Tutorial:Baseline 2D Platformer

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