Although 3-D-graphics applications have been around for some time, they have never been plebeian. If you wanted 3-D graphics, you had to use workstations. However, inexpensive 3-D-graphics accelerators that render complex 3-D images are about to transform the desktop PC in-to a sophisticated workstation. Neil Trevitt, vice president of marketing for 3Dlabs, defines an entry-level workstation as one that can draw 300,000 shaded polygons/-sec. Devices with this performance enable myriad ap-plications: virtual reality, animation, medical and engineering visualization, CAD, and engineering design, to name a few.

Until recently, you could not use PCs for many of these applications. For example, realistic flight-simulation software would run only on graphics workstations selling for more than $50,000. The reasons involve the system's performance requirements. For example, a flight simulator's head-up display places two requirements on a system: to update the outside view from a plane's cockpit in real time and to render the scene as realistically as possible. Although only high-performance graphics systems can perform such rendering, now such systems can be PC-based--with the addition of graphics accelerators from manufacturers such as Cirrus Logic, Media Labs, S-MOS Systems, and 3Dlabs. The companies claim their products will bring high-performance, affordable 3-D graphics to PCs. They expect such accelerators to be available on 60% of all PCs by 1997.

One product, the 3DMedia SX, a $2000 plug-in graphics-accelerator card from Media Labs Inc of Houston, promises flight simulation on a PC. The board also suits engineering-visualization and -design, CAD, virtual-reality, and animation applications. As a rasterizer, the board efficiently renders realistic images for animation and simulation applications.

Based on 3Dlabs' Glint 300SX graphics accelerator, the card supports most display resolutions, color depths, and display types. In addition, the card provides high-end graphics features, such as a 24-bit depth buffer; a stencil mask; fast-clear planes; and 32 bits for red, green, blue, and alpha (RGBA) true-color output. (Alpha makes the card suitable for composite-image applications.) Users can employ the board as a system adapter via the IEEE-P1275 OpenBoot draft. The board contains a 64-kbyte ROM with pro-cessor-specific executable or symbolic boot code for each of the operating systems that the board supports.

The device also maintains output-format flexibility. For example, the board, including the video palette, supports any color depth the Glint chip supports. All output resolutions support double buffering. The only limitation to image resolution is the 4-Mbyte video memory: Because 1600×1280-pixel resolution requires a 2-Mbyte memory, double buffering requires a 4-Mbyte memory.

The design includes a studio-quality encoder that makes the board suit such applications as manipulating and modifying digital-image data by adding textual information, fog, or special effects for nonlinear video editing. More important, the encoder allows you to store presentations on VHS tape. You can also select NTSC, PAL, or S-video output in square-pixel, CCIR601, 4X, or any custom resolution from a pulldown menu.

Proprietary logic on the system board controls data flow and video formats, allowing interlaced, noninterlaced, stereoscopic, field-sequential RGB and virtual-reality display. Hardware, rather than software, supports these display types, reducing or eliminating software overhead. A frequency synthesizer for graphics applications supports any output frequency or resolution. A proprietary gate array offers line-lock capability for some operating systems. Line-lock lets you open a 3-D graphics window with independent color depth in the VGA display. A fast-clear feature enhances animation.

An analog VGA pass-through on the Media Labs board eliminates the pixel-related restrictions of traditional VGA pass-through implementations. Wil de Bont, president of Media Labs, believes that, as 3-D graphics becomes more important, interest in VGA compatibility will wane. "All new operating systems will support a more general boot sequence, which is not tied to the VGA BIOS," he says. In line with that philosophy, the 3DMedia SX supports such environments as OpenGL, Open Inventor, AutoCAD, Microstation, X-Windows, PEX, OS/2, Windows NT, Windows 3.xx, and Windows95. A proprietary library provides functions that standard application-programming interfaces (APIs), such as OpenGL, don't support.

Chips also do the job

Some manufacturers are taking a chip approach to speeding graphics. For example, Cirrus, S-MOS, and 3Dlabs and have developed ICs that accelerate 3-D graphics. Both Cirrus and 3Dlabs and have devices that do the rendering portion of the 3-D graphics.

Cirrus Logic offers a three-chip graphics accelerator ($150). The set includes a VGA controller and VESA VL-Bus/PCI interface (CL-GD5471), a palette DAC (CL-GD5472), a 2-D graphical user interface, and a 3-D rendering accelerator (CL-GD5470). The CLGD-5470 handles 250,000 shaded, alpha-blended polygons/sec. All the chips are available in 226-pin QFPs.

S-MOS's SPC1500 ($450), a single-chip, 3-D-graphics geometry processor suits point-of-view movement, perspective, clipping, lighting, texture-mapping, and fog-computation applications (Fig 1). The product complies with OpenGL and Programmers Hierarchical Interactive Graphics System (PHIGS+) graphics-application-programming languages.

The 223-pin pin-grid array comprises a floating-point/integer ALU, multiply and accumulate units, a DMA processor for data fetches, a microcode ROM, and a RAM cache to store custom instructions. The 33-MHz, asynchronous, DMA-mastering bus has a 32-bit CPU interface. Secondary 32-bit synchronous input and output buses both operate at 50 MHz to move data to and from the rasterization circuitry. The chip lets you implement rasterization with custom circuitry or using the SPC1503 pixel-processor chip. It also lets you easily partition 3-D-related tasks in a graphics environment. The host CPU normally handles the 3-D API, geometry, lighting, and delta calculations. The graphics processor performs rasterization, Gouraud shading, z buffering, texture mapping, alpha blending, antialiasing, and dithering.

The SPC1500 speeds 3-D-graphics performance, which can be painfully slow, even on high-performance µPs, according to Robert Wong, executive director for graphics and standard products at S-MOS. He claims that adding an SPC1500 to a 60-MHz Pentium-based system speeds the following common 3-D-graphics operations: multiply-and-accumulate operations (about eight times faster than without the chip), transform processing (nearly four times faster), matrix multiplications (five times faster), and xyz-vector-lighting calculations (more than 10 times faster).

3Dlabs' Glint 300SX graphics processor ($150) for rendering operations draws 300,000 shaded, z-buffered, antialiased, translucent polygons/sec and provides 24-bit 2- and 3-D acceleration, an on-chip Peripheral Component Interconnect (PCI) interface, and lookup-table-DAC control.

3Dlabs' Trevitt claims that the Glint API spans a broad spectrum of applications. At one end is CAD-related 3-D graphics using OpenGL, which requires accurate rendering. At the other end of the spectrum are games, which require less accurate geometry calculations, allowing engineers to use short cuts in developing games. Because the product is a single chip, board and system manufacturers can lower the cost and increase the performance of 3-D products for CAD, multimedia, simulation, virtual reality, interactive TV, and games. The company will provide reference board designs, manufacturing kits, and software support in the form of drivers for Win32, X11, and OpenGL, as well as application drivers, such as AutoCAD and Microstation.

References

1. Glint Hardware Reference Manual, Version 1.5.

2. Glint Programmer's Reference Manual, Version 2.0.

3. Glint Architecture Overview, Version 1.6a.

4. Foley, van Dam, Feiner, and Hughes. Computer Graphics: Principles and Practice, Second Edition, Addison-Wesley, November 1992.