Material Type Overview-材质类型概述

Material Type Overview

OctaneRender® is blessed with a bevy of material types to choose from, each with its own specific uses and benefits. Choosing the right material type can be daunting for OctaneRender newbies (and might even perplex some old-timers as well, on occasion.) The topics that follow this overview will take a deep dive into each material. This overview section will help get you up to speed as quickly as possible and give you some perspective about all of the Octane material options, as well as when it’s best to use each type.

WHY SO MANY?

The reason for so many different types of materials is evolution. In the early days of Octane, the four original material types (diffuse, glossy, specular and mix) were enough to get the job done.

As time went on the computer imaging world evolved, adding more sophisticated material science and feature support. OctaneRender evolved, too, offering additional material types supporting those new features. Materials were added or expanded to support Physically-Based Rendering (PBR), toon shading and other advancements. Better ways to handle materials in Octane also evolved. Today, the original materials are still included, both for backward compatibility but also for efficiency: sometimes, all you need is a Specular material, for example.

OCTANE IS A HOT ROD

OctaneRender was built for speed, as you can probably tell, given the name “Octane” in the first place. Speed is the name of the game at Otoy, and Octane is the fastest non-biased path tracer out there. The OctaneRender development team have an incessant need for speed and do whatever they can to squeeze as much performance as possible out of OctaneRender. It’s a matter of pride.

You can think of the development team like the gear heads in a garage, always tuning up their cars. They will do anything they can to get the most performance, so the hot rod analogy is very fitting.

As the material types get more sophisticated, they also get more complex. And complexity is the enemy of speed. So, rather than force every material to be so much slower than the originals, it was determined best to offer separate types of materials based upon your creative needs.

EVALUATIONS PER PIXEL

In the sections following, you will see the term “evaluation” and it refers to “evaluations per pixel.” Every time OctaneRender shades a pixel each material or shader that contributes to that pixel must be evaluated. In some cases, a material might need to be evaluated hundreds or thousands of times, based upon what you are asking the material to do.

FASTEST MATERIALS

The diffuse, glossy, specular, and layered materials are the fastest to evaluate (typically only once per pixel.) Many different real world materials can be created with these original materials, it’s best to use them first, as they offer the best performance. If all you need is a diffuse material, use that instead of universal, for example, as universal is one of the slowest materials to evaluate. Let’s look at these materials in a little more detail:

DIFFUSE

About as plain as you can get, the Diffuse material is best used when you don’t need shininess or transparency. It evaluates once per pixel and can be used as one of the two contributing materials of the Mix Material.

GLOSSY

If you need shiny reflections, the Glossy material is the way to go. Like diffuse, it also evaluates once per pixel and can also be used a contributor for the Mix Material. Glossy is effectively diffuse with a clear coat. Glossy works great for shiny plastics. For metallic objects, use the Metallic material instead, as it offers more options, such as a complex IOR feature, to help dial in the look of realistic metallic surfaces.

SPECULAR

Clarity is what you get with the Specular material, as it gives you transparent surfaces. Like the other original types, Specular also evaluates once per pixel and can be used as a contributor of the Mix Material. There are some additional tuning options, such as Fake Shadows, that you can use to get even more speed out of specular. See more here.

LAYERED

As noted, the remainder of the other materials offer more capability, but at the price of speed. However, the Layered material was introduced recently, and it allows you to effectively “custom build” the material you want, via Material layer nodes. You can almost look at the Layered material as custom coding your own shader, without the speed hit (or the learning curve.) If you have need of a more sophisticated look, try to get it with the Layered material first before resorting to the slower-evaluating nodes. Your deadline will thank you.

TOON

Octane is very capable of creating “non photo-realistic” images as well, and the toon material is one way to do this. The toon material mimics the look of the anime art form, by limiting color shading ranges that you can drive with various gradients and nodes. You also have control over outlines, in color, and thickness.

MEDIUM SPEED MATERIALS

Offering a balance between speed and capability, the following materials are useful for more realistic surface representations. Not as fast as the original materials, these materials get you where the others cannot. including support for PBR materials and accurate metals.

UNIVERSAL

The Universal material was developed to interact more easily with Unity, Unreal Engine, Substance, and general PBR-based systems. The Universal material contains every photo-realistic shading option offered by Octane (excluding the Hair material). As a result, it is complex and thus, potentially slow. The Universal material can handle metallic (conductor) and diffuse/glossy (dielectric) and even blend between the two.

METALLIC

Metallic materials, typical of conductors, reflect colored reflections or highlights at different wavelengths. Reflections can be propagated by a full-color specular map. The Metallic material uses the Schlick approximation for the fresnel effect, but a more precise, complex IOR is also available for the ultimate in realistic metals when needed. There are additional channels for Sheen, Film Width and IOR, and more.

SLOWEST MATERIALS

The remaining materials are the slowest mainly because they involve layering or compositing materials with other materials; they have to do more work, essentially:

COMPOSITE

Composite requires sub-materials and each sub-material must be evaluated separately and then together. That will result in a loss of speed. The Composite material was developed to get past the two-material limit of the Mix Material. To do this, a new material type, the Sub-material, was created.

MIX MATERIAL

Like Composite, each Mix Material contributor needs to be evaluated separately and the again, evaluated as a whole, and, again, resulting in a loss of speed. As noted above, the Mix Material is limited to two contributors. Unlike the Composite material, the Mix Material uses the original materials.
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UTILITY MATERIALS

Utility materials, for lack of a better term, do not directly affect the look of a surface, but serve some sort of special function in the rendering process.
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PORTAL

As a rendering technology, path tracing, the basis of OctaneRender, involves following randomized paths of light as they emanate from a camera and bounce around (and sometimes, through) the objects in a given scene. As the tracing is random, noise is introduced. Path tracing creates a ton of information to process. Interior scenes which have a notable amount of illumination coming from outside (via doors, windows, skylights and so on) can often be even noisier and look unappealing, and important contributors to the final illumination can be missed.

Portals are best suited for architectural renderings.

Portals allow for a focused approach to this problem, as objects with the portal material applied act as a target for the light paths emanating from the camera and through the portal to the outside illumination source(s) for the scene. To use portals most effectively, they should conform to the following guidelines:

  - Portal polygons need to be as simple as possible, and the vertices of the portal need to match the vertices of the intended opening.
  - Portal polygons normals should point to the inside of the room.
  - Portal polygons should not self-intersect (degenerate) nor should they intersect with other meshes in the scene.
  - Portal polygons should be used for small openings only. Larger openings will slow down the process considerably.
  - Larger openings my not need portals at all, as the typical routines should provide a satisfactory result in those cases.
  - In the event that the above does not suffice in a given situation, use a black body emitter at a value of 12,000 with an opacity of 0.

SHADOW CATCHER

The Shadow Catcher material is used when you wish to composite scene objects and need the shadows of the scene objects to ground the scene objects into the composited background plate. The shadow catcher material is applied to any object that you need to capture the actual shadow fall. Typically, that would be a flat ground plane, but the material is not limited to flat planes. Note that the Shadow Catcher is only available with the Diffuse and Universal materials, in the Common tab of these materials.

The shadow catcher is effectively a diffuse material with the shadow(s) cast upon it being applied to the alpha channel for transparency.

HAIR MATERIAL

The spectral Hair material significantly improves hair rendering realism in Octane. The difference between the Hair material and traditional diffuse/specular materials is that hair material assumes the geometry it’s assigned to is strictly a hair spline, allowing pre-integration for multi-scattering effects that occur in hair geometry. It works in combination with hair shaders by Cinema 4D, Ornatrix and others.