Immediately, you noticed how the lane lines in the road rush past you, and how the barriers of the race track zoom by your the periphery of your vision. As you come into a street scene the buildings stretch out before you and you can see into the horizon as the road disappears. This feeling of perspective, of materials, and texture, and color, is achieved by a process called perspective-corrected texture-mapping.

Texture mapping allows images, either created in paint programs or scanned in from another source, to be applied to 3D objects. Perspective-corrected texture-mapping calculates how the mapped image would look when viewed from different angles. The buildings you see racing by you are not a collection of doors, windows, bricks and cement modeled in 3D. That would be far too complex. They are blocks that have had building facades mapped on to them. Applying perspective correction means that the textures conform to the viewer’s vantage point and appear to be in perspective from all angles.

The road rushing under you also is a texture mapped image. It’s not possible to model the road as one object. It’s a series of smaller strips with the image of a road surface repeatedly mapped on to them. In some computer games with long corridors, and walls, the walls and floor seem to shimmer as you move by them. Sometimes you can see the seams between the blocks. Filtering techniques can be applied to remove these distortions.

Bi-linear and tri-linear filtered textures are mathematically assessed pixel by pixel. The hardware looks at each pixel of the texture map, looks at the pixels around it, and determines what’s the best pixel to display on screen. The better the filtering, the more likely it is that there will be consistency in the image, and to the user, the impression is of effortless movement. The less accurate the filtering, the more likely it is that as you move around the scene you are going to get some shimmer and shake in the background because the texture display varies every time you change your point of view.

So, what appears normal, or real, is only possible because a great deal of background calculations have to occur. Textures are normally stored in dynamic memory so that they can be accessed quickly. There is a process called mip mapping that stores a number of sizes of a texture. By storing various sizes of the same texture map, the 3D engine can quickly determine which texture to apply to a surface near or far from you. Rather than calculate a shrunken or exploded image of the texture, and apply it to a surface as it moves backwards and forwards in the frame, the images are already pre-rendered and ready for use.

No matter at what angle you look at a surface, and no matter how far or near it is from you, the texture mapped surface of an object adapts accordingly to your view vantage. These texture mapping functions are essential to real time 3D developers. Without them the processor overhead, to create the high levels of realism needed, would be so great you could not use advanced texturing functions. Take texture mapping out of 3D and reduce most of its efficacy.

Back in the racing car. You switch into high gear and the edges of building, barriers and objects become a blur as you speed by. Imagine what it would be like if those lines were not a blur, but they were jagged edges. This does happen under normal circumstances because of the way pixels are drawn on to the screen.

Jaggies	Anti Aliasing

Anti-aliasing removes the jaggies from images. Looking at the above diagram it’s clear that any anti aliasing calculation has to be performed on a pixel by pixel basis. It’s a feature of hardware acceleration that may not be noticed if its not there, but is certainly noticeable when it is there. The enhanced experience of anti-aliased images lets users suspend disbelief and become immersed in the game.

Imagine how it would feel to have your view obstructed by objects on and around the racetrack. A 3D program would have to determine what is in the plane of view, and what is obscured, and only draw those surfaces that lie in front of others. However, it is not enough to merely know which objects are in view and which are hidden behind them. You have to know how they are placed in relation to each other.

Z-buffering is a means of determining the depth of objects in relation to others. A z-buffer is a separate portion of graphics memory that stores the z value of an objects coordinates. The 3D accelerator calculates, on a per pixel basis, the z value of objects in relation to others in the same plane, and draws only those with a lower z value. That’s a big chunk of mathematics. If you add all these calculations together, bear in mind that its a continuous process, and then realize that it changes drastically every time the point of view changes, you can appreciate why the CPU hasn’t processing time to make it all happen quickly enough.

3D graphics subsystems are going even further for more realistic scene effects. Imagine you hit a corner badly, you skid out of control off the track and into the dirt, and the flying dust obscures your view. Fogging can create the illusion of mist or haze clouding your view. It can also create the illusion of distance by gradually fading objects in the far distance. The function of placing a transparent set of images against the background of your 3D world, and controlling that transparency, is something that can only be effectively achieved with hardware acceleration. Fogging’s more official name is alpha blending, where transparent images are smoothly blended in with those of other objects in the same plane of view.

How often do these functions take place? In entertainment software the most important factor in determining performance is not one figure relating to polygons per second, or MIPS, or MOPS. These values are constrained to single functions of the processor whereas the entertainment software experience embraces a number of functions simultaneously. Thus, the benchmark for entertainment software is frames per second. Each frame is the time it takes to react to input, perform 2D and 3D graphics, play the audio, and perform the program logic. The more realistic the game, the more real time if you will, the greater the frame rate. The higher the frame rate the higher the response of the game to the user and the more realistic the results on screen.

One method of increasing frame rate is to store images from one frame into the display memory as another one is being read. This is double buffering and ensures that the screen is updated at a faster rate then sequentially reading in each image. The great thing about double buffering as a feature is that it also allows users to experience stereo vision and further immerse themselves in the experience of their virtual world. Low cost stereo glasses are becoming widely available, and are a driving technology in the development of 3D graphics. After all, the closer the user gets to being inside a frame of action the better the experience.

The frame rate is also a good way of determining the relative performance of one 3D accelerator against another because, various process such as audio, 2D graphics, and program logic are consistent. The only potential bottleneck is the 3D graphics pipeline. The benefit of integrating 3D acceleration with other multimedia functions is that it will ensure a closely coupled set of functions running optimally together. However, the greater computational needs of 3D graphics and the extra memory requirements will no doubt require stand alone 3D accelerators for some applications.