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