Eyeon:Manual/Fusion 6/3D/Materials

In order to render a 3D scene, the renderer must take into account the shape of the object as well as the appearance. The geometry of an object could be said to describes the shape of the object, while the material applied to the object describes it's appearance. Fusion 6 introduces a range of new options for applying materials and textures to geometry.

Tools which describe the geometries response to light are called illumination models. Typically these tools are named according to the names of the authours of the mathematical technique used by the tool. The Blinn, Cook Torrance, Ward and Phong tools are the most frequently used illumination models. These tools are found in the 3D -> Material category of tools.

Most materials also accept textures which can be used to further refine the look of an object, giving it a rough organic appearance or a smooth reflective sheen. Textures can be simple 2D images or they may be more complex bump maps, height maps and reflection maps. These tools are typically found in the 3D Texture category.

Materials can also be combined together to produce elaborate and highly detailed composite materials. The term shader is often used when describing materials which are combined in this way. Materials are calculated on the graphics cards GPU whenever possible, and to do this Fusion compiles all the material tools into a program called a shader which is executed on the graphics cards GPU.

Each tool that creates or loads geometry into the 3D scene also assigns a default basic material, with controls built directly into the tool. The default basic material is a simplified version of the Blinn illumination model. As of Fusion 6 it is now possible to override this basic material using one of several tools which output a 3D Material. These materials provide a greater degree of control over how the geometry reacts to light, providing inputs for diffuse and specular texture maps, bumpmapping and environmental maps which mimic reflection and refraction.

Illumination Models

Illumination models are advanced materials for creating realistic surfaces like carbon fibre, wood or metal. Each illumination model has advantages and disadvantages which make them appropriate for particular looks. An illumination model determines how a surface reacts to light, so these tools require at least one light source to affect the appearance of the object. In Fusion there are four different models: Blinn, Phong, CookTorrance and Ward. The image below shows their characteristics, in the order they were named.

Basic

The basic material provides basic control over the diffuse, specular and transmittance components of the material. It only accepts a single texture map for the diffuse component. The basic material controls are found in the Material tab of all tools which load or create geometry. Connecting any tool which outputs a 3D material to that tools material input will override the basic material and the controls in the Material tab will be hidden. See the Common 3D Controls section of the tool reference for a complete description of this materials options.

Blinn

The Blinn material is a general purpose material which is flexible enough to represent both mettallic and organic surfaces. At first glance it appears identical to the Basic material, but the Blinn tool allows for a greater degree of control by providing additional texture inputs for the specular color, intensity and exponent (falloff), as well as for reflection and refraction environment maps and bumpmap textures. Blinn is generally more efficient than the Phong illumination model.

Cook Torrance

The Cook Torrance material uses fresnel equations to simulate the behavior of light when moving between media of differing refractive indices. Otherwise it is similar to the Blinn illumination model. This illumination model is primarily used for shading metal or other shiny and highly reflective surfaces.

Phong

The Phong material produces a result that is commonly thought to model the behaviour of light against polished or plastic surfaces.

Ward

The Ward illumination model is ideal for simulating brushed metal surfaces, as the highlight can be elongated in along the U or V directions of the mapping co-ordinates. This is known as an "anisotrophic" highlight.

Material Components

Regardless of whether the object uses the Basic, Blinn, Cook Torrance, Phong, Ward materials, or a shader which combines several materials, all illumination models share certain characteristics that must be understood.

Diffuse

The diffuse component of a material describes the appearance of an object where light is reflected from the object at an angle which leads away from the current viewpoint. This diffuse color and texture could be considered to be the base appearance of an object, before taking into account highlights, reflections, and bumpmaps. The opacity of an object is generally set in the diffuse component of the material.

Specular

The specular component of a material describes the appearance of an object where the light is reflected directly back at the current viewpoint. This causes a highlight which is generally brighter than the diffuse component. The more specular a material is, the glossier it appears. Surfaces like plastics and glass tend to have white specular highlights, whereas metallic surfaces like gold have specular highlights that tend to inherit their color from the material color.

Specularity is usually described as color, intensity and exponent. The specular color determines the color of light that reflects from a shiny surface. Specular intensity descibes how large the highlight will be. The following images shows a split view of a sphere with with 50% white as the diffuse color, and 100% white as the specular color. The right side of the sphere has the specular intensity set to 0, while the left one shows the image with specular highlights.

The specular exponent controls the falloff of the specular highlight. The smaller the value, the sharper the falloff and the larger the specular component will be. The following image shows the sphere from the above example with a specular exponent of 9 and again with an exponent of 200.

Transmittance

The transmittance component describes how light passes through a semi transparent material. For example, a solid blue pitcher will cast a black shadow, but one made of translucent blue plastic would cast a much lower density blue shadow. The transmittance component is essential to creating the appearance of stained glass. This component is described in greater detail below.

Note that Fusion allows for adjusting the opacity and transmittance of a material separately. The opacity determines how transparent the actual surface is when it is rendered. This might be a bit counter-intuitive to artists unfamiliar with 3D software at first. It is possible to have a surface that is fully opaque yet transmits 100% of the light arriving upon it (so in a sense it is actually a luminous/emissive surface).

The illustrations below cast a shadow through the following image. The image contains a green-red gradient from left to right. The outside edges are transparent, and the inside is a small semi-transparent circle.

Transmissive surfaces can be further limited using the Alpha and Color Detail control.

Alpha Detail

When this slider is set to 0, the alpha channel of the object is ignored and the entire object casts a shadow. If it is set to 1, the alpha channel detemines what portions of the object cast a shadow. Note that the OpenGL view will always cast a shadow from the entire object, ignoring the alpha. Only the software renderer supports alpha in the shadow maps. Below is an example image with Alpha Detail set to 1.0. The shadow is only cast where the alpha channel is greater than 0.

Color Detail

This modulates light passing through the surface by the diffuse color and texture colors. Use this to throw a shadow that contains color details of the texture applied to the object. Increasing the slider from 0 to 1 brings in more of diffuse color and texture color into the shadow. Note that the alpha and opacity of the object is ignored when transmitting color, allowing an object with a solid alpha to still transmit its color to the shadow. Below is an example image with Color Detail set to 1.0. The gradient is clearly visible in the shadow.

Transmission Color

The Transmission Color determines how much color is passed through the object. For an object to have transmissive shadows, set the transmittance color to (1, 1, 1), which means 100% of green, blue, red light pass through the object. Setting this color to RGB = (1, 0, 0). This means that the material will transmit 100% of the red arriving at the surface, but none of the green or blue light.

Textures

Texture maps are typically either 2D images or 3D materials which are used to modify the appearance of a specific component in an illumination model. This is done by connecting an image (or another material) to the inputs on the material tools tile in the flow editor. When a 2D image is used the UV mapping co-ordinates of the geometry are used to fit the texture over the image, and when each pixel is rendered the material will multiply the value of the component against the value of the corrosponding pixel in the map.

Texture maps are used to modify the diffuse color, specular color, specular exponent, specular intensity, reflection, refraction and bumpmap components of a material. The most commonly used texture maps are applied to the diffuse color component.

The following example shows how to control the roughness of a Cook Torrance material using the image produced by a Fast Noise tool.

A tool that outputs a material is frequently used instead, to provide a finer degree of control over the texture. In the following example a Texture 2D tool is used to translate the texture in the uv-space of the object.

Composite Materials

Building complex materials or shaders is as easy as connecting the output of a material tool to one of the texture inputs of another material of texture tool. When a texture input is supplied with a material instead of a 2D image, it will combine the results of that material with its own calculation. The following example shows how to combine an anisotrophic highlight with a Blinn material.

The output of the Blinn (including its specular) is used to determine the diffuse color of the Ward material. There are times where this is not desirable because the output of the Blinn is relit by the Ward material. The Channel Boolean Material can be used to add the Ward materials specular component to the Blinn material with a greater degree of control.