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));
}
private static VBox[] DoCut(
char color,
VBox vbox,
IReadOnlyList <int> partialsum,
IReadOnlyList <int> lookaheadsum,
int total)
{
int vboxDim1;
int vboxDim2;
switch (color)
{
case 'r':
vboxDim1 = vbox.R1;
vboxDim2 = vbox.R2;
break;
case 'g':
vboxDim1 = vbox.G1;
vboxDim2 = vbox.G2;
break;
default:
vboxDim1 = vbox.B1;
vboxDim2 = vbox.B2;
break;
}
for (var i = vboxDim1; i <= vboxDim2; i++)
{
if (partialsum[i] > total / 2)
{
var vbox1 = vbox.Clone();
var vbox2 = vbox.Clone();
var left = i - vboxDim1;
var right = vboxDim2 - i;
var d2 = left <= right
? Math.Min(vboxDim2 - 1, ~~(i + right / 2))
: Math.Max(vboxDim1, ~~((int)(i - 1 - left / 2.0)));
// avoid 0-count boxes
while (d2 < 0 || partialsum[d2] <= 0)
{
d2++;
}
var count2 = lookaheadsum[d2];
while (count2 == 0 && d2 > 0 && partialsum[d2 - 1] > 0)
{
count2 = lookaheadsum[--d2];
}
// set dimensions
switch (color)
{
case 'r':
vbox1.R2 = d2;
vbox2.R1 = d2 + 1;
break;
case 'g':
vbox1.G2 = d2;
vbox2.G1 = d2 + 1;
break;
default:
vbox1.B2 = d2;
vbox2.B1 = d2 + 1;
break;
}
return(new[] { vbox1, vbox2 });
}
}
throw new Exception("VBox can't be cut");
}