986 Part VII Programming AutoCAD

Introducing Visual LISP

Visual LISP (VLISP) is an integrated development environment (IDE) that provides an easy-to- use interface to help you create code, debug errors, and test programs.

Some useful Visual LISP features include the following:

Syntax checker and highlighting to help correct syntax errors

File compilation for security and faster execution

Debugger, with support for stepping through source code to find errors

Helpful Inspect and Watch windows for querying a value or examining a variable during execution

Context-sensitive help

Management of multiple file applications from a project window

Compiled multiple projects, as well as other files, using the application wizard

Console history, which makes it possible to recall previously entered information

Opening Visual LISP

To start Visual LISP, you can either type Vlide at the AutoCAD command prompt, or choose Tools AutoLISP Visual LISP Editor. At any time, you can switch to Visual LISP using either of these methods. Figure 34-1 shows your screen after you open Visual LISP.

AutoLISP and Visual LISP are discussed throughout Chapters 34, 35, and 36. Although this book does not provide complete coverage of either AutoLISP or Visual LISP, many of the major features are explained within these three chapters.

Opening and loading an AutoLISP file with Visual LISP

As soon as you’re in the Visual LISP environment, you can create a new AutoLISP file or open an existing file.

To edit or view a file in the Visual LISP text editor, follow these steps:

1.Choose File Open File from the Visual LISP menu.

2.In the Open File to Edit/View dialog box, locate and choose the file you want to open.

3.Click Open. Visual LISP opens the file in its own window, as shown in Figure 34-2.

When you open a file, the title bar of its window displays a blank paper icon to show that the file has not been changed. If you make any changes to the file, Visual LISP adds a pencil to the image to show that you’ve edited the file.

You can open as many files as you want.

Figure 34-1: The Visual LISP window.

Figure 34-2: An AutoLISP file open in its own window in the Visual LISP window.

988 Part VII Programming AutoCAD

Loading an AutoLISP file

To use the AutoLISP program in AutoCAD, you must load it. You can load it from within Visual LISP or from within AutoCAD.

If you have a file open in Visual LISP, choose Tools Load Text in Editor or choose Load Active Edit Window from the Tools toolbar.

If you’re in AutoCAD, you can load AutoLISP files into AutoCAD in two ways. One method is on the command line. To load 3DARRAY from the command line, type (load “3darray”) . The parentheses are required, and they indicate that you’re entering an AutoLISP expression. AutoLISP requires the quotation marks because you’re specifying a filename. AutoCAD responds with 3DARRAY loaded.

When you enter the command to load 3DARRAY, AutoCAD searches all support paths for a file called 3darray.lsp. At installation time, AutoCAD automatically configures the support-file search path to include the path of AutoCAD 2005\Support. For a full list of folders in

the support-file search path, choose Tools Options and click the Files tab. Double-click the Support File Search Path item.

Note AutoLISP files have the extension of .lsp. However, for security and speed, you can compile AutoLISP routines as .fas or .vlx project application files. AutoCAD loads .vlx first, then .fas, and .lsp files last. For example, if you have both a redline.vlx and a redline.lsp, AutoCAD loads the redline.vlx file. If, however, the .lsp file is newer than the .fas file, AutoCAD will load the .lsp file. If an AutoLISP routine is associated with a menu, it has an .mnl extension. For more information, see Chapter 33.

If your file is not in a folder in AutoCAD’s support file search path, you must specify the full path name. To specify the full path to the routine type, you would enter:

(load “c:/Program Files/AutoCAD 2005/Support/3darray”) /

or

(load “c:\\Program Files\\AutoCAD 2005\\Support\\3darray”)

The backslash (\) has special meaning in AutoLISP, so you need to use two of them or a regular slash (/) when specifying a path. (The backslash character tells AutoLISP to interpret the following character as a special control code. To use a double quote in an AutoLISP expression, for example, precede it with a backslash.)

You can also load AutoLISP routines with the APPLOAD command by choosing Tools Load Application or by typing appload at the command line. AutoCAD opens the Load/ Unload Applications dialog box, shown in Figure 34-3.

Use this dialog box to load FAS, VLX, and LSP files. (You can also load other types of programming files in this dialog box — ARX, DVB, and DBX files.) If you check Add to History, AutoCAD lists previously loaded applications in the dialog box — just click the History List tab. Locate and choose the file you want to load and click Load.

Figure 34-3: The Load/Unload Applications dialog box.

Using an AutoLISP routine in AutoCAD

After you load an AutoLISP routine, you can use it. How you use the routine depends on the routine. If the program creates a function, you can type the function’s name on the command line like any other AutoCAD command. Most routines contain prompts to guide you in their use.

STEP-BY-STEP: Loading and Using an AutoLISP Routine

1.Use Windows Explorer to copy circle3.lsp from the CD-ROM to your AutoCAD 2005\Support\ folder or to a folder you added to the support file search path.

2.Create a new drawing using any template.

3.Choose Tools AutoLISP Visual LISP Editor. The Visual LISP IDE opens.

4.If any AutoLISP files are displayed in the main area, click their Close boxes.

5.Choose Open on the Standard Visual LISP toolbar. In the Open dialog box, navigate to the folder where you saved circle3.lsp and double-click it. It appears in the Visual LISP window.

6.Choose Load Active Edit Window from the Visual LISP Tools toolbar. The Visual LISP Console window confirms that circle3.lsp has been loaded.

990 Part VII Programming AutoCAD

7.Choose Activate AutoCAD from the Visual LISP View toolbar. Visual LISP returns you to AutoCAD.

8.Now that circle3 has been loaded, at the command prompt, type circle3 .

9.At the Please click a point: prompt, pick any point on-screen. You see a 3-unit radius circle with its center at the point you picked, as shown in Figure 34-4.

Figure 34-4: The circle drawn using the circle3

AutoLISP routine.

10. Save your drawing in your AutoCAD Bible folder as ab34-01.dwg.

Looking at an AutoLISP routine

To examine the contents of the circle3.lsp file, open it in the Visual LISP editor. Figure 34-5 shows the circle3 routine. At this point, ignore the color formatting, which is discussed later in this chapter.

Figure 34-5: The circle3 AutoLISP routine.

This figure illustrates several general characteristics of AutoLISP routines:

As in many programming languages, indentation is used in AutoLISP to make it easier to read the code. It has no effect on the operation of the routine.

The returns at the end of each line also make it easier to read and understand the code. All five lines could be placed on a single line, and the program would work exactly the same way.

All AutoLISP statements are placed in parentheses. Therefore, whenever you open a parenthesis you must close it. Every AutoLISP routine must have the same number of left and right parentheses. The physical location of a right parenthesis is not relevant — it can be placed on a new line or positioned several spaces away from the left parenthesis. In both cases, the pair is interpreted the same way.

AutoLISP is interpreted from the innermost parenthetical elements first. On line 3 of the code shown in Figure 34-5, for instance, (getpoint) is done first, and then the result is

used for the (setq pt (getpoint)) expression. This is analogous to mathematics, as in the expression (3 + (5 × 4)), where 5 × 4 is computed first and the result is added to 3.

At the end of the first line is a comment, ;Creates a circle of radius 3. The program ignores any text preceded by a semicolon. Use this technique to place explanations in your routines to help you and others understand what the routine is doing.

The following explains the routine in Figure 34-5 line by line:

Line 1 begins with an open parenthesis that is balanced with the one on line 5. This pair of parentheses delineates the body of the function. The line begins with defun, which stands for define function, and the function is called c:circle3. When you prefix the function with c:, you can use it in AutoCAD by just entering circle3 at the command line like any other AutoCAD command. (The c: stands for command and has no relation to your hard drive, which is also usually called c:.) You could use just circle3, but you would have to type (circle3) at the command line to use the routine. The last item on Line 1 is (/ pt). The pt after the slash means that pt is a local variable. A variable stores a value for later use in the routine. A local variable is used only in its own routine and is not retained for use in other routines. If you replaced (/ pt) with simply ( ), the pt variable would be available to other AutoLISP routines as well.

Line 2 is the simplest line in this routine — it simply prints the statement Please click a point: at the command line. Anything in the quotes after princ will be printed on the AutoCAD command line. In this case, the statement is used as a prompt to tell the user to pick a point.

Line 3 is typical of AutoLISP routines in which nested parentheses can drive the reader crazy. Remember to read from the innermost parenthetical element outward. So reading from the innermost parenthetical element, you have first (getpoint). This means to simply get a point. Any of the AutoCAD input methods work — clicking the screen, typing coordinates for a point, or using object snaps. Reading outward you have (set q pt (getpoint)). The statement setq means that the variable pt is set to whatever comes back from getpoint. So if you enter the coordinates 2,2 by typing them or selecting them on the screen, the variable pt equals 2,2.

Line 4 reads (command “_circle” pt “3”). The command function in AutoLISP is one of the easier functions to understand. It simply executes whatever AutoCAD command is specified in the quotes that follow, using all subsequent arguments. When the CIRCLE command is invoked in AutoCAD, it asks for the center point first and then the radius. Line 4 starts the CIRCLE command, uses for the center point whatever is assigned to the variable pt, and sets the radius to 3 units.

Note An underscore precedes the CIRCLE command so that it can be translated into other language versions of AutoCAD.

Using the Visual LISP interface

The Visual LISP window contains a number of tools that make your programming life simpler. These tools represent the difference between the old way of writing AutoLISP code — creating text files in a text editor — and the new visual way, with tools that help you format and complete your code. Some of the more useful tools include:

Format Edit Window: Choose Format Edit Window on the Tools toolbar (or

choose Tools Format Code in Editor) to indent code (and comments) so that it’s more readable. Indenting code helps you understand levels of nested parentheses more clearly. Of course, you can indent your code manually, but automatic indenting is a boon to all AutoLISP programmers.

992 Part VII Programming AutoCAD

Format Selection: Select the code you want to format. Then choose Format Selection on the Tools toolbar (or choose Tools Format Code in Selection)

to indent only the selected code.

Check Edit Window: Choose Check Edit Window from the Tools toolbar (or choose Tools Check Text in Editor) to perform a preliminary evaluation prior

to loading the file. This evaluation checks the code for unbalanced parentheses, invalid function definition formatting (an attempt to redefine a built-in or protected function), and many other common errors. Visual LISP opens the Build Output window to show you the results.

Check Selection: Select the code you want to check. Choose Check Selection from

the Tools toolbar (or choose Tools Check Selection) to perform a preliminary evaluation on selected code. Visual LISP opens the Build Output window to show you the results.

Parentheses Matching: The most common error for an AutoLISP programmer is incorrect parentheses matching. Visual LISP enables you to jump between matching parentheses and quickly check your current nesting level as you develop your application. While you can use the menu items (choose Edit Parentheses Matching Match Forward and Match Backward), you’ll find that the keyboard shortcuts distract you less from the code you’re looking at. To find a matching right parenthesis, press Ctrl+]. To find a left matching parenthesis, press Ctrl+[.

Load Selection: You’ve already seen how to load the code in the active window. You can also load selected code. Select the code you want to load and choose

Load Selection from the Tools toolbar or choose Tools Load Selection.

Comment Block: In Figure 34-5, you see an example of a comment. Visual LISP supports several comment styles, which Chapter 35 covers. Visual LISP simplifies

the addition of a 3-semicolon comment. To place a 3-semicolon comment, highlight the text you want to change into a comment and click Comment Block on the Tools toolbar. See Chapter 35 for more information on creating comments.

Uncomment Block: To remove a 3-semicolon comment, click Uncomment Block on the Tools toolbar.

Another feature of Visual LISP is the Console window. The Console window usually resides at the bottom of the Visual LISP window. The Console window is similar to the AutoCAD command line. Just as you can enter AutoLISP expressions on the AutoCAD command line, as explained later in this chapter, you can also enter AutoLISP expressions in the Console window and see the results. Each line uses a _$ prompt.

A nice feature of the Console window is that Visual LISP remembers everything you enter. You can retrieve it by pressing Tab for a forward history or Shift+Tab for a backward history.