Cheng-Ling Lin, WPI CS Department
Introduction
Ray tracing is a versatile technique that uses the same model to integrate aspects of light/object interaction that were previously handled by seperate ad hoc algorithms - reflections, hidden surface removal and showdows.
The idea of ray tracing is tracing the light for ecah pixel, from an eye or view point through the pixel and into the scene.
Description
The method to trace a light from light source and propagate to eye or view point, is called 'backwards ray tracing'. There are infinity of rays emanate from light source and it is difficult, therefore, to trace rays in the direction of light propagation.
In the implementation we trace the rays backward from the view point through each pixel and into these scene. That is we trace in the reverse direction of light propagation. This is because we are only interestd eventually in a fixed number of rays - those that pass through the view plane - say, one per pixel.
Ray/objects intersection and color rendering are two major issues need to be evaluate carefully. There are many existing algorithm to compute the intersection of light with objects. To select a sufficient method for ray/object intersection has a significant effect of performance, because most of time for raytracing is sepnd for intersection. Due to different objects have different characteristics, it is not necessary to apply the same ray/object intersection method for different objects. For example, even the geometric method may good enough for ray/sphere intersection evaluation, but it may not sufficient for ray/quardrics intersection.
After find out the intersec point for ray and objects, the next issue is render the color for that point. Following formula is used to model the color by ray tracing.
I = Ilocal + Krg . Ireflection + Ktg . Itransmitted Where I is the final color of redendering Ilocal is the term by direct illumination Krg is the cofficient of reflection of object Ireflection is reflected light Ktg is the cofficient of transmitted or refraction of object Ireflection is trasnmitted or refracted light
phong model is a good model for local light redering. Reflection and transmitted light need apply some geometric methods and need find out the normal vector of light vector at interection point.
Conclusion
- With a simple implemenation of ray tracing, the effects of shadow, reflection, reflection and transparency are present on the final image without any further extension of algorithm.
- Potentially, we can extend ray tracing to support CSG solid modeling by checking the relationship of intersect points for the same light. What we have to do is based on the boolean operation of each object, compare every intersect point of same light to find out the existing point which nearest to the light.
- A major disadvantage of ray tracing is that its computation complexity is about square of object number. More object on the scene, much more time needed for rendering. Some optimal methods are available to enhance efficient of ray tracing. Bounding volumn, Ray coherence and 3-directional subdivision are some of well known methods.
Examples
Reference
The reference if chapter 8 of Advanced Animation and Rendering Techniques Theory and Practice by Alan Watt and Mark Watt.
cllin@cs.WPI.EDU
FAQs
The computational independence of each ray makes ray tracing amenable to a basic level of parallelization, but the divergence of ray paths makes high utilization under parallelism quite difficult to achieve in practice.
Do we really need ray tracing? ›
Raytracing is only good in areas where light shines down into a dark area so it is noticeable and looks realistic. In sunlight, it's the same thing as just regular lighting because everything is illuminated. All it does most of the time in sunlight is drop your frames.
Do I want ray tracing on or off? ›
The major tradeoff here is that ray tracing trades visuals for performance. With ray tracing turned on, your frame rate will be halved in certain games. This means that many games are nearly impossible to run with certain graphics cards, especially at higher resolutions.
What are the basic 3 rules of ray tracing? ›
Rules for Ray Tracing
A ray entering a diverging lens parallel to its axis seems to come from the focal point F. A ray passing through the center of either a converging or a diverging lens does not change direction. A ray entering a converging lens through its focal point exits parallel to its axis.
Is ray tracing worth it for 1440p? ›
The compromise may be worth it on console and PC if you're okay with 30fps (and even lower in some instances) but to maintain 60fps in 1440p and above, there's a serious cost involved that still makes ray tracing hard to justify, and difficult to recommend.
Is RTX really ray tracing? ›
NVIDIA RTX™ is the most advanced platform for ray tracing and AI technologies that are revolutionizing the ways we play and create. Over 500 top games and applications use RTX to deliver realistic graphics, incredibly fast performance, and new cutting-edge AI features like NVIDIA DLSS 3.5 with Ray Reconstruction.
What percentage of gamers use ray tracing? ›
83% of 40 Series gamers, 56% of 30-series gamers and 43% of 20-series gamers turn ray tracing on," says Nvidia.
Does ray tracing decrease FPS? ›
Yes, enabling ray tracing will reduce FPS. How much frame loss occurs is affected by the hardware capabilities of the console or PC you are playing on. You can improve this by using a GPU that supports ray tracing, as well as using the best hardware within your budget in your gaming PC.
Is AMD bad for Raytracing? ›
AMD has worked hard to improve ray tracing performance over the past few years. As we've seen above, some of AMD's cards already outperform Nvidia's in ray tracing in their respective performance segments despite the lack of dedicated RT cores. Still, the ray tracing performance is only going to get better.
What is ray tracing for dummies? ›
Purpose of Ray Tracing
Since light rays have predictable physical properties, the ray tracing algorithm attempts to calculate the exact coloring of each ray-object intersection. Ray tracing is revolutionary because it allows light rays to bounce from object to object, which is what they do in real life.
GPU: DirectX hardware ray tracing capable GPU like NVIDIA GeForce® RTX 20 Series and higher, and AMD Radeon RX 6000 Series and higher. Hardware: PC. CPU: Intel Core i5 or equivalent. RAM: At least 8 GB of RAM.
How do you start ray tracing? ›
Frame Settings
To enable ray tracing by default: Open the Project Settings window (menu: Edit > Project Settings), then select the HDRP Default Settings tab. Select Camera from the Default Frame Settings For drop-down. In the Rendering section, enable Ray Tracing.
How hard is ray tracing? ›
Ray Tracing is a very computationally intensive technique. Movie makers have traditionally relied on vast numbers of CPU based render farms that still can take multiple days to render complex special effects.
Does anyone actually care about ray tracing? ›
Ray tracing is the LEAST part of a game I am worried about after story,gameplay, bugs,graphics (to a degree) , sound mix. Yes, but no. It's amazing when it's implemented correctly, but it's too much of a power hog and drains your performance.
What is the disadvantage of ray tracing? ›
The main drawback of ray tracing is that it is currently slower than hardware-based rasterization for most scenes. In this work, we investigate the practicality of interactive ray tracing with secondary rays, such as reflection and refraction.
Why is mirror tracing so hard? ›
When you try to trace the star that you see in the mirror, your brain thinks that it is looking at the real image, not the flipped image. This is why you make mistakes. If you keep practicing, your brain will learn that you are looking at the flipped image and you will get better.
