Exercise 4a.1

Write an animation program named Scribbler whose output is like the one shown above (save all of your code for this lab in a directory called lab04a ). Start your scribble in the middle of the output pane and move it a short random distance away from its current position on each successive frame. Ensure that it never leaves the visible part of the canvas shown in the output pane.

To implement the animation, you can follow an algorithm such as this one:

• Data: x & y coordinates (float)
• Setup:
  1. Set the output panel size.
  2. Initialize x & y to the center of the output panel.
• Draw:
  1. Set newX and newY equal to new x-y coordinate values that are a small random distance away from where x and y were in the previous frame (Note that you can invoke the predefined random method to compute a small random number around 0 and the constrain method to ensure that the new coordinates are on the visible output pane);
  2. Draw a line from the previous coordinates (x, y) to the new coordinates (newX, newY);
  3. Set the old coordinates (x, y) equal to the new coordinates (newX, newY) - this ensures that the new coordinate values will be saved and used as the starting point in the next iteration.

Note that in this algorithm the scope of the coordinates (x, y) is global to the whole program while the scope of (newX, newY) is local to the draw() method. When you have your program running, take a moment to ask yourself these questions:

• Could we make x and y local to draw()? Would the animation still run?
• Could we make newX and newY global? Would it be good idea to do it that way?

Include brief answers to these questions in your program documentation.

Exercise 4a.2

Save a copy of your Scribbler from above as InteractiveScribbler and modify it as follows: Modify the copy so that it re-sets the random scribbling to the location specified by the mouse click. Your program should produce output that looks something like the one shown on the right. You can implement this by adding a mousePressed() method to your current prototype that changes the saved (x, y) coordinates to the coordinates of the most recent mouse press (stored automatically by Processing in the mouseX and mouseY variables). Once you have the above version working, improve your code so that each time the user presses the mouse, the color of the lines being drawn is changed to a random color. Do you need a global variable to make this change? Save this version of your program so that you can turn it in later.

Exercise 4a.3

Create an interactive program called Tracer that allows the user to scribble manually. Your program should allow the user to create output that looks something the one shown on the right by pressing and dragging the mouse around on the output pane. You can implement this by using an empty draw() method (required for animation) and then writing a mouseDragged() method that draws a line from the previous mouse location (pmouseX, pmouseY) to the current mouse location (mouseX, mouseY) . Note that with this implementation, your program doesn't need to declare/define any new variables, because Processing already stores the current and previous location of the mouse. Use this version of your program in the next exercise.

Exercise 4a.4

Modify your program from the previous exercise so that when the user presses any key on the keyboard, the program dumps the current image to a JPG image file. You can implement this by adding a keyPressed() method that calls the save() method. Save the image using a hard-coded filename each time. Be sure that you can find the image file that Processing dumps. Hint: Where does Processing like to put auxiliary files?

Save this final version of your Tracer program so that you can turn it in later.

Exercise 4a.5:

1. What do the following statements do (if anything)? You will want to evaluate each statement in turn. If any are invalid, comment them out, and note the error.

   char char1 = 'H';
   char friendlyChar = 'Hi';
   char emptyChar = '';
   String string1 = char1;
   String emptyString = "";
   

   Explain your results.

2. What is the return value of the following expressions (if any)?

   "All your base" + "are belong to us."
   "Somebody" + ' ' + "set us up the bomb."
   "A.D. " + 2101

   Explain your results.

Exercise 4a.6

Create a program called CountAnimation that produces the output shown here, with one line appearing each frame. You can do this as follows: Data: The current line number (an int) and the current output (a String) Setup: Make the output window 300 pixels wide and high Change the background color to something other than gray Initialize the line number to be 1 and the output to be the String 1. Draw: Use text() to place the current output string at a location dependent on the current line number. Update the line number to increase by 1. Update the output to append a space and the new line number.

The default font is fine, but if you would like to use a different one, update your code appropriately.