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Омид Рахмат,  10 января 2000 Страница:   1 2 3 4

Introduction

One of the most interesting primers, and explanations of scene graphs I have read is provided here. Essential reading for the 3D enthusiast.

Although I have the grace and elegance of motion of lead piping, I do take the odd class in Tae Kwon Do, the Korean martial art, and I am fortunate to have studied under Master Wes Bethel. I don't say this as some sort of idle boast, but Mr. Bethel is also an extraordinary engineer and scientist. And, this will make you even more sick, he knows more about 3D graphics than most. So, it is a pleasure for me to introduce the following article from Mr. Bethel on scene graphs. I think it is essential reading for anyone with a deep interest in 3D graphics.

The following article is reproduce with the kind permission of Wes Bethel, Chief Technology Officer, R3vis Corporation. He can be contacted at wbethel@r3vis.com, or for more information, visit http://www.r3vis.com.

What Do All Graphics Applications Have in Common?

Some form of scene graph technology lies at the heart of every graphics application. Despite such a central role in so many applications, this fundamental technology is often misunderstood. In this article, we provide an overview of scene graph technology along with glimpses of how it is used today and how it could affect future applications.

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What Do You Get When You Cross a Mathematician and Hollywood Producer?

The term "scene graph" is the by-product of a collision between the fields of discrete mathematics, computer graphics and cinematography. A "scene" in the computer graphics world refers to a collection of objects, their relationship to one another, and a definition of how a viewer sees the objects in the scene. In cinematography, scenes include things like cameras, lights, actors, backgrounds, and so forth.

To most people, a "graph" is something that shows information, such as the performance of the Dow Jones Industrial average over some period of time. However, we're interested in a different type of graph, one from the world of mathematics. The mathematical, or discrete graph, represents a system built from two fundamental entities: nodes and edges. A familiar example of a visual representation of a discrete graph is a family tree. The nodes of the family tree are people, and edges represent the parent-child relationship. This type of graph is a commonly used tool in discrete mathematics, which is the study of states, and transitions from one state to another.

Of all the different types of discrete graphs, the scene graph is a directed, acyclic graph, sometimes called a "tree." There are many specialized properties of this type of graph, illustrated by the directed, acyclic graph of the family tree. Acyclic means that you can't be the parent of your grandfather; there are no loops in the family tree. Directed means that the parent-child relationship is a one-way proposition. The edge between your parent and you represents a special kind of relationship that exists in just one direction.

The scene graph is also a directed, acyclic graph, or tree, consisting of nodes and edges. Elements of the scene that have some data component, such as viewable objects, light sources, camera locations and so forth are contained in the graph nodes. The edges in the scene are like the edges in the family tree, they define not only parent-child relationships, but also, and more importantly, scope of influence of scene parameters.

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Introduction What Do All Graphics Applications Have in Common? What Do You Get When You Cross a Mathematician and Hollywood Producer? Scene Graph Systems Software Why are Scene Graph Systems Useful? Convenience How Many Widgets? Extensibility Meets Applications Needs Future Applications  Обсуждение в Клубе Экспертов THG