The Tree-mak­ers

Dis­cover how top stu­dios cre­ate re­al­is­tic-looking CG veg­e­ta­tion in hit movies from The Lego Nin­jago Movie to Kong: Skull Is­land

3D World - - CONTENTS -

Visual effects stu­dios reg­u­larly face an ar­ray of sim­u­la­tion chal­lenges on big movies, with fire, wa­ter and de­struc­tion be­ing com­mon re­quire­ments, as is the cre­ation of pho­to­re­al­is­tic fo­liage. This can range from in­di­vid­ual trees to en­tire forests, and also in­clude the re­quire­ment for real and CG char­ac­ters to in­ter­act with that dig­i­tal veg­e­ta­tion.

But how do dif­fer­ent stu­dios ap­proach dig­i­tal fo­liage? 3D World spoke to An­i­mal Logic, ILM, Weta Dig­i­tal and Image­works about their CG veg­e­ta­tion so­lu­tions – made up of a mix of pro­pri­etary toolsets and off-the-shelf soft­ware – used on re­cent films such as The Lego Nin­jago Movie, Kong: Skull Is­land, War for the Planet of the Apes and Kings­man: The Golden Cir­cle.

An­i­mal logic’s rich lego land­scape

Thanks to a slew of Lego films and other an­i­ma­tion and visual effects projects,

“Spruce re­ally quickly gives you a lot of nat­u­ral vari­a­tion” Jean Pascal Leblanc, look de­vel­op­ment su­per­vi­sor, An­i­mal Logic

An­i­mal Logic has re­cently made sev­eral leaps and bounds in its effects ar­se­nal, par­tic­u­larly for in­stanc­ing mil­lions of bricks and in the de­vel­op­ment of a pro­pri­etary path tracer, Glimpse. The studio there­fore looked to lever­age th­ese de­vel­op­ments in in­stanc­ing and ren­der­ing for the dig­i­tal fo­liage of the dense jun­gle scenes in The Lego

Nin­jago Movie. Al­though it was a Lego film, Nin­jago dif­fered slightly to the other projects in that it had pho­to­real nat­u­ral en­vi­ron­ments, such as beaches, wa­ter and a jun­gle that the char­ac­ters would walk and fight amongst.

Ini­tially, the ear­lier work in in­stanc­ing at An­i­mal Logic led to the de­vel­op­ment of a pro­ce­dural point dis­tri­bu­tion tool called Spawn for cre­at­ing rock and ground cov­er­ing and for quickly plac­ing plants and trees. For the trees them­selves, how­ever, which had to hold up to in­tense scru­tiny, An­i­mal Logic de­vel­oped pro­ce­dural build­ing tool Spruce.

“We use Spruce to build the trunk as a li­brary el­e­ment,” ex­plains An­i­mal Logic look de­vel­op­ment su­per­vi­sor Jean Pascal Leblanc. “We build var­i­ous types of branches for the dif­fer­ent types of trees by as­sem­bling them from com­po­nent parts of twigs and leaf vari­ants, which are all built and sur­faced in­di­vid­u­ally as a cat­a­logue of smaller as­sets, cat­e­gorised by type. By cre­at­ing a li­brary of el­e­ments for all the dif­fer­ent parts we can in­clude what­ever we want, flow­ers or ap­ples for ex­am­ple. Spruce loads the cho­sen el­e­ments from the li­brary, analy­ses them and con­structs a tree out of them.”

The growth of the CG trees and plants in Spruce – in­clud­ing many bon­sai-like trees for Nin­jago – starts with a seed that grows based on botan­i­cal con­cepts such as ge­ot­ro­pism (the ef­fect of grav­ity) and pho­totropism (the ef­fect of light). Al­though the growth is ran­domised, artists do have con­trol in Spruce over a de­gree of ro­ta­tional lev­els with the hi­er­ar­chy of branches and leaves.

A ‘keep-alive’ part of the tool also al­lows for sub­tle move­ment of the fo­liage. “Plus we’ve got tools in­side the sys­tem that will deal with in­ter­sec­tions so the leaves and branches don’t in­ter­sect them­selves,” adds Leblanc. “Once you’re done with your recipe for the tree you’ve got the ‘roll the dice’ but­ton, and like any good soft­ware, you press it and re­ally quickly it gives you a lot of nat­u­ral vari­a­tion. Then we use Spawn to take that tree and dis­trib­ute in­stances of it over a vast sur­face.”

ilm goes To Skull is­land

Kong: Skull Is­land takes place on a fic­ti­tious is­land that was ac­tu­ally filmed in mul­ti­ple lo­ca­tions around the world. To help fill out the world with veg­e­ta­tion rang­ing from palm tree-cov­ered ar­eas, rocky bush zones, tree-cov­ered moun­tains, bam­boo forests and river val­ley marsh lands, ILM built a di­verse set of CG trees and plants. That work be­gan in In­ter­ac­tive Data Vi­su­al­iza­tion, Inc.’s Speedtree, one of the in­dus­try-stan­dard tools for mod­el­ling flora.

“We would of­ten start with a Speedtree base li­brary model and mod­ify it to match our de­sired look,” ex­plains ILM se­nior gen­er­al­ist Votch Levi. “Once the look is achieved we build a few vari­a­tions to add di­ver­sity. Speedtree can ex­port mod­els to an XML for­mat that in­cludes the model ge­om­e­try, ma­te­rial as­sign­ments and rigged bones. We built a cus­tom in­ges­tion tool to parse the XML file and read the Speedtree model into our in­ter­nal as­set man­age­ment sys­tem. The in­ges­tion process was able to cre­ate a fully rigged and screen-ready as­set. We also took ad­van­tage of Speedtree’s an­i­ma­tion fea­tures to gen­er­ate wind mo­tion on a few plants and trees. Th­ese canned an­i­mated trees were ex­ported as Alem­bic files and in­gested into our as­set man­ager.”

Around 240 trees and plants were cre­ated and then whit­tled down to 150 se­lects. ILM’S dig­i­tal model shop re­fined some of the Speedtree as­sets into hero mod­els with ex­tra-de­tailed tex­tures. ILM then used Isotropix’s Clarisse to lay out the vast en­vi­ron­ments, in­clud­ing the CG veg­e­ta­tion. “Trees, es­pe­cially, tend to be ge­om­e­try-heavy as­sets and many of our trees and bushes had well over 10 mil­lion tri­an­gles per as­set,” says Levi. “We re­alised early on that Clarisse had no prob­lem han­dling th­ese mod­els, in fact it had no is­sues han­dling the en­tire li­brary all at once. So we built a cat­a­logue and li­brary of all 150 trees and plants in Clarisse and set up tools that al­lowed the en­vi­ron­ment artists to quickly se­lect and place mod­els in the scene.”

“In Clarisse,” adds Levi, “we ren­dered out cards of an­i­mated plants and trees in dif­fer­ent light­ing con­di­tions. Dig­i­tal en­vi­ron­ment artist Mike Wood built a cus­tom gizmo we call ‘Tree Maker’ in The Foundry’s NUKE with an in­ter­face to switch be­tween dif­fer­ent plants, pre­ren­dered light­ing set­ups, and add colour vari­a­tion to th­ese ren­ders. Com­pos­i­tors used Tree Maker to place set­ups in 3D space us­ing NUKE’S Scan­line ren­derer. Th­ese passes added ad­di­tional fore­ground and back­ground plants to shots and be­came an in­dis­pens­able tool through­out the show.”

WETA mim­ics how Trees com­pete

Weta Dig­i­tal has had sig­nif­i­cant ex­pe­ri­ence in dig­i­tal veg­e­ta­tion. For the Hob­bit tril­ogy, the studio de­vised a pro­pri­etary toolset called Lum­ber­jack for cre­at­ing and edit­ing CG trees that mim­icked real-life growth. This was re­cently built upon fur­ther for War for

the Planet of the Apes with a new piece of soft­ware dubbed To­tara, a ref­er­ence to the na­tive New Zealand tree. Lum­ber­jack had an in­ter­nal mod­ule for pro­ce­dural growth called Green­house, a tool based on spa­tial com­pe­ti­tion for re­sources that al­lowed the user to grow a sin­gle tree.

“With To­tara, how­ever,” out­lines Weta Dig­i­tal’s se­nior head of as­sets Marco Reve­lant, “we de­cided to ex­pand the idea of pro­ce­dural growth to mul­ti­ple trees to sim­u­late the in­ter­de­pen­den­cies that oc­cur in a real for­est. To­tara has moved away from the ‘spa­tial com­pe­ti­tion’ idea to fo­cus more on ‘light com­pe­ti­tion’, which af­fects the vol­ume of leaves on the trees and de­ter­mines how much light reaches var­i­ous parts of the tree and neigh­bour­ing plants.”

Weta Dig­i­tal’s team re­searched spe­cific tree va­ri­eties and as­pects of their growth pat­terns, en­cod­ing the in­for­ma­tion to be­gin the sim­u­la­tion process for the growth of a real tree. This happens in a per­fect en­vi­ron­ment on a flat plane with­out other trees, but once the pa­ram­e­ters are tweaked, a fur­ther sim­u­la­tion oc­curs for a whole for­est. “Trees start grow­ing and once they reach ma­tu­rity, will start spawn­ing,” says Reve­lant. “If a tree doesn’t have enough re­source to grow, it will die but the trunk will re­main there as it happens in na­ture. The same thing will

”the branches would bend with the weight of the Sim­u­lated Snow” Dan Lem­mon, visual effects su­per­vi­sor, Weta Dig­i­tal

hap­pen if cer­tain branches die due to the lack of light, the stump of the branch will re­main on the plant cre­at­ing a more re­al­is­tic look. Once we’ve grown an ecosys­tem, we can freeze it and then go in and mod­ify it. We might re­move some trees, shift them around a lit­tle bit to achieve cer­tain sil­hou­ettes and com­po­si­tions, and we can also pep­per in some be­spoke plants.” The fi­nale of War for the Planet

of the Apes in­cludes a ma­jor snow avalanche amongst a group­ing of conifer trees. “To­tara was able to de­liver a very nat­u­ral­look­ing for­est,” says visual effects su­per­vi­sor Dan Lem­mon, “where trees were grow­ing prop­erly with­out in­ter­sect­ing or crashing into each other, and the fo­liage was taken into con­sid­er­a­tion to cre­ate ar­eas of shadow that would im­pede other plants’ growth, con­tribut­ing to in­creased re­al­ism. We were also able to run our snow sim­u­la­tions on top of the for­est and the branches would bend in ac­cor­dance with the weight of the sim­u­lated snow. This means our for­est didn’t just look right in a static en­vi­ron­ment, but re­acted to FX sim­u­la­tions of snow and, later, much larger avalanche sim­u­la­tions.”

Spruce and Spawn were re­lied upon to build trees and also scat­ter veg­e­ta­tion into scenes

A scene from The lego nin­jago movie, which utilised An­i­mal logic’s Spruce and Spawn tools for build­ing a di­verse ar­ray of dig­i­tal trees and plants

Spruce en­abled in­cred­i­bly lush jun­gle en­vi­ron­ments to be crafted, which were then ren­dered in An­i­mal logic’s own path tracer, glimpse

Top: A ren­der of a bon­sai-like tree used for The lego nin­jago movie. Since bon­sais are some­what art-di­rected in real life, An­i­mal logic also en­sured its Spruce tool al­lowed for some man­ual con­trol over the pro­ce­dural gen­er­a­tion of the stump and branches

The fi­nal bat­tle scenes in kong: Skull is­land take place in a river val­ley marsh. ilm used a li­brary of reeds, grass and bushes sim­u­lated in hou­dini to in­ter­act with wa­ter as the two main crea­tures fight

Top: in shots where kong in­ter­acts with plants on the sides of moun­tains, ilm placed all the veg­e­ta­tion in clarisse. The crea­ture team would then sim­u­late the trees in the studio’s pro­pri­etary Zeno soft­ware and send them back to the en­vi­ron­ment team to ren­der in clarisse

Top (op­po­site page) The Tree maker tool ilm built in nuke to aid in cre­at­ing tree vari­a­tions for kong: Skull is­land

Above: A fi­nal shot from the jun­gle fly-over scene in kings­man: The golden cir­cle, for which image­works used its hou­dini work­flow

right: The Sprout ui. Trees and plant as­sets built in Speedtree can be in­gested into the image­works tool

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