public static int[] CalcNeighbourIndexes(int radius, int index)
{
HashSet <int> neighbourIndexSet = new HashSet <int>();
SideFace sideFace = CalcSideFace(radius, index);
int startingIndex = CalcStartingIndex(radius);
int endingIndex = CalcStartingIndex(radius + 1) - 1;
int innerRadiusStartingIndex = radius == 0
? 0
: CalcStartingIndex(radius - 1);
int innerRadiusIndex = CalcNeighbourIndexFromInnerRadius(radius, index, sideFace);
// 1. Get indexes from current radius
if (index != startingIndex)
{
neighbourIndexSet.Add(index - 1);
if (sideFace.Face != 0 && sideFace.RemainingLeft == 0)
{
neighbourIndexSet.Add(index - 2);
}
}
if (index > endingIndex - 2)
{
neighbourIndexSet.Add(startingIndex);
}
// 2. Get indexes from inner radius
neighbourIndexSet.Add(innerRadiusIndex);
if (index > startingIndex + 1)
{
if (sideFace.Remaining > 1)
{
neighbourIndexSet.Add(innerRadiusIndex + 1);
}
if (sideFace.RemainingLeft > 0 && sideFace.Remaining > 0)
{
neighbourIndexSet.Add(innerRadiusIndex - 1);
}
}
else if (index == startingIndex)
{
neighbourIndexSet.Add(innerRadiusStartingIndex);
}
else if (index == startingIndex + 1)
{
neighbourIndexSet.Add(startingIndex - 1);
neighbourIndexSet.Add(innerRadiusStartingIndex + 1);
}
// 3. Cast set to int[]
int[] indexes = new int[neighbourIndexSet.Count];
neighbourIndexSet.CopyTo(indexes);
return(indexes);
}
public static int CalcNeighbourIndexFromInnerRadius(int radius, int index, SideFace sideFace)
{
if (radius < 2)
{
return(0);
}
int startingIndex = CalcStartingIndex(radius);
int endingIndex = CalcStartingIndex(radius + 1) - 1;
if (index == startingIndex || index == endingIndex)
{
return(startingIndex - 1);
}
int indexOffset = (CIRCUMFERENCE_COEF + 2 * sideFace.Face + 1) + CIRCUMFERENCE_COEF * (radius - 2);
if (sideFace.Remaining == 0)
{
indexOffset++;
}
return(index - indexOffset);
}
