Simple Scrolling Function

This is a simple method i made for a scrolling function. It is used in my Halo Genocide Game

So lets start.

First of all we will load the images we will be using for our backgrounds. I use 1 480x272 image for this.

Code:

Background = Image.load("Background.png")

The next step is to set up our background variables. (note that the 3 background variables use the same image (saves memory)

Code:

Background_A = {} ---the first scrolling background (positioned as the first image you see)
Background_A.x = 0
Background_A.y = 0
Background_A.Img = Background_Image

Background_B = {} --- the second scrolling background (positioned directly after Background_A)
Background_B.x = 480
Background_B.y = 0
Background_B.Img = Background_Image

Background_C = {} ---the third scrolling background (positioned directly before Background_A)
Background_C.x = - 480
Background_C.y = 0
Background_C.Img = Background_Image

Now thats done lets move onto the code that will make this scroll.

Code:

function Scroll()

if pad:right() then
Background_A.x = Background_A.x - 4
Background_B.x = Background_B.x - 4
Background_C.x = Background_A.x - 480
end

if pad:left() then
Background_A.x = Background_A.x + 4
Background_B.x = Background_B.x + 4
Background_C.x = Background_C.x + 4
end

if Background_A.x <= -480 then
Background_A.x = 0
end

if Background_B.x <= 0 then
Background_B.x = 480
end

if Background_C.x >= 0 then
Background_C.x = -480
Background_A.x = 0
Background_B.x = 480
end
end

The way this works, is if you press either left or right, the background starts to scroll in the opposite direction.

The code underneath that, basically resets the backgrounds to there original positions so that it should, in theory, scroll indefinitely.

Now we start our main loop

Code:

while true do
screen:clear() ---stops the background from getting garbled
pad = Controls.read() --read pad input

Now to call our scrolling function

Code:

Scroll() ---call scrolling code

Now to blit our backgrounds (note that we only blit them when needed to prevent slowdown)

Code:

if Background_A.x <=480 then
screen:blit(Background_A.x, Background_A.y, Background_A.Img)
end

if Background_B.x <=480 then
screen:blit(Background_B.x, Background_B.y, Background_B.Img)
end

if Background_C.x <=480 then
screen:blit(Background_C.x, Background_C.y, Background_C.Img)
end

Now to wrap it all up

Code:

screen.waitVblankStart()
screen.flip()
end

Hope that helps a few people get started with scrolling. You can test that with any png image. Just make the image 480x272 and name it "Background.png"

The whole code is below :

Code:

Background = Image.load("Background.png")

Background_A = {} ---the first scrolling background (positioned as the first image you see)
Background_A.x = 0
Background_A.y = 0
Background_A.Img = Background_Image

Background_B = {} --- the second scrolling background (positioned directly after Background_A)
Background_B.x = 480
Background_B.y = 0
Background_B.Img = Background_Image

Background_C = {} ---the third scrolling background (positioned directly before Background_A)
Background_C.x = - 480
Background_C.y = 0
Background_C.Img = Background_Image

function Scroll()

if pad:right() then
Background_A.x = Background_A.x - 4
Background_B.x = Background_B.x - 4
Background_C.x = Background_A.x - 480
end

if pad:left() then
Background_A.x = Background_A.x + 4
Background_B.x = Background_B.x + 4
Background_C.x = Background_C.x + 4
end

if Background_A.x <= -480 then
Background_A.x = 0
end

if Background_B.x <= 0 then
Background_B.x = 480
end

if Background_C.x >= 0 then
Background_C.x = -480
Background_A.x = 0
Background_B.x = 480
end
end

while true do
screen:clear() ---stops the background from getting garbled
pad = Controls.read() --read pad input

Scroll() ---call scrolling code

if Background_A.x <=480 then
screen:blit(Background_A.x, Background_A.y, Background_A.Img)
end

if Background_B.x <=480 then
screen:blit(Background_B.x, Background_B.y, Background_B.Img)
end

if Background_C.x <=480 then
screen:blit(Background_C.x, Background_C.y, Background_C.Img)
end

screen.waitVblankStart()
screen.flip()
end