TerrainLodTree

Remarks

CDLOD (Strugar, 2010), for the reasons in [docs/plan/31 § D3]: the node is simultaneously the LOD unit, the cull unit and the draw, and it aligns with the tile — a clipmap's rings align with nothing, because they are centred on the camera and everything else is a rectangle in terrain space.

No skirts, and that is the return on the morph. A finer node has degenerated onto its parent's grid by the time the parent takes over, so a boundary between two levels has no gap to hide. Skirts are what a renderer grows when the morph is wrong, and then keeps.

Arithmetic, deliberately. This assembly has no device — [§ D1] — and the two properties that matter are exactly the ones a device cannot be asked about: whether the shared edge of two adjacent nodes agrees, and whether a vertex moves continuously as the camera does. Both are functions, so both are unit tests. [§ Part 4] says the no-crack test must be written before the renderer, not after it.

Fields and properties (5)

• public const int DefaultGridQuads

  How many quads the shared grid patch spans, by default.

• public TerrainLodRanges Ranges

  Where each level takes over.

• public int GridQuads

  How many quads the shared grid patch spans.

• public int RootQuads

  How many quads the root node spans.

• public int DepthCount

  How deep the tree is, which may be fewer levels than the ranges describe.

Methods (6)

• public TerrainLodTree(TerrainDescription description, TerrainLodRanges ranges, int gridQuads = 32)

  Builds a tree over a terrain's shape.

• public int Select(Vector3 viewPosition, in BoundingFrustum frustum, Terrain terrain, ICollection<TerrainLodNode> nodes)

  Chooses the patches a view draws.

• public BoundingBox BoundsOf(int x, int z, int quads, Terrain terrain)

  Everything a node occupies, in the terrain's own space.

• public Vector2 SampleOf(in TerrainLodNode node, int gridX, int gridZ)

  Where one vertex of the shared grid patch lands, in sample coordinates, after morphing.

• public Vector3 PositionOf(in TerrainLodNode node, int gridX, int gridZ, Terrain terrain)

  Where one vertex of a patch lands in the terrain's own space, after morphing.

• public static float MorphIndex(int index, float morph)

  A grid index after morphing: odd indices slide back onto their even neighbour.

Used by (3)

• TerrainLodTestsVixen.Terrain.Tests
• TerrainRendererVixen.Rendering.Terrain
• TerrainShaderParityTestsVixen.Rendering.Terrain.Tests