AS3: detect if sprite is viewable within scrollRect?

Question

I there a way to "detect" if a particular sprite is within the viewable area of a scrollRect?

I have a list of thumbnails in a scrollRect and I only want to load images for these thumbnails if and when the thumbnail sprite is visible in the scrollRect.

Any tips or suggestions on how to accomplish something like this?

Answer 1

You could always use

if (Sprite.getBounds().intersects(scrollRect)) {
    //In view
}

as a test. Basic rectangle intersection.

Answer 2

Hi there,

I think the easiest way would be to check for overlap between the two rectangles. You can get a bounds rectangle from any DisplayObject with: myObject.getRect():Rectangle, or getBounds():Rectangle. You can then test this against the scroll rectangle for overlap.

There is a native overlap method on Rectangle, (rect1.intersects(rect2)):Boolean. I prefer to use a custom method for performance reasons though:

var overlap:Boolean = (r1.left < r2.right && r1.right > r2.left && r1.top < r2.bottom && r1.bottom > r2.top);

Good luck!