Tutorial:Using Input

Capturing input events with LÖVE is really easy; in this tutorial we'll cover how to capture keyboard and mouse events using both object methods and callbacks. We'll start our tutorial by putting together an almost empty LÖVE program:

local text

function love.load()
   love.graphics.setNewFont(12)
   text = "Nothing yet"
end

function love.update(dt)

end

function love.draw()
   love.graphics.print( text, 330, 300 )
end

Capturing keyboard events

The easiest way to know if the user is pressing a key is calling the love.keyboard.isDown method, which has the following syntax:

love.keyboard.isDown( key )

The key parameter is a string representing the key we want to see if it's currently pressed. A simple example:

if love.keyboard.isDown( " " ) then
   text = "The SPACE key is held down!"
end

You can find the complete list of keys here. The best place to perform this check is inside the love.update callback: that way we're able to get input from the user and update our variables before drawing our stuff into the screen. So, our modified love.update callback should look like this:

function love.update(dt)
   if love.keyboard.isDown( " " ) then
      text = "The SPACE key is held down!"
   end
end

While this is fine and dandy if we only need to know which key or keys are currently pressed, we might also need to specify different behaviors when a certain key is pressed and/or released. An elegant way of doing this is using the keyboard callbacks love.keypressed and love.keyreleased. They work in a similar way of the already known love.update or love.draw callbacks, executing our code every time that event is triggered. For example:

function love.keypressed( key )
   if key == "return" then
      text = "RETURN has been pressed!"
   end
end

function love.keyreleased( key )
   if key == "return" then
      text = "RETURN has been released!"
   end
end

As you can see, these two callbacks will provide you a key variable which you can use to check if a given key has been pressed, released or both. Up to this point, our source file should look like this:

function love.load()
    love.graphics.setFont(12)
    text = "Nothing yet"
end

function love.update(dt)
   if love.keyboard.isDown( " " ) then
      text = "The SPACE key is held down!"
   end
end

function love.draw()
      love.graphics.print( text, 330, 300 )
end

function love.keypressed( key )
   if key == "return" then
      text = "RETURN is being pressed!"
   end
end

function love.keyreleased( key )
   if key == "return" then
      text = "RETURN has been released!"
   end
end

Capturing mouse events

So, we already know how to interact with our users through a keyboard. But what about that little rodent that sits on their desks? Well, mouse input works in a fairly similar way: we have a love.mouse.isDown method and the love.mousepressed and love.mousereleased callbacks. Let's add a few lines to our love.update callback:

if love.mouse.isDown("r") then
   text = "Right mouse button has been pressed"
end

As you can see, it's very similar to the love.keyboard.isDown and, again, you can see the full list of mouse-related parameters here. You can even check if the mouse wheel has been rolled up or down using this method. We also have two handy methods to know the current position of the mouse pointer inside our game window: love.mouse.getX and love.mouse.getY. Each one will return the current coordinate of the mouse pointer. Let's see an example by adding these line to the beginning of our love.update callback:

mouse_x = love.mouse.getX()
mouse_y = love.mouse.getY()

And this line to our love.draw callback:

love.graphics.print( "Mouse X: ".. mouse_x .. " Mouse Y: " .. mouse_y, 10, 20 )

The love.mousepressed and love.mousereleased callbacks work in a very similar way as their keyboard counterparts:

function love.mousepressed(x, y, button)
   if button == 1 then -- "Versions prior to 0.10.0 use the MouseConstant 'l'"
      text = "Left mouse button has been pressed"
   end
end

function love.mousereleased(x, y, button)
   if button == 1 then -- "Versions prior to 0.10.0 use the MouseConstant 'l'"
      text = "Left mouse button has been released"
   end
end

A cool feature of this callback is that you can know not only if a button has been pressed but also the position of the mouse pointer when the user pressed the button. This can be really useful if you need to put together some basic user interface elements like buttons or other objects that can interact with the mouse. A simple example:

function love.mousepressed(x, y, button)
   if button == 'l' then
      text = "Left mouse button has been pressed at X:"..x.." Y: "..y
   end
end

Finally, we have another two useful mouse-related methods: love.mouse.setVisible and love.mouse.isVisible. The first one will let you hide or show the mouse pointer and the second one will obviously let you know if the mouse pointer is visible or not. Let's add even more code to our love.keypressed callback:

if key == 'h' then
   if love.mouse.isVisible() then
      love.mouse.setVisible(false)
   else
      love.mouse.setVisible(true)
   end
   -- OR:
   -- love.mouse.setVisible(not love.mouse.isVisible())
end

In these few lines we check if the mouse pointer is visible or not and then we change its visibility: if it's visible we hide it and if it's already hidden we then show it. Fairly easy, isn't it?

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