public bool Intersects(Line l, ref Point intercept)
{
float this_m = slope;
float l_m = l.slope;
float this_b = yint;
float l_b = l.yint;
// case 1: two vertical lines
if (a.X == b.X && l.a.X == l.b.X)
return a.X == l.a.X;
// case 2: 'l' is vertical. 'this' is not.
if (l.a.X == l.b.X) {
intercept.X = l.a.X;
intercept.Y = (int)atX(l.a.X);
return true;
}
// case 3: 'this' is vertical. 'l' is not.
if (a.X == b.X) {
return l.Intersects(this, ref intercept);
}
// case 4: the way always works unless you try to divide by zero
// Given:
// y == m1*x+b1
// y == m2*x+b2
//
// m1*x+b1 == m2*x+b2
// m1*x - m2*x == b2-b1
// x*(m1-m2) == b2-b1
// Solution:
// x == (b2-b1) / (m1-m2)
// y == m1*x+b1
if (l_m == this_m && a.X != l.a.X) {
// if they're parallel, and not the same line
// then they don't intersect anywhere at all.
return false;
}
intercept.X = (int)((l_b - this_b) / (this_m - l_m));
intercept.Y = (int)(this_m * intercept.X + this_b);
return true;
}
public void DrawLine(Line l, Color c)
{
vertices[0] = new VertexPositionColor(new Vector3(l.A.X, l.A.Y, 0), c);
vertices[1] = new VertexPositionColor(new Vector3(l.B.X, l.B.Y, 0), c);
effect.VertexColorEnabled = true;
device.DepthStencilState = DepthStencilState.None;
foreach (EffectPass pass in effect.CurrentTechnique.Passes) {
pass.Apply();
device.DrawUserPrimitives<VertexPositionColor>(PrimitiveType.LineStrip, vertices, 0, 1);
}
}
public void DrawLine(Line l)
{
DrawLine(l, Color.White);
}
// UGLY
bool Touches(Line l, ref Point intercept)
{
// If the bounding boxes that the lines live in don't touch, then we don't need to do any more work.
if (a.X < l.a.X && a.X < l.b.X && b.X < l.a.X && b.X < l.b.X)
return false;
if (a.X > l.a.X && a.X > l.b.X && b.X > l.a.X && b.X > l.b.X)
return false;
if (a.Y < l.a.Y && a.Y < l.b.Y && b.Y < l.a.Y && b.Y < l.b.Y)
return false;
if (a.Y > l.a.Y && a.Y > l.b.Y && b.Y > l.a.Y && b.Y > l.b.Y)
return false;
if (!Intersects(l, ref intercept))
return false;
// now we know that the lines, if extended infinitely, touch. And we know where they touch.
// All that remains is to verify that this point is on both line segments.
if ((intercept.X < a.X && intercept.X < b.X) || (intercept.X > a.X && intercept.X > b.X))
return false;
if ((intercept.Y < a.Y && intercept.Y < b.Y) || (intercept.Y > a.Y && intercept.Y > b.Y))
return false;
if ((intercept.X < l.a.X && intercept.X < l.b.X) || (intercept.X > l.a.X && intercept.X > l.b.X))
return false;
if ((intercept.Y < l.a.Y && intercept.Y < l.b.Y) || (intercept.Y > l.a.Y && intercept.Y > l.b.Y))
return false;
return true;
}
