This chapter addresses visual rendering, which specifies what the visual display should show through an interface to the virtual world generator (VWG). Chapter 3 already provided the mathematical parts, which express where the objects in the virtual world should appear on the screen. This was based on geometric models, rigid body transformations, and viewpoint transformations. We next need to determine how these objects should appear, based on knowledge about light propagation, visual physiology, and visual perception. These were the topics of Chapters 4, 5, and 6, respectively. Thus, visual rendering is a culmination of everything covered so far.
Sections 7.1 and 7.2 cover the basic concepts; these are considered the core of computer graphics, but VR-specific issues also arise. They mainly address the case of rendering for virtual worlds that are formed synthetically. Section 7.1 explains how to determine the light that should appear at a pixel based on light sources and the reflectance properties of materials that exist purely in the virtual world. Section 7.2 explains rasterization methods, which efficiently solve the rendering problem and are widely used in specialized graphics hardware, called GPUs. Section 7.3 addresses VR-specific problems that arise from imperfections in the optical system. Section 7.4 focuses on latency reduction, which is critical to VR, so that virtual objects appear in the right place at the right time. Otherwise, many side effects could arise, such as VR sickness, fatigue, adaptation to the flaws, or simply having an unconvincing experience. Finally, Section 7.5 explains rendering for captured, rather than synthetic, virtual worlds. This covers VR experiences that are formed from panoramic photos and videos.