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To change the color of an image or a texture, use tint()."

The version of the fill method called in Listing 5 requires a single parameter of type color or a hex value. In this case, a value of type color is passed as a parameter.

The call to the fill method in Listing 5 causes one of the rectangles in Image 3 to be filled with a red color and causes the other rectangle to be filled with a blue color. Note however that the rectanglesdon't exist when the fill method returns. The call to the fill method simply determines what the fill color will be when shapes such as rectangles are created later.

The rectMode method

To make a long story short, the call to the rectMode method in Listing 5 , passing CENTER as a parameter specifies that the position parameters used later to specify the location of a rectangle willbe interpreted as the center of the rectangle, as opposed to the upper-left corner of the rectangle.

I will leave it as an exercise for the student to investigate this further in the documentation for the rectMode method.

The rect method

We have finally arrived at the ultimate purpose of the display method, which is

  • to draw a rectangle
  • with a specific width and height,
  • at a specific location,
  • with specific border and fill colors,
  • on the display window.

The Cars class inherits three overloaded versions of the rect method from the PApplet class. Here is part of what the documentation has to say about the rect method.

Draws a rectangle to the screen. A rectangle is a four-sided shape with every angle at ninety degrees. By default, the first two parameters set the location of the upper-left corner, the third sets the width, and the fourth sets the height. The way these parameters are interpreted, however, may be changed with the rectMode() function.

To draw a rounded rectangle, add a fifth parameter, which is used as the radius value for all four corners.

To use a different radius value for each corner, include eight parameters. When using eight parameters, the latter four set the radius of the arc at each corner separately, starting with the top-left corner and moving clockwise around the rectangle.

The version of the rect method called in Listing 5 requires four parameters.

The first two parameters passed to the rect method in Listing 5 are the x and y coordinate values for the center of the rectangle. These values are stored in the instance variables shownin Listing 3 . You will see later that the x-coordinate values are modified by the drive method so that the rectangle will be drawn at a different position each time the display method is called.

The last two parameters passed to the rect method specify that the rectangle will have a width of 20 pixels and a height of 10 pixels.

That completes the discussion of the display method shown in Listing 5 .

The drive method of the Car class

The drive method of the Car class is shown in its entirety in Listing 6 .

Listing 6. the drive method of the car class.

void drive() { xpos = xpos + xspeed;if (xpos>width) { xpos = 0;}//end if statement }//end method named drive}//end class named Car
Listing 6. The drive method of the Car class.

The purpose of the drive method is to increase the x-coordinate position value stored in the instance variable in Listing 3 each time the method is called. However, when the value of the x-coordinate (the center of the rectangle) goes off the right side of the display window in Image 3 , the x-coordinatevalue is reset to 0.

Putting it all together

Thus, the process of (1) erasing the display window, (2) calling the Car object's display method, and (3) calling the Car object's drive method each time the draw method is called in Listing 4 , causes the rectangles to appear to move from left to right across the display window and then to start over on the left sidewhen they reach the right side.

There you have it; a detailed object-oriented explanation of an animated Processing sketch written using OO techniques.

Click here to view the JavaScript version of this sketch in your HTML 5 compatible browser.

Run the program

I encourage you to copy the code from Listing 1 and Listing 2 into your PDE, being careful to copy the code from Listing 2 into the leftmost PDE tab.

Run the sketch and observe the results. Experiment with the code. Make changes, run the sketch again, and observe the results of your changes. Changethe speed. Change the color. Change the initial position. Change the size and background color of the display window. Make certain that youcan explain why your changes behave as they do.

Don't forget to also create and run the JavaScript version of your sketch in your HTML 5 compatible browser.

If you have a programmable Android device, try creating and running the Android version of your sketch in your Android device.

Summary

In this module, I taught you about the anatomy of the Processing framework by dissecting and explaining an animated sketch.

Click here to view the JavaScript version of this sketch in your HTML 5 compatible browser.

Miscellaneous

This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Pr0110-Anatomy of the Processing Framework
  • File: Pr0110.htm
  • Published: 02/22/13
Disclaimers:

Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.

I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.

In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.

Affiliation : I : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.

-end-

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Source:  OpenStax, The processing programming environment. OpenStax CNX. Feb 26, 2013 Download for free at http://cnx.org/content/col11492/1.5
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