Boulder dash

You know what it’s like. You pop out to the local milliners to arm yourself with a stylish new piece of headgear and, returning titillated with your new titfer, you decide to take the short cut back. You know, the one past the ruined temple? Before you can say “ancient Inca curse”, you’re being harried back to the office by a humongous sphere of rolling rock that flattens everything in its path – not least the shiny new hat you’ve just spent your hard-earned cash on. Bloody Incas – they must have something serious against hats. 

While death-defying stunts like this are, admittedly, fairly rare in real life, attempts to reproduce the illusion with computer graphics are more popular and slightly safer. To this end, we invite you to take a stab at the effect using the popular combination of LightWave 3D and After Effects. 

This is a reasonably straightforward project, with regard to both the 3D and 2D elements involved, and so it’s a good starting point for anyone who’s new to the process of incorporating CG elements into live-action, moving backgrounds. 

Over the following four pages of this tutorial, we’ll be using some basic measurements taken from the location shoot to build a simplistic 3D model of the alleyway. We’ll then line up a camera in LightWave so we can add the ball and animate it, so it can roll down with dramatic timing. We’ll then render passes for both the ball and the shadow it casts on the ground. 

Like a rolling stone
While simpler techniques would achieve the shadow merely by darkening the footage (sometimes within LightWave itself), here we’ll use the rendered shadow information to do the darkening in After Effects, so we can get the same quality in the shadows as you can see in the footage. It’s generally easier to tweak the look of details like this in a composite, and it saves you from potentially re-rendering the time-consuming 3D renders. 

Click here to download the support files (~54MB)