BASIC became popular due to its core benefit, ease of use. As such, it was widely used during the early home computer era. In fact, there are bits and pieces of BASIC incarnations implemented on varying technologies likeApple's App Store, Android devices, OpenOffice.org Basic, programmable calculators, Nintendo Famicom, just to mention a few.

There's a good amount of resources (written and in video format) that can walk you through on how to convert existing objects of differing formats (i.e.: DWG, IFC, 3DS, SKP, etc.) into an ArchiCAD object. This playlist is a good start: Eric Bobrow | Creating and Customizing Library Parts. There are certain situations where modeling elements with ArchiCAD basic tools and saving it as an object can be an adequate approach to start building-up your library database.

All set? Let's start with the 2D script...

HOTSPOT2 should always be included on all of your library objects, there should be no exemptions! This lets you create clickable nodes that enables your users to easily select the objects you create. In the example below, I have created 4 lines of hotspot commands to create nodes based on the lines of the symbol. This helps the user to easily place the 2D symbol in their projects, for this case in the middle of doors or along slabs that requires a drop symbol.

!Default syntax: HOTSPOT2 xvalue, yvalue
HOTSPOT2 0, 0
HOTSPOT2 A, 0
HOTSPOT2 A, -B
HOTSPOT2 2*A, -B
 

You will notice on the above code that the first line includes a ! symbol, followed by the default syntax for hotspot example. It is always a good habit to practice this in all your codes, this is especially helpful for beginners. This type of remark lets you easily identify what the numbers or variables represent. This technique is what's commonly known as comment in computer programming environment.

In this case, instead of using a numerical value for the hotspots, use the values for A and B parameters. This makes it easier to change the size of these lines in the future if we need to instead of changing the values one by one.

It is also a good idea to enable users the ability to change the PEN color of parts within your object. For this case, we want the user to be able to change the pen color of the lines and arrow head.

!Default syntax: PEN indexPen
PEN dp_linepen
 

Starting with a LINE2 syntax, this draws the first line horizontally from origin towards the right. Instead of a numeric value use the variable A instead, which is equivalent to 250mm. To draw the next line, move the cursor from origin to the end point of the 1st line. This is done using ADD2 syntax and use the A parameter for the xvalue.

!Default syntax: LINE2 xStartPoint, yStartPoint, xEndPoint, yEndPoint
!1st Line, Horizontal
LINE2 A, 0, 0, 0
!Default syntax: ADD2 xvalue,yvalue
!Move the cursor to the end point of 1st Line
ADD2 A, 0
 

Continue drawing the next 2 lines to complete the drop line symbol. After each LINE2 command, make sure to move the cursor to the end of each line before continuing with the next by using the ADD2 syntax.

!2nd Line, Vertical
LINE2 0, -B, 0, 0
!Move the cursor to the end point of 2nd Line
ADD2 0, -B

!3rd Line, Horizontal
LINE2 A, 0, 0, 0
!Move the cursor to the end point of 3rd line
ADD2 A, 0
 

At the end of the 3rd line, you can start drawing the arrowheads individually, for this case use the ROT2 syntax to change the axis into a 45 degree angle. Use dp_arrowhead as the value for the arrowhead length itself.

!Default syntax: ROT2 anglevalue
!1st Line of the arrow head
ROT2 -45
LINE2 -dp_arrowhead, 0, 0, 0
 

At this point, change the angle to the other side to complete the arrow head. Use the DEL syntax to undo the cursor movement one at a time by specifying a numeric value (i.e.: DEL 1, DEL 2, and so on). All that's left to do now is to complete the other half of the arrow head.

!Default syntax: DEL value
!Move back the cursor to end point of 3rd Line
DEL 1
 
!2nd Line of the Arrowhead
ROT2 45
LINE2 -dp_arrowhead, 0, 0, 0
 

Since the cursor is at the end point of the 3rd line, we want the cursor back to the origin. This is done by using a DEL 4 syntax. Note that ADD2 and ROT2 are considered cursor movements and have to be considered whenever you are using the DEL syntax.

!Move back the cursor to origin
DEL 4
 

Start identifying the PEN and FILL parameters to setup the circle marker.

!Setup the circle marker parameters
PEN dp_fillpen
!Default syntax: FILL value
FILL dp_filltype
 

To draw the circle marker, use the POLY2_B syntax. n value is the number of points that makes up the shape, +1 point to close the shape. While framefill lets you choose whether lines and/or fills are shown, the value of 7 is used to make the object show everything. Using the dp_circlesize parameter here makes it easier for us to code the shape, this also enables the user to change the circle marker size if needed.

!Draw the circle marker
!Default syntax: POLY2_B n, framefill, x1, y1, ..., xn, yn
POLY2_B 7, 7+64, dfillp, dfillt,
	0, -dp_circlesize, 1,
	0, 0, 901,
	0, 180, 4001,
	0, dp_circlesize, 1,
	0, 0, 901,
	0, 180, 4001,
	0, -dp_circlesize, -1
 

At this point, inserting an IF statement enables the user the ability to turn off or on the text itself. Make sure that the text codes are inside the IF ~ ENDIF statement for this to work.

!IF statement to give an option to turn text on or off
IF dp_displaytext then
 

Setup the text parameters with appropriate PEN syntax, thus giving the user freedom to choose which pen color is appropriate. DEFINE STYLE sorts out the appropriate style and size of the text itself. ROT2 syntax lets the user rotate the text if needed.

!Setup the text parameters
PEN dp_textpen
DEFINE STYLE "dp_textstyle" dp_fontstyle, dp_fontsize, 8, 0
SET STYLE "dp_textstyle"
ROT2 dp_textrot
 

To end the 2D script, don't forget to put an ENDIF syntax.

!Close the IF statement
ENDIF