Have a trial of ShoesComposite and ShoesLayout for Shoes 4

3buttons_on_slot1.rb

require 'java'
require 'swt'

module Swt
  include_package 'org.eclipse.swt.graphics'
  include_package 'org.eclipse.swt.events'
  module Widgets
    import org.eclipse.swt.widgets.Layout
  end
end

class ShoesComposite < Swt::Widgets::Composite
  def initialize *cs
    @cs = cs[0]
    super @cs, Swt::SWT::DEFAULT
  end

  def setSize(w,h)
    @width, @height = w, h
  end

  def setLocation(x,y)
    @x, @y = x, y
  end

  def add_paint_listener blk
    # Wrap the block so the paint callback happens at the right (x,y)   
    wrapped_blk = proc do |e|
      gc = e.gc
      transform = ::Swt::Transform.new(::Swt.display)
      transform.translate @x, @y
      gc.transform = transform
      blk.call(e)
      transform.dispose
    end
    @cs.add_paint_listener wrapped_blk
  end
end

class ShoesStackLayout < Swt::Widgets::Layout
  def computeSize *args
    Swt::Graphics::Point.new 200, 200-1
  end
  
  def layout *args
    eles = args[0].getChildren
    x, y = 0, 0
    eles.each do |e|
      size = e.computeSize Swt::SWT::DEFAULT, Swt::SWT::DEFAULT
      e.setBounds x, y, size.x, size.y
      y += size.y
    end
  end
end

$display = display = Swt::Widgets::Display.new
white = display.getSystemColor(Swt::SWT::COLOR_WHITE)
red = display.getSystemColor(Swt::SWT::COLOR_RED)
green = display.getSystemColor(Swt::SWT::COLOR_GREEN)

shell = Swt::Widgets::Shell.new display, Swt::SWT::SHELL_TRIM
shell.setLayout ShoesStackLayout.new
shell.addListener Swt::SWT::Close, proc{Swt.display.dispose}

# Implicit top slot
cs0 = Swt::Widgets::Composite.new shell, Swt::SWT::NULL
cs0.setBackground white
cs0.setSize 200, 200
cs0.setLayout ShoesStackLayout.new

# Slot 1 (green circle)
cs1 = ShoesComposite.new cs0
cs1.setLayout ShoesStackLayout.new
blk = proc do |e|
  gc = e.gc
  gc.setBackground green
  gc.fillOval 25, 25, 100, 100
end
cs1.add_paint_listener(blk)

# Slot 2 (red circle)
cs2 = ShoesComposite.new cs0
cs2.setLayout ShoesStackLayout.new
cs2.setLocation 50, 50
blk = proc do |e|
  gc = e.gc
  gc.setBackground red
  gc.fillOval 25, 25, 100, 100
end
cs2.add_paint_listener(blk)

# Three buttons on Slot 1
3.times do |i|
  b = Swt::Widgets::Button.new cs1, Swt::SWT::PUSH
  b.setText "button #{i}"
end

# Button
b = Swt::Widgets::Button.new cs0, Swt::SWT::PUSH
b.setText 'button'
b.pack

# Animation
class Anim
  def initialize &blk
    @blk = blk
  end
  def run
    @blk.call
    $display.timerExec 100, self
  end
end

i = 0
a = Anim.new do
  i+=1
  b.setLocation i, i
  shell.redraw
end
display.timerExec 100, a

shell.pack
shell.open

Swt.event_loop{Swt.display.isDisposed}

3buttons_on_slot2.rb

require 'java'
require 'swt'

module Swt
  include_package 'org.eclipse.swt.graphics'
  include_package 'org.eclipse.swt.events'
  module Widgets
    import org.eclipse.swt.widgets.Layout
  end
end

class ShoesComposite < Swt::Widgets::Composite
  def initialize *cs
    @cs = cs[0]
    super @cs, Swt::SWT::DEFAULT
  end

  def setSize(w,h)
    @width, @height = w, h
  end

  def setLocation(x,y)
    @x, @y = x, y
  end

  def add_paint_listener blk
    # Wrap the block so the paint callback happens at the right (x,y)   
    wrapped_blk = proc do |e|
      gc = e.gc
      transform = ::Swt::Transform.new(::Swt.display)
      transform.translate @x, @y
      gc.transform = transform
      blk.call(e)
      transform.dispose
    end
    @cs.add_paint_listener wrapped_blk
  end
end

class ShoesStackLayout < Swt::Widgets::Layout
  def computeSize *args
    Swt::Graphics::Point.new 200, 200-1
  end
  
  def layout *args
    eles = args[0].getChildren
    x, y = 0, 0
    eles.each do |e|
      size = e.computeSize Swt::SWT::DEFAULT, Swt::SWT::DEFAULT
      e.setBounds x, y, size.x, size.y
      y += size.y
    end
  end
end

$display = display = Swt::Widgets::Display.new
white = display.getSystemColor(Swt::SWT::COLOR_WHITE)
red = display.getSystemColor(Swt::SWT::COLOR_RED)
green = display.getSystemColor(Swt::SWT::COLOR_GREEN)

shell = Swt::Widgets::Shell.new display, Swt::SWT::SHELL_TRIM
shell.setLayout ShoesStackLayout.new
shell.addListener Swt::SWT::Close, proc{Swt.display.dispose}

# Implicit top slot
cs0 = Swt::Widgets::Composite.new shell, Swt::SWT::NULL
cs0.setBackground white
cs0.setSize 200, 200
cs0.setLayout ShoesStackLayout.new

# Slot 1 (green circle)
cs1 = ShoesComposite.new cs0
cs1.setLayout ShoesStackLayout.new
blk = proc do |e|
  gc = e.gc
  gc.setBackground green
  gc.fillOval 25, 25, 100, 100
end
cs1.add_paint_listener(blk)

# Slot 2 (red circle)
cs2 = ShoesComposite.new cs0
cs2.setLayout ShoesStackLayout.new
cs2.setLocation 50, 50
blk = proc do |e|
  gc = e.gc
  gc.setBackground red
  gc.fillOval 25, 25, 100, 100
end
cs2.add_paint_listener(blk)

# Three buttons on Slot 2
3.times do |i|
  b = Swt::Widgets::Button.new cs2, Swt::SWT::PUSH
  b.setText "button #{i}"
end

# Button
b = Swt::Widgets::Button.new cs0, Swt::SWT::PUSH
b.setText 'button'
b.pack

# Animation
class Anim
  def initialize &blk
    @blk = blk
  end
  def run
    @blk.call
    $display.timerExec 100, self
  end
end

i = 0
a = Anim.new do
  i+=1
  b.setLocation i, i
  shell.redraw
end
display.timerExec 100, a

shell.pack
shell.open

Swt.event_loop{Swt.display.isDisposed}

The above two files are almost the same. This is a diff.

C:\tmp>diff 3buttons_on_slot1.rb 3buttons_on_slot2.rb
92c92
< # Three buttons on Slot 1

---
> # Three buttons on Slot 2
94c94
<   b = Swt::Widgets::Button.new cs1, Swt::SWT::PUSH

---
>   b = Swt::Widgets::Button.new cs2, Swt::SWT::PUSH