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| Listing 9 - Perform the concatenated transform . |
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Graphics2D g2 = (Graphics2D)result.getGraphics();
g2.drawImage(pic.getImage(),translateTransform,null);return result;
}//end rotatePicture}//end class Prob01Runner |
Call the getGraphics method
Listing 9 begins by calling Ericson's getGraphics method on the new Picture object and casting the returned value to the standard type Graphics2D .
A cast is required
Ericson's getGraphics method returns a reference to the graphics context of the Picture object as type Graphics . That reference must be cast to type Graphics2D before the drawImage method can be called on the reference.
Call the drawImage method
Then Listing 9 calls the standard drawImage method on the reference to the graphics context passing three parameters to the method. Thisis one of two overloaded versions of the drawImage method defined in the standard Graphics2D class.
The first parameter
The first required parameter for this version of the drawImage method is a reference to an object of type Image containing the image that is to be drawn. In this case, Ericson's getImage method is called on the Picture object to get the image and pass it as the first parameter.
The second parameter
The second required parameter is a reference to an AffineTransform object that is to be applied to the image before it is drawn. Our concatenatedtransform object is passed as the second parameter.
The third parameter
The third required parameter is a reference to an object of the standard type ImageObserver or null . If you would like to know more about the use of an ImageObserver object, go to Google and search for the following keywords:
richard baldwin java imageobserver
We don't need an image observer in this case so Listing 9 passes null for the third parameter.
When the drawImage method returns
When the drawImage method returns, the image will have been rotated, translated, and drawn in the center of the new Picture object as shown in Figure 3 .
Return a Picture and terminate the method
Listing 9 returns a reference to the Picture object, (which now contains the rotated image) and terminates, returning control to the run method in Listing 3 .
Return to the run method
Returning to the run method in Listing 3 , we see that the remaining code in the run method:
I encourage you to copy the code from Listing 10 . Compile the code and execute it. Experiment with the code, making changes, andobserving the results of your changes. For example, try reversing the order of translation and rotation beginning with Listing 7 . Make certain that you can explain why your changes behave as they do.
Click Prob01.jpg to download the required input image file.
You learned how to scale images and how to rotate and translate images using the AffineTransform class.
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