using dt in external functions

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1u4
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using dt in external functions

Post by 1u4 » Sat Sep 13, 2014 5:25 am

Hi, In player.lua, I have

Code: Select all

function player_move()
    
    if love.keyboard.isDown("left") then
        player.x = player.x - (player.speed * dt)
    end
    if love.keyboard.isDown("right") then
        player.x = player.x + (player.speed * dt)
    end
    
end

In main.lua, I have

Code: Select all

function love.update(dt)
    player_move()
end
Which returns the error, dt has a null value (or similar). How can I apply delta time when using functions outside of main?

Thanks.
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Zilarrezko
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Location: Oregon

Re: using dt in external functions

Post by Zilarrezko » Sat Sep 13, 2014 5:39 am

Simple fix. You have to pass dt into the player_move function. Like so...

Code: Select all

function player_move(dt) --Notice I put it as a parameter here
    
    if love.keyboard.isDown("left") then
        player.x = player.x - (player.speed * dt)
    end
    if love.keyboard.isDown("right") then
        player.x = player.x + (player.speed * dt)
    end
    
end

Code: Select all

function love.update(dt)
    player_move(dt)           --And then passed love.update's dt parameter to player_move's parameter
end
It will work then.

The reason you have to do that is because when a parameter is passed into a function, it creates a local variable that is used inside that function. So to pass that local variable to another function, you give that function the variable as a parameter when calling that function. So that way that function can then use it. If you have any other questions man, just ask.

sphyrth
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Re: using dt in external functions

Post by sphyrth » Sat Sep 13, 2014 6:56 am

Another possible solution is you use the love.timer.getDelta() function for getting the DeltaTime if you prefer it.

Code: Select all

function player_move()
    dt = love.timer.getDelta()

    if love.keyboard.isDown("left") then
        player.x = player.x - (player.speed * dt)
    end
    if love.keyboard.isDown("right") then
        player.x = player.x + (player.speed * dt)
    end
    
end

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