Kapitel 9

AutoCad III: Zugriff auf geometrische Einheiten und die System Umgebung

9.1 AutoCad Database

AutoLisp provides a set of functions to access and modify graphic entities and their properties. Additionally, some other functions provide direct access to input devices like keyboard, digitizer, and output devices like screen. These functions are specific to AutoLisp and are not part of the standard LISP programming language.

Drawing entities created as part of any AutoCad drawing are stored internally in a database of information. Whenever you perform any operation- addition of a new entity, modification of an entity, or deletion of an entity, the drawing database is updated with new information. To access this database, AutoLisp provides two special data types, called entity names and selection sets.

9.2 Entity Access

9.2.1 Entity Name Functions

(entnext)
Returns the name of the first nondeleted entity in the database.
(entnext ename)
Returns the name of the first nondeleted entity following ename in the database.
(entlast)
Returns the name of the last nondeleted entity in the database.
(entsel)
Prompts the user for selecting an entity by a point pick, and returns a list containing selected entity name and coordinates of point used to select that entity.
(entsel prompt)
Same as above but uses the value of prompt string for entity selection.

9.2.2 Entity Data Functions

(entdel ename)
If entity ename is currently in the drawing, it is deleted; and undeleted if it has been deleted during the current editing session.

(entget ename)
Returns an association list of definition data for entity ename. Data in the association list follow group code specification.
Example: If a line is drawn on layer "test", starting from (1 1 0) to (2 3 0), then its entity data may look like the following:

(entget (entlast))
((-1 . ) ; entity name
(0 . "LINE") ; entity type
(8 . "TEST") ; layer
(10 1.0 1.0 0.0) ; starting point
(11 2.0 3.0 0.0) ; ending point
)

(entmod elist)
Performs entity data modification. Argument elist to this function is an association list- the kind returned by the function entget. Entity data can be modified using a function like subst, and then invoking this function- entmod.
Example: If the line entity in above example were to be changed to another layer "test2", following sequence will be required:

(setq linedata (entget (entlast)))

;get definition data for line

(setq linedata
(subst
(cons 8 "test2") ;new layer value
(assoc 8 linedata) ;old layer value
linedata ;old entity data
)
)
(entmod linedata);finally update database

(entupd ename)
Entity is updated and regenerated on screen following any modification after above function entmod is executed.

9.2.3 Selection Set Functions

(ssget)

Selects entities using standard Select Objects: prompt

(ssget mode)

Same as above using one of the valid mode values:

W (world), C (crossing), L (last), P (previous)

(ssget pt1)

Selects entity passing through point pt1

(ssget "X" filter)

Selects entities matching the filter.

Example:

(ssget "X" (list (cons 8 "test")))

will return a selection set containing all entities on layer "test".

A complete list of group codes for filters is given in

AutoLisp Programmer's Reference, Pages 68-69.

(sslength selset)

Returns the number of entities in the selection set- selset.

(ssname selset num)

Returns the name of num'th entity in the selection set- selset.

(ssadd)

Constructs a new selection with no members.

(ssadd ename)

Constructs a new selection set with ename as its member.

(ssadd ename selset)

Add entity ename to the selection set- selset.

(ssdel ename selset)

Deletes entity ename from the selection set- selset.

9.2.4 Symbol Table Access

Information about layer, linetypes, views, text styles, and blocks is stored in symbol tables. This information can be accessed using following functions.

(tblnext tname)

Returns data stored in symbol table specified by tname. Valid values for tname are: layer, ltype, view, style, block, ucs, vport. If this function is called repeatedly, it returns the next entry in the same table.

(tblsearch tname sym)

Searches the symbol table tname for the symbol specified by sym, and returns the data if any match is found.

9.3 Device Access

(grclear)

Clears the current viewport.

(grdraw pt1 pt2 color)

Draws a vector from pt1 to pt2 in the color specified.

(grtext box text)

Displays the string text in teh menu area specified by box

(grread)

Returns a list whose first element is the input device code, and the second element is either an integer or a point list.

After using any of these functions, you may need to use redraw to regenerate drawing.

9.4 Pull Down Menus

AutoCad provides a set of standard and customizable interaction techniques, using which users can execute various commands. A subset of these techniques involves using menus of various kinds- screen, pull down, icon, button, and tablet menus. Commands to implement these techniques are placed in the acad.mnu file.

A menu file is a plain text file containing command strings. All menu files must have extension .mnu (compiled version will have extension .mnx). Each menu item may consist of a command, a parameter, or a sequence of commands and parameters. By convention, each menu item resides on a separate line in the menu file.

Example: Following is a simple command menu file.

circle

zoom e

zoom p

When you select any of these options, AutoCad will execute corresponding command.

Menu File Section Labels

Section labels in a menu file assign various options/commands to different devices. In the following example,



labels preceded by *** specify sections of command menu to different devices; in this case, first section to screen menu, and the next one to pop up menu 1. Also note that commands may be given descriptive titles enclosed in [] followed by actual commands to be executed when that option is selected.

Submenus and referencing

Menu items can be broken down into logical units and organized to form a hierarchy of main and submenus. Submenus are identified in a menu file by a label of the form **name where name is a valid character string. Submenus can be activated or deactivated using the following construct:

$S = submenu_name ; for screen submenu

$Pn = submenu_name ; for pop up menu where n between 1-10

Following menu file is available in: /homes2/prog/ausgabe/09_demo.mnu



9.5 Uebung 9

Modify the program you wrote for bung 7 so that your program now supports following menus and options.

Menu G_Design with following menu options:

Set_Width Allows on-screen specification of overall width

Set_Hgt1 Allows keyboard entry to specify height of bottom elements

Set_NumV Allows keyboard entry to specify number of elements Set_Hgt2 Allows keyboard entry to specify height of top element

Set_Offset Allows keyboard entry to specify offset distance

Generate Invokes your program and develops a composition

AcadMenu Returns standard AutoCad menus and options

Menu M_Design with following menu options:

ModThick Allows a user to select any number of elements and change their current thickness

ModColor Allows user to select any number of elements and change their current color

A template menu file is provided: /homes2/prog/ausgabe/09_name.mnu. Copy this file into your directory and add appropriate commands and functions to it. You are required to submit your program (09_name.lsp) and menu files (09_name.mnu).

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@ by Architektur und CAAD 1994.......... The Teacher Team