This code shows the interaction between a character (sprite) and a sword (image). I created this for a student of mine to reference.

sprites_in_ruby2d.rb

system('clear')

require 'ruby2d'

set title: 'Sprite animation'
set background: 'blue'

Zero = 0

# hero parameters
@hero_width = 78
@hero_height = 99
@hero_time = 150
@hero_direction = ''

@move_by = 4
@sprint_speed = 2

# sword parameters
@sword_height = 64
@sword_width = 64
# @sword_x = 150
# @sword_y = 390
@sword_x = Window.width/2 - @sword_width/2
@sword_y = Window.height/2 - @sword_height/2


# load assests

# images
@sword = Image.new(
  './assets/sword.png',
  height: @sword_height,
  width: @sword_width,
  rotate: 180,
  x: @sword_x,
  y: @sword_y
)

# sprites
@hero = Sprite.new(
  './assets/hero.png',
  width: @hero_width,
  height: @hero_height,
  clip_width: @hero_width,
  clip_height: @hero_height,
  x: Zero,
  y: Window.height - @hero_height,
  time: @hero_time,
  animations: {
    walk: 1..2,
    climb: 3..4,
    cheer: 5..6
  }
)

# methods

# this method ensures that objects stay within the game window
# e.g. call set_boundaries(@hero) to keep @hero within the limits
def set_boundaries(obj)
  # x-axis boundaries
  if obj.x >= Window.width - obj.width
    obj.x = Window.width - obj.width
  end

  if obj.x <= Zero
    obj.x = Zero
  end

  #y-axis boundaries
  if obj.y >= Window.height - obj.height
    obj.y = Window.height - obj.height
  end

  if obj.y <= Zero
    obj.y = Zero
  end
end

# this method determines if two objects have collided
def is_collided(obj_one, obj_two)
  # if first_object.x <= second_object.x + second_object.width && first_object.x + first_object.width >= second_object.x && first_object.y <= second_object.y + second_object.height && first_object.y + first_object.height >= second_object.y
  if obj_one.x <= obj_two.x + obj_two.width && obj_one.x + obj_one.width >= obj_two.x && obj_one.y <= obj_two.y + obj_two.height && obj_one.y + obj_one.height >= obj_two.y
    puts 'object one is colliding with object two :)'
  else
    puts 'object one is not colliding with object two :)'
  end
end

# handle user input
on :key_held do |event|
  case event.key
    when 'left'
     # animation
     @hero.play animation: :walk, loop: false, flip: :horizontal

     # movement
     @hero.x = @hero.x - @move_by
     @hero_direction = 'left'
    when 'right'
     # animation
     @hero.play animation: :walk, loop: false

     # movement
     @hero.x = @hero.x + @move_by
     @hero_direction = 'right'
    when 'up'
     # animation
     @hero.play animation: :climb, loop: false

     # movement
     @hero.y = @hero.y - @move_by
     @hero_direction = 'up'
    when 'down'
     # animation
     @hero.play animation: :climb, loop: false

     # movement
     @hero.y = @hero.y + @move_by
     @hero_direction = 'down'
    when 'c'
     @hero.play animation: :cheer, loop: false
   when 's'

     # update so character stops moving when hero_direction key is released
     if @hero_direction == 'left'
      @hero.x = @hero.x - @move_by - @sprint_speed
     end

     if @hero_direction == 'right'
      @hero.x = @hero.x + @move_by + @sprint_speed
     end

     if @hero_direction == 'up'
      @hero.y = @hero.y - @move_by - @sprint_speed
     end

     if @hero_direction == 'down'
      @hero.y = @hero.y + @move_by + @sprint_speed
     end
  end

  # pass hero to the method responsible for keeping objects within the game screen boundaries
  set_boundaries(@hero)
  is_collided(@hero, @sword)
end

on :key_up do |event|
  case event.key
    when 'left'
      @hero_direction = ''
    when 'right'
      @hero_direction = ''
    when 'up'
      @hero_direction = ''
    when 'down'
      @hero_direction = ''
  end
end

show