add gravity to my world and make an image jump.

[goosingout]

my character curently runs left to right at a speed of 200. if ou hold down "right" it speed up to 400 and if you hold down ~"left is speed goes to 50. That and the background and world scrolling all work perfectly to the world.speed. I am trying to get my character to obay the laws of physics and gravity and be able to jump.

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loader = require("AdvTiledLoader.Loader")

function state:init( )
	windowx = love.graphics.getWidth()
	
	bg1 = {}
	bg1.img = love.graphics.newImage("/images/Citybackgroundnight.png")
	bg1.x = 0
	bg1.width = bg1.img:getWidth()

	bg2 = {}
	bg2.img = love.graphics.newImage("/images/Citybackgroundnight.png")
	bg2.x = windowx
	bg2.width = bg2.img:getWidth()

	ninja1 = love.graphics.newImage("/images/Character1.png")
	ninja2 = love.graphics.newImage("/images/Character2.png")
	ninja3 = love.graphics.newImage("/images/Character3.png")
	
	tx = 0
	ty = 0
	loader.path = "maps/"
	map = loader.load("level1.tmx")
	map:setDrawRange (tx,ty, map.width * map.tileWidth, map.height * map.tileHeight)

	world = 	{
			speed = 200,
			gravity = -400,
			}
	
	player = 	{
			x = 50,
			y = 300,
			y_vel = 0,
			speed = 200,
			jump_vel = -500,
			jumpheight = 300,
			grounded = false,
			}
		
end

Code: Select all

function state:update( dt )
	if dt > 0.05 then
		dt = 0.05
	end

	bg1.x = bg1.x - world.speed * dt
	bg2.x = bg2.x - world.speed * dt
	
	if bg1.x < -800 then
		bg1.x = bg1.x + bg1.width
	end
	if bg2.x < 0 then
		bg2.x = bg2.x + bg2.width
	end

	if love.keyboard.isDown("right") then
		world.speed = 400
	elseif love.keyboard.isDown("left") then
		world.speed = 50
	elseif love.keyboard.isDown("up") then
		player:jump()
	end
	
	tx = tx - (world.speed * dt)	
end

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function state:draw( )
	love.graphics.setColor(255,255,255,255)
	love.graphics.draw(bg1.img, bg1.x, 0)
	love.graphics.draw(bg2.img, bg2.x, 0)
	
	love.graphics.print("FPS: "..tostring(love.timer.getFPS( )), 10, 10)
	
	local ftx, fty = math.floor(tx), math.floor(ty)
	love.graphics.push()
	love.graphics.scale(scale)
	love.graphics.translate(ftx, fty)
	map:draw()
	love.graphics.pop()
	
	love.graphics.draw(ninja1, player.x, player.y,0,1,1,64,103 )
end

PS. I am using Hump, AdvTiledLoader, and .tmx tilemap

[thebassinator143]

I'm sort of n00b but I'll try to help.

Anyways, think of gravity as constant downward force. When you jump, you are temporarily overcoming this force, until finally it brings you back down. So how to simulate this? Simply add the following code to your state.update function!

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player.y_vel = player.y_vel - (world.gravity*dt)

Now the world.gravity will subtract from the player's y_vel over each instance of dt until eventually your character begins to fall.

[micha]

To me it looks like you are moving the background and not the player. Is that correct? In that case I highly recommend moving the player instead.

The equations of movement are

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player.vx = player.vx + player.ax * dt
player.vy = player.vy + player.ay * dt
player.x = player.x + player.vx * dt
player.y = player.y + player.vy * dt

If you want to implement gravity, then assign a non-zero value to player.ay (ay stands for acceleration in y-direciton)

[goosingout]

@micha yeah the background and the map are moving. I tried to move the player but i need the background to scroll continuously. that why I tried it this way round.

@thebass i have tried that and it doesnt work for some reason

there must be a way to allow the one image to have gravity. and then in turn all it to be able to jump with the "up" button

[Autophoenix]

Well, i have done this in a recent game mine:

In love.load() i put 2 variables. It controlls the jump time and if the player can jump

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jumpTime = 0
jump = true

Now, in love.update, I put two IF conditions and the variable 'jumpTime' will increase at every moment:

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jumpTime = jumpTime + 1

if love.keyboard.isDown("up") and jump == true then
    player.y = player.y - VELOCITY*dt
    if jumpTime > LIMIT_OF_JUMPING_TIME then -- Remeber to change the 'LIMIT_OF_JUMPING_TIME' to a number.
        jump = false
    end
elseif not love.keyboard.isDown("up") then
    jump = true
end

Remember to modify the code. Try to do something like 'if the player is at the ground then jump will be true'

[Robin]

You'd want to use:

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jumpTime = jumpTime + dt

Otherwise the time you can jump is framerate-dependent (and adjust LIMIT_OF_JUMPING_TIME accordingly).

Also, the code as-is is more flying than jumping, and you can get to any height by repeatedly holding the up arrow key.

[Autophoenix]

I know, and that's why i said:

Remember to modify the code. Try to do something like 'if the player is at the ground then jump will be true'