Hello World: 5 Exercises and Suggestions

After studying the Hello World sample application and reading the System Architecture chapter, you may be ready to try some exercises before embarking on your application. It is strongly suggested that you spend some time modifying the Hello World program to get used to the programming environment and the Goc UI definition syntax. Some things you might try are outlined below--some are extremely easy; some are more difficult. Some will require you to read other chapters in this and the User Interface manual. In any case, you should go on to read the GEOS Programming chapter to understand the various keywords and constructs of the Goc programming language.

Some simple UI exercises you can incorporate into the Hello World program include the following suggestions:

Add a new menu item that brings up a dialog box letting the user select a point size for the text. In the dialog box you would use a GenValue object or perhaps a list of point sizes (or even one or more triggers) to take the user's input. The GenValue sends out a message with a new number when the user sets it, and your Process object would handle this message and set the point size. Your HelloDrawText() routine would then have to set the point size of the text as well as the color.
Add a feature that lets the user set the position and/or rotation of the text. This exercise will help you get used to the GEOS coordinate space.
Make HelloView scalable. To do this, you will create a new menu or dialog box that lets the user specify the scale. Most likely you will create a number of GenTriggers that apply a pre-specified scale; each of these triggers will send MSG_GEN_VIEW_SET_SCALE_FACTOR to HelloView. You may even try using a GenViewControlClass object.
Add background graphics to get used to the coordinate system. Perhaps draw a colored rectangle behind the text that changes colors to be the inverse of the text (i.e. when the text turns blue, the rectangle turns yellow).
Add printing. This is not nearly as difficult as you might think. To do this, you should read the Printing chapter. This exercise essentially consists of adding a trigger to invoke printing and a message handler for the printing message. This handler will create a printing GState and call the drawing routine. Instead of drawing to the screen, it draws to the Spooler's input.

Some of the exercises may have been implemented in the sample programs provided. You should look through the samples for insight into how the exercises may be completed. You are also encouraged to make up your own exercises to build on Hello World.

If you are new to GEOS programming, you should work through the Tutorial; otherwise, you will likely be overwhelmed by the complexity and depth of the system and not know where to begin.

GEOS SDK TechDocs |

4 The Source File and Source Code