MPC did a lot more intensive environmental work for both the Quidditch trials (here) and the snowy match.

Full CG clothes so close to the camera required a lot more resolution. For some shots they had live-action actors without capes so they extended the capes later in CG. Between the trials and the match they had three different types of material to deal with.

"Trying to simulate the cloth on fast moving characters wasn't really realistic," Aithadi adds, "so we decided to remove the translation on the Quidditch players and simulate the cloth at the origin; then we were using winds in Maya to simulate the translation."

Environments, of course, were full CG. MPC created panoramas from the production stills and created a 3D geometry using the trees in the photographs to determine scale of the mountains around the stadium. It had to be 3D in order to get proper parallax and proper depth. Hazing and clouds were added later by the compositing team. For the match, the original environment used in the tryout sequence was snowed up and MPC used particle systems to create the falling snow.

Rising Sun had its biggest contribution yet to Harry Potter, delivering nearly 300 shots. The most important work was the introduction of Professor Slughorn (Jim Broadbent) and the transformation of his chair (into his human form) and room. "There are a lot of props, including a grand piano and a chandelier and grandfather clock," offers Gregory Yepes, Rising Sun's visual effects supervisor. "It's all broken apart when Harry and Dumbledore enter the room because Slughorn is hiding from the Death Eaters. Dumbledore realizes it's a spell and counters the spell to straighten everything out. Our people did some really clever things for this sequence. For instance, there's a picture frame on the wall and it tilts to straighten itself out. That's the only moving practical thing on the set."

Everything else moving in the sequence is CG. Rising Sun used Maya for animation and Houdini for vfx and composited in Shake (they have since started using Nuke).

Rising Sun Pictures got to play with the Slughorn transformation scene, which involved a lot of clever fun with CG props.

"Tim and David Yates gave us the rough boundaries for the sequence and we just played around with it," adds Yepes. "It was such an overwhelming amount of objects, but we got great reference from Tim and his team of digital pictures and a catalog of every object in the room. For some of the bigger pieces, we got them cyber scanned. We also had a lighter on set to make the tracking and camera matchmove done. We modeled low-res versions of every prop in the room so that when we started doing animation layout, we picked from a catalogue and per a designated camera move. That was carefully driven by Tim and David. The whole point was to avoid spending a lot of weeks working on models and textures. There were a lot of layers, especially debris."

Bill Desowitz is senior editor of AWN and VFXWorld.