# Tutorial:Platformer Jumping

| This tutorial is incomplete. Do you want to complete it? |

Due to a request on IRC, this guide has been written to show a basic implementation of platformer-style jumping physics for a player character.

The tutorial is fairly basic and even a newbie should have no issue understanding.

First, let's start off with our basic code, without any jumping.

    function love.load()
    	player = { -- nice and organised.
    		x = 0,
    		y = 0,
    		image = love.graphics.newImage("hamster.png") -- let's just re-use this sprite.
    	}

    	winW, winH = love.graphics.getWidth(), love.graphics.getHeight() -- this is just
    	-- so we can draw it in a fabulous manner.
    end

    function love.draw()
    	love.graphics.rectangle("fill", 0, winH / 2, winW, winH / 2)
    	love.graphics.translate(winW / 2, winH / 2) -- you don't need to understand this

    	love.graphics.draw(player.image, player.x, -player.y, 0, 1, 1, 64, 103) -- trust me
    	-- on the origin position. just trust me.
    end

  Note: The hamster.png file is File:Resource-HamsterBall.png.

You should get something that looks like this:

Now, it's time to make it jump. To do this, we'll give the player an upwards velocity, create a gravity variable and a jump height variable.

Add this to your love.load function:

    	player = {
    		...
    		y_velocity = 0,
    	}
    	...
    	gravity = 400
    	jump_height = 300

When the player presses the jump button (spacebar for this tutorial) we will increase the x_velocity by the jump_height.

Then, we will move the player upwards while decreasing the velocity by the gravity. We'll add a love.update and love.keypressed callback to make this work.

    function love.update(dt)
    	if player.y_velocity ~= 0 then -- we're probably jumping
    		player.y = player.y + player.y_velocity * dt -- dt means we wont move at
    		-- different speeds if the game lags
    		player.y_velocity = player.y_velocity - gravity * dt
    		if player.y < 0 then -- we hit the ground again
    			player.y_velocity = 0
    			player.y = 0
    		end
    	end
    end

    function love.keypressed(key)
    	if key == " " then
    		if player.y_velocity == 0 then -- we're probably on the ground, let's jump
    			player.y_velocity = jump_height
    		end
    	end
    end

Yay, jumping!

However, this is not true platformer-style jumping. In a lot of platformers, holding the jump key makes you jump higher. Let's implement this.

First, let's create a new player variable in love.load.

    	player = {
    		...
    		jetpack_fuel = 0.5, -- note: not an actual jetpack. variable is the time (in seconds)
    		-- you can hold spacebar and jump higher.
    		jetpack_fuel_max = 0.5,
    	}

Now, we remove our love.keypressed callback. We won't exact time, which is just bothersome to find out using keypressed and keyreleased. Instead, we'll move that logic to love.update.

....glhf

    function love.update(dt)
    	if player.jetpack_fuel > 0 -- we can still move upwards
    	and love.keyboard.isDown(" ") then -- and we're actually holding space
    		player.jetpack_fuel = player.jetpack_fuel - dt -- decrease the fuel meter
    		player.y_velocity = player.y_velocity + jump_height * (dt / player.jetpack_fuel_max)
    	end
    	if player.y_velocity ~= 0 then -- we're probably jumping
    		player.y = player.y + player.y_velocity * dt -- dt means we wont move at
    		-- different speeds if the game lags
    		player.y_velocity = player.y_velocity - gravity * dt
    		if player.y < 0 then -- we hit the ground again
    			player.y_velocity = 0
    			player.y = 0
    			player.jetpack_fuel = player.jetpack_fuel_max
    		end
    	end
    end

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