Question

What is the difference between window and viewport in computer graphics in versus form with number of lines?

Answer 1

Windows and Viewports

A window defines a rectangular area in world coordinates. You define a window with a GWINDOW statement. You can define the window to be larger than, the same size as, or smaller than the actual range of data values, depending on whether you want to show all of the data or only part of the data.

A viewport defines in normalized coordinates a rectangular area on the display device where the image of the data appears. You define a viewport with the GPORT command. You can have your graph take up the entire display device or show it in only a portion, say the upper right part.

Mapping Windows to Viewports

A window and a viewport are related by the linear transformation that maps the window onto the viewport. A line segment in the window is mapped to a line segment in the viewport such that the relative positions are preserved.

You don't have to display all of your data in a graph. In Figure 12.4, the graph on the left displays all of the ACME stock data, and the graph on the right displays only a part of the data. Suppose that you wanted to graph only the last ten years of the stock data, say from 1977 to 1986. You would want to define a window where the YEAR axis ranges from 77 to 86, while the PRICE axis could range from 120 to 160. Figure 12.4shows stock prices in a window defined for data from 1977 to 1986 along the horizontal direction and from 120 to 160 along the vertical direction. The window is mapped to a viewport defined by the points (20,20) and (70,60). The appropriate GPORT and GWINDOW specifications are as follows:

call gwindow({77 120, 86 160}); call gport({20 20, 70 60}); The window, in effect, defines the portion of the graph that is to be displayed in world coordinates, and the viewport specifies the area on the device on which the image is to appear.