Computer Graphics World

May/June 2014

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C G W M ay / Ju n e 2 014 ■ 29 Digging deeper down to the feather level, the deployer took each groom, which was initially designed in a rest position, and applied it to the animated birds, recalculating feather positions frame by frame to maintain relative angles from one feather to the next. "The idea here was that because of the high volume of birds, we couldn't solve for collisions between individual feathers. Looking at averages, the deployer detected outliers and brought those feathers in line with the others surrounding it," says Zeevalk. "This was essentially a method of avoiding most collisions, when a true collision detection system was out of reach for the scale on which we were working." The deployer also handled the caching of feather geometry, which was then instanced at render time, communicating with Side Effects' Houdini to define exactly what needed rendering – that is, avoiding feathers that weren't visible to camera – and applying static and dynamic noise to feathers for ruffling and air resistance as the birds flew. Part of the Flock The second major system Look built was a flocking system. The group started with a series of loopable animation cycles and progressed to different ranges of motion, building a library to draw from. Because there were a number of shots that required flocking, the group created multiple ways to generate a flock. For shots outside the ark, they were able to work more loosely, generally using curves to drive direction. Inside the ark, they followed a 3D volumetric approach using the geom- etry of the interior to confine the movement of the flocking birds. The system would then choose which animation cycle to use and when to transition – based on a bird's motion in the world. To prevent collisions, each bird had a field of view of close to 120 degrees. Anything outside of that range was ignored, and as the birds moved around and past one another, their flight paths were constantly updated and re-calculated based on what they "saw" in front of them. "This flocking AI was the backbone of our system," says Zeevalk. Birds were then instanced to create the full count needed for each shot. In addition, every bird would spawn a mate, and these would stay in close proximity in order to fly two-by-two as required by the story. Another key piece of the system gave the appearance of feathers, without the added data of actually feathering all the flocking birds. The artists generated shaders based on each of the grooms and applied it to the flocking birds. "This made them appear consistent with our hero birds but saved us a lot of processing that we didn't have to do because of their distance from camera," Zeevalk explains. The role a dove plays in the biblical tale is significant, as was Look Effects' role in the film's visual effects. ■ CGW Karen Moltenbrey is the chief editor of CGW. COMPUTER GRAPHICS WORLD Ad Reservations: July 7 • e-mail for advertising inquiries SIGGRAPH is where the left- brainers and right-brainers come together. Which one are you? Either way, CGW has you covered. Which one are you? The July/August (SIGGRAPH) issue of Computer Graphics World will highlight the latest trends and technologies in our industry, including a supplement on Education and Training, as well as a special section focused on the VFX and animation presented in this summer's blockbusters. You will learn and be informed. You will be entertained and impressed. Left Brain: Detailed Information Right Brain: Artistic-Driven Features

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