public QuadTreeWalker(Terrain *terrain, Aabb aabb)
{
m_Terrain = terrain;
m_LevelIndex = 0;
m_Index = 0;
m_ChildIndex = 0;
Bounds = new FourTransposedAabbs();
// Initialize the stack with a single node
fixed(int *stack = m_Stack)
{
m_Top = stack;
// Clamp the query AABB to the terrain bounds
int2 min = math.clamp((int2)aabb.Min.xz, 0, terrain->Size - 2); // Size - 1 is number of quads, Size - 2 is the highest valid quad index
int2 max = math.clamp((int2)aabb.Max.xz, 0, terrain->Size - 2);
// Find the deepest node that fully contains the query AABB, by finding the highest bit in which the AABB min and max differ
// We can begin the query from that node instead of the root, and this is much faster than traversing the tree.
int level = 0;
int2 diffs = min ^ max;
int diff = diffs.x | diffs.y;
int bit = 1 << (terrain->Levels.Length - 1);
while ((diff & bit) == 0 && bit > 1)
{
level++;
bit = bit >> 1;
}
int2 coord = min >> (terrain->Levels.Length - level);
// Push the node onto the stack
*m_Top = level;
*(m_Top + k_StackSize) = coord.x;
*(m_Top + k_StackSize + k_StackSize) = coord.y;
m_Top++;
}
}
// If the stack is not empty, removes the top node and sets the current state from it, then returns true.
// Otherwise returns false.
public bool Pop()
{
fixed(int *stack = m_Stack)
{
if (m_Top == stack)
{
return(false); // stack is empty
}
}
m_Top--;
m_LevelIndex = *m_Top;
m_Index = new int2(*(m_Top + k_StackSize), *(m_Top + k_StackSize + k_StackSize));
// Get the node
Level level = m_Terrain->Levels[m_LevelIndex];
int levelOffset = (m_Index.y & ~1) * level.Pitch + ((m_Index.y & 1) << 1) + ((m_Index.x & ~1) << 1) + (m_Index.x & 1); // swizzled, see comment on Nodes
Node node = m_Terrain->Nodes[level.Base + levelOffset];
// Calculate the AABBs of the node's children
m_ChildIndex = m_Index + m_Index;
float3 boundsX = (float3)(m_ChildIndex.x + new int3(0, 1, 2)) * level.Scale;
float3 boundsZ = (float3)(m_ChildIndex.y + new int3(0, 1, 2)) * level.Scale;
Bounds = new FourTransposedAabbs
{
Lx = boundsX.xyxy,
Hx = boundsX.yzyz,
Lz = boundsZ.xxyy,
Hz = boundsZ.yyzz,
Ly = node.Min4,
Hy = node.Max4
};
return(true);
}
