From: Paul Duncan <pabs@...>
Date: 2002-04-23T04:07:23+09:00
Subject: Imlib2-Ruby Image#draw_pixel Bug (was Re: [ANNOUNCE] Imlib2-Ruby 0.4.0)

* Phlip (phlip_cpp@yahoo.com) wrote:
> Paul:
> 
> Below my sig is a Ruby script that is attempting to convert a color PNG to 
> black and white, and to burn and dodge so near-white is white and 
> near-black is black. One invokes the script like this:
> 
> ruby convert.rb --in input.png \
>         --minGrey 180 --maxGrey 200 \
>         --out output.png
> 
> The problem is 'draw_pixel' does not appear to do anything. I can muddle by 
> with fill_rect, but this seems to blend pixels.
> 
> How can we make 'draw_pixel' do anything?

Hi Phlip,

It looks like there's a bug in Imlib2::Image#draw_pixel for the
three-argument form of the commands (the array or hash-version of the
command work correctly).  Unfortunately there also appears to be a bug
in Imlib2's imlib_image_draw_pixel().  I fixed the problem with
Imlib2::Image#draw_pixel, and I added an override in Imlib2-Ruby for the
Imlib2 bug; I'll take a better look at it this evening and see if I
can't pin the problem down.  Anyway, I applied the fixes above, your
suggestion from the previous email, and a few other minor changes and
released Imlib2-Ruby 0.4.1; you can find it at
http://www.pablotron.org/software/imlib2-ruby/ (or skip straight to the
tarball at http://www.pablotron.org/download/imlib2-ruby-0.4.1.tar.gz).

A few comments about your code below: you should probably be using
Imlib2::Image::load instead of Imlib2::Image::load_image; the former is
the ruby-ized version of image loading, complete with exceptions, and
the latter is a wrapper for imlib_load_image() (eg no error return, no
exceptions, etc).  I also noticed you shell out to remove a file before
saving it.  You can probably save the file w/o removing the previous
one; your OS should automatically remove the existing file when you call
Imlib2::Image#save.

Anyway, nice to see people using stuff I've made.  Thanks for the
suggestsions, and feel free to holler at me if you have any more
problems. :)

> -- 
>   Phlip
> 
> #!/usr/bin/env ruby
> 
> require 'imlib2'
> require 'parsearg'
> 
> 
> def colorIsLessThan pix, threshold
>         return ( pix.red   < threshold or 
>                  pix.green < threshold or 
>                  pix.blue  < threshold )
> end
> 
> 
> def convert
>         im = Imlib2::Image.load_image $OPT_in
>         w, h = im.width, im.height
> 
>         rect = [0, 0, 1, 1]
>         blackness    = $OPT_minGrey.to_i
> 
>         puts im.get_format
>         puts im.query_pixel(2, 2).red
>         puts im.query_pixel(2, 2).green
>         puts im.query_pixel(2, 2).blue
>         puts im.has_alpha
>         
>         return if $OPT_minGrey == nil
> 
> # TODO more realistic argument response
>         
>         puts "Converting..."
>         
>         palegreyness = $OPT_maxGrey.to_i
>         diff = palegreyness - blackness
>         darkgreyness = diff / 3.0
>         greyness     = 2 * diff / 3.0
>         
>         levels = [[blackness,    Imlib2::Color::BLACK]]
>         
>         rate = 255 / (palegreyness - blackness)
>         
>         ((blackness + 1)..palegreyness).each do | tick |
>                 puts tick
>                 level = (tick - blackness) * rate
>                 puts level
>                 color = Imlib2::Color::RgbaColor.new (level, level, level, 0)
> 
>                 '''puts color.red
>                 puts color.green
>                 puts color.blue'''
> 
>                 levels << [tick, color]
>         end     
> 
> 0.upto(w) { |x|
>   0.upto(h) { |y|
>       pix = im.query_pixel(x, y)
>       
>       rect[0] = x
>       rect[1] = y
>       nuColor = Imlib2::Color::WHITE
> 
>       levels.each do | test, aColor |
> 
>       if colorIsLessThan(pix, test) then
>          nuColor = aColor
>          break       
>       end
> 
>         end
>       
>       # im.fill_rect rect, nuColor
>       im.draw_pixel x, y, nuColor
>   }
> }
> 
>         system 'rm -f ' + $OPT_out
>         im.save $OPT_out
>         system 'kview ' + $OPT_out
> 
> end
> 
> 
> parseArgs(0, nil, "", "in:", "out:", "minGrey:", "maxGrey:")
> 
> convert
> exit

-- 
Paul Duncan <pabs@pablotron.org>        pabs in #gah (OPN IRC)
http://www.pablotron.org/               OpenPGP Key ID: 0x82C29562