nVidia's New Pipeline

nVidia Quadro FX 2000 and Programmable Chips

nVidia’s Quadro FX 2000 is currently the fastest graphic boardat the high end. Its compatibility with RenderMan makes it a renderingcontender..

Writing about graphic boards is like writing about dry ice. Graphicboards change so quickly that by the time a review is published a newboard has set a new performance standard. Until recently the evolutionof these boards was largely measured in terms of sheer speed, but thelatest generation of chips aimed at visual effects professionals offerfeatures that are expected to substantially improve renderingquality.

Graphic boards power monitors and 2D and 3D graphics butMillimeter readers are really interested in high-end 3D pixelpushing. Wasting no time, here's the bottom line on Santa Clara,Calif.-based nVidia's Quadro FX 2000: It's currently the fastestgraphic board at the high end (as of March 20, 2003). The competitionis 3Dlabs Wildcat 7210 and the ATI Fire GL X1. You can check out theSPEC Viewperf 7.0 benchmarks for the Quadro FX at www.spec.org/gpc/opc.data/vp7/summary.html.

Here's the overview of the nVidia Quadro FX architecture: Begin withthe first true 128-bit floating point design. There's also an eightpipeline, programmable graphics engine and three parallel vertexengines and an on chip vertex cache supported by very fast DDR-II SDRAMmemory. Quadro FX supports up to 3840×2400 pixel resolutionmonitors (such as ViewSonic's VP 2290b) with full scene anti-aliasing.Multiple monitors are also supported (2048×1536 per analog displayor 1600×1200 per DVI digital displays). The board is fullycompliant with OpenGL 2.0 and DirectX 9.0.

Even without a honking graphics card, artists can still work inwireframe mode, but hardware based OpenGL allows artists to judge thelook of a scene in a shaded mode that roughly approximates the surfaceof models. For about a decade OpenGL was fairly crude in this regard,allowing only the most basic decisions to be made regarding lighting,composition, and color. On top of that, scenes of extreme complexitybogged OpenGL down fairly easily. Today, the latest chip technologyfrom ATI, 3Dlabs, and nVidia has reached the point that reasonablysophisticated realtime rendering is possible. It's not just thehardware that's improved, OpenGL 2.0 and DirectX 9.0 have evolved alongwith the hardware.

Until recently, realtime hardware/software has provided predefinedshading solutions, which is not what is needed at the high end. Byhigh end I mean visual effects for the movies and broadcast. Inthat world custom shaders are created for every movie project, usuallyin Pixar's photo-realistic RenderMan. The ideal realtime shadingsolution for visual effects artists would be a preview render of customshaders. This of course means that artists would have to be able towrite their realtime custom shaders in OpenGL and DirectX. Naturally,the preview shaders are only going to approximate shaders that takeminutes per frame to render, but even this can save an artist a lot oftime. Achieving this new level of visual realism requires programmablechips and a shading language written to the chips. That's where theindustry has been heading, and nVidia's Quadro FX is the most advancedgraphics board pushing this agenda.

Programmable chips from ATI, 3Dlabs, and nVidia started appearingover a year ago, but the Quadro FX really raises the bar with theirshading API called Cg. The Holy Grail in this regard is to haverealtime rendering of visual phenomenon such as colored translucence,bump maps, global illumination, and other custom shaders. nVidia isgambling that their solution will become a standard much likeRenderMan. In the best of all possible worlds, nVidia would become thefavored solution, and Cg preview shaders and the people who write themwould proliferate. nVidia already has a user base that is trading,swapping, and sharing assets and information. (See www.cgshaders.org.)In addition, publisher Addison-Wesley is publishing The Cg Tutorial:The Definitive Guide to Programmable Real-Time Graphics.

What might a nVidia-enabled pipeline look like? Effects for a motionpicture begin with “look” development. This is created by arelatively small number of art directors, tech directors, and softwareengineers. Because they are creating the elements used for finaloutput, such as shaders, texture maps, and models, their output testrenders must be full renders. When this is all approved, the large teamof artists goes to work to create the individual shots using theappropriate materials. At this point, the majority of the work islighting the CG sets. The lighting technical director places lights andshadows and tweaks individual shader attributes. Preview renders areenormously useful in judging the lighting, or at least would be ifOpenGL or DirectX could accurately preview final renders. This is wherenVidia's Cg shading language fits in. The ideal pipeline would have thenVidia Cg shaders written at the same time as the RenderMan shadersduring the look development for a movie. nVidia wrote Cg so that thesyntax is very close to RenderMan. That makes importing shaders fromRenderMan to Cg fairly easy.

Getting back to the main innovations of Quadro FX, here are thecomponents that make up the programmable board solution.

Pixel Shader 2.0 allows programming at the pixel and vertex level inhardware enabling the graphics board to take over whole types ofeffects normally handled by the general purpose CPU without all theattendant bottlenecks. For example, a pixel shader can be programmed tovary the surface properties of a surface based on light direction. Thebiggest boost in programming in the latest implementation of Cg isgreatly increased programmability. The possible number Pixel Shaderinstructions has increased from 64 to thousands. This permits thecreation of complex resolution independent procedural surfaces.

Intellisample is nVidia's feature set that enables what the companycalls “cinematic effects.” The technology includes colorcompression (lossless 4:1), dynamic gamma correction, adaptive texturefiltering, and new anti-aliasing modes.

nVidia has gone beyond both 3Dlabs and ATI with the Quadro FX bothin terms of sheer horsepower and programmability. This is a verycompetitive market, so expect a lot of leapfrogging between productreleases. The Quadro FX is clearly aimed at high-end users. Whereas theboard is a very fast graphics card for artists who don't write shaders,the high-level programmability is a major step forward for real timegraphics.

nVidia has bet on a RenderMan friendly connection, although MentalRay can also take advantage of Cg. However, it remains to be seenwhether or not nVidia's vision of how an effects pipeline should workis adopted by the major effects studios. A TD friend of mine inHollywood who is familiar with the Q FX and Cg questioned the usabilityof the shaders because lights are defined as shaders not separateobjects. He found this to be problematic for the way he works. However,he allowed that nVidia was on the right track and that the need andultimate success of some kind of realtime rendering preview wasinevitable.

Effects houses are notoriously conservative, contrary to theirreputation for cutting edge technology. In-the-trenches effectsproduction does not permit wholesale tampering with the pipeline justto include the latest technology. What makes nVidia's initiativecompelling is its targeting of the high end through a RenderMan savvyapproach. This is still in the early stages, but nVidia is takingserious steps to get us there eventually.

Nvidia is the first board to introduce a high-level realtime shadinglanguage to the professional and prosumer market, but this idea is farfrom new. Years ago RenderMan had the idea of a realtime,hardware-assisted render solution in the API called Quick RenderMan.History aside, the Pixar/nVidia lineage is real today because nVidiamerged with Exluna, developers of Entropy, a new shader languagewritten by ex-Pixar personnel, including Larry Gritz of BMRT (Blue MoonRendering Tools). This saved nVidia from a copyright infringement suitby RenderMan, and has opened the door to a new generation of graphicboards that will change the way visual effects are designed.