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Figures in the middle group
The process of computing the horizontal position coordinate value continues in Listing 8 .
| Listing 8 . Don't change position for middle group of sprite images. |
|---|
}else if(frame<2*oneThird){
//Sprite is stationary. Don't change position |
Listing 8 tests to determine if the current frame is in the middle group. If so, it causes the update method to return without changing the horizontal position coordinate value,thus allowing the sprite to remain in a stationary position.
Figures in the third group
The horizontal position values computed in Listing 9 make it appear that the sprite is running from right to left across the gamewindow.
This is one of those opportune times when it is appropriate to say that I will leave it as an exercise for the student to dust off their high-schoolalgebra books and figure out how the code in Listing 9 achieves the desired result.
| Listing 9 . Run from right to left. |
|---|
}else if(frame<3*oneThird){
//Cause the sprite to turn around and start// moving to the left toward the starting point.
//Reduce frame count by number of frames during// which the sprite wasn't moving.
frame -= oneThird;//Compute the new position.
spriteX = (2*oneThird - frame)*stepSize;}//end else if}//end update |
Listing 9 also signals the end of the update method.
Now it's time to realize the benefit of all of the hard work that went into planning for and writing the code in the init and update methods. The code in the render method, which is shown in Listing 10 , is almost trivial.
| Listing 10 . The render method. |
|---|
public void render(GameContainer gc, Graphics g)
throws SlickException{g.setDrawMode(g.MODE_NORMAL);
g.setBackground(Color.gray);animation.draw(spriteX,spriteY);
}//end render}//end class Slick0190 |
There is nothing left for the render method to do other than to send a message to the Animation object once during each iteration of the game loop asking it to draw the current frame.
Listing 10 signals the end of the render method, the end of the Slick0190 class, and the end of the program.
I encourage you to copy the code from Listing 11 . Compile the code and execute it,making changes, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.
In this module, you learned how to use objects of the SpriteSheet class and the Animation class to perform more complex sprite sheet animations than was the case in the previous module.
In the next module, you will learn how to develop a sprite class from which you can instantiate and animate swarms of sprite objects.
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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