Real-time rendering is concerned with rapidly making images on the computer. It is the most highly interactive area of computer graphics. An image appears on the screen, the viewer acts or reacts, and this feedback affects what is generated next. This cycle of reaction and rendering happens at a rapid enough rate that the viewer does not see individual images, but rather becomes immersed in a dynamic process.

实时渲染与快速在电脑上生成图像有关。它是计算机图形学中最交互式的领域。一张图像出现在屏幕上，观众采取行动或反应，这种反馈会影响下一步生成的内容。这种反应和渲染的循环以足够快的速度进行，观众看不到单独的图像，而是沉浸在动态过程中。

The rate at which images are displayed is measured in frames per second (FPS) or Hertz (Hz). At one frame per second, there is little sense of interactivity; the user is painfully aware of the arrival of each new image. At around 6 FPS, a sense of interactivity starts to grow. Video games aim for 30, 60, 72, or higher FPS; at these speeds the user focuses on action and reaction.

图像显示的速度以每秒帧数（FPS）或赫兹（Hz）度量。每秒1帧，交互性很小；用户会感到痛苦地意识到每张新图像的到来。在每秒6帧左右，交互性开始增强。电子游戏的目标是30、60、72或更高的FPS；在这些速度下，用户会专注于行动和反应。

Movie projectors show frames at 24 FPS but use a shutter system to display each frame two to four times to avoid flicker. This refresh rate is separate from the display rate and is expressed in Hertz (Hz). A shutter that illuminates the frame three times has a 72 Hz refresh rate. LCD monitors also separate refresh rate from display rate.

电影放映机每秒显示24帧，但使用快门系统将每帧显示两到四次以避免闪烁。这种刷新率与显示率是独立的，并以赫兹（Hz）表示。三次照亮帧的快门有72Hz的刷新率。LCD显示器也将刷新率与显示率分开。

Watching images appear on a screen at 24 FPS might be acceptable, but a higher rate is important for minimizing response time. As little as 15 milliseconds of temporal delay can slow and interfere with interaction [1849]. As an example, head-mounted displays for virtual reality often require 90 FPS to minimize latency.

在24 FPS的速度下观看屏幕上的图像可能是可以接受的，但更高的速度对于最小化响应时间很重要。仅有15毫秒的时间延迟就可减慢并干扰交互 [1849]。例如，虚拟现实的头戴显示器通常需要90 FPS才能最小化延迟。

There is more to real-time rendering than interactivity. If speed was the onlycriterion, any application that rapidly responded to user commands and drew anythingon the screen would qualify. Rendering in real time normally means producing threedimensional images.

实时渲染不仅仅是交互性。如果速度是唯一的标准，任何快速响应用户命令并在屏幕上绘制任何内容的应用程序都将符合条件。在实时渲染中通常意味着生成三维图像。

Interactivity and some sense of connection to three-dimensional space are suffi-cient conditions for real-time rendering, but a third element has become a part ofits definition: graphics acceleration hardware. Many consider the introduction of the3Dfx Voodoo 1 card in 1996 the real beginning of consumer-level three-dimensionalgraphics [408]. With the rapid advances in this market, every computer, tablet, andmobile phone now comes with a graphics processor built in. Some excellent examplesof the results of real-time rendering made possible by hardware acceleration are shownin Figures 1.1 and 1.2.

交互性和与三维空间的某种联系是实时渲染的充分条件，但是第三个元素已经成为它的定义的一部分：图形加速硬件。许多人认为1996年3Dfx Voodoo 1卡的推出是消费级三维图形真正开始的时刻 [408]。随着这个市场的快速发展，现在每台电脑、平板电脑和手机都内置了图形处理器。图形加速硬件所带来的实时渲染的一些出色示例如图1.1和1.2所示。

Figure 1.1. A shot from Forza Motorsport 7. (Image courtesy of Turn 10 Studios, Microsoft.)

图1.1 Forza Motorsport 7的一张截图（图片由Turn 10 Studios提供，Microsoft拥有版权。）

Figure 1.2. The city of Beauclair rendered in The Witcher 3. (CD PROJEKT®, The Witcher® are registered trademarks of CD PROJEKT Capital Group. The Witcher game© CD PROJEKT S.A.Developed by CD PROJEKT S.A. All rights reserved. The Witcher game is based on the prose ofAndrzej Sapkowski. All other copyrights and trademarks are the property of their respective owners.)

图1.2 The Witcher 3中渲染的Beauclair城市（CD PROJEKT®、The Witcher®是CD PROJEKT Capital Group的注册商标。The Witcher©游戏由CD PROJEKT S.A.开发。版权所有。The Witcher游戏基于Andrzej Sapkowski的文章。所有其他版权和商标均属于其各自的所有者。）

Advances in graphics hardware have fueled an explosion of research in the fieldof interactive computer graphics. We will focus on providing methods to increasespeed and improve image quality, while also describing the features and limitations ofacceleration algorithms and graphics APIs. We will not be able to cover every topic indepth, so our goal is to present key concepts and terminology, explain the most robustand practical algorithms in the field, and provide pointers to the best places to go formore information. We hope our attempts to provide you with tools for understandingthis field prove to be worth the time and effort you spend with our book.

图形硬件的进步促进了交互式计算机图形学领域的爆炸式发展。我们将专注于提供提高速度和改善图像质量的方法，同时还将描述加速算法和图形API的特点和限制。我们将无法深入涵盖每个主题，因此我们的目标是介绍关键概念和术语，解释该领域中最健壮和实用的算法，并提供最佳信息来源的指针。我们希望我们为您提供的理解这一领域的工具能够证明与我们的书相关的时间和努力是值得的。