OptiX

Key takeaways

OptiX belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect OptiX to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of OptiX from memory before moving on to harder problems.

Reference excerpt

Nvidia OptiX (OptiX Application Acceleration Engine) is a ray tracing API that was first developed around 2009. The computations are offloaded to the GPUs through either the low-level or the high-level API introduced with CUDA. CUDA is only available for Nvidia's graphics products. Nvidia OptiX is part of Nvidia GameWorks. OptiX is a high-level, or "to-the-algorithm" API, meaning that it is designed to encapsulate the entire algorithm of which ray tracing is a part, not just the ray tracing itself. This is meant to allow the OptiX engine to execute the larger algorithm with great flexibility without application-side changes. Commonly, video games use rasterization rather than ray tracing for their rendering. According to Nvidia, OptiX is designed to be flexible enough for "procedural definitions and hybrid rendering approaches". Aside from computer graphics rendering, OptiX also helps in optical and acoustical design, radiation and electromagnetic research, artificial intelligence queries and collision analysis.

Ray tracing with OptiX

OptiX works by using user-supplied instructions (in the form of CUDA kernels) regarding what a ray should do in particular circumstances to simulate a complete tracing process. A light ray (or perhaps another kind of ray) might have a different behavior when hitting a particular surface rather than another one, OptiX allows to customize these hit conditions with user-provided programs. These programs are written in CUDA C or directly in PTX code and are linked together when used by the OptiX engine. In order to use OptiX a CUDA-capable GPU must be available on the system and the CUDA toolkit must be installed. Using the OptiX engine in a ray tracing application usually involves the following steps:

Defining programs for ray generation (e.g. rays can be shot in parallel, in a perspective fashion or like a gradient field), ray missing (when a ray doesn't intersect any object), an optional exception program (when the ray cannot be shot for some reason), a bounding box program (the program that provides a bounding box intersection test for a given object) and an intersection program. Several examples for these programs are available with the program's SDK

Bounding box programs are used to define bounding volumes used to accelerate ray tracing process within acceleration structures as kd-trees or bounding volume hierarchies

Create material any hit and closest hit programs: these two programs determine a ray behavior when encountering its first intersection (closest hit) or a generic intersection (any hit)

Define buffers, variables that might be used inside the supplied programs. Buffers are memory areas that allow host code (i.e. normal CPU code) to communicate with device code (i.e. the code that gets executed on the GPU) and vice versa. Variables are OptiX's internal way of communicating and using buffers to transfer data back and forth. Define the OptiX hierarchy of geometry objects, groups, selectors and other nodes to generate a tree graph of the entire scene to be rendered

In order to render a complex scene or trace different paths for any ray OptiX takes advantage of GPGPU computing by exploiting Nvidia CUDA platform. Since the process of shooting rays and setting their behavior is highly customizable, OptiX may be used in a variety of other applications aside from ray tracing.

OptiX Prime Starting from OptiX 3.5.0 a second library called OptiX Prime was added to the bundle which aims to provide a fast low-level API for ray tracing - building the acceleration structure, traversing the acceleration structure, and ray-triangle intersection. Prime also features a CPU fallback when no compatible GPU is found on the system. Unlike OptiX, Prime is not a programmable API, so lacks support for custom, non-triangle primitives and shading. Being non-programmable, OptiX Prime does not encapsulate the entire algorithm of which ray tracing is a part. Thus, Prime cannot recompile the algorithm for new GPUs, refactor the computation for performance, or use a network appliance like the Quadro VCA, etc.

Software using OptiX Blender has OptiX support since version 2.81 (7.1 in 2.92) The Blender Add-on D-NOISE uses OptiX binaries for AI-accelerated denoising At SIGGRAPH 2011 Adobe showcased OptiX in a technology demo of GPU ray tracing for motion graphics. At SIGGRAPH 2013 OptiX was featured in Pixar's realtime, GPU-based lighting preview tool. OptiX has been integrated into the GameWorks developers library along with PhysX and other CUDA powered graphics engines and frameworks. Adobe After Effects CC Daz Studio had OptiX Prime Acceleration since its Iray integration, however support was removed in version 4.12.1.8 Luxrender 2.5: up to 600% acceleration

Illustrations

Worked examples

Example 1 — a first encounter with OptiX

Start with the simplest possible case. Write down what OptiX claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to OptiX before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about OptiX ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of OptiX

In research: OptiX appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses OptiX in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: OptiX is common in secondary-school and first-year university syllabi. It links to neighbouring topics Nvidia software, Proprietary commercial software for Linux, Proprietary freeware for Linux, so understanding it makes those chapters shorter.
In everyday life: Look for OptiX outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study OptiX in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what OptiX means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain OptiX out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is OptiX in simple terms?

Nvidia OptiX (OptiX Application Acceleration Engine) is a ray tracing API that was first developed around 2009. The computations are offloaded to the GPUs through either the low-level or the high-level API introduced with CUDA.

Why does OptiX matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study OptiX?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on OptiX.