Cairo warped / curved text demo in ruby. Ported from example included in pycairo

gistfile1.rb

require 'cairo'
require 'rubygems'
require 'ruby-debug'

def warp_path(context, &block)
  first = true

  context.copy_path.each do |type, points|

    case type
    when Cairo::PATH_MOVE_TO
      if first
        context.new_path
        first = false
      end
      x, y = block.call(points[0].x, points[0].y)
      context.move_to(x, y)

    when Cairo::PATH_LINE_TO
      x, y = block.call(points[0].x, points[0].y)
      context.line_to(x, y)

    when Cairo::PATH_CURVE_TO
      x1, y1 = block.call(points[0].x, points[0].y)
      x2, y2 = block.call(points[1].x, points[1].y)
      x3, y3 = block.call(points[2].x, points[2].y)
      context.curve_to(x1, y1, x2, y2, x3, y3)

    when Cairo::PATH_CLOSE_PATH
      context.close_path()
    end
  end

end


def spiral(x, y, width, height)
  height = 512
  width = 512

  theta0 = -Math::PI * 3 / 4
  theta = x / width * Math::PI * 2 + theta0
  radius = y + 200 - x/7
  xnew = radius*Math.cos(theta)
  ynew = radius*Math.sin(-theta)
  [xnew + width/2, ynew + height/2]
end

def curl(x, y, width, height, text_width, text_height)
  xn = x - text_width/2
  # yn = y - text_height/2
  xnew = xn
  ynew = y + xn ** 3 / ((text_width/2)**3) * 70
  [xnew + width/2, ynew + height*2/5]
end


height = 800
width = 800

surface = Cairo::ImageSurface.new(width, height) 
c = Cairo::Context.new(surface)

c.set_font_size(80.0) 
c.move_to 0, 0
c.set_source_rgba [0,0,0,255]
c.text_path("ruby " * 5);
warp_path(c) { |x, y| spiral(x, y, 500, 500) }
c.fill


c.move_to 0, 300
c.text_path("I am curly");
extents = c.text_extents("I am curly")
warp_path(c) { |x, y| curl(x, y, width, height, extents.width, extents.height) }
c.fill

c.target.write_to_png("ruby_warped.png")