Acknowledgment

This lab was originally developed by Dr. Henry L. Welch and revised by Dr. Christopher C. Taylor.

Purpose

The purpose of this laboratory assignment is to add the following functionality to your graphics shell: drawing lines and ellipses and specifiying colors.

Assignment

Your are to do the following:

• Add a command line command that accepts two points (as x/y pairs) and draws a line between the to points.
• Add a command line command that draws an ellipse give the center point (as an x/y pair) and two distances (radii along the x and y axes).
• Update your button pressing code so that you can draw both lines and ellipses using the mouse. (You may remove drawing points using the mouse, but you should keep points on the command line.) Here are some issues which you should consider:
  • You may find it helpful to differentiate between the two mouse buttons or to look at the shift key during a button event.
  • Keep in mind that separate events will be used for each point specified. Therefore, state information will have to be shared between callbacks. Generally speaking, it is better to use static objects which are local to the member function than to use a data member of the class since doing so would make it accessible to other member functions.
  • You may want to experiment with pressing/releasing the mouse button outside of the drawing window. Are the results what you expected?
  • For an additional challenge use the motion event to "draw" the line or ellipse in progress; although this is not a requirement.
  • There are a number of dynamic memory challenges involved with storing objects of varying sizes (ellipses, lines, and point objects). Be sure to review your understanding of dynamic memory allocation. Depending on how you proceed, this may complicate your memory recovery operations in some of your destructors.
• Add a command line color command that either accepts RGB values, uses one of the standard X color names from the standard list in the file /usr/lib/X11/rgb.txt or by using the Color class. Once a new color is selected, all subsequent objects should appear in that color until a new and correct color editor command is entered. During an exposure redraw each object should appear in the color in which it was first drawn so you will need to save the color information (as a GC or pixel value) with the object itself. Unfortunately, both of these present a problem since both graphical contexts and pixel values in the colormap are dynamically allocated on both Torres and the PC. Consequently you will need to keep track of them and then free them before exiting using either XFreeGC or XFreeColors respectively (see additional information). This is probably best handled in a special member function of the image class or in the image class destructor.
• Update your help information.

You may use XDrawLine in your line drawing code; however, you may not use any of the XDrawArc variants in your ellipse drawing code.

Although not required, you may find it useful to implement the file reads and writes.

There are areas for extra credit with this assignment, however you must complete the basic requirements in order to receive the extra credit.

Lab report (due 4:30pm, October 13, 1999)

The lab reports should be self-contained. That is, it should be possible for someone to understand what you did and why without seeing anything other than your report and any previous reports that you have submitted. Your report should include:

• Purpose
• Problem Statement
• Procedure -- what approach you used to solve the problem
• Documented source code (clearly identifying any changes made since your last submission). Note: you should include all the source code necessary to compile your project except for unmodified source code written by Dr. Welch. For example, you don't need to include shell.cpp if you didn't modify it.
  You may wish to use gensrc, a shell script which will produce one file containing all of your source code files and Makefile with the markup commands required by my electronic submission procedure.
• Discussion including:
  • A tally of the number of new Non-commented Lines Of Code (NLOC) written for this lab assignment. You may use the CLC perl script on your code. If possible, break the NLOC down into the various features you needed to implement.
  • A summary of your activity log indicating how much time you spent on each phase of the assignment.
  • A narrative describing any specific problems you encountered and how you solved them.
• Conclusions (what you learned, suggestions of how the lab could be improved, things you would have done differently, etc.)

As with any report you submit, correct spelling and grammar are required. In addition, your report should be submitted electronically following the Electronic Submission Guidelines. (You may wish to consult the sample report before submitting your report.) Be sure to keep copies of all your files, in case something gets lost. It may be wise to keep a diskette backup as well.

If you have any questions, consult the instructor.

This page was created by Dr. Christopher C. Taylor.