def science { }: Cairo for barcodes

Continuing my discussion about Gbarcode 2, I tested my theory of using Cairo for creation of barcodes. It turns out that this is not so hard, but it was a bit of a lerning curve, to say the least. I used the ruby DL library to load the cairo shared libs from the system (thanks to the GD2 gem for the code hints here). A few small methods where all that were needed for bare minimum functionality: creating bars and adding text. No fancy formating here.

Next, I used gnu barcode to get layout information for a barcode, so I could test the drawing methods independently of barcode creation logic.

The result is the picture posted above. Neat huh? Code is posted below, but I think for a production gem, I'll probably not use DL, since I have to wrap the gnu C libs for actually creating barcodes from text strings anyway.

Without further ado, the test script:

require 'dl'
require 'rbconfig'

module BC
VERSION = '1.5.0'.freeze

def self.cairo_library_name
case Config::CONFIG['arch']
when /darwin/
  'libcairo.2.dylib'
when /mswin32/, /cygwin/
  'cairo.dll'
else
  'libcairo.so.2'
end
end
def self.name_for_symbol(symbol, signature)
case Config::CONFIG['arch']
when /mswin32/, /cygwin/
  sum = -4
  signature.each_byte do |char|
    sum += case char
    when ?D: 8
    else     4
    end
  end
  "#{symbol}@#{sum}"
else
  symbol.to_s
end
end

private_class_method :cairo_library_name, :name_for_symbol

LIB = DL.dlopen(cairo_library_name)
SYM = {
:cairo_image_surface_create   => 'PIII',
:cairo_create    => 'PP',
:cairo_get_target    => 'PP',
:cairo_destroy    => '0P',
:cairo_surface_destroy    => '0P',
:cairo_surface_write_to_png    => '0PS',
:cairo_set_source_rgb    => '0PDDD',
:cairo_move_to    => '0PDD',
:cairo_line_to    => '0PDD',
:cairo_set_line_width    => '0PD',
:cairo_stroke    => '0P',
:cairo_select_font_face    => '0PSII',
:cairo_set_font_size    => '0PD',
:cairo_show_text    => '0PS'
}.inject({}) { |x, (k, v)| x[k] = LIB[name_for_symbol(k, v), v]; x }

class LibraryError < rs =" SYM[:cairo_image_surface_create].call(0,w,h)" rs =" SYM[:cairo_create].call(s)"> #{s.class}] :: R[#{r} =>  #{r.class}] :: RS[#{rs} =>  #{rs.class}]"
  SYM[:cairo_set_source_rgb].call(r,0.0,0.0,0.0)
  puts "S [#{s} => #{s.class}] :: R[#{r} =>  #{r.class}] :: RS[#{rs} =>  #{rs.class}]"
  return r
end

def self.ctx w,h
  context(surface(w,h))
end

def self.add_bar ctx,x,y,w,h
  # cairo_move_to(cr,11.0,20.5);
  # cairo_line_to(cr,11.0,70.5);
  # cairo_set_line_width(cr,1.85);
  # cairo_stroke(cr);
  SYM[:cairo_move_to].call(ctx,x,y)
  SYM[:cairo_line_to].call(ctx,x,h)
  SYM[:cairo_set_line_width].call(ctx,w)
  SYM[:cairo_stroke].call(ctx)
end

def self.add_text(ctx,txt,x,y)
  # cairo_select_font_face (cr, "serif", CAIRO_FONT_SLANT_NORMAL = 0, CAIRO_FONT_WEIGHT_BOLD = 1);
  # cairo_set_font_size (cr, 12.0);
  # cairo_move_to (cr, 21.0, 90.0);
  # cairo_show_text (cr, "TEST1234");  
  SYM[:cairo_select_font_face].call(ctx,"serif",0,1)
  SYM[:cairo_set_font_size].call(ctx,12.0)
  SYM[:cairo_move_to].call(ctx,x,y)
  SYM[:cairo_show_text].call(ctx,txt)
end

def self.draw(ctx,fname)
  # surface = cairo_get_target(cr)
  # cairo_destroy(cr);
  # cairo_surface_write_to_png (surface, "hello.png");
  # cairo_surface_destroy (surface);
  r,rs = SYM[:cairo_get_target].call(ctx)
  SYM[:cairo_destroy].call(ctx);
  SYM[:cairo_surface_write_to_png].call(r,fname)
  SYM[:cairo_surface_destroy].call(r);
end
end
end

include BC
c = B.ctx 132, 100

B.add_bar(c,  11.00 , 20.00,  1.85, 70.0)
B.add_bar(c,  13.50 , 20.00,  0.85, 70.0)
B.add_bar(c,  16.50 , 20.00,  0.85, 70.0)
B.add_bar(c,  22.00 , 20.00,  1.85, 70.0)
B.add_bar(c,  25.50 , 20.00,  2.85, 70.0)
B.add_bar(c,  30.50 , 20.00,  0.85, 70.0)
B.add_bar(c,  32.50 , 20.00,  0.85, 70.0)
B.add_bar(c,  37.00 , 20.00,  1.85, 70.0)
B.add_bar(c,  39.50 , 20.00,  0.85, 70.0)
B.add_bar(c,  44.00 , 20.00,  1.85, 70.0)
B.add_bar(c,  47.50 , 20.00,  2.85, 70.0)
B.add_bar(c,  50.50 , 20.00,  0.85, 70.0)
B.add_bar(c,  55.00 , 20.00,  1.85, 70.0)
B.add_bar(c,  58.50 , 20.00,  2.85, 70.0)
B.add_bar(c,  63.50 , 20.00,  0.85, 70.0)
B.add_bar(c,  65.50 , 20.00,  0.85, 70.0)
B.add_bar(c,  68.50 , 20.00,  2.85, 70.0)
B.add_bar(c,  73.00 , 20.00,  3.85, 70.0)
B.add_bar(c,  76.50 , 20.00,  0.85, 70.0)
B.add_bar(c,  79.00 , 20.00,  1.85, 70.0)
B.add_bar(c,  83.50 , 20.00,  2.85, 70.0)
B.add_bar(c,  87.50 , 20.00,  0.85, 70.0)
B.add_bar(c,  91.50 , 20.00,  0.85, 70.0)
B.add_bar(c,  94.00 , 20.00,  1.85, 70.0)
B.add_bar(c,  99.50 , 20.00,  2.85, 70.0)
B.add_bar(c, 103.00 , 20.00,  1.85, 70.0)
B.add_bar(c, 105.50 , 20.00,  0.85, 70.0)
B.add_bar(c, 110.00 , 20.00,  1.85, 70.0)
B.add_bar(c, 115.50 , 20.00,  2.85, 70.0)
B.add_bar(c, 118.50 , 20.00,  0.85, 70.0)
B.add_bar(c, 121.00 , 20.00,  1.85, 70.0)


B.add_text(c,"TEST1234", 21.0, 90.0)
B.draw(c,"test_bc.png")

Thursday, September 27, 2007

Cairo for barcodes