One of the goals of computer graphics is physical realism, that is, making images that look like they could be photographs of reality. This is not the only goal. For example, for scientific visualization, the goal is to use computer graphics to present information accurately and clearly. Artists can use computer graphics to create abstract rather than realistic art. However, realism is a major goal of some of the most visible uses of computer graphics, such as video games, movies, and advertising.
One important aspect of physical realism is lighting: the play of light and shadow, the way that light reflects from different materials, the way it can bend or be diffracted into a spectrum as it passes through translucent objects. The techniques that are used to produce the most realistic graphics can take all these factors and more into account.
However, another goal of computer graphics is speed. OpenGL, in particular, was designed for real-time graphics, where the time that is available for rendering an image is a fraction of a second. For an animated movie, it’s OK if it takes hours to render each frame. But a video game is expected to render sixty frames every second. Even with the incredible speed of modern computer graphics hardware, compromises are necessary to get that speed. And twenty years ago, when OpenGL was still new, the compromises were a lot bigger
In this chapter, we look at light and material in OpenGL 1.1. You will learn how to configure light sources and how to assign material properties to objects. Material properties determine how the objects interact with light. And you will learn how to apply an image to a surface as a texture. The support for light, material, and texture in OpenGL 1.1 is relatively crude and incomplete, by today’s standards. But the concepts that it uses still serve as the foundation for modern real-time graphics and, to a significant extent, even for the most realistic computer graphics.