// Returns true if point lies in the viewing plane, false otherwise
protected bool ClipSegment(IAxis x_axis, IAxis y_axis,
ref Point a, ref Point b)
{
long x_min, x_max;
x_axis.GetGridClipRegion(out x_min, out x_max);
long y_min, y_max;
y_axis.GetGridClipRegion(out y_min, out y_max);
// Use the Cohen-Sutherland algorithm to clip points
// described http://www.cim.mcgill.ca/~langer/557B/Jan16.html
int outcode_a, outcode_b;
while (true)
{
outcode_a = Convert.ToInt32(a.Y > y_max) << 3;
outcode_a |= Convert.ToInt32(a.Y < y_min) << 2;
outcode_a |= Convert.ToInt32(a.X > x_max) << 1;
outcode_a |= Convert.ToInt32(a.X < x_min);
outcode_b = Convert.ToInt32(b.Y > y_max) << 3;
outcode_b |= Convert.ToInt32(b.Y < y_min) << 2;
outcode_b |= Convert.ToInt32(b.X > x_max) << 1;
outcode_b |= Convert.ToInt32(b.X < x_min);
// Trivially accept edge if bitwise OR of outcodes is 0000
if ((outcode_a | outcode_b) == 0)
{
return(true);
}
// Trivially reject edge if the bitwise AND of the two outcomes is other than 0000
if ((outcode_a & outcode_b) != 0)
{
return(false);
}
// Now, we know that at least one of the points needs to be clipped.
Point p = a, o = b;
int current_outcode = outcode_a;
if (outcode_a == 0)
{
p = b;
o = a;
current_outcode = outcode_b;
}
double m = (b.Y - a.Y) / ((double)b.X - a.X);
p.IsClipped = true;
// handle vertical lines specially, since
// Cohen-Sutherland doesn't specifically
// discuss them
bool is_vertical = (m == Double.PositiveInfinity);
if ((current_outcode & 8) == 8) // Above
{
p.Y = y_max;
p.X = (is_vertical) ? p.X : Convert.ToInt64(((p.Y - o.Y) / m) + o.X);
}
else if ((current_outcode & 4) == 4) // Below
{
p.Y = y_min;
p.X = (is_vertical) ? p.X : Convert.ToInt64(((p.Y - o.Y) / m) + o.X);
}
else if ((current_outcode & 2) == 2) // Right
{
p.X = x_max;
p.Y = (is_vertical) ? p.Y : Convert.ToInt64(((p.X - o.X) * m) + o.Y);
}
else if ((current_outcode & 1) == 1) // Left
{
p.X = x_min;
p.Y = (is_vertical) ? p.Y : Convert.ToInt64(((p.X - o.X) * m) + o.Y);
}
if (outcode_a != 0)
{
a = p;
}
else
{
b = p;
}
}
}
