AutoCAD 2000 Visual LISP Tutorial, Notas de estudo de Engenharia Mecânica

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VISUAL LISP™ TUTORIAL

00120-010000-5080 January 29, 1999

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Copyright © 1999 Autodesk, Inc.

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In This Chapter

Introduction

This tutorial is designed to demonstrate several

powerful capabilities of the Visual LISP™^ programming

environment for AutoCAD®^ and introduce features of

the AutoLISP ®^ language that may be new to you.

The purpose of the tutorial is to draw a garden path

using an automated drawing tool that minimizes

drafting time and shows the power of parametric

programming. You will learn how to create a drawing

routine that automates the generation of a complex

shape—the kind of drafting operation you do not want

to draw over and over again, if it means starting from

scratch each time.

n The Garden Path Revisited: Working in Visual LISP n Tutorial Overview

2 | I Introduction

The Garden Path Revisited: Working in Visual

LISP

This tutorial is intended for experienced AutoCAD users and assumes you have some familiarity with either LISP or AutoLISP. It also assumes you understand basic Windows ®^ file management tasks such as creating direc- tories, copying files, and navigating through the file system on your hard disk or network. If you are familiar with AutoLISP and have used earlier versions of the Garden Path tutorial, you will notice several differences:

n The Visual LISP (VLISP™^ ) environment is introduced. This environment provides you with editing, debugging, and other tools specific to the cre- ation of AutoLISP applications. Previous versions of the Garden Path tutorial taught AutoLISP language concepts—not VLISP development tools. n New ActiveX™^ and Reactor functions of AutoLISP are demonstrated, as well as several other extensions to the AutoLISP language provided with VLISP. n The tutorial has been thoroughly redesigned. Even if you are familiar with the previous version, you will encounter entirely different source code and a much more extensive tutorial. n There are two possible execution contexts for the Garden Path tutorial. The application may be run as interpreted LISP in piecemeal files and/or functions that are loaded into a single document. Alternately, the program code can be compiled into a VLX application, denoted by a *.vlx execut- able. A VLX operates from a self-contained namespace that can interact with the application-loading document.

In This Lesson

Designing and Beginning

the Program

In this first lesson, you'll begin by defining what the

application will do. Using the Visual LISP (VLISP) devel-

opment environment, you'll create a LISP file and begin

writing AutoLISP code to support your application.

In the process, you'll begin to discover how VLISP

facilitates application development.

n Defining Overall Program Goals n Getting Started with Visual LISP n Looking at Visual LISP Code Formatting n Analyzing the Code n Filling the Gaps in the Program n Letting Visual LISP Check Your Code n Running the Program with Visual LISP n Wrapping Up Lesson 1

Getting Started with Visual LISP | 7

To run the supplied example 1 From the AutoCAD Tools menu, choose Load Application. 2 Select gardenpath.vlx from the Tutorial\VisualLISP directory, and choose Load. 3 Press Close. 4 At the Command prompt, enter gpath. 5 Respond to the first two prompts by picking a start point and an endpoint in the AutoCAD graphics window. 6 Enter 2 at the Half Width of Path prompt. 7 Choose OK when prompted by the Garden Path Tile Specifications dialog box.

Getting Started with Visual LISP

Now that you’ve seen how the application is supposed to work, you can begin developing it with VLISP. But first, it helps to demonstrate what can happen when VLISP is waiting for control to return from AutoCAD. You may have already encountered this.

To see Visual LISP wait for control to return from AutoCAD 1 At the AutoCAD Command prompt, enter vlisp^ to start Visual LISP. 2 Switch back to the AutoCAD window (either select AutoCAD from the task- bar or press ALT^ +^ TAB^ and choose AutoCAD), and enter^ gpath^ at the AutoCAD Command prompt. 3 Before responding to the prompts from gpath , switch back to the VLISP window. In the VLISP window, the mouse pointer appears as a VLISP symbol and you cannot choose any commands or enter text anywhere in the VLISP window. The pointer symbol is a reminder that there is an activity you must complete in AutoCAD before resuming work with VLISP. Remember this whenever you see the VLISP pointer. 4 Return to the AutoCAD window and respond to all the prompts from gpath.

Now you are ready to begin building the garden path application.

8 | Lesson 1 Designing and Beginning the Program

To begin application development with Visual LISP 1 From the VLISP File menu, choose New File. 2 Enter the following code in the text editor window (it is the window titled “<Untitled-0>”); you can omit the comments, if you wish: ;;; Function C:GPath is the main program function and defines the ;;; AutoCAD GPATH command. (defun C:GPath () ;; Ask the user for input: first for path location and ;; direction, then for path parameters. Continue only if you have ;; valid input. (if (gp:getPointInput) ; (if (gp:getDialogInput) (progn ;; At this point, you have valid input from the user. ;; Draw the outline, storing the resulting polyline ;; "pointer" in the variable called PolylineName. (setq PolylineName (gp:drawOutline)) (princ "\nThe gp:drawOutline function returned <") (princ PolylineName) (princ ">") (Alert "Congratulations - your program is complete!") ) (princ "\nFunction cancelled.") ) (princ "\nIncomplete information to draw a boundary.") ) (princ) ; exit quietly ) ;;; Display a message to let the user know the command name. (princ "\nType gpath to draw a garden path.") (princ) 3 Choose File ä Save As from the menu, and save the code in the new file as \Tutorial\VisualLISP\MyPath\gpmain.lsp. 4 Review your work.

Looking at Visual LISP Code Formatting

VLISP recognizes the various types of characters and words that make up an AutoLISP program file and highlights the characters in different colors. This makes it easier for you to spot something incorrect quickly. For example, if you miss a closing quotation mark following a text string, everything you type continues to display in magenta, the color denoting strings. When you enter the closing quotation mark, VLISP correctly colors the text following the string, according to the language element it represents.

10 | Lesson 1 Designing and Beginning the Program

For now, you will just write stubbed-out function definitions. A stubbed-out function serves as a placeholder for the complete function that is to follow. It allows you to try out pieces of your code before adding all the detail needed to complete the application.

To define stubbed-out functions for the application 1 Position your cursor at the top of the program code in the text editor window and press ENTER^ a couple of times to add blank lines. 2 Enter the following code, beginning where you inserted the blank lines: ;;; Function gp:getPointInput will get path location and size (defun gp:getPointInput() (alert "Function gp:getPointInput will get user drawing input" ) ;; For now, return T, as if the function worked correctly. T ) ;;; Function gp:getDialogInput will get path parameters (defun gp:getDialogInput () (alert "Function gp:getDialogInput will get user choices via a dialog" ) ;;For now, return T, as if the function worked correctly. T ) ;;; Function gp:drawOutline will draw the path boundary (defun gp:drawOutline () (alert (strcat "This function will draw the outline of the polyline" "\nand return a polyline entity name/pointer." ) ) ;; For now, simply return a quoted symbol. Eventually, this ;; function will return an entity name or pointer. 'SomeEname ) Right before the end of each input function is a line of code that contains only a T. This is used as a return value to the calling function. All AutoLISP functions return a value to the function that called them. The letter T^ is the symbol for “true” in AutoLISP, and adding it causes the function to return a true value. The way gpmain.lsp is structured, each input function it calls must return a value other than nil (which indicates “no value”) for the program to proceed to the next step. An AutoLISP function will, by default, return the value of the last expression evaluated within it. In the stubbed-out functions, the only expression is a call to the alert function. But alert always returns nil. If this is left as the last

Letting Visual LISP Check Your Code | 11

expression in gp:getPointInput , it will always return nil, and you will never pass through the if^ to the^ gp:getDialogInput^ function. For a similar reason, the end of the gp:DrawOutline function returns a quoted symbol ('SomeEname) as a placeholder. A quoted symbol is a LISP con- struct that is not evaluated. (If you are curious about how the LISP language works, there are a number of good books available, mentioned at the end of this tutorial.)

Letting Visual LISP Check Your Code

VLISP has a powerful feature for checking your code for syntactical errors. Use this tool before trying to run the program. You can catch common typing errors such as missing parentheses or missing quotation marks, and other syntactical problems.

To check the syntax of your code 1 Make sure the text editor window containing gpmain.lsp is the active win- dow. (Click in the title bar of the window to activate it.) 2 From the VLISP menu, choose Tools ä Check Text in Editor. 3 The Build Output window appears with the results of the syntax check. If VLISP did not detect any errors, the window contains text similar to the following: [CHECKING TEXT GPMAIN.LSP loading...] ...... ; Check done. If you have problems and need help, refer to the “Developing Programs with Visual LISP” chapter of the Visual LISP Developer’s Guide. See if you can deter- mine where the problem is located. If you are spending too much time locating the problem, use the sample gpmain.lsp file provided in the lesson directory to continue with the tutorial.

To use the supplied gpmain.lsp program (if necessary) 1 Close the text editor window containing the gpmain.lsp code you entered. 2 Choose File ä Open File from the VLISP menu, and open the gpmain.lsp file in the \Tutorial\VisualLISP\lesson1 directory. 3 Choose File ä Save As and save the file in your \Tutorial\VisualLISP\MyPath directory as gpmain.lsp , replacing the copy you created.

In This Lesson

Using Visual LISP

Debugging Tools

This lesson teaches you how to use several valuable

VLISP debugging tools that speed up the development

of AutoLISP programs. You will also learn the difference

between local and global variables, and when to use

them. Your program will become more active—prompt-

ing users to enter some information. The information

will be stored in a list and you’ll begin to understand

the power of using lists within your AutoLISP programs.

After all, LISP got its name because it is a LISt Processing

language.

n Differentiating between Local and Global Variables n Using Association Lists to Bundle Data n Examining Program Variables n Revising the Program Code n Commenting Program Code n Setting a Breakpoint and Using More Watches n Wrapping Up Lesson 2

14 | Lesson 2 Using Visual LISP Debugging Tools

Differentiating between Local and Global

Variables

This lesson discusses the use of local variables versus global document variables. Global variables are accessible by all functions loaded within a doc- ument (an AutoCAD drawing). These variables may retain their value after the program that defined them completes. Sometimes, this is what you want. You’ll see an example of this later in the tutorial. Local variables retain their value only as long as the function that defined them is running. After the function finishes running, the local variable val- ues are automatically discarded, and the system reclaims the memory space the variable used. This is known as automatic garbage collection, and is a fea- ture of most LISP development environments, such as VLISP. Local variables use memory more efficiently than global variables.

Another big advantage is that local variables make it easier to debug and maintain your applications. With global variables, you are never sure when or in which function the variable’s value might be modified; with local vari- ables you don’t have as far to trace. You usually end up with fewer side effects (that is, one part of the program affecting a variable from another part of the program). Because of the advantages cited, this tutorial uses local variables almost exclusively.

FunA (setq localvara "boo") (setq localvara "hoo") (setq globalvara "foo") (funB) (print localvara) "boo" (print globalvara) "whenever"

FunB (print localvara) nil (print localvarb) nil (print globalvara) "foo" (setq globalvara "whatever) (setq localvara "fie") (funC) FunC (print localvara) nil (print globalvara) "whatever" (setq globalvara) "whenever"