void Swap(int i, int j)
{
if (i != j)
{
ObjectWithBox t = geometries[i];
geometries[i] = geometries[j];
geometries[j] = t;
}
}
private void FindSeeds(int first, int count, out int seed0, out BBox b0, out int seed1)
{
seed0 = first;
b0 = geometries[seed0].Box;
double area = -1.0f;
//looking for seed0
for (int i = first + 1; i < first + count; i++)
{
ObjectWithBox g = geometries[i];
BBox b = g.Box;
double ar = CommonArea(ref b0, ref b);
if (ar > area)
{
seed0 = i;
area = ar;
}
}
//looking for seed1
seed1 = first;//I'm getting a compiler error: there is no need actually to init seed1
area = -1.0f;
b0 = geometries[seed0].Box;
for (int i = first; i < first + count; i++)
{
if (i == seed0)
{
continue;
}
ObjectWithBox g = geometries[i];
BBox b = g.Box;
double ar = CommonArea(ref b0, ref b);
if (ar > area)
{
seed1 = i;
area = ar;
}
}
if (seed0 > seed1)
{
int t = seed1;
seed1 = seed0;
seed0 = t;
}
}
private void SplitOnGroups(int first, int count, int seed0, ref BBox b0, int seed1, out BBox b1, out int count0, out int count1)
{
b0 = geometries[seed0].Box;
b1 = geometries[seed1].Box;
//reshuffling in place:
//put the next element of the first group on the first not occupied place on from the left
//put the next element of the second group to the last not occupied place to the right
Swap(first, seed0); //this puts the seed0 the most left position
Swap(first + count - 1, seed1); //this puts seed1 to the right most position
double ratio = 2;
//lp points to the first not assigned element to the right of group 0
int lp = first + 1;
//rp
int rp = first + count - 2; //seed1 stands at first +count-1
count0 = 1;
count1 = 1;
while (count0 + count1 < count)
{
//First check the ratio of numbers of elements of the groups.
//We need to keep the tree balanced. Let's watch that the ratio of the numbers of elements of the
// two groups is between ratio and 1/ratio.
ObjectWithBox g = geometries[lp];
if (count0 * ratio < count1)
{
AddToTheLeftGroup(ref b0, ref count0, ref lp, g);
}
else if (count1 * ratio < count0)
{
AddToTheRightGroup(ref b1, ref count1, lp, ref rp, g);
}
else //make decision based on the growing of the group boxes
{
BBox b = g.Box;
double squareGrouth0 = CommonArea(ref b0, ref b) - b0.Area;
double squareGrouth1 = CommonArea(ref b1, ref b) - b1.Area;
if (squareGrouth0 < squareGrouth1)
{
AddToTheLeftGroup(ref b0, ref count0, ref lp, g);
}
else
{
AddToTheRightGroup(ref b1, ref count1, lp, ref rp, g);
}
}
}
}
private static void AddToTheLeftGroup(ref BBox b0, ref int count0, ref int lp, ObjectWithBox g) {
lp++;
count0++;
b0.Add(g.Box);
}
private void AddToTheRightGroup(ref BBox b1, ref int count1, int lp, ref int rp, ObjectWithBox g) {
Swap(lp, rp);
rp--;
b1.Add(g.Box);
count1++;
}
private static void AddToTheLeftGroup(ref BBox b0, ref int count0, ref int lp, ObjectWithBox g)
{
lp++;
count0++;
b0.Add(g.Box);
}
private void AddToTheRightGroup(ref BBox b1, ref int count1, int lp, ref int rp, ObjectWithBox g)
{
Swap(lp, rp);
rp--;
b1.Add(g.Box);
count1++;
}