Class: PerfectShape::Line

Inherits:
Object
  • Object
show all
Defined in:
lib/perfect_shape/line.rb

Overview

Mostly ported from java.awt.geom: docs.oracle.com/javase/8/docs/api/java/awt/geom/Line2D.html

Class Method Summary collapse

Class Method Details

.relative_ccw(x1, y1, x2, y2, px, py) ⇒ Object

Returns an indicator of where the specified point (px,py) lies with respect to the line segment from (x1,y1) to (x2,y2). The return value can be either 1, -1, or 0 and indicates in which direction the specified line must pivot around its first end point, (x1,y1), in order to point at the specified point (px,py). <p>A return value of 1 indicates that the line segment must turn in the direction that takes the positive X axis towards the negative Y axis. In the default coordinate system used by Java 2D, this direction is counterclockwise. <p>A return value of -1 indicates that the line segment must turn in the direction that takes the positive X axis towards the positive Y axis. In the default coordinate system, this direction is clockwise. <p>A return value of 0 indicates that the point lies exactly on the line segment. Note that an indicator value of 0 is rare and not useful for determining collinearity because of floating point rounding issues. <p>If the point is colinear with the line segment, but not between the end points, then the value will be -1 if the point lies “beyond (x1,y1)” or 1 if the point lies “beyond (x2,y2)”.

Parameters:

  • x1 —

    the X coordinate of the start point of the specified line segment

  • y1 —

    the Y coordinate of the start point of the specified line segment

  • x2 —

    the X coordinate of the end point of the specified line segment

  • y2 —

    the Y coordinate of the end point of the specified line segment

  • px —

    the X coordinate of the specified point to be compared with the specified line segment

  • py —

    the Y coordinate of the specified point to be compared with the specified line segment

Returns:

  • an integer that indicates the position of the third specified coordinates with respect to the line segment formed by the first two specified coordinates.

Since:

  • 1.2



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# File 'lib/perfect_shape/line.rb', line 66

def relative_ccw(x1, y1, x2, y2, px, py)
  x2 -= x1;
  y2 -= y1;
  px -= x1;
  py -= y1;
  ccw = px * y2 - py * x2;
  if ccw == 0.0
    # The point is colinear, classify based on which side of
    # the segment the point falls on.  We can calculate a
    # relative value using the projection of px,py onto the
    # segment - a negative value indicates the point projects
    # outside of the segment in the direction of the particular
    # endpoint used as the origin for the projection.
    ccw = px * x2 + py * y2;
    if ccw > 0.0
      # Reverse the projection to be relative to the original x2,y2
      # x2 and y2 are simply negated.
      # px and py need to have (x2 - x1) or (y2 - y1) subtracted
      #    from them (based on the original values)
      # Since we really want to get a positive answer when the
      #    point is "beyond (x2,y2)", then we want to calculate
      #    the inverse anyway - thus we leave x2 & y2 negated.
      px -= x2;
      py -= y2;
      ccw = px * x2 + py * y2;
      ccw = 0.0 if ccw < 0.0
    end
  end
  (ccw < 0.0) ? -1 : ((ccw > 0.0) ? 1 : 0);
end