Add an ellipsoid tileset loader for flat terrain generation

CHANGES.md

@@ -11,6 +11,7 @@
 - Added full support for custom ellipsoids by setting `TilesetOptions::ellipsoid` when creating a tileset.
   - Many methods have been updated with an additional ellipsoid parameter to support this. The WGS84 ellipsoid is used as a default parameter here to ensure API compatibility.
   - `CESIUM_DISABLE_DEFAULT_ELLIPSOID` can be defined to disable the WGS84 default parameter, exposing through errors the places in your code that are still assuming a WGS84 ellipsoid.
+- Added `EllipsoidTilesetLoader` that will generate a tileset by tesselating the surface of an ellipsoid, producing a simple globe tileset without any terrain features.
 
 ##### Fixes :wrench:
 

Cesium3DTilesSelection/include/Cesium3DTilesSelection/EllipsoidTilesetLoader.h

@@ -0,0 +1,63 @@
+#pragma once
+
+#include <Cesium3DTilesSelection/Tile.h>
+#include <Cesium3DTilesSelection/TileLoadResult.h>
+#include <Cesium3DTilesSelection/Tileset.h>
+#include <Cesium3DTilesSelection/TilesetContentLoader.h>
+#include <Cesium3DTilesSelection/TilesetExternals.h>
+#include <Cesium3DTilesSelection/TilesetOptions.h>
+#include <CesiumAsync/Future.h>
+#include <CesiumGeometry/QuadtreeTileID.h>
+#include <CesiumGeometry/QuadtreeTilingScheme.h>
+#include <CesiumGeospatial/BoundingRegion.h>
+#include <CesiumGeospatial/Ellipsoid.h>
+#include <CesiumGeospatial/GeographicProjection.h>
+#include <CesiumGltf/Model.h>
+
+#include <glm/fwd.hpp>
+
+#include <cstdint>
+#include <memory>
+#include <vector>
+
+using namespace CesiumGltf;
+using namespace CesiumAsync;
+using namespace CesiumUtility;
+using namespace CesiumGeometry;
+using namespace CesiumGeospatial;
+
+namespace Cesium3DTilesSelection {
+class EllipsoidTilesetLoader : public TilesetContentLoader {
+public:
+  EllipsoidTilesetLoader(const Ellipsoid& ellipsoid CESIUM_DEFAULT_ELLIPSOID);
+
+  static std::unique_ptr<Tileset> createTileset(
+      const TilesetExternals& externals,
+      const TilesetOptions& options = TilesetOptions{});
+
+  Future<TileLoadResult> loadTileContent(const TileLoadInput& input) override;
+  TileChildrenResult createTileChildren(
+      const Tile& tile,
+      const CesiumGeospatial::Ellipsoid& ellipsoid
+          CESIUM_DEFAULT_ELLIPSOID) override;
+
+private:
+  struct Geometry {
+    std::vector<uint16_t> indices;
+    std::vector<glm::vec3> vertices;
+    std::vector<glm::vec3> normals;
+  };
+
+  void createChildTile(
+      const Tile& parent,
+      std::vector<Tile>& children,
+      const QuadtreeTileID& childID) const;
+
+  BoundingRegion createBoundingRegion(const QuadtreeTileID& quadtreeID) const;
+  Geometry createGeometry(const Tile& tile) const;
+  Model createModel(const Geometry& geometry) const;
+
+  GeographicProjection _projection;
+  QuadtreeTilingScheme _tilingScheme;
+};
+} // namespace Cesium3DTilesSelection

Cesium3DTilesSelection/src/EllipsoidTilesetLoader.cpp

@@ -0,0 +1,279 @@
+#include <Cesium3DTilesContent/ImplicitTilingUtilities.h>
+#include <Cesium3DTilesSelection/EllipsoidTilesetLoader.h>
+#include <Cesium3DTilesSelection/Tile.h>
+#include <Cesium3DTilesSelection/TileContent.h>
+#include <Cesium3DTilesSelection/TileLoadResult.h>
+#include <Cesium3DTilesSelection/TileRefine.h>
+#include <Cesium3DTilesSelection/Tileset.h>
+#include <Cesium3DTilesSelection/TilesetContentLoader.h>
+#include <Cesium3DTilesSelection/TilesetExternals.h>
+#include <Cesium3DTilesSelection/TilesetOptions.h>
+#include <CesiumAsync/Future.h>
+#include <CesiumGeometry/Axis.h>
+#include <CesiumGeometry/QuadtreeTileID.h>
+#include <CesiumGeometry/QuadtreeTilingScheme.h>
+#include <CesiumGeospatial/BoundingRegion.h>
+#include <CesiumGeospatial/Cartographic.h>
+#include <CesiumGeospatial/Ellipsoid.h>
+#include <CesiumGeospatial/GeographicProjection.h>
+#include <CesiumGeospatial/GlobeRectangle.h>
+#include <CesiumGeospatial/calcQuadtreeMaxGeometricError.h>
+#include <CesiumGltf/Accessor.h>
+#include <CesiumGltf/AccessorSpec.h>
+#include <CesiumGltf/Buffer.h>
+#include <CesiumGltf/BufferCesium.h>
+#include <CesiumGltf/BufferView.h>
+#include <CesiumGltf/Mesh.h>
+#include <CesiumGltf/MeshPrimitive.h>
+#include <CesiumGltf/Model.h>
+#include <CesiumGltf/Node.h>
+#include <CesiumGltf/Scene.h>
+
+#include <glm/detail/type_vec3.hpp>
+#include <glm/ext/matrix_transform.hpp>
+#include <glm/fwd.hpp>
+
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <memory>
+#include <optional>
+#include <type_traits>
+#include <variant>
+#include <vector>
+
+using namespace Cesium3DTilesContent;
+
+namespace Cesium3DTilesSelection {
+EllipsoidTilesetLoader::EllipsoidTilesetLoader(const Ellipsoid& ellipsoid)
+    : _projection(ellipsoid),
+      _tilingScheme(
+          _projection.project(_projection.MAXIMUM_GLOBE_RECTANGLE),
+          2,
+          1) {}
+
+/*static*/ std::unique_ptr<Tileset> EllipsoidTilesetLoader::createTileset(
+    const TilesetExternals& externals,
+    const TilesetOptions& options) {
+  std::unique_ptr<EllipsoidTilesetLoader> pCustomLoader =
+      std::make_unique<EllipsoidTilesetLoader>(options.ellipsoid);
+  std::unique_ptr<Tile> pRootTile =
+      std::make_unique<Tile>(pCustomLoader.get(), TileEmptyContent{});
+
+  pRootTile->setRefine(TileRefine::Replace);
+  pRootTile->setUnconditionallyRefine();
+
+  std::vector<Tile> children;
+  uint32_t rootTilesX = pCustomLoader->_tilingScheme.getRootTilesX();
+  children.reserve(rootTilesX);
+
+  for (uint32_t x = 0; x < rootTilesX; x++) {
+    pCustomLoader->createChildTile(
+        *pRootTile,
+        children,
+        QuadtreeTileID{0, x, 0});
+  }
+
+  pRootTile->createChildTiles(std::move(children));
+
+  return std::make_unique<Tileset>(
+      externals,
+      std::move(pCustomLoader),
+      std::move(pRootTile),
+      options);
+}
+
+Future<TileLoadResult>
+EllipsoidTilesetLoader::loadTileContent(const TileLoadInput& input) {
+  return input.asyncSystem.createResolvedFuture(TileLoadResult{
+      createModel(createGeometry(input.tile)),
+      Axis::Z,
+      std::nullopt,
+      std::nullopt,
+      std::nullopt,
+      nullptr,
+      {},
+      TileLoadResultState::Success});
+}
+
+TileChildrenResult EllipsoidTilesetLoader::createTileChildren(
+    const Tile& tile,
+    const CesiumGeospatial::Ellipsoid& ellipsoid) {
+  // We don't use the ellipsoid parameter, since we already have an ellipsoid
+  // specified, but if we don't use the variable we'll get an error. This line
+  // counts as using it.
+  (void)ellipsoid;
+
+  const QuadtreeTileID* pParentID =
+      std::get_if<QuadtreeTileID>(&tile.getTileID());
+
+  if (pParentID) {
+    std::vector<Tile> children;
+    QuadtreeChildren childIDs =
+        ImplicitTilingUtilities::getChildren(*pParentID);
+    children.reserve(childIDs.size());
+
+    for (const QuadtreeTileID& childID : childIDs) {
+      createChildTile(tile, children, childID);
+    }
+
+    return TileChildrenResult{
+        std::move(children),
+        TileLoadResultState::Success};
+  }
+
+  return TileChildrenResult{{}, TileLoadResultState::Failed};
+}
+
+void EllipsoidTilesetLoader::createChildTile(
+    const Tile& parent,
+    std::vector<Tile>& children,
+    const QuadtreeTileID& childID) const {
+  BoundingRegion boundingRegion = createBoundingRegion(childID);
+  const GlobeRectangle& globeRectangle = boundingRegion.getRectangle();
+
+  Tile& child = children.emplace_back(parent.getLoader());
+  child.setTileID(childID);
+  child.setRefine(parent.getRefine());
+  child.setTransform(glm::translate(
+      glm::dmat4x4(1.0),
+      _projection.getEllipsoid().cartographicToCartesian(
+          globeRectangle.getNorthwest())));
+  child.setBoundingVolume(boundingRegion);
+  child.setGeometricError(
+      6.0 * calcQuadtreeMaxGeometricError(_projection.getEllipsoid()) *
+      globeRectangle.computeWidth());
+}
+
+BoundingRegion EllipsoidTilesetLoader::createBoundingRegion(
+    const QuadtreeTileID& quadtreeID) const {
+  return BoundingRegion(
+      _projection.unproject(_tilingScheme.tileToRectangle(quadtreeID)),
+      0.0,
+      0.0,
+      _projection.getEllipsoid());
+}
+
+EllipsoidTilesetLoader::Geometry
+EllipsoidTilesetLoader::createGeometry(const Tile& tile) const {
+  static constexpr uint16_t resolution = 24;
+
+  std::vector<uint16_t> indices(6 * (resolution - 1) * (resolution - 1));
+  std::vector<glm::vec3> vertices(resolution * resolution);
+  std::vector<glm::vec3> normals(vertices.size());
+
+  const Ellipsoid& ellipsoid = _projection.getEllipsoid();
+  const GlobeRectangle& rectangle =
+      std::get<BoundingRegion>(tile.getBoundingVolume()).getRectangle();
+
+  double west = rectangle.getWest();
+  double east = rectangle.getEast();
+  double north = rectangle.getNorth();
+  double south = rectangle.getSouth();
+
+  double lonStep = (east - west) / (resolution - 1);
+  double latStep = (south - north) / (resolution - 1);
+
+  glm::dmat4 inverseTransform = glm::inverse(tile.getTransform());
+
+  for (uint16_t x = 0; x < resolution; x++) {
+    double longitude = (lonStep * x) + west;
+    for (uint16_t y = 0; y < resolution; y++) {
+      double latitude = (latStep * y) + north;
+      Cartographic cartographic(longitude, latitude);
+
+      uint16_t index = static_cast<uint16_t>((resolution * x) + y);
+      vertices[index] = glm::dvec3(
+          inverseTransform *
+          glm::dvec4(ellipsoid.cartographicToCartesian(cartographic), 1.0));
+      normals[index] = ellipsoid.geodeticSurfaceNormal(cartographic);
+
+      if (x < resolution - 1 && y < resolution - 1) {
+        uint16_t a = index + 1;
+        uint16_t b = index + resolution;
+        uint16_t c = b + 1;
+        indices.insert(indices.end(), {b, index, a, b, a, c});
+      }
+    }
+  }
+
+  return Geometry{std::move(indices), std::move(vertices), std::move(normals)};
+}
+
+Model EllipsoidTilesetLoader::createModel(const Geometry& geometry) const {
+  const std::vector<uint16_t>& indices = geometry.indices;
+  const std::vector<glm::vec3>& vertices = geometry.vertices;
+  const std::vector<glm::vec3>& normals = geometry.normals;
+
+  size_t indicesSize = indices.size() * sizeof(uint16_t);
+  size_t verticesSize = vertices.size() * sizeof(glm::vec3);
+  size_t normalsSize = verticesSize;
+
+  Model model;
+  model.buffers.resize(1);
+  model.bufferViews.resize(3);
+  model.accessors.resize(3);
+  model.materials.resize(1);
+  model.meshes.resize(1);
+  model.scenes.resize(1);
+  model.nodes.resize(1);
+
+  model.meshes[0].primitives.resize(1);
+  model.scenes[0].nodes.emplace_back(0);
+  model.nodes[0].mesh = 0;
+
+  std::vector<std::byte>& buffer = model.buffers[0].cesium.data;
+  buffer.resize(indicesSize + verticesSize + normalsSize);
+  std::memcpy(buffer.data(), indices.data(), indicesSize);
+  std::memcpy(buffer.data() + indicesSize, vertices.data(), verticesSize);
+  std::memcpy(
+      buffer.data() + indicesSize + verticesSize,
+      normals.data(),
+      normalsSize);
+
+  BufferView& bufferViewIndices = model.bufferViews[0];
+  bufferViewIndices.buffer = 0;
+  bufferViewIndices.byteOffset = 0;
+  bufferViewIndices.byteLength = static_cast<int64_t>(indicesSize);
+  bufferViewIndices.target = BufferView::Target::ELEMENT_ARRAY_BUFFER;
+
+  BufferView& bufferViewVertices = model.bufferViews[1];
+  bufferViewVertices.buffer = 0;
+  bufferViewVertices.byteOffset = static_cast<int64_t>(indicesSize);
+  bufferViewVertices.byteLength = static_cast<int64_t>(verticesSize);
+  bufferViewVertices.target = BufferView::Target::ARRAY_BUFFER;
+
+  BufferView& bufferViewNormals = model.bufferViews[2];
+  bufferViewNormals.buffer = 0;
+  bufferViewNormals.byteOffset =
+      static_cast<int64_t>(indicesSize + verticesSize);
+  bufferViewNormals.byteLength = static_cast<int64_t>(normalsSize);
+  bufferViewNormals.target = BufferView::Target::ARRAY_BUFFER;
+
+  Accessor& accessorIndices = model.accessors[0];
+  accessorIndices.bufferView = 0;
+  accessorIndices.count = static_cast<int64_t>(indices.size());
+  accessorIndices.componentType = Accessor::ComponentType::UNSIGNED_SHORT;
+  accessorIndices.type = Accessor::Type::SCALAR;
+
+  Accessor& accessorVertices = model.accessors[1];
+  accessorVertices.bufferView = 1;
+  accessorVertices.count = static_cast<int64_t>(vertices.size());
+  accessorVertices.componentType = Accessor::ComponentType::FLOAT;
+  accessorVertices.type = Accessor::Type::VEC3;
+
+  Accessor& accessorNormals = model.accessors[2];
+  accessorNormals.bufferView = 2;
+  accessorNormals.count = static_cast<int64_t>(normals.size());
+  accessorNormals.componentType = Accessor::ComponentType::FLOAT;
+  accessorNormals.type = Accessor::Type::VEC3;
+
+  MeshPrimitive& primitive = model.meshes[0].primitives[0];
+  primitive.attributes["POSITION"] = 1;
+  primitive.attributes["NORMAL"] = 2;
+  primitive.indices = 0;
+  primitive.material = 0;
+
+  return model;
+}
+} // namespace Cesium3DTilesSelection