A Light at Both Ends of the Tunnel
November 2, 2014 12:24 pm
GPU Ray Tracing Gives New Life to 3D Workflows
As a former 3D technical director and visual effects artist in film and games - and later for a number of creative agencies - I have often joked half-heartedly about the number of years of my life wasted waiting for computers to render. Sadly, the joke is on us artists, and our employers. We wait, and we pray, for our images to come back from the render farm beautiful and perfect. When they don’t, we fix, mix, and render again. Nothing kills creativity, or production budgets, like that molasses march - render bucket, by agonizing render bucket - to the grave.
There is a better way: progressive, physically-based, globally-illuminated, GPU-accelerated ray tracing. This does what we always wished 3D rendering could do: simulate light the way it works in the real world. Sometimes referred to as brute force ray tracing, this dispenses with most of the cheats that make other kinds of renderers fast, but which also require expert users to produce good results. Such renderers, currently the staple of the creative industry, are highly biased, which means they sacrifice realism to achieve acceptable speeds. Artists use lots of hard-won experience and tricks to work around the compromises made by these renderers. Without the tricks, the renders don’t look very good.
Physically-based ray tracing drastically simplifies the work required to create great-looking photo-realistic images. To light a scene, the artist simply shines a light into it, using physically-based lights (a 100 watt light bulb acts just like the real thing) or using image-based lighting (IBL) which captures the light and environmental reflections from a real-world location into a single image. The light illuminates, diffuses, reflects and refracts, on and through realistic materials that behave as real materials do. In the case of IBL, it’s child’s play to exactly match the lighting and reflections of that real-world location. The 3D artist is no longer a technician, but a photographer, set designer, and lighter working in a virtual studio.
Brute force ray tracing allows for progressive rendering which quickly and unambiguously renders a complete, low-resolution image that resolves over time. Depending on the processing power, this can be highly interactive, meaning you can see the effect of changes instantly and unambiguously. Speaking as a production artist, it’s difficult to overstate the impact of this feature on the entire workflow. Because rendering is not limited to specialists at the last stages of the process, creative decisions made early on are no longer guesswork, and are far more likely to come out shiny and whole at the other end. In creative endeavors, iterations, are the key to perfecting an idea. This type of rendering takes the pain out of iteration.
“Sounds great,” you say, “but what does it cost?” The answer: “Computation power. Lots of it.” Brute force ray tracing requires the calculation of tens of billions of ray bounces to produce a smoothly-resolved, film-quality image. It’s something that challenges even the most powerful CPUs. But an NVIDIA GPU with CUDA – any Quadro, Tesla, or GeForce card - is a scalable supercomputer on a chip tailor made for this type of massively-parallel processing. Scalability means you can simply add more processors for more rendering power. The ultimate example is our 8-GPU rendering appliance, NVIDIA VCA, which itself can be multiplied into massively-powerful VCA clusters. NVIDIA’s GPUs, powering ray tracing rendering software such as NVIDIA’s Iray and the Chaos Group’s V-Ray RT, will transform the art of 3D, the visual effects industry, and the lives of 3D artists.
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