The Materials and Geometry Format

Version 1.0, May 1995

Greg Ward, Lawrence Berkeley Laboratory, GJWard@Lbl.Gov

Introduction

What makes MGF special?

There are three principal reasons to use MGF as an input language for lighting simulation and physically-based rendering:

  1. It's the only existing format that describes materials physically.
  2. It is endorsed by the Illuminating Engineering Society of North America (IESNA) as part of their LM-63-1995 standard for luminaire data.
  3. It's easy and fun to support since it comes with a standard parser and sample scenes and objects at the web site, http://radsite.lbl.gov/mgf/HOME.html.
The standard parser provides both immediate and long-term benefits, since it presents a programming interface that is more stable even than the language itself. Unlike AutoCAD DXF and other de facto standards, a change to the language will not break existing programs. This is because the parser gives the calling software only those entities it can handle. If the translator understands only polygons, it will be given only polygons. If a new geometric primitive is included in a later version of the standard, the new parser that comes with it will still be able to express this entity as polygons. Thus, the urgency of modifying code to support a changing standard is removed, and long-term stability is assured.

This notion of extensibility is a cornerstone of the format, and it goes well beyond the extensibility of other languages because is guarantees that new versions of the standard will not break existing programs, and the new information will be used as much as possible. Other languages either require that all translators stay up to date with the latest standard, or allow forward compatibility by simply ignoring new entities. In MGF, if NURBS are added at some point and the translator or loader does not handle them directly, the new version of the parser will automatically convert them to smoothed polygons without changing a single line of the calling program. It is merely necessary to link to the new library, and all the new entities are supported.

What does MGF look like?

MGF's place in the world of standards

MGF Basics

Entities and Contexts

Hierarchical Contexts and Transformations

Detailed MGF Example

MGF Entity Reference

MGF Translators

MGF Parser Library

Application Notes

Relation to Standard Practices in Computer Graphics

Relation to IESNA LM-63 and Luminaire Catalogs

Credits