Gosu, how to detect when key is pressed?

I want to move my character left and right when the player is pressing Left cursor or right cursor.

How do I detect in the update function in Gosu when a key is pressed?

There are 2 ways to detect when a button is pressend.

Using the event listener

• Gosu::Window#button_down

This method is called before #update if a button is pressed while the window has focus.

Ideal when you want to trigger something only in the moment the button pass from released to pressed (shoot, jump, ...)

Checking is the button is down in this frame

• Gosu.button_down?

Returns whether the button id is currently pressed

Ideal when you want to keep doing something as far the key is still pressed (moving, ...)

Here is a code that contains both systems:

class MyGame < Gosu::Window
  def initialize
    @x = 100
    @y = 100
    @velocity = 3
  end

  def button_down(button_id)
    case button_id
    when Gosu::KB_ESCAPE
      close
    when Gosu::KB_SPACE
      shoot
    else
      super
    end
  end

  def update
    move_left if Gosu.button_down? Gosu::KB_LEFT
    move_right if Gosu.button_down? Gosu::KB_RIGHT
    move_up if Gosu.button_down? Gosu::KB_UP
    move_down if Gosu.button_down? Gosu::KB_DOWN
  end

  def shoot
    puts "Shoot!"
  end
  
  def move_left
    @x -= @velocity
  end
  
  def move_right
    @x += @velocity
  end
  
  def move_up
    @y -= @velocity
  end
  
  def move_down
    @y += @velocity
  end
end