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The new code
The only code in Listing 4 that is new to this module is the call to the setClip method.
The setClip method is defined in the Graphics class and inherited into the Graphics2D class.
(Among other things, that means that it wasn't necessary for me to cast the Graphics object to type Graphics2D in Listing 4 .)
The setClip method
There are a couple of overloaded versions of the setClip method. The one used in Listing 4 requires an incoming parameter of the interface type Shape .
The Shape interface
Briefly, Sun tells us that the Shape interface "provides definitions for objects that represent some form of geometric shape."
There are several dozen classes that implement the Shape interface, one of which is the class named Ellipse2D.Double . Therefore, the object of that type that is instantiated in Listing 4 satisfies the type requirement for being passed to the setClip method.
Behavior of the setClip method
With regard to the behavior of the setClip method, Sun tells us that the method
"Sets the current clipping area to an arbitrary clip shape."
What is the significance of the clipping area?
The closest answer that I can find for that question is the following statement in Sun's description of the Graphics class:
"All rendering operations modify only pixels which lie within the area bounded by the current clip, which is specified by a Shape in user space and is controlled by the program using the Graphics object."
In other words...
The clipping area is analogous to the current clip . In this case, the position and shape of the current clip is the position and shape ofthe ellipse.
When the image is later drawn on the red Picture object, only those pixels within the ellipse are modified to show the image. Theremaining pixels retain their original color, which was set to red early in Listing 4 .
End of discussion
That concludes my explanation of this program. You will find the methods that I didn't discuss in Listing 5 near the end of the module.
I encourage you to copy the code from Listing 5 . Compile the code and execute it. Experiment with the code, making changes, andobserving the results of your changes. Make certain that you can explain why your changes behave as they do.
Click Prob04a.jpg to download the required input image file.
In this module, you learned how to use shapes to clip images during the drawing process.
In the next module, you will learn how to merge pictures.
While not a requirement of the course, you can select the following link to view an optional online video lecture on the material in this module.
This section contains a variety of miscellaneous information.
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 am a professor of Computer Information Technology at Austin Community College in Austin, TX.
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