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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