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Then Listing 9 calls the drawString method on the graphics context received as an incoming parameter of type Graphics to display the value in the first line of text near the center of Figure 1 .

The drawString method takes three parameters. The first is the string that is to be drawn in the game window and the next two are the horizontal and verticalcoordinates for the location in which the string is to be drawn.

Draw the saved value of delta

Then Listing 9 calls the drawString method again to draw the saved value of delta from the most recent call to the update method as the second line of text near the center of Figure 1 .

End of discussion

That concludes the discussion of the program named Slick0130a . Although this is a simple program, it should provide a little more insight intoone approach to creating a game program using the Slick2D library.

Run the program

I encourage you to copy the code from Listing 10 . 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.

Summary

You learned about a property of the GameContainer class named running , and how it is used by the start method to keep the game loop running.

You learned about the salient features of the gameLoop method of the AppGameContainer class.

You learned about the updateAndRender method of the GameContainer class and how it decides when and if to call the update and render methods of the object of the Game class that is wrapped by the container.

You touched on the difference between normal delta and smoothed delta.

You learned about minimumLogicInterval and maximumLogicInterval and how the contents of those two variables are used to determine if, when, and how many times to call the update method during each iteration of the game loop. You also learned how the contents of these twovariables are used to determine the value that is passed as delta each time the update method is called.

You learned that the render method is normally called once and only once during each iteration of the game loop.

You saw a simple example of how you can use the value of delta that is received by the update method to control the behavior of a game program.

You learned that you can set the size of the game window when you instantiate an object of the AppGameContainer class by passing dimension parameters to the constructor.

You learned that you can set the target frame rate by calling the setTargetFrameRate method on the GameContainer object.

You learned how to display text in the game window.

What's next?

In the next module, we will take a look at displaying images with transparency.

Miscellaneous

This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Slick0130: The game loop
  • File: Slick0130.htm
  • Published: 02/04/13
  • Revised: 06/09/15 for 64-bit
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 am a professor of Computer Information Technology at Austin Community College in Austin, TX.

Complete program listing

Listing 10 provides a complete listing of the program named Slick0130a .

Listing 10 . Source code for the program named Slick0130a.
/*Slick0130a.java Copyright 2012, R.G.BaldwinA very skinny Slick program. Barely more than a skeleton. Tested using JDK 1.7 under WinXP*********************************************************/ import org.newdawn.slick.AppGameContainer;import org.newdawn.slick.BasicGame; import org.newdawn.slick.GameContainer;import org.newdawn.slick.Graphics; import org.newdawn.slick.SlickException;public class Slick0130a extends BasicGame{//Instance variables for use in computing and // displaying total time since program start and// time for each frame. double totalTime = 0;int incrementalTime = 0; public Slick0130a(){//Call to superclass constructor is required. super("Slick0130a, Baldwin.");}//end constructor //----------------------------------------------------//public static void main(String[] args)throws SlickException{ try{AppGameContainer app = ( new AppGameContainer(new Slick0130a(),400,200,false)); app.start();}catch(SlickException e){ e.printStackTrace();}//end catch }//end main//----------------------------------------------------// @Overridepublic void init(GameContainer gc) throws SlickException {//Set the frame rate in frames per second. gc.setTargetFrameRate(2);}//end init//----------------------------------------------------// @Overridepublic void update(GameContainer gc, int delta) throws SlickException{//Compute and save total time since start in seconds. totalTime += delta/1000.0;//Save delta for display in render method.incrementalTime = delta;}//end update //----------------------------------------------------//public void render(GameContainer gc, Graphics g) throws SlickException{//Truncate totalTime to one decimal digit and // displaydouble time = (int)(totalTime*10)/10.0; g.drawString("totalTime: "+time,100.0f,100.0f);//Display incremental time.g.drawString("incrementalTime: " + incrementalTime, 100.0f,120.0f);}//end render }//end class Slick0130a

-end-

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biomolecules are e building blocks of every organics and inorganic materials.
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Source:  OpenStax, Anatomy of a game engine. OpenStax CNX. Feb 07, 2013 Download for free at https://legacy.cnx.org/content/col11489/1.13
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