private int? IsInNineBox(int x, int y, int pX, int pY)
{
for (int i = 0; i < 3; i++)
for (int j = 0; j < 3; j++)
{
Rectangle rect = new Rectangle(
x + (ColorBoxSize + ColorBoxBorder) * i,
y + (ColorBoxSize + ColorBoxBorder) * j,
ColorBoxSize,
ColorBoxSize);
if (IsInRectangle(rect, pX, pY))
return 3 * j + i;
}
return null;
}