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Screen Collision [BEGINNER]
Posted: Tue Jul 12, 2016 1:44 pm
by Semeon
Hey,
I am kinda new in the world of LOVE2D and I was looking for some "around the screen collision" but it seems like when I use my player to try to see if he is colliding, part of the player moves off the screen and when his speed is really high he goes off the screen. Bellow I have the code with the player's speed high so you can see the effect mentioned above. By the way the collision for the right part of the screen hasn't been done because I stopped during the process of writing the code cause I got mad
!!!
Code: Select all
function love.load()
player = {}
player.x = 100
player.y = 100
player.w = 100
player.h = 100
player.speed = 100
end
function love.update(dt)
if player.x < 0 then
player.x = 0
end
if player.y < 0 then
player.y = 0
end
if player.y + player.h >= 600 then
player.y = 600 - player.h
end
if love.keyboard.isDown("left") then
player.x = player.x - player.speed
end
if love.keyboard.isDown("right") then
player.x = player.x + player.speed
end
if love.keyboard.isDown("up") then
player.y = player.y - player.speed
end
if love.keyboard.isDown("down") then
player.y = player.y + player.speed
end
end
function love.draw()
love.graphics.rectangle("fill", player.x, player.y, player.w, player.h)
end
Re: Screen Collision [BEGINNER]
Posted: Tue Jul 12, 2016 2:45 pm
by palmettos
Your player is going off-screen because you're updating its positions according to its speed after the collision check. Here's what's happening:
love calls update -> you check the player's position and set the position inside the playable area -> you update the player's position according to its speed (even if player.x == 0 and player.y == 0 before this step, player.x and player.y could now be negative or greater than screen width/height) -> love calls draw -> your rectangle is drawn at a position that could be either negative (off-screen) or greater than the screen width/height (off-screen).
You can fix this by performing your collision checks after updating positions.
You also probably want to multiply player.speed with dt in your movement expressions so that it's moving by that amount per second, not per frame.
Re: Screen Collision [BEGINNER]
Posted: Tue Jul 12, 2016 7:43 pm
by Semeon
Hey,
I sort of understand my mistake but how can I get the code working. But the thing I don't understand is your refrence "You can fix this by performing your collision checks after updating positions" , what do you really mean?
So this is and edit to the original message so what you are saying is to perform player control checks before I check for collision?
Thank you!
Re: Screen Collision [BEGINNER]
Posted: Tue Jul 12, 2016 8:23 pm
by palmettos
Semeon wrote:so what you are saying is to perform player control checks before I check for collision?
Thank you!
Yes. This will give you the results you would expect:
Code: Select all
function love.load()
player = {}
player.x = 100
player.y = 100
player.w = 100
player.h = 100
player.speed = 100
end
function love.update(dt)
if love.keyboard.isDown("left") then
-- multiplying player.speed by dt makes the object move player.speed units per second
-- otherwise it adds +/- 100 every frame, which will result in very fast movement
player.x = player.x - player.speed * dt
end
if love.keyboard.isDown("right") then
player.x = player.x + player.speed * dt
end
if love.keyboard.isDown("up") then
player.y = player.y - player.speed * dt
end
if love.keyboard.isDown("down") then
player.y = player.y + player.speed * dt
end
-- check collisions after calculating movement in case the player moved out of bounds this iteration
if player.x < 0 then
player.x = 0
end
if player.x + player.w >= 800 then
player.x = 800 - player.w
end
if player.y < 0 then
player.y = 0
end
if player.y + player.h >= 600 then
player.y = 600 - player.h
end
end
function love.draw()
love.graphics.rectangle("fill", player.x, player.y, player.w, player.h)
end
Hopefully this makes sense.