/// <summary>
/// If dx =1 , dy = ??
/// </summary>
/// <param name="line"></param>
/// <returns></returns>
public static double GetDy(this LineF line)
{
var dx = Math.Abs(line.X1 - line.X2);
var dy = line.Y1 - line.Y2;
return(dy / dx);
}
public static List <Point> Intersection(this LineF line, RectangleF rectangle)
{
var result = new List <Point>();
AddIfIntersect(line, rectangle.X, rectangle.Y, rectangle.X2, rectangle.Y, result);
AddIfIntersect(line, rectangle.X2, rectangle.Y, rectangle.X2, rectangle.Y2, result);
AddIfIntersect(line, rectangle.X2, rectangle.Y2, rectangle.X, rectangle.Y2, result);
AddIfIntersect(line, rectangle.X, rectangle.Y2, rectangle.X, rectangle.Y, result);
return(result);
}
private static void AddIfIntersect(LineF line, double x1, double y1, double x2, double y2, ICollection <Point> result)
{
var l2 = new LineF(x1, y1, x2, y2);
var intersection = line.Intersection(l2);
if (intersection != null)
{
result.Add(intersection.Value);
}
}
/// <summary>
/// Calculates intersection - if any - of two lines
/// </summary>
/// <param name="otherLine"></param>
/// <returns>Intersection or null</returns>
/// <remarks>Take from http://tog.acm.org/resources/GraphicsGems/gemsii/xlines.c </remarks>
public Point? Intersection(LineF otherLine)
{
var a1 = Y2 - Y1;
var b1 = X1 - X2;
var c1 = X2 * Y1 - X1 * Y2;
/* Compute r3 and r4.
*/
var r3 = a1 * otherLine.X1 + b1 * otherLine.Y1 + c1;
var r4 = a1 * otherLine.X2 + b1 * otherLine.Y2 + c1;
/* Check signs of r3 and r4. If both point 3 and point 4 lie on
* same side of line 1, the line segments do not intersect.
*/
if (r3 != 0 && r4 != 0 && Math.Sign(r3) == Math.Sign(r4))
{
return null; // DONT_INTERSECT
}
/* Compute a2, b2, c2 */
var a2 = otherLine.Y2 - otherLine.Y1;
var b2 = otherLine.X1 - otherLine.X2;
var c2 = otherLine.X2 * otherLine.Y1 - otherLine.X1 * otherLine.Y2;
/* Compute r1 and r2 */
var r1 = a2 * X1 + b2 * Y1 + c2;
var r2 = a2 * X2 + b2 * Y2 + c2;
/* Check signs of r1 and r2. If both point 1 and point 2 lie
* on same side of second line segment, the line segments do
* not intersect.
*/
if (r1 != 0 && r2 != 0 && Math.Sign(r1) == Math.Sign(r2))
{
return (null); // DONT_INTERSECT
}
/* Line segments intersect: compute intersection point.
*/
var denom = a1 * b2 - a2 * b1;
if (denom == 0)
{
return null; //( COLLINEAR );
}
var offset = denom < 0 ? -denom / 2 : denom / 2;
/* The denom/2 is to get rounding instead of truncating. It
* is added or subtracted to the numerator, depending upon the
* sign of the numerator.
*/
var num = b1 * c2 - b2 * c1;
var x = (num < 0 ? num - offset : num + offset) / denom;
num = a2 * c1 - a1 * c2;
var y = (num < 0 ? num - offset : num + offset) / denom;
return new Point(x, y);
}
/// <summary>
/// Calculates intersection - if any - of two lines
/// </summary>
/// <param name="otherLine"></param>
/// <returns>Intersection or null</returns>
/// <remarks>Take from http://tog.acm.org/resources/GraphicsGems/gemsii/xlines.c </remarks>
public Point?Intersection(LineF otherLine)
{
var a1 = Y2 - Y1;
var b1 = X1 - X2;
var c1 = X2 * Y1 - X1 * Y2;
/* Compute r3 and r4.
*/
var r3 = a1 * otherLine.X1 + b1 * otherLine.Y1 + c1;
var r4 = a1 * otherLine.X2 + b1 * otherLine.Y2 + c1;
/* Check signs of r3 and r4. If both point 3 and point 4 lie on
* same side of line 1, the line segments do not intersect.
*/
if (r3 != 0 && r4 != 0 && Math.Sign(r3) == Math.Sign(r4))
{
return(null); // DONT_INTERSECT
}
/* Compute a2, b2, c2 */
var a2 = otherLine.Y2 - otherLine.Y1;
var b2 = otherLine.X1 - otherLine.X2;
var c2 = otherLine.X2 * otherLine.Y1 - otherLine.X1 * otherLine.Y2;
/* Compute r1 and r2 */
var r1 = a2 * X1 + b2 * Y1 + c2;
var r2 = a2 * X2 + b2 * Y2 + c2;
/* Check signs of r1 and r2. If both point 1 and point 2 lie
* on same side of second line segment, the line segments do
* not intersect.
*/
if (r1 != 0 && r2 != 0 && Math.Sign(r1) == Math.Sign(r2))
{
return(null); // DONT_INTERSECT
}
/* Line segments intersect: compute intersection point.
*/
var denom = a1 * b2 - a2 * b1;
if (denom == 0)
{
return(null); //( COLLINEAR );
}
var offset = denom < 0 ? -denom / 2 : denom / 2;
/* The denom/2 is to get rounding instead of truncating. It
* is added or subtracted to the numerator, depending upon the
* sign of the numerator.
*/
var num = b1 * c2 - b2 * c1;
var x = (num < 0 ? num - offset : num + offset) / denom;
num = a2 * c1 - a1 * c2;
var y = (num < 0 ? num - offset : num + offset) / denom;
return(new Point(x, y));
}
