Class: PerfectShape::Polygon

Inherits:
Shape
  • Object
show all
Includes:
MultiPoint
Defined in:
lib/perfect_shape/polygon.rb

Overview

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

Instance Attribute Summary

Attributes included from MultiPoint

#points

Instance Method Summary collapse

Methods included from MultiPoint

#initialize, #max_x, #max_y, #min_x, #min_y

Methods inherited from Shape

#==, #bounding_box, #center_x, #center_y, #height, #max_x, #max_y, #min_x, #min_y, #normalize_point, #width

Instance Method Details

#contain?(x_or_point, y = nil) ⇒ @code true

Checks if polygon contains point (two-number Array or x, y args) using the Ray Casting Algorithm (aka Even-Odd Rule): en.wikipedia.org/wiki/Point_in_polygon

the polygon, false if the point lies outside of the polygon’s bounds.

Parameters:

  • x —

    The X coordinate of the point to test.

  • y (defaults to: nil) —

    The Y coordinate of the point to test.

Returns:

  • (@code true) —

    if the point lies within the bound of



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# File 'lib/perfect_shape/polygon.rb', line 40

def contain?(x_or_point, y = nil)
  x, y = normalize_point(x_or_point, y)
  return unless x && y
  npoints = points.count
  xpoints = points.map(&:first)
  ypoints = points.map(&:last)
  return false if npoints <= 2 || !bounding_box.contain?(x, y)
  hits = 0

  lastx = xpoints[npoints - 1]
  lasty = ypoints[npoints - 1]

  # Walk the edges of the polygon
  npoints.times do |i|
    curx = xpoints[i]
    cury = ypoints[i]

    if cury == lasty
      lastx = curx
      lasty = cury
      next
    end

    if curx < lastx
      if x >= lastx
        lastx = curx
        lasty = cury
        next
      end
      leftx = curx
    else
      if x >= curx
        lastx = curx
        lasty = cury
        next
      end
      leftx = lastx
    end

    if cury < lasty
      if y < cury || y >= lasty
        lastx = curx
        lasty = cury
        next
      end
      if x < leftx
        hits += 1
        lastx = curx
        lasty = cury
        next
      end
      test1 = x - curx
      test2 = y - cury
    else
      if y < lasty || y >= cury
        lastx = curx
        lasty = cury
        next
      end
      if x < leftx
        hits += 1
        lastx = curx
        lasty = cury
        next
      end
      test1 = x - lastx
      test2 = y - lasty
    end

    hits += 1 if (test1 < (test2 / (lasty - cury) * (lastx - curx)))
  end

  (hits & 1) != 0
end