Rendering materials

Materials describe how the surfaces of the objects in the three-dimensional scene reflect light. They determine, for example, whether particles look dull or glossy, and whether a surface mesh appears like plastic or like polished metal. Materials are independent of the colors of the objects: colors continue to be determined by the visualized data (e.g. the per-particle colors assigned by the Color coding modifier) and by the settings of the visual elements. Likewise, transparency is not part of a material.

Every scene contains a list of rendering materials, which can be managed on the Materials tab of the rendering page of the command panel. The first entry of the list is the default material, which is used by all objects that have no other material assigned to them. The default material cannot be deleted. Use the New and Delete buttons to manage the list, and double-click a material to rename it. A new material starts out with the parameters of the material that is currently selected in the list. The parameters of the selected material are shown below the list.

Assigning materials to objects

Each visual element that renders shaded surfaces (particles, bonds, surface meshes, vector arrows, etc.) provides a Rendering material selector among its parameters in the pipeline editor, which lets you pick the material to use from the list of materials of the scene. Selecting New material… creates a new material, initialized with the parameters of the material the visual element currently uses, and assigns it to the visual element right away. As soon as a material other than the default material is selected, an additional Rendering material rollout appears below, in which the parameters of that material can be edited directly. This is convenient for tuning the appearance of a particular object. Note that the edits affect the material itself, i.e. all objects sharing that material. The parameters of the default material can only be edited on the Materials tab of the rendering page. The Surface mesh visual element lets you assign separate materials to the surface and to the cap polygons.

Materials are stored in the session state file together with the rest of the scene. When a session state written by an older OVITO version is loaded, the material settings that used to be part of the OSPRay and VisRTX rendering engines are transferred to the default material of the scene.

Material parameters

The parameters of a material are expressed in a form that is independent of the rendering engine. Each rendering engine translates them to its own native material model as faithfully as it can. The interactive viewports and the standard renderer show a real-time approximation of the material, while the ray-tracing engines produce more realistic renditions.

Shading model

The reflection model used for shading the surface:

Diffuse: Purely diffuse (matte) reflection without specular highlights. The remaining parameters have no effect.
Glossy: Diffuse reflection plus a specular highlight. Rendering engines based on the Phong reflection model (Tachyon, the OBJ material of OSPRay) use this mode natively.
Physically based: Metallic-roughness model as used by physically-based path tracers (the Principled material of OSPRay, the physically-based material of VisRTX) and by the glTF file format. Rendering engines that do not support it fall back to a Phong-like approximation.

Roughness

Controls the microscopic roughness of the surface and thus the size of the specular highlight (default value: 75%). A value of 0% gives a perfectly polished surface with a very tight highlight, while a value of 100% gives a completely matte surface.

Metalness

Controls the mixture of a dielectric (diffuse) and a metallic reflection model (default value: 0%). A value of 100% gives a completely metallic material, which reflects light only specularly and tints the reflection with the color of the object.

Specular

The strength of the specular reflection of the dielectric component of the material (default value: 50%).

Index of refraction

The index of refraction of the dielectric component of the material, which is used by the physically-based shading model to compute the strength of reflections (default value: 1.5). For most materials, the value is between 1.0 (air) and 4.0 (germanium).

The parameter values of the default material are memorized by OVITO and used as the initial values of the default material in new sessions.