New Words & Expressions

　　output primitives 输出图元 analog device 模拟设备

　　vector n. 矢量 pen plotter 笔式绘图仪

　　random-scan display 随机扫描显示器 endpoint n. 端点

　　horizontal a. 水平的 vertical a. 垂直的

　　deflection n. 偏转，偏差 voltage n. 电压，伏特数

　　digital device 数字设备 high-resolution 高分辨率的

　　Typically, graphics programming packages provide functions to describe a scene in terms of these basic geometric structures, referred to as output primitives, and to group sets of output primitives into more complex structures [1]. Each output primitive is specified with input coordinate data and other information about the way that the object is to be displayed. Points and straight-line segments are the simplest geometric components of pictures. Additional output primitives that can be used to construct a picture include circles and other conic sections, quadric surfaces, spline curves and surfaces, polygon color areas, and character strings.

　　通常，图形编程软件包提供了一些功能来描述场景，这些功能使用了称为输出图元的基本几何结构并将输出图元组合成更复杂的结构。每个输出图元是由输入的坐标数据和有关物体显示的一些信息来指定。点和直线是最简单的几何成分，其它可以用来构造图形的输出图元有：圆及其它圆锥曲线、二次曲面、样条曲线和曲面、多边形填色区域以及字符串等。

　　Points and Lines

　　Point plotting is accomplished by converting a single coordinate position furnished by an application program into appropriate operations for the output device in use. With a CRT monitor, for example, the electron beam is turned on to illuminate the screen phosphor at the selected location. How the electron beam is positioned depends on the display technology.

　　点和线

　　通过将应用程序提供的单个坐标位置转换成输出设备的相应操作，可以进行点的绘制。例如，对于CRT监视器，则是打开电子束，从而在选中的位置上照亮屏幕的荧光层。电子束的定位方法取决于显示技术。

　　Points and Lines

　　Line drawing is accomplished by calculating intermediate positions along the line path between two specified endpoint positions. An output device is then directed to fill in these positions between the endpoints. For analog devices, such as a vector pen plotter or a random-scan display, a straight line can be drawn smoothly from one endpoint to the other. Linearly varying horizontal and vertical deflection voltages are generated that are proportional to the required changes in the x and y directions to produce the smooth line.

　　通过计算沿线路径上两指定端点间的中心位置，可以绘制一条线段，输出设备则按指令在端点间的这些位置直接填充。对于笔式绘图仪或随机扫描显示器这类模拟设备，可以从一个端点至另一端点绘制光滑线段。这是根据x方向和y方向需要修改的实际量，线性地改变水平和垂直偏转电压而实现的。

　　Points and Lines

　　To load a specified color into the frame buffer at a position corresponding to column x along scan line y, we will assume we have available a low-level procedure of the form

　　setPixel (x, y)

　　为了将对应于扫描线y、列x的位置上指定的颜色装入帧缓冲器，我们假设有如下形式的低层程序： setPixel (x, y)

　　We sometimes will also want to be able to retrieve the current frame-buffer intensity setting for a specied location. We accomplish this with the low-level functon

　　GetPixel (x, y)

　　有时，我们也要求能提取某个特定位置的当前帧缓冲器的强度设置，可以使用下列低层函数来完成： getPixel (x, y)

　　FILL-AREA FUNCTIONS

　　We display a filled polygon in PHIGS and GKS with the function

　　fillArea (n, wcVertices)

　　The displayed polygon area is bounded by a series of n straight line segments connecting the set of vertex positions specified in wcVertices. These packages do not provide fill functions for objects with curved boundaries.

　　区域填充函数

　　在PHIGS和GKS中，利用下列函数显示填充的多边形：

　　fillArea (n, wcVertices)

　　显示的多边形区域，由一系列在wcVertices中指定的顶点连接起来的n条直线段包围。这些软件包没有提供曲线边界对象的填充功能。