VRML Browsers and Other 3D Apps

• Cosmo Player
  
• WorldView/MSVRML
  
• blaxxun Contact
  
• Viscape Universal
  
• LibVRML97/Lookat
  
• FreeWRL
  
• VRMLView
  
• Other VRML Browsers
  
• Other 3D Applications
  

VRML, the Virtual Reality Modeling Language, is a file format and a language for defining three-dimensional virtual objects, their appearances and their behaviors. As of early 1999, it has seen two major versions, and the design of a third is currently underway. Version 1.0 included little more than static geometry and never saw wide use. Version 2.0, released in August 1996 and approved as an ISO/IEC international standard in December 1997, added animation, scripting, and a much more rigorous specification of all aspects of the format. It also mandated PNG as one of two image formats required for minimal conformance. (JPEG was the other.) No doubt due to PNG's rampant popularity,[39] VRML 2.0--or VRML97, as the ISO standard is known--achieved dramatically greater recognition and acceptance than VRML 1.0, with shipments of VRML97 browsers reaching levels of between 25 million and 75 million units by the autumn of 1998.

[39] Well, in part, anyway...

How is PNG actually used in a 3D, text-based file format? A complete answer would require considerable discussion of 3D rendering engines, CPU and memory performance, Moore's Law, and so forth. But in a nutshell, VRML is designed for interactive 3D--particularly Web-based, immersive, interactive 3D. A truly realistic animated object, such as the dinosaurs in the movie ''Jurassic Park'' or the flying cow in "Twister," would require far more computational power to render in ``real time'' at reasonable frame rates (say, more than 15 frames per second) than even today's fastest processors can manage. And that's just one object; imagine every rock, tree, bug, cloud, and blade of grass rendered at the same level of realism, responding to dynamic effects like wind, sunlight, and other moving objects. Doing all of that is likely to remain out of reach of typical personal computers for a decade or more.

As a result, VRML is all about trickery, and one of the most efficient forms of 3D trickery is known as texture-mapping. Instead of creating a highly detailed 3D object out of many tiny polygons, it is often possible to create a very realistic approximation of it out of just a few polygons, with an appropriate image (or texture) drawn over them. Anyone who has studied a 3D game like Quake or Descent is probably familiar with the concept; the buildings and even the characters are actually quite crude, but with stone or metal textures and lighting effects applied, the world suddenly becomes a realistically gloomy dungeon or sewer system or a bright and shiny high-tech laboratory.[40]

[40] In the case of characters, animation and sound effects also aid the illusion tremendously.

PNG's role in this is as a format for the textures. VRML references PNG images in much the same way that HTML pages do, via a URL that points at the PNG file. A VRML viewer then fetches the PNG image, applies it to the polygons of the relevant object according to the rules in the VRML specification, and displays the result within the 3D scene.

Because both raw VRML objects and PNG textures support not only colors but also transparency and partial transparency (loosely, ``translucency''), a number of interesting effects are possible. On the other hand, the potential number of interactions and combinations is immense, so the VRML97 spec defines some basic rules regarding VRML materials and how textures modify them:

• A one-component texture--i.e., grayscale--absorbs and modulates the underlying polygon's color and transparency. For example, an opaque yellow triangle with a gray, gradient texture applied to it will turn into an opaque triangle with a yellow gradient. The orientation of the gradient depends on how the author specified the coordinates of the texture.

• A two-component texture (grayscale plus an alpha channel) absorbs the underlying polygon's color, but any transparency in the base polygon is replaced by the transparency of the texture.

• A three-component texture (RGB color) replaces the underlying polygon's color but inherits its transparency (if any); a blue texture applied to a red polygon with 50% transparency turn its into a 50% transparent blue polygon.

• A four-component texture (RGB plus an alpha channel, or RGBA) completely overrides the color and transparency of the underlying polygon.