Platformer Movement

Questions
1

Hello,
I’m trying to make a 2D platfomer game and i’m running into some problems, mainly with getting the player to move around a game world. I have this code for player movement left right and jumping but its not working how I intended.

function update(self, dt)

	--Movement

	--Normalizing the direction so that diagonal isn't faster than horizontal/vertical
	if vmath.length_sqr(self.input)> 1 then
		self.input = vmath.normalize(self.input)
	end

	-- setting the acceleration to 200 pixels per second in the direction of the player's input
	local acceleration = self.input * 200

	local dv = acceleration * dt 
	local v0 = self.velocity
	local v1 = self.velocity + dv
	local movement = (v0 + v1) * dt * 0.5

	local p = go.get_position()
	go.set_position(p + movement)

	self.velocity = v1 -- So input veolcity next time is the final velocity of the previous time
	self.input = vmath.vector3() -- Changes the vector back to 0 for next useage
end

When I press a key the player moves in a direction forever and never stops and when I repeatedly press a key it gets faster. When i hold down a key its like I’ve only pressed it once. I don’t know what to do. Any help would be appreciated.

2

You can use the action parameter in the input function to find out if the button has been released. Something like this:

function on_input(self, action_id, action)
    if action.pressed and action_id == hash("...") then
        -- Put code for when a button is pressed here
    end
    if action.released then
        --Put code for when it is released here
    end
end

You also could reset the self.input variable every frame, which (I think) would work the same way.

1 Like
3

I tried that by adding when the action is released set the self.input variable to 0 and it didn’t change anything, and at the end of the on update I am changing the self.input to 0 anyway

4

Oops, my apologies, I missed that at the end. But I think I now know what’s causing it…
In every frame after pressing a movement button, self.velocity will be greater than 0. Even if the acceleration is 0, you are always making the movement variable at least equal to:

v0 * dt * 0.5

Since (v0 + v1) would always equal v0 whenever you aren’t pressing a button, the script will constantly be applying the original force every frame.

5

That’s a good point, do you know of any fixes for that?

6

I would change this line to self.velocity = vmath.vector().

But I wasn’t quite sure what you meant in this comment, and I wouldn’t want to ruin what you are trying to accomplish here.

7

I’ve just tried that and now the player doesn’t move at all for some reason.

8

Anyone else got any ideas of how to make a smooth movement? I’ve only got it to work as very jumpy.

9

I think the first code you posted was pretty close, but it was missing one thing: friction to slow down the player once the keys are released.

Maybe give this a try? It seems to work okay with minimal changes to your previous code.

function init(self)
	msg.post(".", "acquire_input_focus")
	self.input = vmath.vector3(0,0,0)
	self.velocity = vmath.vector3(0,0,0)
end

function update(self, dt)

	if vmath.length_sqr(self.input)> 1 then
		self.input = vmath.normalize(self.input)
	end
	
	local acceleration = self.input * 100

	local friction = self.velocity/10

	self.velocity = self.velocity + acceleration - friction

	local movement = self.velocity * dt

	go.set_position(go.get_position() + movement)

	self.input = vmath.vector3(0,0,0)
	
end

function on_input(self, action_id, action)
	if not action.released then
		if action_id == hash("right") then
			self.input.x = 1
		elseif action_id == hash("left") then
			self.input.x = -1
		elseif action_id == hash("up") then
			self.input.y = 1
		elseif action_id == hash("down") then
			self.input.y = -1
		end
	end
end
1 Like
10

Due to not being able to find a way I decided to not do acceleration anymore and it works a lot better without giving me a headache, thanks for your help. I may use this in a future project.

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