1.1 Introduction The term computer graphics includes almost everything on computers that is not text or sound. Today almost every computer can do some graphics, and people have even come to expect to control their computer through icons and pictures rather than just by typing. Here in our lab at the Program of Computer Graphics, we think of computer graphics as drawing pictures on computers, also called rendering. The pictures can be photographs, drawings, movies, or simulations - pictures of things, which do not yet exist and maybe could never exist. Or they may be pictures from places we cannot see directly, such as medical images from inside your body. We spend much of our time improving the way computer pictures can simulate real world scenes. We want images on computers to not just look more realistic, but also to be more realistic in their colors, the way objects and rooms are lighted, and the way different materials appear. We call this work “realistic image synthesis”. 1.2 Interactive Graphics In interactive computer graphics user have some control over the picture i.e user can make any change in the produced image. One example of it is the ping pong game. The conceptual model of any interactive graphics system is given in the picture shown in Figure 1.1. At the hardware level (not shown in picture), a computer receives input from interaction devices, and outputs images to a display device. The software has three components. The first is the application program, it creates, stores into, and retrieves from the second component, the application model, which represents the the graphic primitive to be shown on the screen. The application program also handles user input. It produces views by sending to the third component, the graphics system, a series of graphics output commands that contain both a detailed geometric description of what is to be viewed and the attributes describing how the objects should appear. After the user input is processed, it sent to the graphics system is for actually producing the picture. Thus the graphics system is a layer in between the application program and the display hardware that effects an output transformation from objects in the application model to a view of the model.
Applicati on Model Applicatio n Program Graphics system Figure 1.1: Conceptual model for interactive graphics The objective of the application model is to captures all the data, objects, and relationships among them that are relevant to the display and interaction part of the application program and to any nongraphical postprocessing modules. 1.3 Passive Graphics A computer graphics operation that transfers automatically and without operator intervention. Non-interactive computer graphics involves one way communication between the computer and the user. Picture is produced on the monitor and the user does not have any control over the produced picture. 1.4 Advantages of Interactive Graphics Graphics provides one of the most natural means of communicating with a computer, since our highly developed 2D and 3D pattern-recognition abilities allow us to perceive and process pictorial data rapidly and efficiently. In Many design, implementation, and construction processes today, the information pictures can give is virtually indispensable. Scientific visualization became an important field in the late 1980s, when scientists and engineers realized that they could not interpret the data and prodigious quantities of data produced in supercomputer runs without summarizing the data and highlighting trends and phenomena in various kinds of graphical representations. Creating and reproducing pictures, however, presented technical problems that stood in the way of their widespread use. Thus, the ancient Chinese proverb “a picture is worth
ten thousand words” became a cliché in our society only after the advent of inexpensive and simple technology for producing pictures—first the printing press, then photography. Interactive computer graphics is the most important means of producing pictures since the invention of photography and television; it has the added advantage that, with the computer, we can make pictures not only of concrete, “real-world” objects but also of abstract, synthetic objects, such as mathematical surfaces in 4D and of data that have no inherent geometry, such as survey results. Furthermore, we are not confined to static images. Although static pictures are a good means of communicating information, dynamically varying pictures are frequently even better–to time-varying phenomena, both real (e.g., growth trends, such as nuclear energy use in the United States or population movement form cities to suburbs and back to the cities). Thus, a movie can show changes over time more graphically than can a sequence of slides. Thus, a sequence of frames displayed on a screen at more than 15 frames per second can convey smooth motion or changing form better than can a jerky sequence, with several seconds between individual frames. The use of dynamics is especially effective when the user can control the animation by adjusting the speed, the portion of the total scene in view, the amount of detail shown, the geometric relationship of the objects in the another, and so on. Much of interactive graphics technology therefore contains hardware and software for usercontrolled motion dynamics and update dynamics. With motion dynamics, objects can be moved and tumbled with respect to a stationary observer. The objects can also remain stationary and the viewer can move around them , pan to select the portion in view, and zoom in or out for more or less detail, as though looking through the viewfinder of a rapidly moving video camera. In many cases, both the objects and the camera are moving. A typical example is the flight simulator, which combines a mechanical platform supporting a mock cockpit with display screens for windows. Computers control platform motion, gauges, and the simulated world of both stationary and moving objects through which the pilot navigates. These multimilliondollar systems train pilots by letting the pilots maneuver a simulated craft over a simulated 3D landscape and around simulated vehicles. Much simpler fight simulators are among the most popular games on personal computers and workstations. Amusement
parks also offer “motion-simulator” rides through simulated terrestrial and extraterrestrial landscapes. Video arcades offer graphics-based dexterity games and racecar-driving simulators, video games exploiting interactive motion dynamics: The player can change speed and direction with the “gas pedal” and “steering wheel,” as trees, buildings, and other cars go whizzing by. Similarly, motion dynamics lets the user fly around the through buildings, molecules, and 3D or 4D mathematical space. In another type of motion dynamics, the “camera” is held fixed, and the objects in the scene are moved relative to it. For example, a complex mechanical linkage, such as the linkage on a stream engine, can be animated by moving or rotating all the pieces appropriately. Update dynamics is the actual change of the shape, color, or other properties of the objects being viewed. For instance, a system can display the deformations of an airplane structure in flight or the state changes in a block diagram of a nuclear reactor in response to the operator’s manipulation of graphical representations of the many control mechanisms. The smoother the change, the more realistic and meaningful the result. Dynamic interactive graphics offers a large number of user-controllable modes with which to encode and communicate information: the 2D or 3D shape of objects in a picture, their gray scale or color, and the time variations of these properties. With the recent development of digital signal processing (DSP) and audio synthesis chips, audio feedback can now be provided to augment the graphical feedback and to make the simulated environment even more realistic. Interactive computer graphics thus permits extensive, high-bandwidth user-computer interaction. This significantly enhances our ability to understand data, to perceive trends, and to visualize real or imaginary objects–indeed, to create “virtual worlds” that we can explore from arbitrary points of view. By making communication more efficient, graphics make possible higher-quality and more precise results or products, greater productivity, and lower analysis and design costs. 1.5 How The Interactive Graphics Display Works The modern graphic display is very simple in construction. It consists of the three components shown in figure 1.2 below.