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Relatively smooth motion

When I compile and run this program, I see the sprite moving with a relatively smooth motion. Unless your computer is very slow, you should probablysee the same thing.

Beginning of the class named Slick0150a

Listing 1 shows the beginning of the class definition for the class named Slick0150a .

Listing 1 . Beginning of the class named Slick0150a.
public class Slick0150a extends BasicGame{Image bug = null; Image background = null;float backgroundWidth;float backgroundHeight;float bugX = 100; float bugY = 100;float bugWidth; float bugHeight;float bugXDirection = 1.0f;//initial direction to rightfloat bugYDirection = 1.0f;//initial direction is downfloat xStep = 4.0f;//horizontal step size float yStep = 3.0f;//vertical step sizefloat bugScale = 0.75f;//drawing scale factor//Used to compute and display the time required for the// bug to make each round trip across the game window // and back.long oldTime = 0; long traversalTime = 0;//Frame rate we would like to see and maximum frame// rate we will allow. int targetFPS = 60;

Listing 1 consists entirely of instance variable declarations. The purpose of each of these variables shouldbecome clear as they are used later in the code. No explanation beyond the embedded commentsshould be needed at this point.

The constructor and the main method

There is nothing new in the constructor and the main method. You can view them both in Listing 9 .

The init method

The init method is shown in Listing 2 . I will explain the new material in this method.

Listing 2 . The init method for Slick0150a.
public void init(GameContainer gc) throws SlickException {oldTime = gc.getTime(); bug = new Image("ladybug.png");background = new Image("background.jpg");backgroundWidth = background.getWidth(); backgroundHeight = background.getHeight();bugWidth = bug.getWidth()*bugScale;bugHeight = bug.getHeight()*bugScale;System.out.println( "backgroundWidth: " + backgroundWidth);System.out.println( "backgroundHeight: " + backgroundHeight);System.out.println("bugWidth: " + bugWidth); System.out.println("bugHeight: " + bugHeight);gc.setTargetFrameRate(targetFPS);//set frame rate}//end init

Get the time

The GameContainer class provides a method named getTime , which is described simply as:

"Get the accurate system time."

I am interpreting this to mean that the method will return the system time good to one millisecond relative to a well-defined time origin.

(Standard Java uses January 1, 1970 as the origin or epoch of time but Slick2D may use a different origin. Since we will be working with changes intime and not absolute time, the time origin doesn't matter.)

The init method in Listing 2 calls the getTime method to get and save the time in an instance variable named oldTime . The values in this variable will be used later to compute the round-trip timerequired for the sprite to move across the game window and back to the starting point at the right edge of the window.

Questions & Answers

how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
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abeetha Reply
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Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
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anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
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silver nanoparticles could handle the job?
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I'm interested in Nanotube
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Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
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bamidele Reply
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Smarajit Reply
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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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