size_util.dart

import "dart:math";

class Line {
  ///y = kx + c
  static double normalLine(x, {k = 0, c = 0}) {
    return k * x + c;
  }

  ///Calculate the param K in y = kx +c
  static double paramK(Point p1, Point p2) {
    if (p1.x == p2.x) return 0;
    return (p2.y - p1.y) / (p2.x - p1.x);
  }

  ///Calculate the param C in y = kx +c
  static double paramC(Point p1, Point p2) {
    return p1.y - paramK(p1, p2) * p1.x;
  }
}

/// start point p1, end point p2,p2 is center of the circle,r is its radius.
class LineInterCircle {
  /// start point p1, end point p2,p2 is center of the circle,r is its radius.
  /// param a: y = kx +c intersect with circle,which has the center with point2 and radius R .
  /// when derive to x2+ ax +b = 0 equation. the param a is here.
  static double paramA(Point p1, Point p2) {
    return (2 * Line.paramK(p1, p2) * Line.paramC(p1, p2) -
        2 * Line.paramK(p1, p2) * p2.y -
        2 * p2.x) /
        (Line.paramK(p1, p2) * Line.paramK(p1, p2) + 1);
  }

  /// start point p1, end point p2,p2 is center of the circle,r is its radius.
  /// param b: y = kx +c intersect with circle,which has the center with point2 and radius R .
  /// when derive to x2+ ax +b = 0 equation. the param b is here.
  static double paramB(Point p1, Point p2, double r) {
    return (p2.x * p2.x -
        r * r +
        (Line.paramC(p1, p2) - p2.y) * (Line.paramC(p1, p2) - p2.y)) /
        (Line.paramK(p1, p2) * Line.paramK(p1, p2) + 1);
  }

  ///the circle has the intersection or not
  static bool isIntersection(Point p1, Point p2, double r) {
    var delta = sqrt(paramA(p1, p2) * paramA(p1, p2) - 4 * paramB(p1, p2, r));
    return delta >= 0.0;
  }

  ///the x coordinate whether or not is between two point we give.
  static bool _betweenPoint(x, Point p1, Point p2) {
    if (p1.x > p2.x) {
      return x > p2.x && x < p1.x;
    } else {
      return x > p1.x && x < p2.x;
    }
  }

  static Point _equalX(Point p1, Point p2, double r) {
    if (p1.y > p2.y) {
      return Point(p2.x, p2.y + r);
    } else if (p1.y < p2.y) {
      return Point(p2.x, p2.y - r);
    } else {
      return p2;
    }
  }

  static Point _equalY(Point p1, Point p2, double r) {
    if (p1.x > p2.x) {
      return Point(p2.x + r, p2.y);
    } else if (p1.x < p2.x) {
      return Point(p2.x - r, p2.y);
    } else {
      return p2;
    }
  }

  ///intersection point
  static Point intersectionPoint(Point p1, Point p2, double r) {
    if (p1.x == p2.x) return _equalX(p1, p2, r);
    if (p1.y == p2.y) return _equalY(p1, p2, r);
    var delta = sqrt(paramA(p1, p2) * paramA(p1, p2) - 4 * paramB(p1, p2, r));
    if (delta < 0.0) {
      //when no intersection, i will return the center of the circ  le.
      return p2;
    }
    var a_2 = -paramA(p1, p2) / 2.0;
    var x1 = a_2 + delta / 2;
    if (_betweenPoint(x1, p1, p2)) {
      var y1 = Line.paramK(p1, p2) * x1 + Line.paramC(p1, p2);
      return Point(x1, y1);
    }
    var x2 = a_2 - delta / 2;
    var y2 = Line.paramK(p1, p2) * x2 + Line.paramC(p1, p2);
    return Point(x2, y2);
  }
}