How does graphics rendering work

Because user interaction is high in such environments, real-time image creation is required. Dedicated graphics hardware and pre-compiling of the available information has improved the performance of real-time rendering.

Pre-Rendering: This rendering technique is used in environments where speed is not a concern and the image calculations are performed using multi-core central processing units rather than dedicated graphics hardware. This rendering technique is mostly used in animation and visual effects, where photorealism needs to be at the highest standard possible. For these rendering types,the three major computational techniques used are: Scanline Raytracing Radiosity.

Share this Term. Ray Casting RenderMan Radiosity. Tech moves fast! The image is a digital image or raster graphics image. The term may be by analogy with an "artist's rendering" of a scene. It is one of the major sub-topics of 3D computer graphics , and in practice always connected to the others.

In the 'graphics pipeline' it's the last major step, giving the final appearance to the models and animation. With the increasing sophistication of computer graphics since the s onward, it has become a more distinct subject. It has uses in: computer and video games , simulators, movies or TV special effects, and design visualisation, each employing a different balance of features and techniques. As a product, a wide variety of renderers are available. On the inside, a renderer is a carefully engineered program, based on a selective mixture of disciplines related to: light physics , visual perception , mathematics, and software development.

In the case of 3D graphics, rendering may be done slowly, as in pre-rendering , or in real time. Pre-rendering is a computationally intensive process that is typically used for movie creation, while real-time rendering is often done for 3D video games which rely on the use of graphics cards with 3D hardware accelerators.

When the pre-image a wireframe sketch usually is complete, rendering is used, which adds in bitmap textures or procedural textures , lights, bump mapping , and relative position to other objects.

The result is a completed image the consumer or intended viewer sees. For movie animations, several images frames must be rendered, and stitched together in a program capable of making an animation of this sort.

Most 3D image editing programs can do this. A rendered image can be understood in terms of a number of visible features. Rendering research and development has been largely motivated by finding ways to simulate these efficiently.

Some relate directly to particular algorithms and techniques, while others are produced together. Many rendering algorithms have been researched, and software used for rendering may employ a number of different techniques to obtain a final image. Tracing every ray of light in a scene would be impractical and would take gigantic amounts of time.

Even tracing a portion large enough to produce an image takes an inordinate amount of time if the sampling is not intelligently restricted. Therefore, four loose families of more-efficient light transport modelling techniques have emerged: rasterisation , including scanline rendering , considers the objects in the scene and projects them to form an image, with no facility for generating a point-of-view perspective effect; ray casting considers the scene as observed from a specific point-of-view, calculating the observed image based only on geometry and very basic optical laws of reflection intensity, and perhaps using Monte Carlo techniques to reduce artifacts; radiosity uses finite element mathematics to simulate diffuse spreading of light from surfaces; and ray tracing is similar to ray casting, but employs more advanced optical simulation, and usually uses Monte Carlo techniques, to obtain more realistic results, at a speed which is often orders of magnitude slower.

Most advanced software combines two or more of the techniques to obtain good-enough results at reasonable cost. A high-level representation of an image necessarily contains elements in a different domain from pixels.

These elements are referred to as primitives. In a schematic drawing, for instance, line segments and curves might be primitives. In a graphical user interface, windows and buttons might be the primitives. In 3D rendering, triangles and polygons in space might be primitives. If a pixel-by-pixel approach to rendering is impractical or too slow for some task, then a primitive-by-primitive approach to rendering may prove useful. Here, one loops through each of the primitives, determines which pixels in the image it affects, and modifies those pixels accordingly.

The only reason why this image on the canvas actually looks accurate to our brain, is because objects gets smaller as they get further away from where you stand, an effect called foreshortening. If you are not convinced yet, think of an image as nothing more than a mirror reflection.

The surface of the mirror is perfectly flat, and yet, we can't make the difference between looking at the image of a scene reflected from a mirror and looking directly at the scene: you don't perceive the reflection, just the object. It's only because we have two eyes that we can actually get a sense of seeing things in 3D, something we call stereoscopic vision. Each eye looks at the same scene from a slightly different angle, and the brain can use these two images of the same scene to approximate the distance and the position of objects in 3D space with respect to each other.

However stereoscopic vision is quite limited in a way as we can't measure the distance to objects or their size very accurately which computers can do. Human vision is quite sophisticated and an impressive result of evolution, but it's nonetheless a trick, and it can be fooled easily many magicians tricks are based on this.

To some extent, computer graphics is a mean by which we can create images of artificial worlds and present them to the brain through the mean of vision , as an experience of reality something we call photo-realism , exactly like a mirror reflection.

This theme is quite common in science fiction, but technology is not far from making this actually possible. What have we learned so far? That the world is three-dimensional, that the way we look at it is two-dimensional, and that if you can replicate the shape and the appearance of objects, the brain can not make the difference between looking at this objects directly, and looking at an image of these objects.

Computer graphics is not limited to creating photoreal images but while it's easier to create non photo-realistic images than creating perfectly photo realistic ones, the goal of computer graphics is clearly realism as much in the way things move than they appear. All we need to do now, is learn what the rules for making such a photo-real image are, and that's what you will also learn here on Scratchapixel. Figure 1: a 2D Cartesian coordinative systems defined by its two axis x and y and the origin.

This coordinate system can be used as a reference to define the position or coordinates of points within the plane. Figure 2: a box can be described by specifying the coordinates of its eight corners in a Cartesian coordinate system. One of the simplest and most important concept we learn at school is the idea of space in which points can be defined. The position of a point is generally defined with relation to an origin. On a ruler, this is generally the tick marked with the number zero.

If we use two rulers, one perpendicular to the other, we can define the position of points in two dimensions. Add a third ruler, perpendicular to the first two, and you can define the position of points in three dimensions. The actual numbers representing the position of the point with respect to one of the tree rulers are called the points coordinates.

We are all familiar with the concept of coordinates to mark were we are with respect to some reference point or line for example the Greenwich meridian. We can now define points in three dimensions.

Let's imagine that you just bought a computer. This computer probably came in a box, and this box has eight corners sorry for stating the obvious. One way of describing this box, is to measure the distance of these 8 corners with respect to one of the corners. This corner acts as the origin of our coordinate system and obviously the distance of this reference corner with respect to itself will be 0 in all dimensions.

However the distance from the reference corner to the other seven corners, will be different than 0. Let's image that our box has the following dimensions:. Figure 3: a box can be described by specifying the coordinates of its eight corners in a Cartesian coordinate system. The first number represent the width, the second number the height, and the third number the corner's depth.

Corner 1 as you can see, is the origin from which all the over corners have been measured. All you need to do from here, is somehow write a program in which you will define the concept of a three-dimensional point, and use it to store the coordinates of the eight points you just measured.

Like in any language, there is always different ways of doing the same thing. You have somehow created your first 3D program. It doesn't produce an image yet, but you can already store the description of a 3D object in memory.

In CG, the collection of these objects is called a scene a scene also includes the concept of camera and lights but we will talk about this another time. As suggested before, we are lacking two very important things to make the process really complete and interesting. First to actually represent the box in the memory of the computer, ideally, we also need a system that defines how these eight points are connected to each other to make up the faces of the box.

In CG, this is called the topology of the object an object is also called a model. We will talk about this in the Geometry section and the 3D Basic Render section in the lesson on rendering triangles and polygonal meshes. Topology refers to how points which we generally call vertices are connected to each other to form faces or flat surfaces.

These faces are also called polygons. The box would be made of six faces or six polygons and the set of polygons forms what we call a polygonal mesh or simply a mesh. Software rendering is categorized as either real-time software rendering, which is used to interactively render a scene in such applications as 3D computer games, with each frame being rendered in milliseconds; or as pre-rendering, which is used to create realistic movies and images, in which each frame may take several hours or even days to complete.

The main attraction to software rendering is capability. While hardware in GPU rendering is generally limited to its present capabilities, software rendering is developed with fully customizable programming, can perform any algorithm, and can scale across many CPU cores across several servers.

Software can also expose different rendering paradigms. Software rendering stores the static 3D scene to be rendered in its memory while the renderer samples one pixel at a time. GPU rendering renders the scene one triangle at a time into the frame buffer. Techniques such as ray tracing, which focus on producing lighting effects and are more commonly implemented in software, use software rendering instead of GPU rendering.