Scrolling tile problem

[Digitalic]

I have created an active obect which is a seamless image (640,480) of sky that scrolls left to right on the screen. I have placed one image on the game screen, and then I have duplicated it and placed the duplicate to the left of the game screen.

I repeatedly scroll the tiles to the right (bouncing ball movement), and then when X>640, I set the x to -639 and this works perfectly most of the time, but sometimes a gap appears between the tiles.

I am guessing that it is something to do with the speed of the tiles and the fact that sometimes the check for X>640 might occur a couple of pixels 'too late'. At a speed of 5, I have watched for a few minutes without any problems, but the faster the speed (e.g. 10+) the gap appears more regularly.

Is there a better way to produce this effect, or is there a recommended method of mitigating this problem?

Thanks in advance.

[LB]

Move the tiles by setting thier X position relative to themselves instead of using a build in movement.

[Digitalic]

Thanks for the suggestion; it works well. I don't know why I didn't try that earlier!

If I use an odd number for the X increment, I still end up with a gap, but it works for even increments of any size which is good enough for me!

Now I need to work diagonal tile scrolling!

Thanks

[Digitalic]

Now I need to work diagonal tile scrolling!

Oh! Easier than I thought!

The way I have done this is to have four tiles (640x480) scrolling X+n and Y+n, and then repositioning as they leave the screen.

It works, and there is nothing at all wrong with it (as far as I can see), but I wonder if anyone has achieved this effect differently.