/// <summary>
/// Outside code should only call this on the root. This method will recursively construct an entire quadtree starting
/// from the root node. It will continue to expand a branch of the tree until any new nodes would have to
/// have a resolution greater than that of the heightmap itself.
/// </summary>
public void RecursivelyBuildTree()
{
// Get this chunk's index.
index = quadTree.GetNextChunkIndex();
// First compute the net world transform for this node.
worldTransform = Matrix.CreateScale(scaleFactor, 1.0f, scaleFactor) * Matrix.CreateTranslation(centerWorldPosition);
// Calculate the texture coordinate range for this chunk.
textureCoordinates = new TerrainChunkTextureCoordinates();
float terrainDimension = 2 * quadTree.Parameters.TerrainScale;
textureCoordinates.UStart = ((centerWorldPosition.X - scaleFactor / 2.0f + terrainDimension / 2.0f) / terrainDimension - 0.25f) * 2f;
textureCoordinates.UEnd = ((centerWorldPosition.X + scaleFactor / 2.0f + terrainDimension / 2.0f) / terrainDimension - 0.25f) * 2f;
textureCoordinates.VStart = ((centerWorldPosition.Z - scaleFactor / 2.0f + terrainDimension / 2.0f) / terrainDimension - 0.25f) * 2f;
textureCoordinates.VEnd = ((centerWorldPosition.Z + scaleFactor / 2.0f + terrainDimension / 2.0f) / terrainDimension - 0.25f) * 2f;
// Construct the bounding box to be used for frustum culling
boundingBox = new BoundingBox(new Vector3(centerWorldPosition.X - scaleFactor / 2.0f, 0.0f, centerWorldPosition.Z - scaleFactor / 2.0f),
new Vector3(centerWorldPosition.X + scaleFactor / 2.0f, quadTree.Parameters.MaxHeight, centerWorldPosition.Z + scaleFactor / 2.0f));
// If this node has a lower resolution than the heightmap itself, we expand it into four children.
// Otherwise, this branch of the tree ends.
children = new List<TerrainChunk>();
if (quadTree.HeightMap.Width / quadTree.Parameters.TerrainScale >= quadTree.CommonGrid.Dimension / scaleFactor)
{
// This isn't a leaf chunk, so we compute/look up its geometric error.
if (quadTree.Parameters.DoPreprocessing)
{
// Compute it manually
geometricError = ComputeRawGeometricError();
quadTree.ChunkGeometricErrors[index] = geometricError;
}
else
{
// Look it up from the precomputed table
geometricError = quadTree.ChunkGeometricErrors[index];
}
// Expand into four children
TerrainChunk child1 = new TerrainChunk(quadTree, this,
centerWorldPosition + new Vector3(scaleFactor / 4.0f, 0.0f, scaleFactor / 4.0f),
scaleFactor / 2.0f);
TerrainChunk child2 = new TerrainChunk(quadTree, this,
centerWorldPosition + new Vector3(scaleFactor / 4.0f, 0.0f, -scaleFactor / 4.0f),
scaleFactor / 2.0f);
TerrainChunk child3 = new TerrainChunk(quadTree, this,
centerWorldPosition + new Vector3(-scaleFactor / 4.0f, 0.0f, scaleFactor / 4.0f),
scaleFactor / 2.0f);
TerrainChunk child4 = new TerrainChunk(quadTree, this,
centerWorldPosition + new Vector3(-scaleFactor / 4.0f, 0.0f, -scaleFactor / 4.0f),
scaleFactor / 2.0f);
children.Add(child1);
children.Add(child2);
children.Add(child3);
children.Add(child4);
child1.RecursivelyBuildTree();
child2.RecursivelyBuildTree();
child3.RecursivelyBuildTree();
child4.RecursivelyBuildTree();
}
// Finally, as the recursion unwinds, we accumulate the geometric error from children.
if (children.Count > 0)
{
geometricError += (float)Math.Max(children[0].GeometricError, Math.Max(children[1].GeometricError,
Math.Max(children[2].GeometricError, children[3].GeometricError)));
}
minimumDistanceToSplit = geometricError / quadTree.Parameters.MaxScreenSpaceError * quadTree.Parameters.PerspectiveScalingFactor;
}
/// <summary>
/// This method constructs the terrain quad tree structure, creating all the terrain chunks and geometry.
/// </summary>
private void ConstructQuadTree()
{
// Set up the root node centered at the origin and scaled to fit the entire terrain.
rootNode = new TerrainChunk(this, null, new Vector3(), parameters.TerrainScale);
// This will take care of the rest!
rootNode.RecursivelyBuildTree();
}