Virtual World Structure

A Unigine-based virtual world is a scene that includes a set of different built-in objects with certain properties. Almost all of the objects can be seen in the virtual world. However, some of them are pseudo-objects, which cannot be displayed in a normal mode (such as physicals, sectors, occluders and so on).

In general, a world includes the following:

• Built-in objects called nodes, which, in turn, may refer to other nodes (*.node), meshes (*.mesh), audio files (*.oga), paths (*.path) or scripts (*.h).
  Notice

  A world can store both nodes themselves and/or references to nodes stored in external *.node files. A *.node file, in turn, can also store both nodes and references to other external *.node files.
• Materials and properties organized in libraries.
• Shaders and textures to which material libraries refer.
• General rendering, physics, sound and game settings.

A new world can be created via the Menu bar of UnigineEditor or via Unigine SDK Browser when creating a new project.

Each world is stored on the disk in a separate file in the XML format with the .world extension.

• A world script has no implementation. In this case, the world content is created and managed via UnigineEditor.
• A .world file is empty. In this case, the world content is generated and managed via the world script.

Worlds can be as large as a level designer wishes as Unigine supports data streaming, and required resources — meshes, textures, animations, sounds — are dynamically loaded in run-time. Resources that are no longer needed are unloaded from memory.

For convenience of a large world designing and editing, a world can be split into several parts.

The 3D space in Unigine is represented by the right-handed Cartesian coordinate system: X and Y axes form a horizontal plane, Z axis points up. When exporting an animation from 3D editors, Y is considered a forward direction.

Positive rotation angle sets the rotation counterclockwise. It corresponds to the right-hand rule: if you set right hand thumb along the axis, other fingers wrapped will show rotation direction.

Unigine provides a set of built-in objects allowing you to add to a world practically all of the objects existing in real life. For convenience, they are divided into several groups that are responsible for different kinds of operations.

A world can store both nodes themselves and/or references to nodes stored in external files with the .node extension.

Nodes of object-related types may have surfaces and physical bodies (including collision shapes connected with joints). Surfaces contain references to particular materials and properties of the corresponding libraries. Such references are created automatically when you assign a material or a property to a surface.

A surface serves as an atomic rendering unit and can represent:

• A part of the object that needs to have its own separate material.
• Different levels of details (LODs) (including reflection LODs and shadow LODs). In this case, they represent the same object or its part in more or less detailed variants (a high-polygonal and a low-polygonal model). Which of these surfaces is visible at any given time is determined by the surface properties.

Taking into account the information given above, the scheme of world's components can be extended as follows:

Node Hierarchy

Surface Hierarchy

Besides being only a non-interactive environment, objects can take part in physical simulation. To be effective and at the same time keep the overall framerate high, physics is always a very rough approximation of the real world. Its main aim is to detect collisions between the objects.

For that, an object should be assigned a body that describes how it can behave and what physical properties it possesses. For example, whether it is a rigid body that always stays solid and undeformed or a cloth which can be folded and torn.

However, the type of the object's body is not enough for an object to start interacting. Its volume should be approximated using some kind of a physical primitive (or a set of them) — a shape. Unigine provides several types of such primitives: a box, a sphere, a capsule, a cylinder, a convex hull, or an arbitrary mesh shape. The shape is used to compute collisions between the objects.

A couple of shapes can be connected with one of the joints: fixed, ball, hinge, prismatic, cylindrical, wheel or suspension. They describe how two shapes can possibly move relative to each other.

Nodes themselves are not visible in a scene. The information on how a node is to be rendered is stored in the materials assigned to particular surfaces of the node. A material is a set of properties (states, options, parameters) and assets (2D, 3D textures), based on which surfaces are rendered, namely:

• Options. The set of options is pre-defined and invariable for all materials. Each option either enables or disables some kind of behavior. Option values for base materials, which are contained in the Unigine material library by default, are hard-coded; values for all other materials can be changed.
• States. They define conditions, basing on which Unigine selects appropriate shaders, textures, and parameters among all defined. For example, one can define a state turning on and off drawing of foam in water simulation and provide different shaders for both states (with and without foam).
• Textures. Usually, the material has several textures defined. The common reasons for it are the following:
  • A shader may need more than one texture for processing.
  • Usually, different textures are used on different render passes.
  • States also may influence the number of textures, for example, each state may require its own texture.
• Parameters. They are passed as arguments to shaders, which require them.
• Shaders. They are the very core of materials. It is shaders which actually draw the material based on different conditions. Each material is usually equipped with several shaders, and the appropriate one is chosen according to the current render pass and state.

Material Hierarchy

In Unigine, materials are organized in a hierarchy, like nodes, but are completely independent from the node hierarchy.

By default, Unigine provides a set of base materials, which are always at the top of the material hierarchy. If you need to extend properties of a base material or modify it, you can create a new material by inheriting from the required base material: the base material will pass its properties to the inherited material. Then you can add new properties or override the existing ones.

Notice

All inherited and non-overridden properties will be updated automatically, if they are updated in the parent material.

Hierarchy of Materials in the Materials Window

Look at the picture below, for example.

Cube Primitive with mesh_base Material Assigned	Cube Primitive with a Material Inherited from mesh_base

The left cube is rendered using one of the base materials from the standard Unigine material library. The right cube inherits its material from that base and simply changes 2 textures (a diffuse and a normal texture). There is no need to set other properties, as they are inherited. However, if one needs, they may change any property, just like we've changed the texture for the cube.

All material properties (except shaders) can easily be overridden in UnigineEditor. However, if you need to extend the set of existing properties or override shaders, you need to edit the XML file with your material definition manually. In this case, refer to the Material File Format article, as it contains a thorough description of material declarations in XML.

Material Libraries

For the object to be correctly integrated in the world, defining its position, inherent characteristics and outside appearance will be insufficient. The properties specify the way the object will behave and interact with other objects and the scene environment. For example, they specify if the object is interactive and whether it is a switch. For a character, properties can specify the character health points or gold amount. Thus, the properties make the nodes comply with the game/application logic.

Properties are organized according to the same principles as materials.

Property Hierarchy

Property Libraries