Overlapping circles - modelling living populations

Here's a slightly better version that uses the overlapping status of a circle to change its color. (It doesn't do anything with pairs of circles, though that'd also be easy...you just have to know how you'd want to visualize it.)

# http://downloads.sourceforge.jp/ruby-svg/2288/ruby-svg-1.0.3.tar.gz
require 'svg/svg'

class Array
  def each_unique_pair
    self.each_with_index{ |a,i|
      self[(i+1)..-1].each{ |b| yield a,b }
    }
  end
end

class SVG::Circle
  # test (and save) result
  def overlaps?( other_circle )
    center_distance = Math.sqrt(
      ( cx - other_circle.cx ) ** 2 +
      ( cy - other_circle.cy ) ** 2
    )

    intersects = center_distance < ( r + other_circle.r )
    
    # Save the result on both circles
    other_circle.overlaps[ self ] = intersects
    self.overlaps[ other_circle ] = intersects
  end
  
  def overlaps
    # Make sure we have a hash to save a set of overlappers
    @overlapping_circles ||= {}
  end
  
  # An array of all circles this one overlaps
  def overlapping_list
    # Make sure we have a hash to save a set of overlappers
    @overlapping_circles ||= {}
    @overlapping_circles.select{ |circle,status|
      status == true
    }.map{ |circle,status|
      circle
    }
  end
end

# Create/manage your populations
populations = []
20.times{
  # Randomly add populations
  x = rand 800 + 100
  y = rand 800 + 100
  radius = rand 100 + 10
  populations << SVG::Circle.new( x, y, radius )
}

# Make sure the overlapping list is valid
populations.each_unique_pair{ |a,b|
  a.overlaps?( b )
}

# Make the picture
svg = SVG.new('100%', '100%', '0 0 1000 1000')

# Your grid here
0.step( 1000, 20 ){ |i|
  svg << SVG::Line.new( i, 0, i, 1000 )
  svg << SVG::Line.new( 0, i, 1000, i )
}

# Make all circles have a common style
svg << g = SVG::Group.new{
  self.style = SVG::Style.new(
    :fill => '#ffe', :stroke => 'blue', :stroke_width => 1.5
  )
}

# Need opacity per element, not on the group
low_opacity = SVG::Style.new( :opacity => 0.6 )

# Override style for circles that overlap
olap_style = SVG::Style.new( :fill=>'#ff9', :stroke=>'red', :opacity=>0.4 )

populations.each{ |circle|
  if circle.overlapping_list.empty?
    circle.style = low_opacity
  else
    circle.style = olap_style
  end
  g << circle
}

File.open( 'populations.svg', 'w' ){ |file|
  file << svg.to_s
}

# view in your favorite SVG viewer, like FF 1.5
# for an example, see http://phrogz.net/svg/populations.svg

Gavin,

Here's a slightly better version that uses the overlapping status of a circle to change its color. (It doesn't do anything with pairs of circles, though that'd also be easy...you just have to know how you'd want to visualize it.)

# http://downloads.sourceforge.jp/ruby-svg/2288/ruby-svg-1.0.3.tar.gz
require 'svg/svg'

class Array
  def each_unique_pair
    self.each_with_index{ |a,i|
      self[(i+1)..-1].each{ |b| yield a,b }
    }
  end
end

class SVG::Circle
  # test (and save) result
  def overlaps?( other_circle )
    center_distance = Math.sqrt(
      ( cx - other_circle.cx ) ** 2 +
      ( cy - other_circle.cy ) ** 2
    )

    intersects = center_distance < ( r + other_circle.r )
    
    # Save the result on both circles
    other_circle.overlaps[ self ] = intersects
    self.overlaps[ other_circle ] = intersects
  end
  
  def overlaps
    # Make sure we have a hash to save a set of overlappers
    @overlapping_circles ||= {}
  end
  
  # An array of all circles this one overlaps
  def overlapping_list
    # Make sure we have a hash to save a set of overlappers
    @overlapping_circles ||= {}
    @overlapping_circles.select{ |circle,status|
      status == true
    }.map{ |circle,status|
      circle
    }
  end
end

# Create/manage your populations
populations = []
20.times{
  # Randomly add populations
  x = rand 800 + 100
  y = rand 800 + 100
  radius = rand 100 + 10
  populations << SVG::Circle.new( x, y, radius )
}

# Make sure the overlapping list is valid
populations.each_unique_pair{ |a,b|
  a.overlaps?( b )
}

# Make the picture
svg = SVG.new('100%', '100%', '0 0 1000 1000')

# Your grid here
0.step( 1000, 20 ){ |i|
  svg << SVG::Line.new( i, 0, i, 1000 )
  svg << SVG::Line.new( 0, i, 1000, i )
}

# Make all circles have a common style
svg << g = SVG::Group.new{
  self.style = SVG::Style.new(
    :fill => '#ffe', :stroke => 'blue', :stroke_width => 1.5
  )
}

# Need opacity per element, not on the group
low_opacity = SVG::Style.new( :opacity => 0.6 )

# Override style for circles that overlap
olap_style = SVG::Style.new( :fill=>'#ff9', :stroke=>'red', :opacity=>0.4 )

populations.each{ |circle|
  if circle.overlapping_list.empty?
    circle.style = low_opacity
  else
    circle.style = olap_style
  end
  g << circle
}

File.open( 'populations.svg', 'w' ){ |file|
  file << svg.to_s
}

# view in your favorite SVG viewer, like FF 1.5
# for an example, see http://phrogz.net/svg/populations.svg

Many thanks for that! I will have to go over this in detail to
understand what is happening but it looks nice! A couple of things:

1. There seems to be some doubt about the survival of SVG . .

2. Opera supports SVG natively! (which seems to go against the first
point)

Regards,

Phil.

···

On Sun, 2006-09-10 at 00:44 +0900, Gavin Kistner wrote:
--
Philip Rhoades

Pricom Pty Limited (ACN 003 252 275 ABN 91 003 252 275)
GPO Box 3411
Sydney NSW 2001
Australia
Mobile: +61:(0)411-185-652
Fax: +61:(0)2-8221-9599
E-mail: phil@pricom.com.au