WHEN YOUR CREA­TURE IS… A PARA­CHUTE

Fred Chap­man, Head of Crea­ture (Van­cou­ver) at DNEG, de­tails the cre­ation of the para­chute cloth for a key jump se­quence from Dead­pool 2

3D World - - FEATURE -

Layer 1: an­i­ma­tion

For this scene we built para­chute an­i­ma­tion rigs that gave the an­i­ma­tors con­trol to pose the gen­eral shape and po­si­tion of the para­chute and its at­tach­ment to the X-force mem­ber. The model and rig needed to be cre­ated so that the ropes stayed straight, as they were al­ways un­der ten­sion.

The model for this rig and an­i­ma­tion layer should be quite coarse as it is just used for the pri­mary place­ment and shape, not for any de­tails of the cloth. It also doesn’t mat­ter if the cloth de­forms a lit­tle in an­i­ma­tion as the later sim lay­ers will cor­rect for this. When the an­i­ma­tion is ready it can be writ­ten out as an alem­bic cache to keep fu­ture lay­ers clean and fast. It also al­lows us to up­date the an­i­ma­tion in­put into the cloth lay­ers by read­ing in dif­fer­ent caches.

Layer 2: Base cloth sim

It’s time to add our base layer of nCloth sim. This layer will be on the same lowres­o­lu­tion mesh, and will form the coarse move­ment of the cloth, af­fected by grav­ity, drag, wind, tur­bu­lence and any col­li­sions. Con­straints were added to the ends of the base para­chute so that it would fol­low the anim cache. Other con­straints were added to this layer to at­tach the ropes, and to help pre­serve the vol­ume of the para­chute when needed.

Dur­ing each shot, the con­straint val­ues can be an­i­mated to give greater or lesser amounts of at­tract to the an­i­ma­tion de­pend­ing on whether those ar­eas should look un­der ten­sion and more rigid, or looser al­low­ing more re­ac­tion to wind and other forces. If col­li­sions or self-col­li­sions are needed they can be added to this layer as the low res­o­lu­tion means they can be cal­cu­lated much quicker than on the later higher-res­o­lu­tion lay­ers.

Layer 3: Rip­ples

Now that we have the broader move­ment of the cloth added on top of the an­i­ma­tion, the next layer to add is the rip­ples. Be­cause the rip­ple layer doesn’t need to re­act to the move­ment of the para­chute in the scene, we don’t need it to be sim’d in situ. We’ll cre­ate a du­pli­cate of the model at the ori­gin and use a wind force to cre­ate the smaller rip­ples. Once we’re happy with the look of the rip­ples, a blend­shape can be used to add the rip­ple mo­tion on top of the base cloth sim on the para­chute.

One thing to also re­mem­ber dur­ing this process is that sim­u­la­tions such as cloth can be time-con­sum­ing to process – those many it­er­a­tions add up to a lot of time, of­ten time that we don’t have avail­able. So it’s im­por­tant to us that as well as look­ing good, our pro­cesses should be fast, and give us lots of con­trol over the out­put.

Layer 4: wrin­kles

We have a mesh with both coarse and medium-level cloth de­tail that fol­lows the an­i­ma­tion, so our fi­nal layer is the very fine wrin­kle layer. This layer adds dy­namic cloth wrin­kles to main­tain sur­face area where the cloth sur­face com­presses. As the de­tail is much finer than the previous lay­ers, we need to sub­di­vide the para­chute mesh by smooth­ing 1-2 lev­els on both the out­put of the rip­ple layer and our wrin­kle nCloth mesh.

We use an in­put at­tract be­tween the rip­ple mesh and the wrin­kle mesh with a value of around 90% so that the wrin­kle mesh fol­lows all the previous lay­ers. We don’t use any ad­di­tional forces on the cloth but we do set the stretch and com­pres­sion re­sis­tance of the cloth to be much higher than in the base sim. This forces the cloth to stick to the rip­ple layer wher­ever pos­si­ble, but still form nat­u­ral-look­ing wrin­kles as the cloth moves around.

Layer 2

Layer 1

Layer 3

Layer 4

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