end());
 
       for (const Tile& child : parentB3DM.getChildren()) {
+        // parentB3DM's children are all done loading and are rendered.
         REQUIRE(child.getState() == TileLoadState::Done);
+        REQUIRE(std::find(ttr.begin(), ttr.end(), &child) != ttr.end());
 
         if (*std::get_if<std::string>(&child.getTileID()) !=
             "tileset3/tileset3.json") {
@@ -622,21 +629,20 @@ TEST_CASE("Test additive refinement") {
           // external tilesets get unconditionally refined
           REQUIRE(root->getUnconditionallyRefine());
 
-          // expect the children to meet sse and begin loading the content
+          // expect the children to meet sse and begin loading the content,
+          // while also getting rendered.
           REQUIRE(child.getChildren().size() == 1);
           REQUIRE(
               doesTileMeetSSE(viewState, child.getChildren().front(), tileset));
           REQUIRE(
               child.getChildren().front().getState() ==
               TileLoadState::ContentLoading);
+          REQUIRE(
+              std::find(ttr.begin(), ttr.end(), &child.getChildren().front()) !=
+              ttr.end());
         }
       }
 
-      REQUIRE(result.tilesToRenderThisFrame.size() == 3);
-      REQUIRE(result.tilesToRenderThisFrame[0] == pTilesetJson);
-      REQUIRE(result.tilesToRenderThisFrame[1] == root);
-      REQUIRE(result.tilesToRenderThisFrame[2] == &parentB3DM);
-
       REQUIRE(result.tilesFadingOut.size() == 0);
 
       REQUIRE(result.tilesVisited == 8);
@@ -1554,21 +1560,30 @@ void runUnconditionallyRefinedTestCase(const TilesetOptions& options) {
       pRawLoader->createRootTile(),
       options);
 
-  // On the first update, we should render the root tile, even though nothing is
-  // loaded yet.
+  // On the first update, we should refine down to the grandchild tile, even
+  // though no tiles are loaded yet.
   initializeTileset(tileset);
+  const Tile& child = tileset.getRootTile()->getChildren()[0];
+  const Tile& grandchild = child.getChildren()[0];
   CHECK(
       tileset.getRootTile()->getLastSelectionState().getResult(
           tileset.getRootTile()->getLastSelectionState().getFrameNumber()) ==
+      TileSelectionState::Result::Refined);
+  CHECK(
+      child.getLastSelectionState().getResult(
+          tileset.getRootTile()->getLastSelectionState().getFrameNumber()) ==
+      TileSelectionState::Result::Refined);
+  CHECK(
+      grandchild.getLastSelectionState().getResult(
+          tileset.getRootTile()->getLastSelectionState().getFrameNumber()) ==
       TileSelectionState::Result::Rendered);
 
-  // On the third update, the grandchild load will still be pending.
-  // But the child is unconditionally refined, so we should render the root
-  // instead of the child.
+  // After the third update, the root and child tiles have been loaded, while
+  // the grandchild has not. But the child is unconditionally refined, so we
+  // can't render that one. Therefore the root tile should be rendered, after
+  // the child and grandchild are kicked.
   initializeTileset(tileset);
   initializeTileset(tileset);
-  const Tile& child = tileset.getRootTile()->getChildren()[0];
-  const Tile& grandchild = child.getChildren()[0];
   CHECK(
       tileset.getRootTile()->getLastSelectionState().getResult(
           tileset.getRootTile()->getLastSelectionState().getFrameNumber()) ==