Question

The project I’m working on has a massive background image (800px wide by 2585px tall) that slowly scrolls upwards.

Before, I was using the code at: http://www.ilike2flash.com/2010/08/endless-scrolling-background-in-as3.html

I modified the code to scroll upwards, but in addition to having a weird intermittent bug that occasionally displays a pixel-tall blank line after the image and before looping the next, it really doesn’t seem to handle dynamic loading well (I’ve tried using several different preloader scripts and it breaks all of them), something that may not have been an issue with the initial implementation but is now that I’m using a monstrously huge image.

Thus, my question:

a. Is there another bit of free, Flash-based infinite scroll code floating around that has support for lazy-loading background objects (Say, the existing background chopped in 6)?

b. If not, any idea how I could modify the above link to do so?

Thanks! My AS3 is as follows:

stop();

//The speed of the scroll movement.
var scrollSpeed:uint = 2;

//This adds two instances of the movie clip onto the stage.
var s1:ScrollBg = new ScrollBg();
var s2:ScrollBg = new ScrollBg();
addChild(s1); 
addChild(s2);
setChildIndex(s1, 0);
setChildIndex(s2, 0);

//This positions the second movieclip next to the first one.
s1.y = 0;
s2.y = s1.height;

//Adds an event listener to the stage. 
stage.addEventListener(Event.ENTER_FRAME, moveScroll); 

//This function moves both the images to top. If the first and second 
//images goes past the top stage boundary then it gets moved to 
//the other side of the stage. 
function moveScroll(e:Event):void{
  s1.y -= scrollSpeed;  
  s2.y -= scrollSpeed;  

  if(s1.y <= -s1.height){
     s1.y = s1.height - scrollSpeed;
  }else if(s2.y <= -s2.height){
     s2.y = s2.height - scrollSpeed;
  }
}

Answer 1

howdy ændrew
the link has about 15 lines of code.
it creates two instances of the object, it then moves moves both 1px every frame and checks if the first clip is out of the view, at which point it moves the movieClip over to the edge of the other clip. There’s not a lot of room for error… but if I had to point it out out, I’d say it’s right here

if(s1.x < -s1.width){
  s1.x = s1.width;
}else if(s2.x < -s2.width){
  s2.x = s2.width;
}

should be: (notice the <= instead of <)

if(s1.x <= -s1.width){
  s1.x = s1.width;
}else if(s2.x <= -s2.width){
  s2.x = s2.width;
}

this removes the few pixels gap between the movieclips

As far as dealing with loading a big asset goes, just add the scroll function once it has loaded. you can look for a sample at http://drawlogic.com/2007/09/20/howto-using-loaders-in-as3/ but there are bunch of others.