public HeightmapChunk(Rectangle range, int mipLevel, HeightmapChunk left, HeightmapChunk top) : base(null, range)
{
Adjacent[3] = left;
Adjacent[0] = top;
if (left != null)
{
left.Adjacent[1] = this;
}
if (top != null)
{
top.Adjacent[2] = this;
}
MipLevel = mipLevel;
}
//how the simplification works:
//we generate a "maximum second derivative" map from the heightmap.
//we then create a maximum value image pyramid with the maximum value in the 4 pixels beneath
//when generating the mesh, we fall into quadrants below if the second derivative is above a threshold.
public void GenerateFullTree()
{
//how the algorithm works:
//build a base structure with quad trees
Chunks = new List <HeightmapChunk>();
var levels = SecondDerivativePyramid.Length;
var chunkSize = 1 << levels;
var cw = Size / chunkSize;
for (int y = 0; y < Size; y += chunkSize)
{
for (int x = 0; x < Size; x += chunkSize)
{
var chunk = new HeightmapChunk(new Rectangle(x, y, chunkSize, chunkSize), levels,
(x == 0) ? null : Chunks.Last(),
(y == 0) ? null : Chunks[Chunks.Count - cw]);
Chunks.Add(chunk);
}
}
var thresholds = HighDetailThresholds;
var toTraverse = new Queue <HeightmapQuadTreeNode>(Chunks);
while (toTraverse.Count > 0)
{
var node = toTraverse.Dequeue();
var mipLevel = node.MipLevel;
var sd = SecondDerivativePyramid[mipLevel - 1];
var mipWidth = Size >> (mipLevel - 1);
var pos = (node.Range.X >> (mipLevel - 1)) + (node.Range.Y >> (mipLevel - 1)) * mipWidth;
//check the max second derivative of the 4 potential derivatives.
var threshold = HighDetailThresholds[mipLevel - 1];
if (sd[pos] >= threshold) //top left
{
var newNode = node.GetOrAdd(0, true);
if (mipLevel > 1)
{
toTraverse.Enqueue(newNode);
}
}
if (sd[pos + 1] >= threshold) //top right
{
var newNode = node.GetOrAdd(1, true);
if (mipLevel > 1)
{
toTraverse.Enqueue(newNode);
}
}
if (sd[pos + mipWidth] >= threshold) //bottom left
{
var newNode = node.GetOrAdd(2, true);
if (mipLevel > 1)
{
toTraverse.Enqueue(newNode);
}
}
if (sd[pos + mipWidth + 1] >= threshold) //top right
{
var newNode = node.GetOrAdd(3, true);
if (mipLevel > 1)
{
toTraverse.Enqueue(newNode);
}
}
}
}
