public void SwapIndexRangeToBack(int sectionIndex, int sectionLength, int swapIndex, int swapRange)
{
if (sectionIndex < 0)
{
throw new ArgumentException($"{nameof(sectionIndex)} must be 0 or higher.");
}
if (sectionLength < 0)
{
throw new ArgumentException($"{nameof(sectionLength)} must be 0 or higher.");
}
if (swapIndex < 0)
{
throw new ArgumentException($"{nameof(swapIndex)} must be positive.");
}
if (swapIndex + swapRange > sectionLength)
{
throw new ArgumentException($"{nameof(swapIndex)} ({swapIndex}) + {nameof(swapRange)} ({swapRange}) must be smaller than {nameof(sectionIndex)} ({sectionIndex}).");
}
if (sectionLength == 0 || swapRange == 0)
{
return;
}
var lengthBehindSwapIndex = sectionLength - swapIndex;
var tempOffset = indexToID.Length;
// aaaaaabbbbcc ....
// aaaaaabbbbcc .... bbbb
// | ^
// |___________|
// Copy the original indices to beyond the end of the list
// Make space for these indices, hopefully the index list already has the capacity for
// this and no allocation needs to be made
indexToID.Resize(tempOffset + swapRange, NativeArrayOptions.UninitializedMemory);
indexToID.MemMove(tempOffset, sectionIndex + swapIndex, swapRange);
// aaaaaabbbbcc .... bbbb
// aaaaaaccbbcc .... bbbb
// ^ |
// |__|
// Move indices behind our swapIndex/swapRange on top of where our swap region begins
var count = lengthBehindSwapIndex - swapRange;
indexToID.MemMove(sectionIndex + swapIndex, sectionIndex + swapIndex + swapRange, count);
// aaaaaaccbbcc .... bbbb
// aaaaaaccbbbb .... bbbb
// ^ |
// |___________|
// Copy the original indices to the end
indexToID.MemMove(sectionIndex + swapIndex + count, tempOffset, swapRange);
// aaaaaaccbbbb .... bbbb
// aaaaaaccbbbb ....
// Resize indices list to remove the temporary data, this is basically just
// indexToID.length = tempOffset
indexToID.Resize(tempOffset, NativeArrayOptions.UninitializedMemory);
for (int index = sectionIndex + swapIndex, lastIndex = sectionIndex + sectionLength; index < lastIndex; index++)
{
var idInternal = indexToID[index] - 1;
var idLookup = idToIndex[idInternal];
idLookup.index = index;
idToIndex[idInternal] = idLookup;
}
}