Checking for going off the screen

[Ertain]

Hello again, LÖVErs.

In my little game I try to determine if some object (picture, enemy, what have you) has left the screen by checking to see if its "x" and "y" components are greater than the length and/or width. Is this a good way of telling this? How about for multiple objects? I would like to find a method for detecting whether they've gone off the screen, yet doesn't take up a whole lot of processing and resources.

[Robin]

Is this a good way of telling this?

Yes.

How about for multiple objects?

Use tables and the same method.

I would like to find a method for detecting whether they've gone off the screen, yet doesn't take up a whole lot of processing and resources.

Code: Select all

function offscreen(object) -- assuming (x, y) is the top-left position of the object.
    return object.x < -object.width or object.y < -object.height object.x > love.graphics.getWidth() or object.y > love.graphics.getHeight()
end

[Kadoba]

Try this:

Code: Select all

-- This function returns true if the object is out of the screen. 
-- trans_x and trans_y must be what you feed to love.graphics.translate()
-- scale must be what you feed to love.graphics.scale()
-- If scale and translate are not used then you only have to provide the object
function out_of_screen(object, trans_x, trans_y, scale)

local scr_left = -trans_x or 0
local scr_top = -trans_y or 0
local scr_bottom = scr_top +  love.graphics.getWidth() * (scale or 1)
local scr_right= scr_left + love.graphics.getWidth() * (scale or 1)

local obj_left = object.x
local obj_top = object.y
local obj_right = object.x + object.width
local obj_bottom = object.y + object.height

return obj_left > scr_right or obj_top > scr_bottom or obj_right < scr_left or obj_bottom < scr_top

to use it on multiple objects you would just do something like this:

Code: Select all

for key, value in pairs(objects)
     if out_of_screen(value) do 
        --something
    end
end 

[Ertain]

Thanks for the input, guys.