Eternally scrolling bushes, V1

One of the things that had vexed and puzzled us most in creating the animatic was how to achieve the effect of the scrolling background in the scene where the crow is fleeing from the hang glider. We knew from the start that we wanted her to run on the spot as the scarecrow approached from behind, with the bushes and ground scrolling past into the distance to give the effect of movement.

Demonstrating the desired composition of the shot.

We'd come up with a few solutions as to how this could be achieved but they mostly involved laboriously animating each bush, pushing it further and further into the distance. This was both time consuming and impractical; if we wanted to alter the timing or length of the shot at all we would have to re-tweak the keyframes manually in order to compensate. We'd also considered simply drawing a line of bushes far longer than we needed and simply scrolled that into the distance, but this, again, was problematic; we didn't know exactly how long the shot would be and needed flexibility to make adjustments as necessary. The ideal solution would be to somehow have an endless loop of scrolling bushes that would dynamically adjust its length in accordance with the length of the clip. A simple enough idea, but it was the technical execution that proved to be a stumbling block.

A bit of poking around online (and the guidance of a friendly message board visitor) revealed a rather nice "Motion Tile" effect within After Effects. The Motion Tile basically allows you to take any layer, image or object and replicate (or "tile") it across the entire composition. Altering the "Tile Center" property moves the tile within the constraints of its bounding box without needing to move the layer itself. By keyframing this parameter, you can create a sort of conveyor belt effect with almost any image.

I created a simple test using a basic circle to represent the bushes to see whether or not we would be able to achieve the desired effect in this way.

I actually animated the bushes next to each other, scrolling in a straight line. The illusion of perspective was created by placing the animated bushes within a new composition and making it a 3D layer. I was then able to adjust the Y and Z rotations so that the bushes ran alongside the path, appearing to vanish into the distance. Unfortunately there's a sharp cut on the last bush which, fortunately, we were able to disguise by placing the crow over the top — ideally, however, we'll be able to find a way to rectify this more neatly as we're otherwise very restricted as to where we can position the bird.

The animation does loop seamlessly and certainly works for these purposes, aside from a few kinks that need to be worked out. The perspective needs to be tightened up — ideally, we'll find a way to get the desired perspective without distorting the artwork too much. As it is we're needing to seriously re-scale the bushes which will inevitably lead to horrible image quality — though it's less noticeable with such a simple circle.

At least we know now that we can get the kind of effect we need. Certainly it needs refinement, but the basic principle is there! Hopefully we can do something similar with the ground texture, although creating a loopable ground tile could prove to be much trickier. I'm going to investigate potential solutions for the ground tiles and replace the circle with an actual bush to see how it works out.