From: Martin DeMello <martindemello@...>
Date: 2006-09-09T18:26:20+09:00
Subject: Re: DRAW 1280, 1024

On 9/9/06, Benjohn Barnes <benjohn@fysh.org> wrote:
> 20 years ago, the subject line would have drawn me a line across one
> of my screen's diagonals. Ruby is awesomely more powerful than BBC
> BASIC, but why no trivial graphics support?
>
> My two requirements are that it should be really easy to draw, and it
> should be possible to do so interactively (from irb).

You could build something atop Rubygame [  http://rubygame.seul.org/ ]
fairly easily. In fact you could probably write a BBC graphics
emulator, though the cursor-based thing would seem slightly odd in
this day and age :) A QBasic graphics emulator otoh might be a
worthwhile effort - IIRC it was pretty well thought-out and simple to
use. Here's a quick example using plain Rubygame:

irb(main):001:0> require 'rubygems'
=> true
irb(main):002:0> require 'rubygame'
=> false
irb(main):003:0> Rubygame.init
=> nil
irb(main):004:0> screen = Rubygame::Screen.set_mode([640, 480])
=> #<Rubygame::Screen:0xb78ebc20>
irb(main):005:0> red = [255, 0, 0]
=> [255, 0, 0]
irb(main):006:0> Rubygame::Draw.line(screen, [0, 0], [639, 479], red)
=> #<Rubygame::Screen:0xb78ebc20>
irb(main):007:0> screen.update
=> #<Rubygame::Screen:0xb78ebc20>

The simplest way would be to have a class that automatically
initialized a screen and held it as an instance variable, and a set of
methods that wrapped the methods in Rubygame::Draw but passed in the
default screen and remembered the last colour that was used in case no
colour was supplied. For example
-------------------------------------------------------------------------------------------
require 'rubygems'
require 'rubygame'

class Sketchpad
  def initialize(x,y)
    @screen = Rubygame::Screen.set_mode([x, y])
    @color = [255, 255, 255] #white
    Thread.new {
      loop {
        @screen.update
        sleep 0.01
      }
    }
  end

  def line(x1, y1, x2, y2, color=@color)
    @color = color
    Rubygame::Draw.line(@screen, [x1, y1], [x2, y2], @color)
    @screen.update
  end
end
-------------------------------------------------------------------------------------------
irb(main):001:0> require 'sketchpad.rb'
=> true
irb(main):002:0>  s = Sketchpad.new(640, 480)
=> #<Sketchpad:0xb791b808 @color=[255, 255, 255],
@screen=#<Rubygame::Screen:0xb791b7cc>>
irb(main):003:0> s.line(0, 0, 639, 479)
=> #<Rubygame::Screen:0xb791b7cc>
irb(main):004:0> s.line(0, 479, 639, 0, [0, 0, 255])
=> #<Rubygame::Screen:0xb791b7cc>

martin