gem 'gosu-spritesheet'

require 'gosu'
require 'gosu/spritesheet'

class Game < Gosu::Window
  def initialize
    tiles = Gosu::Image.load_tiles 'path/to/your/tiles.png', 10, 10
    @spritesheet = Gosu::Spritesheet.new { :tiles => tiles }
  end

  def draw
    x, y, z = #...the position of your animation on screen.

    # Just draws the next animation frame on each iteration.
    @spritesheet.animation(:default).step.draw x, y, z
  end
end

Game.new.show

require 'gosu'
require 'gosu/spritesheet'

class Character
  # x, y, z are our character's initial position.
  def initialize(x, y, z)
    @x, @y, @z = x, y, z
    tiles = Gosu::Image.load_tiles 'path/to/your/tiles.png', 10, 10
    
    # Suppose your tile has 8 frames.
    #
    # The first 4 frames are your character walking left.
    # And the other 4 your character walking right.
    @spritesheet = Gosu::Spritesheet.new({
      :tiles => tiles,
      :animations => {
        # Here we are taking the first 4 frames as the walking left
        # animation frames.
        :walk_left => { range: [0..3], duration: 0.2 },
        # The other 4 are the frames of walking right.
        :walk_right => { range: [4..7], duration: 0.2 }
      }
    })

    # By default our character starts facing left and stopped.
    @move_direction = :left
    @moving = false
  end
  
  def draw
    # Let's decide which animation to draw.
    animation_key = @move_direction == :left ? :walk_left : :walk_right

    if @moving
      # If our character is moving let's animate it!
      @spritesheet.animation(animation_key).step.draw @x, @y, @z
    else
      # When our character isn't moving let's just draw its stopped frame.
      @spritesheet.animation(animation_key).stop.draw @x, @y, @z
    end
  end

  def walk(direction, speed)
    @moving = true
    @x += direction == :right ? speed : -speed
  end
  
  def stop_moving
    @moving = false
  end
end

class Game < Gosu::Window
  def initialize
    super 800, 600 
    # Let's start our character at the center of the screen.
    @char = Character.new 400, 300, 1
  end

  def draw
    @char.draw
  end

  def update
    if pressing_right?
      @char.walk :right, 2
    end

    if pressing_left?
      @char.walk :left, 2
    end
  end

  def button_up(id)
    # When the user stops pressing any button let's tell our character to stop
    # moving.
    @char.stop_moving
  end

  # Let's define some helper functions
  def pressing_right?
    Gosu::button_down?(Gosu::KbRight) or Gosu::button_down?(Gosu::GpRight)
  end

  def pressing_left?
    Gosu::button_down?(Gosu::KbLeft) or Gosu::button_down?(Gosu::GpLeft)
  end
end

Game.new.show