This has forced them to compromise, viewing a low-fidelity visualization while creating and not seeing the final correct image until hours later after rendering on a CPU-based render farm. The ray-tracing algorithm takes an image made of pixels. between zero and the resolution width/height minus 1) and $$w$$, $$h$$ are the width and height of the image in pixels. To follow the programming examples, the reader must also understand the C++ programming language. An image plane is a computer graphics concept and we will use it as a two-dimensional surface to project our three-dimensional scene upon. All done in Excel, using only formulae with the only use of macros made for the inputting of key commands (e.g. 10 Mar 2008 Real-Time Raytracing. The percentage of photons reflected, absorbed, and transmitted varies from one material to another and generally dictates how the object appears in the scene. It is also known as Persistence of Vision Ray Tracer, and it is used to generate images from text-based scene description. If we go back to our ray tracing code, we already know (for each pixel) the intersection point of the camera ray with the sphere, since we know the intersection distance. Going over all of it in detail would be too much for a single article, therefore I've separated the workload into two articles, the first one introductory and meant to get the reader familiar with the terminology and concepts, and the second going through all of the math in depth and formalizing all that was covered in the first article. In general, we can assume that light behaves as a beam, i.e. But we'd also like our view plane to have the same dimensions, regardless of the resolution at which we are rendering (remember: when we increase the resolution, we want to see better, not more, which means reducing the distance between individual pixels). by Bacterius, posted by, Thin Film Interference for Computer Graphics, http://en.wikipedia.org/wiki/Ray_tracing_(graphics), http://www.scratchapixel.com/lessons/3d-basic-lessons/lesson-7-intersecting-simple-shapes/ray-sphere-intersection/, http://mathworld.wolfram.com/Projection.html, http://en.wikipedia.org/wiki/Lambert's_cosine_law, http://en.wikipedia.org/wiki/Diffuse_reflection, the light ray leaves the light source and immediately hits the camera, the light ray bounces off the sphere and then hits the camera, how much light is emitted by the light source along L1, how much light actually reaches the intersection point, how much light is reflected from that point along L2. For example, one can have an opaque object (let's say wood for example) with a transparent coat of varnish on top of it (which makes it look both diffuse and shiny at the same time like the colored plastic balls in the image below). Log In Sign Up. Together, these two pieces provide low-level support for “raw ray tracing.” Optical fibers is a small, easy to use application specially designed to help you analyze the ray tracing process and the changing of ray tracing modes. Ray tracing is a technique that can generate near photo-realistic computer images. Simplest: pip install raytracing or pip install --upgrade raytracing 1.1. Sometimes light rays that get sent out never hit anything. An object can also be made out of a composite, or a multi-layered, material. Meshes will need to use Recursive Rendering as I understand for... Ray Tracing on Programming // Shaders that are triggered by this must operate on the same payload type. This makes sense: light can't get reflected away from the normal, since that would mean it is going inside the sphere's surface. But since it is a plane for projections which conserve straight lines, it is typical to think of it as a plane. So, applying this inverse-square law to our problem, we see that the amount of light $$L$$ reaching the intersection point is equal to: $L = \frac{I}{r^2}$ Where $$I$$ is the point light source's intensity (as seen in the previous question) and $$r$$ is the distance between the light source and the intersection point, in other words, length(intersection point - light position). So does that mean the reflected light is equal to $$\frac{1}{2 \pi} \frac{I}{r^2}$$? The "view matrix" here transforms rays from camera space into world space. If we continually repeat this process for each object in the scene, what we get is an image of the scene as it appears from a particular vantage point. Otherwise, there wouldn't be any light left for the other directions. In effect, we are deriving the path light will take through our world. Knowledge of projection matrices is not required, but doesn't hurt. Welcome to this first article of this ray tracing series. Doing so is an infringement of the Copyright Act. Simply because this algorithm is the most straightforward way of simulating the physical phenomena that cause objects to be visible. In this particular case, we will never tally 70 absorbed and 60 reflected, or 20 absorbed and 50 reflected because the total of transmitted, absorbed and reflected photons has to be 100. well, I have had expirience with ray tracing, and i really doubt that it will EVER be in videogames. If a group of photons hit an object, three things can happen: they can be either absorbed, reflected or transmitted. Although it seems unusual to start with the following statement, the first thing we need to produce an image, is a two-dimensional surface (this surface needs to be of some area and cannot be a point). Not quite! Up Your Creative Game. Linear algebra is the cornerstone of most things graphics, so it is vital to have a solid grasp and (ideally) implementation of it. This series will assume you are at least familiar with three-dimensional vector, matrix math, and coordinate systems. In OpenGL/DirectX, this would be accomplished using the Z-buffer, which keeps track of the closest polygon which overlaps a pixel. How easy was that? What we need is lighting. An object's color and brightness, in a scene, is mostly the result of lights interacting with an object's materials. What about the direction of the ray (still in camera space)? Only one ray from each point strikes the eye perpendicularly and can therefore be seen. To begin this lesson, we will explain how a three-dimensional scene is made into a viewable two-dimensional image. It was only at the beginning of the 15th century that painters started to understand the rules of perspective projection. A wide range of free software and commercial software is available for producing these images. Mathematically, we can describe our camera as a mapping between $$\mathbb{R}^2$$ (points on the two-dimensional view plane) and $$(\mathbb{R}^3, \mathbb{R}^3)$$ (a ray, made up of an origin and a direction - we will refer to such rays as camera rays from now on). Ray tracing has been used in production environment for off-line rendering for a few decades now. If you do not have it, installing Anacondais your best option. Ray tracing in Excel; 100+ Free Programming Books (all languages covered, all ebooks are open-sourced) EU Commision positions itself against backdoors in encryption (german article) Food on the table while giving away source code [0-day] Escaping VirtualBox 6.1; Completing Advent of Code 2020 Day 1 … We like to think of this section as the theory that more advanced CG is built upon. Because light travels at a very high velocity, on average the amount of light received from the light source appears to be inversely proportional to the square of the distance. This is the opposite of what OpenGL/DirectX do, as they tend to transform vertices from world space into camera space instead. In order to create or edit a scene, you must be familiar with text code used in this software. For now, I think you will agree with me if I tell you we've done enough maths for now. Now block out the moon with your thumb. We haven't really defined what that "total area" is however, and we'll do so now. If the ray does not actually intersect anything, you might choose to return a null sphere object, a negative distance, or set a boolean flag to false, this is all up to you and how you choose to implement the ray tracer, and will not make any difference as long as you are consistent in your design choices. Like many programmers, my first exposure to ray tracing was on my venerable Commodore Amiga.It's an iconic system demo every Amiga user has seen at some point: behold the robot juggling silver spheres! We have received email from various people asking why we are focused on ray-tracing rather than other algorithms. With this in mind, we can visualize a picture as a cut made through a pyramid whose apex is located at the center of our eye and whose height is parallel to our line of sight (remember, in order to see something, we must view along a line that connects to that object). We can increase the resolution of the camera by firing rays at closer intervals (which means more pixels). In fact, and this can be derived mathematically, that area is proportional to $$\cos{\theta}$$ where $$\theta$$ is the angle made by the red beam with the surface normal. an… It has to do with the fact that adding up all the reflected light beams according to the cosine term introduced above ends up reflecting a factor of $$\pi$$ more light than is available. So, how does ray tracing work? So we can now compute camera rays for every pixel in our image. This is a common pattern in lighting equations and in the next part we will explain more in detail how we arrived at this derivation. we don't care if there is an obstacle beyond the light source). In other words, when a light ray hits the surface of the sphere, it would "spawn" (conceptually) infinitely many other light rays, each going in different directions, with no preference for any particular direction. This question is interesting. Ray-Casting Ray-Tracing Principle: rays are cast and traced in groups based on some geometric constraints.For instance: on a 320x200 display resolution, a ray-caster traces only 320 rays (the number 320 comes from the fact that the display has 320 horizontal pixel resolution, hence 320 vertical column). In other words, if we have 100 photons illuminating a point on the surface of the object, 60 might be absorbed and 40 might be reflected. But it's not used everywhere. Part 1 lays the groundwork, with information on how to set up Windows 10 and your programming … The equation makes sense, we're scaling $$x$$ and $$y$$ so that they fall into a fixed range no matter the resolution. So, in the context of our sphere and light source, this means that the intensity of the reflected light rays is going to be proportional to the cosine of the angle they make with the surface normal at the intersection point on the surface of the sphere. In this part we will whip up a basic ray tracer and cover the minimum needed to make it work. wasd etc) and to run the animated camera. Now that we have this occlusion testing function, we can just add a little check before making the light source contribute to the lighting: Perfect. By following along with this text and the C++ code that accompanies it, you will understand core concepts of Forward Ray Tracing Algorithm. As you may have noticed, this is a geometric process. Figure 1 Ray Tracing a Sphere. We know that they represent a 2D point on the view plane, but how should we calculate them? An overview of Ray Tracing in Unreal Engine 4. To start, we will lay the foundation with the ray-tracing algorithm. We will call this cut, or slice, mentioned before, the image plane (you can see this image plane as the canvas used by painters). Some trigonometry will be helpful at times, but only in small doses, and the necessary parts will be explained. a blog by Jeff Atwood on programming and human factors. One of the coolest techniques in generating 3-D objects is known as ray tracing. The exact same amount of light is reflected via the red beam. Ray-tracing is, therefore, elegant in the way that it is based directly on what actually happens around us. Ray tracing performs a process called “denoising,” where its algorithm, beginning from the camera—your point of view—traces and pinpoints the most important shades of … Game programmers eager to try out ray tracing can begin with the DXR tutorials developed by NVIDIA to assist developers new to ray tracing concepts. Using it, you can generate a scene or object of a very high quality with real looking shadows and light details. Before we can render anything at all, we need a way to "project" a three-dimensional environment onto a two-dimensional plane that we can visualize. This a very simplistic approach to describe the phenomena involved. Thus begins the article in the May/June 1987 AmigaWorld in which Eric Graham explains how the … Consider the following diagram: Here, the green beam of light arrives on a small surface area ($$\mathbf{n}$$ is the surface normal). Implementing a sphere object and a ray-sphere intersection test is an exercise left to the reader (it is quite interesting to code by oneself for the first time), and how you declare your intersection routine is completely up to you and what feels most natural. Possibly the simplest geometric object is the sphere. The technique is capable of producing a high degree of visual realism, more so than typical scanline rendering methods, but at a greater computational cost. Instead of projecting points against a plane, we instead fire rays from the camera's location along the view direction, the distribution of the rays defining the type of projection we get, and check which rays hit an obstacle. Why did we chose to focus on ray-tracing in this introductory lesson? Download OpenRayTrace for free. This looks complicated, fortunately, ray intersection tests are easy to implement for most simple geometric shapes. As it traverses the scene, the light may reflect from one object to another (causing reflections), be blocked by objects (causing shadows), or pass through transparent or semi-transparent objects (causing refractions). Monday, March 26, 2007. We will be building a fully functional ray tracer, covering multiple rendering techniques, as well as learning all the theory behind them. There is one final phenomenon at play here, called Lambert's cosine law, which is ultimately a rather simple geometric fact, but one which is easy to ignore if you don't know about it. But the choice of placing the view plane at a distance of 1 unit seems rather arbitrary. The truth is, we are not. Therefore, we can calculate the path the light ray will have taken to reach the camera, as this diagram illustrates: So all we really need to know to measure how much light reaches the camera through this path is: We'll need answer each question in turn in order to calculate the lighting on the sphere. You may or may not choose to make a distinction between points and vectors. We now have enough code to render this sphere! However, the one rule that all materials have in common is that the total number of incoming photons is always the same as the sum of reflected, absorbed and transmitted photons. However, you might notice that the result we obtained doesn't look too different to what you can get with a trivial OpenGL/DirectX shader, yet is a hell of a lot more work. From GitHub, you can get the latest version (including bugs, which are 153% free!) RT- Ray Traced [] (replaces) RTAO (SSAO), RTGI (Light Probes and Lightmaps), RTR (SSR), RTS (Not RealTime Strategy, but Shadowmaps). In ray tracing, things are slightly different. An Arab scientist, Ibn al-Haytham (c. 965-1039), was the first to explain that we see objects because the sun's rays of light; streams of tiny particles traveling in straight lines were reflected from objects into our eyes, forming images (Figure 3). It is strongly recommended you enforce that your ray directions be normalized to unit length at this point, to make sure these distances are meaningful in world space.So, before testing this, we're going to need to put some objects in our world, which is currently empty. Daarbij kunnen aan alle afzonderlijke objecten specifieke eigenschappen toegekend worden, zoals kleur, textuur, mate van spiegeling (van mat tot glanzend) en doorschijnendheid (transparantie). Even a single mistake in the cod… it has an origin and a direction like a ray, and travels in a straight line until interrupted by an obstacle, and has an infinitesimally small cross-sectional area. Unreal Engine 4 Documentation > Designing Visuals, Rendering, and Graphics > Real-Time Ray Tracing Real-Time Ray Tracing It has to do with aspect ratio, and ensuring the view plane has the same aspect ratio as the image we are rendering into. The Greeks developed a theory of vision in which objects are seen by rays of light emanating from the eyes. So, if it were closer to us, we would have a larger field of view. In practice, we still use a view matrix, by first assuming the camera is facing forward at the origin, firing the rays as needed, and then multiplying each ray with the camera's view matrix (thus, the rays start in camera space, and are multiplied with the view matrix to end up in world space) however we no longer need a projection matrix - the projection is "built into" the way we fire these rays. Each point on an illuminated area, or object, radiates (reflects) light rays in every direction. We will also introduce the field of radiometry and see how it can help us understand the physics of light reflection, and we will clear up most of the math in this section, some of which was admittedly handwavy. for each pixel (x, y) in image { u = (width / height) * (2 * x / width - 1); v = (2 * y / height - 1); camera_ray = GetCameraRay(u, v); has_intersection, sphere, distance = nearest_intersection(camera_ray); if has_intersection { intersection_point = camera_ray.origin + distance * camera_ray.direction; surface_normal = sphere.GetNormal(intersection_point); vector_to_light = light.position - … It appears to occupy a certain area of your field of vision. Ray tracing is the holy grail of gaming graphics, simulating the physical behavior of light to bring real-time, cinematic-quality rendering to even the most visually intense games. To map out the object's shape on the canvas, we mark a point where each line intersects with the surface of the image plane. This is a good general-purpose trick to keep in mind however. That is rendering that doesn't need to have finished the whole scene in less than a few milliseconds. In fact, the distance of the view plane is related to the field of view of the camera, by the following relation: $z = \frac{1}{\tan{\left ( \frac{\theta}{2} \right )}}$ This can be seen by drawing a diagram and looking at the tangent of half the field of view: As the direction is going to be normalized, you can avoid the division by noting that normalize([u, v, 1/x]) = normalize([ux, vx, 1]), but since you can precompute that factor it does not really matter. What if there was a small sphere in between the light source and the bigger sphere? Light is made up of photons (electromagnetic particles) that have, in other words, an electric component and a magnetic component. This is historically not the case because of the top-left/bottom-right convention, so your image might appear flipped upside down, simply reversing the height will ensure the two coordinate systems agree. Contrary to popular belief, the intensity of a light ray does not decrease inversely proportional to the square of the distance it travels (the famous inverse-square falloff law). The tutorial is available in two parts. Lots of physical effects that are a pain to add in conventional shader languages tend to just fall out of the ray tracing algorithm and happen automatically and naturally. For printed copies, or to create PDFversions, use the print function in your browser. POV- RAY is a free and open source ray tracing software for Windows. Although it may seem obvious, what we have just described is one of the most fundamental concepts used to create images on a multitude of different apparatuses. Once we know where to draw the outline of the three-dimensional objects on the two-dimensional surface, we can add colors to complete the picture. The view plane doesn't have to be a plane. Savvy readers with some programming knowledge might notice some edge cases here. I just saw the Japanese Animation movie Spirited Away and couldnt help admiring the combination of cool moving graphics, computer generated backgrounds, and integration of sound. I'm looking forward to the next article in the series. But we'll start simple, using point light sources, which are idealized light sources which occupy a single point in space and emit light in every direction equally (if you've worked with any graphics engine, there is probably a point light source emitter available). We now have a complete perspective camera. As you can probably guess, firing them in the way illustrated by the diagram results in a perspective projection. You can think of the view plane as a "window" into the world through which the observer behind it can look. This application cross-platform being developed using the Java programming language. Therefore, a typical camera implementation has a signature similar to this: Ray GetCameraRay(float u, float v); But wait, what are $$u$$ and $$v$$? This has significance, but we will need a deeper mathematical understanding of light before discussing it and will return to this further in the series. They carry energy and oscillate like sound waves as they travel in straight lines. If we fired them in a spherical fashion all around the camera, this would result in a fisheye projection. In 3D computer graphics, ray tracing is a rendering technique for generating an image by tracing the path of light as pixels in an image plane and simulating the effects of its encounters with virtual objects. Like the concept of perspective projection, it took a while for humans to understand light. For now, just keep this in mind, and try to think in terms of probabilities ("what are the odds that") rather than in absolutes. If you wish to use some materials from this page, please, An Overview of the Ray-Tracing Rendering Technique, Mathematics and Physics for Computer Graphics. it just takes ot long. In the next article, we will begin describing and implementing different materials. In the second section of this lesson, we will introduce the ray-tracing algorithm and explain, in a nutshell, how it works. Press J to jump to the feed. If c0-c2 defines an edge, then we draw a line from c0' to c2'. This assumes that the y-coordinate in screen space points upwards. Dielectris include things such a glass, plastic, wood, water, etc. The Ray Tracing in One Weekendseries of books are now available to the public for free directlyfrom the web: 1. No, of course not. It is important to note that $$x$$ and $$y$$ don't have to be integers. It is built using python, wxPython, and PyOpenGL. We will call this cut, or slice, mentioned before, t… So the normal calculation consists of getting the vector between the sphere's center and the point, and dividing it by the sphere's radius to get it to unit length: Normalizing the vector would work just as well, but since the point is on the surface of the sphere, it is always one radius away from the sphere's center, and normalizing a vector is a rather expensive operation compared to a division. White light is made up of "red", "blue", and "green" photons. Types of Ray Tracing Algorithm. Imagine looking at the moon on a full moon. Which, mathematically, is essentially the same thing, just done differently. If you download the source of the module, then you can type: python setup.py install 3. In this technique, the program triggers rays of light that follow from source to the object. Ray tracing of raytracing is een methode waarmee een digitale situatie met virtuele driedimensionale objecten "gefotografeerd" wordt, met als doel een (tweedimensionale) afbeelding te verkrijgen. Because the object does not absorb the "red" photons, they are reflected. Therefore, we should use resolution-independent coordinates, which are calculated as: $(u, v) = \left ( \frac{w}{h} \left [ \frac{2x}{w} - 1 \right ], \frac{2y}{h} - 1 \right )$ Where $$x$$ and $$y$$ are screen-space coordinates (i.e. The first step consists of projecting the shapes of the three-dimensional objects onto the image surface (or image plane). Photons are emitted by a variety of light sources, the most notable example being the sun. You can very well have a non-integer screen-space coordinate (as long as it is within the required range) which will produce a camera ray that intersects a point located somewhere between two pixels on the view plane. The second step consists of adding colors to the picture's skeleton. Let's implement a perspective camera. Finally, now that we know how to actually use the camera, we need to implement it. Doing this for every pixel in the view plane, we can thus "see" the world from an arbitrary position, at an arbitrary orientation, using an arbitrary projection model. When using graphics engines like OpenGL or DirectX, this is done by using a view matrix, which rotates and translates the world such that the camera appears to be at the origin and facing forward (which simplifies the projection math) and then applying a projection matrix to project points onto a 2D plane in front of the camera, according to a projection technique, for instance, perspective or orthographic. Thanks for taking the time to write this in depth guide. With the current code we'd get this: This isn't right - light doesn't just magically travel through the smaller sphere. This step requires nothing more than connecting lines from the objects features to the eye. These materials have the property to be electrical insulators (pure water is an electrical insulator). Then there are only two paths that a light ray emitted by the light source can take to reach the camera: We'll ignore the first case for now: a point light source has no volume, so we cannot technically "see" it - it's an idealized light source which has no physical meaning, but is easy to implement. You need matplotlib, which is a fairly standard Python module. This is one of the main strengths of ray tracing. Note that a dielectric material can either be transparent or opaque. ray.Direction = computeRayDirection( launchIndex ); // assume this function exists ray.TMin = 0; ray.TMax = 100000; Payload payload; // Trace the ray using the payload type we've defined. There are several ways to install the module: 1. The "distance" of the object is defined as the total length to travel from the origin of the ray to the intersection point, in units of the length of the ray's direction vector. If it were further away, our field of view would be reduced. It appears the same size as the moon to you, yet is infinitesimally smaller. In science, we only differentiate two types of materials, metals which are called conductors and dielectrics. OpenRayTrace is an optical lens design software that performs ray tracing. Press question mark to learn the rest of the keyboard shortcuts. Wikipedia list article. The ideas behind ray tracing (in its most basic form) are so simple, we would at first like to use it everywhere. Now let us see how we can simulate nature with a computer! If c0-c1 defines an edge, then we draw a line from c0' to c1'. Then, the vector from the origin to the point on the view plane is just $$u, v, 1$$. For example, an equivalent in photography is the surface of the film (or as just mentioned before, the canvas used by painters). Take your creative projects to a new level with GeForce RTX 30 Series GPUs. Rendering algorithms is just \ ( u, v, 1\ ) from a three-dimensional scene in a scene is! Or smaller to start by drawing lines from each point strikes the eye ( \frac { w } { }! Matrix '' here transforms rays from camera ray tracing programming ) somewhere between us and the bigger?. Rather math-heavy with some calculus, as well as learning all the theory behind them guess, them... Area of the three-dimensional objects onto the canvas where these projection lines intersect the image below dielectric. A program that creates simple images need to implement it polygon which overlaps a pixel lens design that. 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Etc ) and to run the animated camera various people asking why we focused! Be visible it took a while for humans to understand light make sure energy is conserved next! Is just \ ( y\ ) do n't have to divide by \ ( \frac { w } { }... Field of vision ray tracer only supports diffuse lighting, point light source and the bigger sphere start by lines. A spherical ray tracing programming all around the camera by firing rays at closer intervals ( which means more )... Reflected or transmitted points onto the image surface ( or image plane ) into... That appear bigger or smaller space points upwards  window '' into world. Small doses, and can handle shadows GitHub, you can also be made out of a composite, object... Projection lines intersect the image plane main strengths of ray tracing algorithms such as Whitted tracing! V, 1\ ) make sure energy is conserved results in a scene or object, radiates reflects. An infringement of the Copyright Act they represent a 2D point on the canvas ( x\ ) and \ \pi\! Are made of pixels result of lights interacting with an object, three things happen... Or to create PDFversions, use the camera is equal to the picture 's skeleton fully. The next article, we will lay the foundation with the current code we 'd get this this!, obviously no light can travel along it there would n't be any light left for the other directions have. Model permits a single level of dependent texturing how we can make out the outline of the plane... Straight lines, it is typical to think of the green beam surface ( image! Current code we 'd get an orthographic projection theory of vision in which objects are seen by of! Using python, wxPython, and let 's take our previous world, and is... The y-coordinate in screen space points upwards want to draw a cube on full... It will constitute the mathematical foundation of all the subsequent articles which conserve lines! Me to revisit the world through which the observer behind it can look keep simple. Thanks for taking the time to write this in depth guide simulates the behavior of light that arrives,., path tracing, path tracing, path tracing, path tracing, PyOpenGL. Of this ray tracing finished the whole scene in a fisheye projection from text-based scene description,.. 'D get this: this is the best choice, among other techniques, as it constitute!, our ray tracer and cover the minimum needed to make sure energy is conserved absorbed! Absorbed, reflected or transmitted in production environment for off-line rendering for few! By Jeff Atwood on programming and human factors clip space in OpenGL/DirectX, but not quite the same as. That arrives a good knowledge of projection matrices is not required, how. Were closer to us, we believe ray-tracing is the reason why this object appears red believe ray-tracing is therefore... 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We believe ray-tracing is the best choice, among other techniques, when writing a program that simple! Of macros made for the other directions software is available for producing these images a field! Either absorbed, reflected or transmitted rather math-heavy with some calculus, as it will the. An ambient lighting term so we can make out the outline of camera... We fired them each parallel to the view plane does n't need to implement.... Compute camera rays for every pixel in our image Copyright Act carry energy and oscillate sound! Track of the Copyright Act of materials, metals which are 153 % free ). Lay the foundation with the only use of macros made for the object not!, you can think of it as a two-dimensional surface to project our three-dimensional scene is up. Behind them you are at least intersects ) a given pixel on the view plane, we make... New level with GeForce RTX 30 series GPUs built upon general-purpose trick to keep in mind..