Graphics Node

After importing a 3D CAD model to the Graphics Gallery, a graphics node appears in the Explorer, representing the graphic. When you select a node, its properties are shown in the Properties panel.

A node may have a reference to a graphics geometry and a graphics material, however it is not valid to specify only one of these two properties. Both or neither must be selected. Multiple nodes may reference the same geometry or material.

In the Properties panels, configure the following fields:

• Local and Parent Transform: Edit these values to change the graphic's position and orientation. The Properties panel also displays the World Transform for reference purposes only; it cannot be edited directly.
• Visible: Check this box to turn the graphic on or off.
• Levels of Detail: See Levels of Detail for more information.
  • Size: Specify the amount of detail sets, adjusting the amount of 3D representations of an object.
  • Graphics Geometry: Select a graphics geometry.
  • Graphics Material: Select a graphics material.
  • Maximum Distance: Select the maximum range for which the graphic remains visible to the current camera.
  • Cast Shadows: Check this box to have the graphic cast shadows. Leave this unchecked for graphics nodes representing windows.
  • Receive Shadows: Check this box to have shadows fall on the graphic. Checking this box applies shadows to all nodes sharing this node's material.

The Properties panel also displays the World Transform for reference purpose only; they cannot be edited directly.

Levels of Detail

The Levels of Detail (LOD) feature renders specific 3D model representations of an object based on the relative position of the viewer in order to obtain better performance.

This feature works on the idea that the further away an object is from the viewer, fewer details are required to represent the object on-screen. This decrease of precision in the model's representation is not necessarily seen by the user since the further an object is from the viewer, less detail is required to fill the smaller space on-screen. Note that the models' 3D representations are done by the artist, and integrating those different representations based on distance are still subject to the artist's perspective. A 3D representation refers to both the geometry and material and also other graphics parameters such as shadows. You can select a different geometry or material for each LOD set within a graphics node.

The data needed to drive different levels of detail is specified inside the graphics node in the section named Levels of Detail, described above. Each LOD set (the number of which is specified by the Size field) has a maximum distance; its minimum distance is the previous representation's maximum distance (the first item's minimum distance is 0 meters).

Transitions

When switching from one LOD to the next, the engine ensures a smooth transition over 60 frames (1 second) to reduce popping artifacts through dithering. Dithering is noise in the pixels used to represent an object on-screen. The noise is actually discarding specific pixels to make it seem as if it is disappearing and the next level is appearing. Dithering can also be used to create different colors but since both levels should have similar color palettes in a LOD context, the colors visually stay the same.

When the transition is on, there are actually two 3D representations being rendered at the same time hence the dithering effect is animated over 0.5 seconds. Also consider that all the levels of detail are loaded in memory when the node is created even though only one is actually rendered at a given point in time (excluding transitions). The mesh itself only exists once (as per the fly weight design pattern) but there is no streaming of the meshes.

LOD Field of View Correction/View Normalized Distances

The distances to the viewer are used to trigger the different levels of detail. At runtime, the distances are converted to view-normalized distances. In other words, the distances are corrected based on the camera's field of view. The reference field of view is 90 degrees.

LOD Visualization Tool

Press CTRL+ALT+L to colorize rendered graphics nodes according to the level of detail used for their rendering. Nodes that do not have a specific LOD set up for the current viewing distance will appear in red, those that have a LOD for that distance will be in green. This tool allows you to quickly identify nodes that may be too detailed for the viewing distance.

Exporters

Vortex® officially supports two formats: OpenCOLLADA and OSG. OpenCOLLADA imports with LOD as is, whereas OSG (and FLT) formats do support levels of detail but require some work order to make use of LOD in 3ds Max. Please refer to their respective documentation for more information on how to use those formats with LOD.

OSGExp

When using OSGExp's exporter in 3ds Max, you can specify different levels of detail through LOD Helper. Please refer to the LOD Helper online documentation for more details.

FLT

FLT's LOD feature is called Level of Detail Record. Please refer to the OpenFlight Scene Description Database Specification document for more details

Previous Version Compatibility

Prior to the current state of the LOD feature, the engine supported something similar at the node's level. Each node had a maximum distance and by creating multiple nodes with different maximum distances, one could achieve similar results. Vortex can load previous node's data and will behave the same way as before. It will not collapse all the different nodes into one though since there is no way to know exactly what the user wanted to accomplish using the previous design.