AutoLisp programming

AutoCAD 2013 Prof Rajendra Salokhe

AutoLISP PROGRAMMING

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CHAPTER VIII AutoLISP PROGRAMMING

INTRODUCTION:

W

hen you are drawing in AutoCAD , you are actually issuing the commands. If you combine these commands, store them in a file and ask the compiler to execute them line by line , then what these set of commands become is a program. AutoLISP is exactly this, a programming language. AutoLISP allows creating user-defined functions, which can be called in the drawing. AutoLISP is mostly used for creating such functions.

Command Menu Ribbon

VLISP Tools → AutoLISP →Visual LISP Editor Manage tab → Applications panel → Visual LISP Editor

Tools Toolbar

Standard Toolbar View Toolbar

Debug Toolbar

Console Window

Each function starts with (defun and ends with a closing parenthesis. Function body is typed into a text file using EDIT command and saved with extension .LSP. You can issue EDIT command at AutoCAD command prompt. You must load this .LSP file before using the program. One thing to remember is that whenever you make any changes to LISP program, you must load this file because AutoLISP program is interpreted not compiled. This chapter is just to introduce you to AutoLISP. VLISP is out of scope of this book.



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UNDERSTANDING EXPRESSIONS AND EVALUATIONS: Open a new file in AutoCAD. At the command prompt, type following (+ 1.2 1) AutoLISP evaluates the above formula, returns the value 2.2, and displays it at the prompt line. The structure (+ 1.2 1) is called an expression and answer 2.2 returned by it is called a value of that expression. Here + is called an 'operator' i.e. it is an instruction to take some specific action such as adding or multiplying two numbers. All AutoLISP expressions follow this structure and are enclosed by parenthesis. Here + operator is treated as a function and the 1.2 and 1 are treated as arguments. Along with +, -, *, / are also mathematical operators available to and AutoLISP program. Enter the following expression at the command prompt.

(* 2 (+ 0.2 1)) It returns the value 2.4. The above expression is called nested expression. Here * operator takes two arguments viz. 2 and (+ 0.2 1). It works as follows:

(* 2 (+ 0.2 1)) =(* 2 1.2) = 2.4 DATA TYPES IN AUTOLISP:

As it is clear from above that values of above expressions are not stored. To store the value, a variable can be used e.g. Val1, Val2 etc. Each variable has its own data type like Integer (e.g. 10,12,100), Real Number (e.g. 1.2, 0.4), String (e.g. "AutoLISP"), List (e.g. (2 2 2)), Subrs (e.g. setq, setvar) are used. Integer:

Integers are whole numbers. Their range is -32768 to 32767. (C or C++ programmers may know this.) Thus, the value returned by expression containing only integers will always be an integer e.g. if you enter the expression (/ 101 2), you will get the value as 50 because decimal places are simply ignored. The correct expression will be (/ 101.0 2). This expression will return the correct value as 50.5. In this expression integer 101 is simply type casted to real number. Type casting is converting lower data type into higher data type. Real Number:



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The real numbers are the numbers that involve decimal places. You must precede decimal point by zero if the value of real number is between zero and one. So in some prior expression, 0.2 is correct not .2. Subrs:

The Subrs are built in functions offered by AutoLISP e.g. setq, setvar.

(setq price 100) In the above expression, the variable price is assigned a value 100. You can check the value of the variable price by entering !price at the command prompt. You may even change current colour in colour control window to any colour say yellow by typing following at the command prompt.

(setvar "CECOLOR" "2") This changes the current colour to yellow in Colour Control Window on Object Properties Toolbar.

Strings Strings are set of characters or text. It is enclosed in double quotes and used for prompts. e.g. (setvar "gridunit" '(10 10)) Lists: Many times you have to specify x,y,z co-ordinates of a point . At such time the data is enclosed in parenthesis as (5,6,7). This type of data is called list and it is a basic data structure in AutoLISP. Consider following expression

(setvar "gridunit" '(10 10)) With this expression current grid spacing is changed to 10 for both X and Y spacing. Here gridunit is a string since we want to read it as it is without evaluating it. (10 10) is called as list, which assigns the value 10 to grid X and Y spacing. You will observe a single quote before list expression. It is to ensure that AutoCAD don't evaluate it and treat it as argument only. Another example of list expression is

(setq p1 (list 2 3)) You can get the value of p1 by typing !p1 at the command prompt. Here 2 3 are X and Y co-ordinates of point p1. You may read X and Y co-ordinate of point p1 by using CAR and CADR functions as follows (car p1) will return a value 2 while (cadr p1) will return a value 3



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FUNCTIONS FOR ASSIGNING VALUES TO VARIABLES: Setq

You can assign values to the variable with setq function. e.g. (Setq xyz 0.8) Setvar

Setvar function changes the value of system variable as e.g. (setvar “surftab1” 16) car

car function returns X co-ordinate value from the list cadr

cadr returns Y co-ordinate value. Until now, you have assigned values to variables directly. Sometimes it becomes necessary to get information from user. E.g. center of circle, angle etc. This can be achieved using function. All These functions are identified by their GET prefix. Some of the functions are discussed below. GETPOINT: Accepts co-ordinates of a point e.g. (setq p1(getpoint)) GETCORNER: Selects a point using a window. This function

requires a base point value defining the first corner of the window. The window appears allowing you to select opposite corner

e.g. (setq p2(getcorner p1"Pick opposite corner:")) You may draw line between these point by specifying end points of line as !p1 and !p2. You may even draw a rectangle between these two points also. GETDIST: Accepts distances through mouse or keyboard.

Note , the brackets are necessary while entering the command.

e.g. (getdist) Enter 0,0 ↵ You will be asked to Specify second point: 3,4 ↵

You will get the value as 5 GETANGLE: Accepts angle, but returns a value in radians.

Enter (getangle) at command prompt Enter 90↵ You will observe the value 1.5708 which is in radians.



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GETORIENT: Accepts angles based on Units command setting for angles.

Type (getorient) at the command prompt Type 0,0↵ Specify second point: 3,3 ↵ You will get value 0.785398 in radians orientation is 45 °.

SAMPLE PROGRAMS: After a brief introduction to AutoLISP fundamentals, we shall now go through few AutoLISP programs. First three programs are about circle. First program issues a CIRCLE command only. The second program draws circle. The third program accepts center and radius of circle from the user and draws the circle. Let us how these programs work. PROGRAM 1 At the command prompt, type EDIT ↵ At File to edit: prompt, type

or type VLISP at the command prompt. The VLISP editor as shown in the above figure will popup. Type and save the program. (AutoCAD 2013 users type VLIDE at the command prompt.) Type following program code in the file.

(defun C: CIRCLE01() (command "circle") )


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Exit the DOS Shell after saving the program. This program is a simple AutoLISP program. It starts with (defun function as discussed earlier in the introductory part of this chapter. CIRCLE01 is a function that will issue command circle. First, we shall load this file. Type (load "CIRCLE01.LSP") ↵ at AutoCAD command prompt. Type CIRCLE01↵ at next command prompt. You will observe regular circle command issued in command window. Now you can select center point of circle and radius through mouse or keyboard. PROGRAM 2

Using EDIT command type following program in a file CIRCLE02.LSP and save it

(defun C:CIRCLE02() (command "circle" "4,4" "3") ) Again, load this file by typing following line at command prompt.

(load "CIRCLE02.LSP")↵ Type CIRCLE02↵ A circle with center 4,4 and radius 3 will be drawn inside the drawing area. PROGRAM 3 Type following program in another file named CIRCLE03.LSP and save it.

(defun C:CIRCLE03.LSP(/ CEN RAD) (setq CEN(getpoint"\nSpecify center point for the (setq RAD(getint"\n Specify radius for the circle: ")) (command "circle" CEN RAD) )

circle:"))

Load this file in the same manner as above and run it by typing CIRCLE03 at command prompt. You will be asked to Specify center point for the circle: 4,5 ↵ Specify radius for the circle: 4 ↵ A circle with center 4,5 and radius 5 will be drawn inside the drawing area. In the third program, you will observe the first line as

(defun C:CIRCLE03.LSP(/ CEN RAD) Here, the arguments to defun are C:CIRCLE03, followed by argument list. CEN and RAD are variable to store co-ordinates of center and radius of circle, respectively.



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Next, look at the following line

(setq CEN(getpoint"\nSpecify center point for the circle:")) Here getpoint function accepts the co-ordinates for the circle and assign them to variable CEN. Similar is the case with next setq statement. One more thing that you will observe is that the files are saved with same name as that of the function name. It is not necessary to do the same. You can save the file with different name than that of the function name.

PROGRAM 4

This program draws rectangle by accepting corner points from user.

(defun C:RECT01.LSP(/ p1 p2 p3 p4) ; Accepting co-ordinates for corners of rectangle (setq p1(getpoint"\nSpecify co-ordinates for first corner: ") p3(getcorner p1"\nSpecify co-ordinates for opposite corner: ")) ; Defining co-ordinates for points p2 and p4 (setq p2(list(car p3)(cadr p1)) p4(list(car p1)(cadr p3))) ; Drawing the rectangle (command "line" p1 p2 p3 p4 "c") ) The above program is self-explanatory. Every line is already explained in earlier part of this chapter. In the above program, we draw a rectangle through three steps viz. getting co-ordinates for two corners of rectangle, defining remaining two corners for rectangle and finally drawing rectangle. We can write codes for above three steps in a separate function and call them in our main program. This helps overall readability of program when program size becomes bigger. This is illustrated in following program.

(defun getcorners() ; Accepting co-ordinates for corners of rectangle (setq p1(getpoint"\nSpecify co-ordinates for first corner: ") p3(getcorner p1"\nSpecify co-ordinates for opposite corner: ")) )



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(defun define() ; Defining co-ordinates for points p2 and p4 (setq p2(list(car p3)(cadr p1)) p4(list(car p1)(cadr p3))) ) (defun draw() ; Drawing the rectangle (command "line" p1 p2 p3 p4 "c") ) (defun C:RECT02(/ p1 p2 p3 p4) (getcorners) (define) (draw) ) You may add more functions to above code e.g. you may add function named thick() to give the above drawn rectangle a thickness so that it behaves as a 3D object. You will come to know this fact by going through following program. Save the file 'RECT02.LSP' AS 'RECT03.LSP'. by using SAVE AS option in File Menu in DOS Shell. Now type following function body for giving thickness to latest drawn rectangle after the draw() function.

(defun thick() ; Get thickness for rectangle (setq h(getint""\nSpecify thickness for this rectangle:)) (command "change" "l" "" "p" "t" h "") ) The main defun function will look like as follows.

(defun C:RECT03(/ p1 p2 p3 p4 h) (getcorners) (define) (draw) (thick) ) We shall add one more function called box() to add 3D face to above drawing so that it will look like box in Isometric view. So just write following function code after definition of function thick(). Save RECT03.LSP file as RECT04.LSP and in that do the required modifications.



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(defun box() (command "3dface" p1 p2 p3 p4 "" "3dface" ".xy" p1 h ".xy" p2 h ".xy" p3 h ".xy" p4 h "") ) (defun C:RECT04(/ p1 p2 p3 p4 h) (getcorners) (define) (draw) (thick) (box) ) PROGRAM 5 The program demonstrates a design created by polar array of circles. You can use 3DCORBIT command in conjunction with the output of above program to have some fun. Let see how it is done.

(defun C:DESIGN() ; Setting color of the given circle (command "CECOLOR" "1" "') (command "circle" "5,5" "3" "') ; Making polar array of the above circle. (command "array" "l" "p" "8,3" "" "" "10" "" "") ) After loading and running this program, issue 3DCORBIT command at the command prompt. Now, inside drawing area, hold left click and drag the mouse suddenly to upper side of the drawing and release the click. All this action should happen quickly so that circles revolve with a good speed. While circles are revolving, right click inside drawing area, a menu will pop up. Select 'Preset View' option from it and then select 'Top' or 'Bottom' option from the next cascading menu. To make UCS icon off, select option 'Visual Aids' from the same pop up menu by right clicking inside the drawing area. If 'UCS Icon' is checked, select it. Now, you will observe circles are revolving like wheels of an automobile. Revolving speed will vary upon how fast you click, drag and left mouse click.



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PROGRAM 6 Next, we shall generate following drawing through AutoLISP program.

(defun C:DRAWING() ; Setting working area for drawing (command "limits" "0,0" "60,40") (command "grid" "10") (command "snap" "10") (command "zoom" "all") ; Starting with the drawing (command "pline" "0,0" "60,0" "60,40" "0,40" "c") (command "extrude" "l" "" "10" "") (command "pline" "50,0" "60,0" "60,10" "50,10" "c") (command "extrude" "l" "" "20" "") (command "pline" "0,30" "10,30" "10,40" "0,40" "c") (command "extrude" "l" "" "20" "") ; Let us UNION these three objects (command "union" "all" "") ; Drawing rectangle at the central portion (command "pline" "20,15" "40,15" "40,25" "20,25" "c") ; Drawing circle at one end of above rectangle (command "circle" "20,20" "5" "") ; Let us Mirror this circle at other end of this rectangle. (command "mirror" "l" "" "30,0" "30,40" "") ; Let us Extrude above three objects (command "extrude" "w" "10,10" "45,35" "" "10" "" "")



; Let us UNION these three objects (command "union" "w" "10,10" "45,35" "" "") ; Subtracting central objects from rest of the drawing (command "subtract" "c" "0,10" "10,0" "" "l" "" "") ; Viewing this drawing in SW Isometric View (command "-view" "swiso" "") (command "hide") ); End of defun function

End of chapter 08

Chapter 8 Page 340

AutoLisp programming

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