In the world of modern PC graphics hardware, all the buzz right now is about a rendering technique call ray tracing. This is mainly due to the release of Nvidia’s RTX development platform and Microsoft announcing its compatible DirectX Raytracing (DXR) API for DirectX 12 for Windows, both having taken place earlier this year. DXR allows Windows developers to utilize modern GPUs to accelerate the process of ray tracing a 3D environment in real time. This is big news for gamers because ray tracing allows for a much more realistic rendering of light and it’s real-world behavior within a 3D scene. Or…it will be as, presently, only a few games have been updated to utilize the rendering features that DXR brings to the table. And there aren’t a lot of GPUs out there yet with hardware designed with DXR in mind, directly targeting the acceleration of ray tracing calculations. Even still, it seems that ray tracing has become the new hotness and it’s even driven some observers fairly well out of their mind. It’s what’s new in tech.

Or is it?

Reading through today’s tech media, the casual observer could be forgiven for thinking so. One of the first articles I read about Nvidia’s new GPU’s (MarketWatch, Aug. 14) stated,

Nvidia on Monday announced its next-generation graphics architecture called Turing, named after the early-20th century computer scientist credited as the father of artificial intelligence.

The new graphics processing unit (GPU) does more than traditional graphics workloads, embedding accelerators for both artificial-intelligence (AI) tasks and a new graphics rendering technique called ray tracing.

But ray tracing is not a new technique. In fact, it’s almost as old as the earliest of 3D computer graphics techniques.

So, what is ray tracing? As A.J. van der Ploeg describes in his “Interactive Ray Tracing: The Replacement of Rasterization?” [ PDF ],

In computer graphics, if we have a three dimensional scene we typically want to know how our scene looks trough a virtual camera. The method for computing the image that such a virtual camera produces is called the rendering method.

The current standard rendering method, know as rasterization, is a local illumination rendering method. This means that only the light that comes directly from a light source is taken into account. Light that does not come directly from a light source, such as light reflected by a mirror, does not contribute to the image.

In contrast ray tracing is a global illumination rendering method. This means that light that is reflected from other surfaces, for example a mirror, is also taken into account. This is essential for advanced effects such as reflection and shadows. For example if we want to model a water surface reflecting the scene correctly we need a global illumination rendering method. With a local illumination rendering method the light from the water surface can only be determined by the light directly on it, not the light from the rest of the scene and thus we will see no reflections.
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Ray tracing works by following the path of light. We follow the path of rays of light, i.e. lines of light. For an example of such a path consider a ray of light from your bathroom light­bulb. This particular ray of light hits your chin, some of it is absorbed, and the rest of the light is reflected in the colour of your skin. The reflected ray is then reflected again by the mirror in your bathroom. This ray then hits your retina, which is useful otherwise you would not see your self shaving. In exactly this way a ray of light in the virtual camera gives the colour of one pixel.

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