Lesson 3 : Pixar Texture and Layer Surface
RenderMan, developed by Pixar Animation Studios, stands tall as one of the pioneering and most influential rendering engines in the realm of computer graphics. It's not just a rendering tool; it's a cornerstone of innovation that has shaped the landscape of visual effects and animation in the film industry. This lesson complements Lesson 2: Texture and Shading
Table of Contents
Â
1. Renderman by Pixar
2. Pixar Surface
3. Pixar Layer Surface
4. Basic Shaders
5. Sources
1. Renderman by Pixar
1974-1986: Beginnings within Lucasfilm
Pixar was initially founded as the Graphics Group, a department within the Computer Division of Lucasfilm, established in 1974 with the recruitment of Edwin Catmull from the New York Institute of Technology. Catmull had been responsible for the university's Computer Graphics Lab (CGL). At NYIT, researchers pioneered many computer graphics techniques now taken for granted and worked on an experimental film called The Works. When the group moved to Lucasfilm, they began developing the precursor to RenderMan, named the Motion Doctor.
​
The team then started working on film sequences produced by Lucasfilm's Industrial Light & Magic for special effects3. After years of work and projects like Star Trek II: The Wrath of Khan and Young Sherlock Holmes, the group, numbering around 45 people at the time, was purchased in 1986 by Steve Jobs shortly after his departure from Apple.
​
Jobs paid $5 million to acquire George Lucas's graphics division. The new company, named Pixar, was registered on February 3, 1986, in California. This independent company was led by Edwin Catmull and Alvy Ray Smith, with Steve Jobs serving as both chairman of the board and chief executive officer.
In 1989, the rendering engine was finally publicly available, under the name RenderMan.It is a high-performance, photorealistic rendering software used to transform digital models and scenes into stunningly realistic images. Known for its exceptional quality and versatility, it's a go-to choice for studios and artists aiming to achieve unparalleled visual fidelity.
RenderMan's prowess lies not only in its ability to generate breathtaking imagery but also in its adaptability. It caters to the diverse needs of artists and pipelines, offering a comprehensive set of tools and capabilities that empower users to craft immersive and lifelike worlds.
​
From its integration with various digital content creation tools to its support for advanced rendering techniques like ray tracing and global illumination, RenderMan is a cornerstone of creative expression in the realm of computer-generated imagery.
​
Its legacy spans iconic films, from the beloved characters of Pixar's animated features to the epic landscapes of blockbuster movies, showcasing its capability to breathe life into imagination. RenderMan continues to evolve, pushing the boundaries of what's possible in visual storytelling and cementing its position as a driving force in the ever-evolving world of computer graphics.
Renderman History
First Publicity 1990
Topicana is one of the early advertisements produced by Pixar. Created in 1988, this advertisement was intended for the company Tropicana to promote their orange juice. It was designed to showcase the capabilities of computer animation and was an attempt to demonstrate how this technology could be used for commercials.
​
The Topicana ad featured a Tropicana orange juice bottle transforming into a human face. This transformation, achieved using advanced 3D animation techniques for that time, showcased Pixar's ability to create stunning animations and bring inanimate objects to life realistically.
This advertisement was one of the initial opportunities for Pixar to showcase their expertise in computer animation to the general public, well before their worldwide fame through animated films like Toy Story. It was also an early example of how computer animation technology could be used for creative and memorable advertising campaigns.
John Lasseter, the creative head of Pixar with Peter Doctor and the team
Toy Story 1995, first Animation Movie in CGI
Toy Story, released in 1995, marked a significant milestone not only for Pixar but also for the entire animation industry. It was the first feature-length film entirely created using computer-generated imagery (CGI).
​
The story follows the adventures of a group of toys, led by Woody, a pull-string cowboy doll, and Buzz Lightyear, a spaceman action figure, belonging to a boy named Andy. When Buzz joins the toy collection, Woody feels threatened and rivalry ensues. However, circumstances force them to work together, leading to a heartwarming journey of friendship, self-discovery, and loyalty.
​
From a technical standpoint, Toy Story was groundbreaking. It showcased Pixar's prowess in storytelling, character development, and animation. The film's success wasn't just due to its technological achievement but also its compelling narrative and relatable characters.
Geri's game (1997) and other movies
Geri's game
Many studios are now working with RenderMan, and as time goes by, RenderMan offers us more and more new features. It's available on Houdini, Blender, and Maya.
2. Pixar Surface
The PxrSurface shader is a fundamental component in the RenderMan rendering engine, used to create complex and realistic materials in Maya. It offers a wide range of parameters to control the visual appearance of surfaces, allowing simulation of various materials, from shiny metals to matte fabrics.
Basic Parameters:
​
-
Diffuse Color / Diffuse Gain: Controls the color and intensity of light diffusion on the surface. This determines the base color of the material.
-
Specular / Specular Face Color / Specular Edge Color: Manages specular reflections. Specular controls the overall intensity, while Specular Face Color and Specular Edge Color allow specifying different colors for different view angles.
-
Roughness: Controls the surface roughness. A high value creates blurry reflections, simulating rough surfaces, while a low value generates sharp reflections on smooth surfaces.
-
Clearcoat / Clearcoat Roughness: Introduces an additional transparent coating layer on the main surface. Clearcoat Roughness controls the roughness of this layer.
-
Metallic: Determines if the surface is metallic or dielectric (non-metallic). Metallic surfaces have sharper reflections and a different appearance from non-metallic materials.
​
Advanced Controls:
​
-
IOR (Index of Refraction): Manages the surface's index of refraction, influencing how light bends when passing through the material. Higher values are used for denser materials like glass.
-
Subsurface (SSS): Controls light diffusion through the surface, simulating translucency effects. It can be used to create effects like skin, wax, or leaves.
-
Emission: Allows the surface to emit light. Useful for creating surfaces that emit their own light, such as screens, light signs, or emissive materials.
-
Normal Map / Bump Map / Displacement: These maps add geometric details to the surface. Normal Maps affect how light interacts with the surface without modifying geometry, while Bump Maps simulate relief details. The Displacement Map actually modifies the geometry.
-
Occlusion / Thin Walled: Additional controls to simulate ambient occlusion and manage the behavior of thin materials (like paper sheets) in terms of light refraction.
Each parameter of the PxrSurface offers granularity of control, allowing artists to create a wide range of realistic and detailed materials in their scenes.
Here are the most commonly used nodes:
-Â the PxrTexture for connecting maps
-Â the PxrNormal for normal maps
- the PxrDisplace accompanied by its DisplaceTransform.
It's the simplest material to use in RenderMan to create a realistic texture in a short amount of time.Â
To start, it's recommended to create procedural materials to fully understand all the parameters. Create metal, gold, plastic using only the parameters of the PxrSurface without adding maps or other nodes.
For example, here we've just created a material resembling beer using only the primary parameters of PxrSurface. We call this procedural
Beer Material
Have fun creating very different materials to understand all aspects of PxrSurface.You can also play around with noise, fractals (procedural maps generated by Maya or RenderMan).Â
Car Paint
Steel
Soap Bubble
For a Soap Bubble material, it's created using a fractal + color correction in the iridescence channel. The creation is limitless. Enjoy yourself !
Index of Refraction (IOR)
If you're creating materials in Physical mode, you'll want to access the physical data of the material you intend to create. Here's a list of some materials from Wikipedia.
3. Pixar Layer Surface
The PxrLayerSurface is an advanced extension of the PxrSurface shader in RenderMan, offering additional flexibility by allowing the combination of multiple material layers to achieve complex and realistic visual effects. Here are its key features:
​
-
Multi-Layered: It enables stacking different material layers with distinct surface properties such as color, roughness, reflection, etc. These layers can be blended and combined in various ways to create diverse effects.
-
Mask Control: PxrLayerSurface uses masks to precisely define the areas where each material layer is applied. This provides granular control over how different materials are distributed on an object's surface.
-
Sophisticated Layer Interactions: It allows adjustments on how each layer interacts with others. For instance, you can define how light reflects or transmits through different layers to achieve effects like translucency, material blending, and more.
-
Advanced Artistic Workflow: By offering a layer-based approach, it simplifies the process of creating complex materials, allowing artists to overlay and adjust different textures and properties intuitively.
-
Rendering Flexibility: It provides significant flexibility to experiment with different materials and visual effects without needing to create complex shader networks.
​
The PxrLayerSurface is extremely useful in scenarios where you need to combine multiple materials or textures to achieve realistic and complex renders, such as simulating clothing, multi-layered surfaces, complex weather effects, etc. It allows artists to finely control the appearance of surfaces in their 3D scenes.
Sometimes, for certain look development, we have no choice but to use the layer model.
For example, imagine you want to create a pen dragged through the earth. There will be two types of shaders:
the transparent plastic and the earth, which are very different types of materials. So, we'll create a base layer with the transparent plastic, and layer 1 will represent the earth. Then, we'll create a mask to define the areas we want to apply the earth material to (it's the same with Mari : lesson 2).
Mask Black and White
Shader 1 Earth
Shader Base Glass
Remember to activate 'enable' on your PXR Layers, otherwise, they won't show up. You can add up to 4. If you want to see just your base, remember to deactivate the mask or set the layer mask to 0 !
Here is an example of the base glass and the earth dirt in layer 1, with a mask generated by an alpha (fractal node) where I can determine the areas I want to see in my render. Feel free to use the invert node if you prefer to recover the black rather than the white from your mask.
4. Basic Shaders
RenderMan has developed a library of pre-made materials (procedural stuffs) to save you time. It's also very helpful if you don't understand how to create a specific effect; you can see how the Pixar team handled their materials. You'll find pre-set PxrMarsHair (fur shader), metals, plastics, and plenty of other very useful resources there.
Simply double-click on one of them to see the ball appear in the Hypershade. Later on, you can assign it to a mesh and modify its parameters (like adding details in the specular, changing the color, etc.).
I hope this lesson has served you well !