/// <summary>
/// Returns true if this triangle collides with (contains) the given point, otherwise, false.
/// </summary>
/// <param name="x">X-coordinate of the given point.</param>
/// <param name="y">Y-coordinate of the given point.</param>
/// <returns>True if this triangle collides with (contains) the given point, otherwise, false.</returns>
public bool Collide(double x, double y)
{
// Get 3 line segments of this triangle.
LineSegment2D lineSegment1 = new LineSegment2D(this.Vertex1, this.Vertex2);
LineSegment2D lineSegment2 = new LineSegment2D(this.Vertex1, this.Vertex3);
LineSegment2D lineSegment3 = new LineSegment2D(this.Vertex2, this.Vertex3);
// Return true if there is a line segment of this triangle that contains the given point.
if ((lineSegment1.Contains(x, y)) ||
(lineSegment2.Contains(x, y)) ||
(lineSegment3.Contains(x, y)))
{
return(true);
}
// Get the horizontal line accross the given point.
Line2D horizontalLine = new Line2D(0, 1, -y);
// Switch references of Line objects to make sure that if there is a horizontal line that contains some segment of this triangle, then it must be line1.
if (lineSegment2.A == 0)
{
SwitchLine(lineSegment1, lineSegment2);
}
else if (lineSegment3.A == 0)
{
SwitchLine(lineSegment1, lineSegment3);
}
if (lineSegment1.A == 0)
{
// If there is a line segment of this triangle is horizontal, then the horizontal line accross the given point will have at most 2 intersections with this triangle.
Point2D intersection1 = lineSegment2.GetIntersectionWith(horizontalLine);
Point2D intersection2 = lineSegment3.GetIntersectionWith(horizontalLine);
return(Collide(intersection1, intersection2, x));
}
else
{
// If there is no line segment of this triangle is horizontal, then the horizontal line accross the given point will have at most 3 intersections with this triangle.
Point2D intersection1 = lineSegment1.GetIntersectionWith(horizontalLine);
Point2D intersection2 = lineSegment2.GetIntersectionWith(horizontalLine);
Point2D intersection3 = lineSegment3.GetIntersectionWith(horizontalLine);
// If there is 1 of the intersections is null, then just check the other 2.
// Otherwise, just check 2 different intersections.
if (intersection1 == null)
{
return(Collide(intersection2, intersection3, x));
}
else if (intersection2 == null)
{
return(Collide(intersection1, intersection3, x));
}
else if (intersection3 == null)
{
return(Collide(intersection1, intersection2, x));
}
else
{
// If program reaches here, it means that the horizontal line accross the given point have 3 intersections with this triangle.
// In other words, 2 of them are the same point.
// So, you need to find out the 3rd point.
if (intersection1.Equals(intersection2))
{
return(Collide(intersection1, intersection3, x));
}
else if (intersection1.Equals(intersection3))
{
return(Collide(intersection1, intersection2, x));
}
else
{
return(Collide(intersection1, intersection3, x));
}
// Or you can just merge the last 2 branches.
}
}
// Note that program will never reach here.
}
