Add a "render-readiness" flag on tiles

Render engine or user-developer customizations can toggle it off to delay
the point at which the tile can be shown, while waiting for some
asynchronous post-processing to finish

Author: GhisBntly

CHANGES.md

@@ -58,6 +58,7 @@
 - Added an overload of `Math::equalsEpsilon` for glm matrices.
 - A tile's bounding volume and content bounding volume are now included in `TileLoadResult` for use in `prepareInLoadThread`.
 - Added `convertAccessorTypeToPropertyType` and `convertPropertyTypeToAccessorType` to `CesiumGltf::PropertyType`.
+- Added `Cesium3DTilesSelection::Tile::setRenderEngineReadiness(bool)`: pass false to delay the point at which the tile can be shown, while waiting for some asynchronous post-processing to finish for example.
 
 ##### Fixes :wrench:
 

Cesium3DTilesSelection/include/Cesium3DTilesSelection/Tile.h

@@ -501,6 +501,17 @@ class CESIUM3DTILESSELECTION_API Tile final {
    */
   bool isRenderable() const noexcept;
 
+  /**
+   * @brief Set by the render engine to notify when a tile needs post-load
+   *  processing before being actually renderable, that will have to happen
+   *  over one or more several main thread loop cycles.
+   *  By default, tiles are assumed immediately renderable when they reach
+   *  TileLoadState::Done status. Render engine can toggle readiness off to
+   *  signify that the tile should not be considered renderable until the flag
+   *  is turned on again.
+   */
+  void setRenderEngineReadiness(bool const renderEngineReady) noexcept;
+
   /**
    * @brief Determines if this tile has mesh content.
    */
@@ -687,6 +698,7 @@ class CESIUM3DTILESSELECTION_API Tile final {
   TilesetContentLoader* _pLoader;
   TileLoadState _loadState;
   bool _mightHaveLatentChildren;
+  bool _renderEngineReadiness = true; ///< Relevant only when _loadState is Done
 
   // mapped raster overlay
   std::vector<RasterMappedTo3DTile> _rasterTiles;

Cesium3DTilesSelection/src/Tile.cpp

@@ -220,6 +220,8 @@ bool Tile::isRenderable() const noexcept {
   }
 
   if (getState() == TileLoadState::Done) {
+    if (!_renderEngineReadiness)
+      return false;
     // An unconditionally-refined tile is never renderable... UNLESS it has no
     // children, in which case waiting longer will be futile.
     if (!getUnconditionallyRefine() || this->_children.empty()) {
@@ -235,6 +237,10 @@ bool Tile::isRenderable() const noexcept {
   return false;
 }
 
+void Tile::setRenderEngineReadiness(bool const renderEngineReady) noexcept {
+  _renderEngineReadiness = renderEngineReady;
+}
+
 bool Tile::isRenderContent() const noexcept {
   return this->_content.isRenderContent();
 }