OptiX

OptiX is a toolkit for programmers, developed by the graphics card company Nvidia. It helps create highly realistic images on a computer. To do this, the computer traces individual light rays: for each pixel, it calculates where the light comes from, which objects it reflects off, and where it is attenuated. This process is called raytracing, or ray tracing. It looks significantly more realistic than older tricks, but costs an enormous amount of computing time. OptiX takes over exactly the parts of this calculation that are particularly tricky and particularly expensive.

Why Nvidia gives raytracing away for free

Films like Pixar or Marvel productions consist of computed images. In the past, such calculations ran for days on large server farms with ordinary processors. A graphics card can perform many thousands of small calculations simultaneously. Light rays are ideal for this, because each ray can be traced independently of the others. OptiX was one of the first ways to make this capability usable for raytracing.

For Nvidia, the toolkit is a business model. It is free, but only runs on Nvidia hardware. Anyone equipping a film studio or an architecture firm therefore buys Nvidia cards. CUDA works similarly, Nvidia’s general-purpose programming environment for graphics cards, on which OptiX is built. This same binding of software to proprietary chips explains a large part of the company’s stock market value.

A common misconception: OptiX is not a rendering program that you launch yourself. It is a middle layer. Well-known programs like Blender, V-Ray, or Arnold rely on it without users noticing anything.

The search for the hit triangle

Objects in 3D scenes are made up of triangles, often hundreds of millions of them. For each light ray, the computer needs to know which triangle it hits first. Checking every triangle individually would be impossible. Instead, OptiX arranges the scene into nested boxes, a search tree. The ray first checks coarse boxes and only descends further where it hits one.

This search is the actual core of OptiX. Since 2018, Nvidia graphics cards have had dedicated circuits for this, the so-called RT cores. OptiX gives programs access to this hardware. The result is a leap in speed, not a minor improvement.

What happens at a hit point is decided by the programmer. They write small pieces of code that are called upon impact. This code specifies, for example, whether the surface is matte or reflective and which ray is sent out next. OptiX takes care of geometry and management, while the appearance of the material remains the application’s responsibility.

From Blender to AI training images

OptiX is most visible in 3D software. In Blender, a free program for 3D graphics, there is an option called Cycles with OptiX when rendering. Anyone who selects it waits minutes instead of hours on a suitable computer. Architects, product designers, and advertising agencies work with it daily.

OptiX is encountered less often in video games. There, raytracing usually runs via DirectX or Vulkan, i.e., via interfaces that also support AMD cards. OptiX targets applications where image quality matters more than millisecond-level response times.

An interesting newer area of application is artificial intelligence. Anyone wanting to teach a robot or a self-driving car to see needs millions of sample images. Some of these are now generated on a computer, because it is cheaper and safer than real test drives. Nvidia’s simulation platform Omniverse uses OptiX for this. So in news about AI training or digital twins, this technology often lurks in the background.