Computer Graphics World

July 2009 60 n n n n Gaming to-one copy of the pictures provided by the Sony prop archives," says senior effects and environmental artist Glenn Gamble. "After I modeled it in 3ds Max and brought it into the game, we slowly started changing it." Gamble built the complex backpack ma- chinery and collaborated with the program- mers to perfect the proton streams. As he points out, the stream in the movie is not accurate, so the game version needed to be "tamed," since a gun that never hits the crosshairs can be incredibly frustrating for the player. e other major issue is that the beam in the movies had been hand drawn and animated, resulting in behaviors and thicknesses that were wildly different from scene to scene. e proton pack was the game's most ex- pensive model, requiring extreme attention to detail and a raft of animations, not only because it is so close to the camera, but be- cause it relays so much crucial information to the player. "e entire thing could easily have spiraled out of control and become incredibly expensive for the processor to handle, but we used a lot of tricks to miti- gate its cost," explains Gamble. "For ex- ample, I shared UVs with many of the fill areas on the pack, which allows for a much higher pixel resolution while using less tex- ture space. To make it render faster, I took three days to remake all the ghostbusters' equipment, including the proton pack, the upgrades, gun, trap, and miscellaneous belt attachments, so that it would fit on a single 1024x1024 texture." e pack itself comprises six separate models, with more than 40 individually animated parts, a full physics-driven cus- tom hose simulation, and well over 100 custom particle effects. In one of the more creative uses of Infer- nal technology, Gamble created a custom shader for faking the depth of the slime in the pack's tubing. "In our original approach to the slime in the tube, we used a series of overlaying eight-bit transparencies, which is expensive and can create rendering issues. After doing some creative tinkering in the Materials tool, I found a better solution: Us- ing a series of facing percentages (a node that returns a value based on a polygon's angle to the camera), I was able to fake the thickness of the slime tubes with a fluid inside, while still maintaining a series of eight-bit alpha transitions with only one set of polygons." Indeed, the game is awash in effects animation for the proton packs and the spectacular incursions from the other side. "ere are a lot of effects in the game … a lot," says Gamble. To simulate the steam expelled from the back of the proton pack, artists used the Trifecta particle tools within Infernal. e steam is a high-speed, cylin- der-shaped emitter with an even higher de- gree of drag. is forces the steam to shoot out fast but come to a quick stop, giving it a look of friction and dissipation. "e stream is lit partially and dynami- cally by the surrounding light. I say 'par- tially lit' because even though the effect is illuminated by the surrounding lights, it never looked right," says Gamble. "By blending between the light values of the set and a specified color value of the particle, I was able to re-create the right look." To create the bounce lighting emitted from the proton streams and reflected onto the characters, the artists placed a small dynamic light that is synchronized to the timing of the stream, or "wand," and color coordinated. e light turns on and off as the player fires the weapon, lighting up the character and anything close to the end of the wand. Another dynamic light at the end of the beam gives the player the same bounce lighting effect when shooting. Haunted Houses e library was the first game level tack- led by the team, which spent eight months perfecting the geometry and lighting, mak- ing it the benchmark for the rest of the game. Because the ghostbusters travel from the open air outside into the dimly lit halls of the library, the team spent a lot of time refining the lighting and radiosity system of the Infernal Engine so that the lighting transitions would be smooth and realistic, while the textured glass windows—mapped with an emissive material—could illumi- nate a room while the player could still see through them. Once inside the library, cards erupt in a plume from drawers, walls catch fire, and books fly off the shelves. Incredibly, every book is an individual model that can be knocked off the shelf, kicked around, or shot at, sending it flying about the room via In- fernal's physics simulation. At last count, says The game's physics were handled within the Terminal Reality Infernal Engine.

• Cover