private static VBox[] MedianCutApply(IReadOnlyList <int> histo, VBox vbox)
{
switch (vbox.Count(false))
{
case 0:
return(null);
case 1:
return(new[] { vbox.Clone(), null });
}
// only one pixel, no split
var rw = vbox.R2 - vbox.R1 + 1;
var gw = vbox.G2 - vbox.G1 + 1;
var bw = vbox.B2 - vbox.B1 + 1;
var maxw = Math.Max(Math.Max(rw, gw), bw);
// Find the partial sum arrays along the selected axis.
var total = 0;
var partialsum = new int[VboxLength];
// -1 = not set / 0 = 0
partialsum.Fill(-1);
// -1 = not set / 0 = 0
var lookaheadsum = new int[VboxLength];
lookaheadsum.Fill(-1);
int i, j, k, sum, index;
if (maxw == rw)
{
for (i = vbox.R1; i <= vbox.R2; i++)
{
sum = 0;
for (j = vbox.G1; j <= vbox.G2; j++)
{
for (k = vbox.B1; k <= vbox.B2; k++)
{
index = GetColorIndex(i, j, k);
sum += histo[index];
}
}
total += sum;
partialsum[i] = total;
}
}
else if (maxw == gw)
{
for (i = vbox.G1; i <= vbox.G2; i++)
{
sum = 0;
for (j = vbox.R1; j <= vbox.R2; j++)
{
for (k = vbox.B1; k <= vbox.B2; k++)
{
index = GetColorIndex(j, i, k);
sum += histo[index];
}
}
total += sum;
partialsum[i] = total;
}
}
else
/* maxw == bw */
{
for (i = vbox.B1; i <= vbox.B2; i++)
{
sum = 0;
for (j = vbox.R1; j <= vbox.R2; j++)
{
for (k = vbox.G1; k <= vbox.G2; k++)
{
index = GetColorIndex(j, k, i);
sum += histo[index];
}
}
total += sum;
partialsum[i] = total;
}
}
for (i = 0; i < VboxLength; i++)
{
if (partialsum[i] != -1)
{
lookaheadsum[i] = total - partialsum[i];
}
}
// determine the cut planes
return(maxw == rw
? DoCut('r', vbox, partialsum, lookaheadsum, total)
: maxw == gw
? DoCut('g', vbox, partialsum, lookaheadsum, total)
: DoCut('b', vbox, partialsum, lookaheadsum, total));
}
