Josh Burker

5/20/2003

When I first set out to take apart Cameron Hayne's DoubleClick World I had no idea of the complexity behind this World. However, Mr. Hayne accomplishes his goals of this World (variable-speed double-clicking practice with audio and visual feedback for the user) using very little code, and it runs beautifully.

For the version of DoubleClick that you can use on the Cocoa Projects page, I set the speed of the World to slow before I Built an AutoPlayer. This seemed to give the best consistency for use as an imbedded plugin or as an AutoPlayer; fast seemed to run too fast, so the user could not get in the second click before the program determined she or he had not clicked fast enough.

This page will lead you through the code in DoubleClick and show you how the program registers that the user has clicked; waits for the second click and provides audio feedback if the user completes the double-click sequence; and if it does not receive a second click, resets itself for the next attempt at double-clicking.

I am assuming that you have the basic understanding of how to create a Click-Response Rule for an object.

I will introduce the Cocoa programmer to the following skills:

• Using Appearances to produce different results from the same Piece
• Variables for different Cocoa Pieces
• World Variables
• Audio Feedback

Throughout this page, when appropriate, you can click on the different pictures I use to illustrate the text to get larger versions of them, which will allow you to see the code for yourself.

Using Appearances in Cocoa

This World depends in part upon the use of Appearances to register that the user has double-clicked on the Practice Area. Clicking on the Practice Area changes the appearance of the Practice Area from ready to waiting (see figures 1 and 2). When the user clicks on the waiting Appearance of Practice Area, the program registers this as a "double-click." If the second click happens within the time limit imposed by the "Double-Click Speed" setting, then the user receives audio feedback to confirm that she or he double-clicked. The Practice Area is a Piece with a Click Response assigned to it. When the user clicks on the Practice Area there is a rule that changes the Appearance of the Practice Area from ready to waiting. Here's a look at the code that causes this Appearance change (see figure 3): figure 3 (click to enlarge) As you can see, the Rule changes the Appearance of the Practice Area from ready to waiting. However, there are also a couple of other Actions that occur during this Rule that make this World function. First, the Rule tells the program to take the "dbl click delay" World Variable and put it in the delay piece variable. We'll look at the uses for variables in the next section. Second, if the user clicks on the waiting Appearance within the time allowed (this is determined by user-defined "Double-Click Speed" settings), the program will offer audio feedback that the user has "Double-Clicked" by playing the Sound "dbl click."

figure 1 figure 2

Variables for Cocoa Pieces

The Practice Area, where the user Clicks, is just another Cocoa Piece, but one with Rules as well as a Variable that makes this World work. This section will explain how this variable works. When the user clicks on the "Double Click Speed" setting on the board, a number value is entered into the World Variable "dbl click delay" (see figure 4). Depending upon which speed the user selects, the variable is anywhere from 8 to 2, the higher number being the "Slow" speed setting. Setting the World Variable is accomplished using a simple Action. These are the Rules that govern how the "dbl click delay" is set into the World Variable. This Rule to the left is the Slow setting. The Rule changes the Appearance of the "radio" buttons on the Board to indicate which speed the user has selected. Next, the Rule puts the appropriate "delay" time into the World Variable "dbl click delay" (see the rule to the left, as well as figure 5). On the Slow setting, this value is 8. So Cocoa will count down from 8 to determine whether the user has clicked fast enough, as set by the "Double Click Speed" board setting. Finally, the program offers audio feedback, stating the speed that you have selected. These are sounds that the author recorded into Cocoa using the standard "New Sound" under the Sound menu. click to enlarge

figure 4 figure 5 click to enlarge

Bringing it All Together

Now we'll examine how these Rules work together to make this World work.

When the User clicks on the waiting appearance of the Practice Area, the Rule not only changes the Appearance of the Practice Area but it also puts the number in the World Variable "dbl click delay" into the Piece variable "delay." Next, the program runs the Rule that starts this "delay" variable counting down (see figure 6):

As you can see from this Rule, every time the Rule runs the program subtracts 1 from the Piece variable "delay." There is an additional Rule ("count down rule") to check whether this "delay" Variable has reached 0. The "time's up" Rule then resets the Practice Area Appearance to ready to reset the board so the Practice Area is ready to be clicked on again. If the user clicks within the time allowed, Cocoa runs the Rule that plays the "dbl click" Sound: As you can see, if the user clicks on the Practice Area within the time allowed by the "Double Click Speed" setting, Cocoa will change the Appearance of the Practice Are to ready (so the user can try again), as well as play the Sound "dbl click."

figure 6 (click to enlarge)

Conclusion

As you can see, Cocoa's Rules can be written in such a way as to allow for Actions that one might not think possible in Cocoa (for example, looking for and recognizing a double-click). As you'll see when you start playing with Cocoa, there are many ways to do the same thing. This particular World, with its well-written Rules and use of World Variables, qualifies as an Advanced Example of programming in Cocoa.