Copyright Goodheart-Willcox Co., Inc. 418 AutoCAD and Its Applications—Advanced NOTE NOTE Many graphics effects in AutoCAD, including the appearance of lines and curves, view transitions, material displays, and rendering, are enhanced by hardware accel- eration. Hardware acceleration is enabled by default if your computer video card and graphics support the system. Hardware acceleration can be turned on or off in the Graphics Performance dialog box, which is accessed by using the GRAPHICSCONFIG command or by right-clicking on the Hardware Acceleration button on the status bar and selecting Graphics Performance…. Isolines The appearance of curved surfaces on a solid model is controlled by the ISOLINES system variable. Isolines represent the edges and curved surfaces of a solid model. This setting does not affect the fi nal rendered model. However, if the Show property in the Edge Settings category in the Visual Styles Manager palette is set to Isolines, isolines are displayed when the visual style is set current. The default ISOLINES value is four. It can have a value from zero to 2047. All solid objects with curved surfaces are affected by changes to the ISOLINES value, as are all visual styles set to display isolines. Figure 16-1 illustrates the difference between ISOLINES settings of four and 12. The setting of the ISOLINES system variable can be changed in the Visual Styles Manager palette. You can also type ISOLINES and enter a new value, or you can change the Contour lines per surface setting in the Display resolution area of the Display tab in the Options dialog box. See Figure 16-2. The settings in the Display tab in the Options dialog box can also be used to control the DISPSILH and FACETRES system variables, discussed next. Creating a Display Silhouette In the 2D Wireframe visual style, a model can appear smooth with only a silhou- ette displayed, similar to the Hidden visual style. This is controlled by the DISPSILH (display silhouette) system variable. The DISPSILH system variable has two values, 0 (off) and 1 (on). Figure 16-3 shows solids with DISPSILH set to 0 and 1 after setting the 2D Wireframe visual style current and then using HIDE. The setting can be changed by typing DISPSILH and entering a new value. You can also set the variable using the Draw true silhouettes for solids and surfaces check box in the Display performance area of the Display tab in the Options dialog box. Refer to Figure 16-2. A preferred technique is to set ISOLINES to 0 and DISPSILH to 1 to ISOLINES Type ISOLINES DISPSILH Type DISPSILH Figure 16-1. Isolines define curved surfaces. A—ISOLINES = 4. B—ISOLINES = 12. A B