dendrogram

dendrogram.rb

class DrawTree
  require 'RMagick'

  def drawdendrogram(tree, labels={}, file='tree.jpg')
    h = tree.width * 20
    w = 1200
    scaling = (w-150).to_f / tree.depth
    canvas = Magick::Image.new(w, h)
    draw = Magick::Draw.new
    draw.line(0,h/2,10,h/2)
    drawnode(draw, tree, 10, h/2, scaling, labels)
    draw.draw(canvas)
    canvas.write(file)
    canvas.destroy!
  end

  private
  def drawnode(draw, tree, x, y, scaling, labels)
    if tree.has_children?
      heights = tree.children.collect {|c| c.width * 20}
      top = y - heights.sum / 2
      bottom = y + heights.sum / 2
      # Line length
      ll = scaling * (tree.respond_to?(:distance) ? tree.distance : 1.0)
      # Vertical line from tree to children
      draw.line(x, top + heights.first/2, x, bottom - heights.last/2)

      sum = 0
      heights.each do |h|
        # Horizontal line to item
        draw.line(x, top + sum + h/2, x + ll, top + sum + h/2)
        sum += h
      end
      sum = 0
      tree.children.each_with_index do |child,i|
        drawnode(draw, child, x + ll, top + sum + heights[i]/2, scaling, labels)
        sum += heights[i]
      end
    end
    draw.text(x+5, y+5, labels[tree.id] || tree.name)
  end

end