Exercise: Simple GENESIS scripting exercises

These exercises were created by Upi Bhalla for the December 1999 modeling course in Bangalore.

1. Go to Chapter 13 of BoG (Page 215.) You have alredy played around with something like the example script. Figure out how to use functions and variables. If you work through the chapter you will get a decent feel for a lot of the script language.
2. Using functions.

   If your script is more than a few lines long you should probably use functions in it. You will also need functions if you want to execute even a slightly complicated operation from a button or dialog.

   • Write a function to create a new dialog. You will need to check if a dialog already exists with the same name, so that you don't overwrite an old dialog.
   • Assign this function to the new dialog, so that you can use the dialog itself to create new ones.

   This is illustrated in ex2.g

3. Messaging is a critical concept in GENESIS. It is the means by which objects exchange information. To get an idea of how it works, create a form and put a graph widget in it. Type showobject xgraph. This lists a lot of stuff, including the legal messages for the graph. You will normally only use message 0, which is named PLOT. Now create a dialog, and send a message from this dialog to the graph. In order to run and display the results, create a button for RUN and RESET as well, just like you did earlier. Set the RUN button to go only 10 steps, so that you can fiddle with the dialog value in between. You will need to put in a reset command after adding any message, to ensure that the simulator has been properly initialised. Now run this little model. Turn the dialog value up and down, and click on RUN each time to see how it controls the graph value. This is illustrated in ex3.g.

4. (Fun for 1:00 AM)
   Take any of the previous examples, and start to fiddle with the graphical elements. There are a bunch of fields relating to the geometry and positioning of buttons etc. These are

   xgeom : x coordinate of top right
   ygeom : y coordinate of top right
   wgeom : width
   hgeom : height

   Each of these fields can be set directly either as pixels, or as percentages.

       // This will move the graph to 20 pixels from the top.
       setfield /form/graph ygeom 20
   
       // This will set the height of the graph to 40% of the parent xform.
       setfield /form/graph hgeom 40%
   

   You can also set foreground and background colours.

        setfield /form/RUN offbg yellow offfg pink
   

   Ugh!!

   You can even set labels on most graphical widgets

       setfield /form/RUN offlabel "Run really fast now"
   

   Note that buttons make a distinction between on and off states, so you have a proliferation of fgs and labels.

Back to the index of exercises