Deep Space 2
Contents
1. Chris Orona CS491B Spring 2005 Contents T IEEE str rte tr treet TTT rere rr rer errr EUK RUNE EET rr rrr rr rr cre 1 2s Technological Back or OU scssccssccssnnsccascastanscoaseeneaaseoaseauenessceuiaumeuaaaeacmmnenne ss 1 Sy SECT ACRILICO 2 Sl Hardware COn Sua EIOTEsrosas55255505555552055 0220 DOOR OUR EROGO ROUEN 2 O52 SOIbWSEte Contorno 2 4 Design and Implementation Details c cece ccc eec eee eeeeeeeeeeneeeeeeseeeneeenes 3 TI UI CS USER OT 3 F2 Care CSI rr 4 AN E 0 4 MERE MIN EINE E RE EE EIE FEE C D PUE 4 q 2 2 Player SDtpSiixuxxis55555550555556505505 E H RN NER EU M DENEN 5 O nem AE Saa 6 q 2 Tq 5prite Patlissaxuuxuss ptit etri ott PORE D RR RR EURENURRU C RR RR UH ARMS 7 ies RRA RRA 11 O DEPOR sotana Icaro eran re TTT 12 PIE AN al EE Es y E A e RE O PEO E OE O 12 5 1 1 Creating a Java Web Start application eese 13 S HN nutriat 14 6 P rlormance Evaluatio recerca 14 D I E is A UI 14 0 2 Expermental RESU S aaoeonsecua d dq2902692299 90899490444 0929929994969 9 5 B2 m nU 14 6 3 Performance Enhancements cceseeeeeeeeeeeeee eese n eese tenere tnn 15 Cis AY Sil PEE EC 15 AED o ERES 16 A S SI A cane sanneascaeseucimeeeusanucnmeenusauecueesnuuanueeesnusaseuatodsedes 16 PES o 16 B 2c APISnd IcIOFE NCC naosep00052000929009000000092090000000020900sDPUUPPDI DI PUIPPDPPCIDPU UM E 16 APPEAU A DID OL U10 5 ADE 17 Aele ROS SAIC o o 17 A 2 WIE2. be presented with the ship selection screen See Figure 5 20 Select Ship d ida A A 4 Deep Space Ship Figure 5 Ship Select There are four different ships you can select from e Deep Space Ship Moves at regular speed It can handle many different kinds of weapons but not the most powerful version of each weapon e Royal Ship This ship moves slowly and fires slow bullets When powered up it can shoot three bullets at once e Hyper Ship This ship fires wave like shots with a large target area When powered up the waves areas are even larger e Speed Ship This ship is small fast and hard to hit It also shoots very rapidly However its attacks do not do much damage When powered up its shots spread out a bit and become faster and weaker 21 B 4 Playing the game Ns Y dd nn a y Figure 6 Game Play The player can be controlled using either the keyboard or mouse Use the keyboard s arrow keys or move the mouse to control the ship and press the spacebar or hold down the primary mouse button to fire The upper left hand corner of the screen displays the score When an alien is shot the score increases Aim for the high score The player starts with three ships If the ship is struck by an alien then it will be destroyed and one of the player s spare ships will be deployed If all ships are destroyed then the game is over During play you may come across additional ar
3. it heading closest towards To do that Ay is compared to Ax However since the screen is wider than it is long the aspect ratio is used as a weight multiplied to Ay before comparing it Once we determine which edge the bullet is heading towards the point slope formula is used y Yo m x xo m is the slope Ay Ax The particular edge being traveled to can be determined by the sign of Ay or Ax depending on which edge is being traveled to most quickly Then we solve for the remaining coordinate to determine the final destination For example our screen is 800 x 600 aspect ratio 1 33 and an alien fires from 0 O to the player at 120 100 This conveniently sets Ay 100 and Ax 7120 Since 120 lt 100 1 33 the y axis will be reached before the x axis In this case y is positive so we know the bottom coordinate y 600 will be the final point Plugging into the equation gives 600 0 100 120 x 0 or 600 0 833x therefore x 720 for a final coordinate of 720 600 With the Zigzag path several intermediate points are calculated from the source and destination points and are translated along an axis to determine the final locations x3 JA Figure 2 A path component modified by the ZigZag class First the path is split into equal segments The segments are given as a series of points xo Yo a yi etc as in Figure 2 Secondly the distance d for each segment is calculated using t
4. ships the player can choose from Depending on the ship chosen the availability of weapons velocity and power are affected The ships the player can choose from are e Deep Space Ship Moves at regular speed It can handle many different kinds of weapons but not the most powerful version of each weapon e Royal Ship This ship moves slowly and fires slow bullets When powered up it can shoot three bullets at once e Hyper Ship This ship fires wave like shots with a large target area When powered up the waves areas are even larger e Speed Ship This ship is small fast and hard to hit It also shoots very rapidly However its attacks do not do much damage When powered up its shots spread out a bit and become faster and weaker In addition the player can acquire power up weapons during the course of the game e Gun Powerup This increases the power level of the ship s gun Which weapon this turns into exactly is dependant on the ship and is covered above e Double Gun Powerup Takes the player s current weapon and creates two of them However this takes into account only the actual bullets not where the player s original gun is shooting them So for example if the player is using the Royal Ship and shooting three bullets at a time picking this up would only shoot two bullets at a time not six e Life Powerup Gives the player an additional life e Shield Powerup When the player picks this up the ship begins blink
5. still only installed with the Java Runtime version 1 4 or below it was not possible to test with these computers 3 2 Software Configuration Software used in this project included e Eclipse IDE for development and testing of Java code e Audacity an open source sound editor used to edit the sound data for the game Sound data was acquired from a sound effects CD and then shortened downsampled for game use e Paint Shop Pro graphics program used for sprite creation 4 Design and Implementation Details 4 1 GUI Design This game runs in full screen mode using the Java 2D API A JPanel is used for the action and separate panels are used for the scrolling backgrounds Additional panels are used for score life and high score placement See Appendix B 2 When the game is started up an Attract mode panel is displayed on the screen In the old arcade games the attract mode was where a demo of the game would be playing and would attract people to play the game However there s no demo in this project The title screen is displayed and the player is invited to start a new game During play or the title screen display the player can open up a menu This menu is implemented as a transparent panel that is overlaid above the screen using a JLayeredPane This is like a regular Java container but can have several panels which are placed above or below it Before play begins the attract panel is replaced with a G
6. there needed to be an easy way to run applications online so Sun created the Java Web Start platform 5 1 1 Creating a Java Web Start application Java Web Start applications are not much different than regular applications All class files and resources must be packaged in JAR files Since this is a recommended practice even for regular applications this part is not a problem The main portion of a Java Web Start application is creating a JNLP Java Network Launching Protocol file which explains the application and the resources used lt xml versionz 1 0 encoding utf 8 gt jnlp spec 1 5 codebase http cs calstatela edu corona cs491 href DeepSpace2 jnlp gt lt information gt lt title gt Deep Space 2 lt title gt lt vendor gt C O lt vendor gt homepage href http cs calstatela edu corona cs491 gt lt description kind short gt Deep Space 2 the game lt description gt icon href DeepSpace2 gif width 50 height 50 gt lt offline allowed gt lt information gt lt resources gt j2se version 1 5 initial heap size 8m gt jar href DeepSpace2 jar gt lt resources gt lt security gt lt all permissions gt lt security gt lt application desc main class DeepSpace2 GameManager gt lt jnlp gt 13 Figure 3 JNLP File A JNLP file is an XML file which contains information such as title software vendor links to the home page and a descrip
7. PING S11 S CC DOTT TT aia 17 Appendix B User MANUA corrida 18 SX NUDO CITUR TINIO UEN COT ETHER 18 BS C Oli Nal OE E recs iiervilesenrdde aicssecbces 19 Fee i I ell Ae O RR ES 19 A PPP NENNEN NIMM Edd 22 Deep Space 2 Abstract Players are always looking for the next new and fun game and Deep Space 2 delivers Using the Java 2D API this project will show that the Java programming language can be used for cross platform game development 1 Introduction Aliens are attacking Earth Five years ago a lone space ship attempted to save mankind from aliens That mission succeeded but now the aliens are back with reinforcements Earth s forces have sent you back once again to eradicate this threat to humanity once and for all In this game youll be able to take control of a ship and attack the enemies head on Using different weapons you can blow up the enemies and destroy them from the face of the universe You too can be a hero 2 Technological Background Deep Space 2 is a 2D game written in the Java programming language The Java language was chosen because of familiarity with the language its cross platform ability and the curiosity to see how well game development can be done in this language This game was based on an earlier project Project Deep Space which used Java 1 2 However due to the lack of graphics support for this project it was not as good as it should have been In a later version of Java 1 4
8. ame panel which handles the actual game This panel contains several layers which are used for the positioning of the menus and scrolling backgrounds The player and enemy sprites are drawn directly on the main level The background is drawn on a layer underneath the action while the score and life displays are drawn above it When the game is over this panel is replaced by a Game Over panel which merely displays the Game Over screen After a few seconds it returns to the title screen 4 2 Game Design Game design is split up into several design components which were used as development cycles The game was designed using a spiral development method in which a basic implementation was designed during the first quarter and improved upon during the second quarter During the first quarter the game was playable but limited The second quarter focused upon improving the quantity and variety of each of the various components 4 2 1 Game Loops When the game begins there are several different threads that run in the background These threads help to maintain game flow and stability The main visible thread that runs is the update loop This refreshes the screen at a constant rate In this game the rate is fixed at 1 refresh per 20 milliseconds or a 50 frame per second rate Previously each component would update itself however they were not able to synchronize well with each other especially as some objects would be m
9. ath itself is not that complex as enemies shoot in a straight line However calculations must be made to determine the end point of the line Sp v A A Figure 1 A shot path showing the extrapolated shot point When an enemy fires a bullet from the point xo yo to the player s point x1 yi it cannot actually have this as an endpoint If it used that path as an endpoint it would stop after reaching that point However the player s ship has most likely moved away from that point during that time Therefore the point needs to be extrapolated past the player s position Since we aren t too concerned with displaying objects that are past the screen edge we need only to find the point x1 yi where the path intersects the edge of the screen However it is necessary to find which edge it will intersect first If the path is heading largely on one axis with very small movement in the other and the wrong axis was checked for the intersect it would be a very long time before it hits that axis which means the bullet would be in play far longer than is necessary To do this the slopes Ay and Ax are calculated from y yo and x xo respectively First we check for the degenerate cases where Ay Ax or both are zero This indicates that the bullet was fired straight along one of the axes This makes it much easier to find the edge in these cases For most cases it is heading toward both axes But which edge is
10. e Paths Non player sprite movement enemies floating power ups etc is determined by the Path object that is attached to them The Path object consists of a listing of points between which the object will move Subclasses of the Path object determine in which direction the object will take between those points These paths are grouped into two categories trivial and non trivial The most basic path is the straight line path A straight line path moves the object only from the source point to the destination point This is most useful for power ups which only move down the screen to give the illusion that they are stationary and the player ship is moving past them Certain enemies will also move simply down the screen but with a high velocity to make them more difficult to hit Another trivial path is the random path An enemy will move to a point on the screen then move to another random point This continues until the enemy is defeated The green aliens in Level 2 will use this path The third trivial path is the oscillating path This path repeats the source and destination points to make the object move repeatedly between these two points The UFO enemy uses this as it flies back and forth across the screen The number of oscillations can be either fixed or infinite The UFOs are set to infinite so they will continue to harass the player until they are dealt with One of the complex paths is the enemy shot path The p
11. he Pythagorean Theorem The angle Oo is also calculated by obtaining the arctangent of yo xo A constant c is given which indicates the number of pixels to move each point segment For each segment c is flipped between c and c to move the path in different directions What we want now is the coordinate of the new point x1 y1 Since we have two edges of a right triangle d and c we can figure out the remaining side d which is the distance between the original point and the new point Now that we have the distance to the new point what is needed is the angle so we can determine where the new x and y are We can obtain the angle 10 Oo by calculating the arctangent of c d Therefore 0o 0o is the angle required for the new point There are several identities in trigonometry which help out at this point sin 0 opposite hypotenuse and cos 0 adjacent hypotenuse We apply Oo 00 as the angle Referring to Figure 2 the hypotenuse is the distance d and the adjacent and opposite sides are x1 and yi Therefore x1 d cos 00 and yi d sin 60 This formula is then applied to all points on the path except the final one creating a jagged path 4 2 5 Levels Levels consist of two main things A set of backdrops for the action to take place and a scheduler that keeps track of items and places them on the screen In addition each level has a number and a music file that plays while t
12. he level is being played The backdrop for the first level is a star field Several threads run one to scroll the star field and the other to change the color of the stars to make the effect more dynamic The position of each star is tracked separately When one moves off the bottom edge it is moved to the top edge in a random position This keeps the playing field looking random In the second level two background layers are created A cloud image is loaded and tiled to create a background with many clouds One of the layers is placed above the player and enemies to give the illusion of depth These two layers scroll independently of each other to further add to the display of depth The scheduler is implemented by a PriorityQueue object This places scheduled events in a tree for fast ordered access of approximately O log n access time There are two kinds of events Level events and item events What the events have in common is the placement time When the level starts 11 objects are placed into the scheduler according to the placement time A level end event is placed into the scheduler also at the end of levels 1 and 2 When a certain time has elapse the level will end and the player will move on to the next level For items and enemies several fields are kept track of the object to be placed the initial position and the Path it is to take when moving When this object is taken off the scheduler it is moved to the in
13. ing and is immune to enemies or enemy bullets for a short while Each powerup weapon has several components associated with it The particular shots it fires the damage it does to enemies and the velocity of the bullets 4 2 3 Enemy Aliens There are several kinds of enemies implemented in the main game AN Green Alien moves slowly in a zigzag pattern across the screen Takes one shot to kill AI Red Alien Moves straight down the screen quickly harder to kill Qoo UFO Moves across the screen firing shots at the player Mothership A large version of the UFO Summons three small UFOs and shoots flames The enemies have set formations and patterns that are created when the level is designed The green aliens primarily move in a zigzag formation down the screen while the red aliens move slightly faster straight down the screen The UFOs tend to move back and forth all the while shooting at the player Each enemy will have a hidden life value which affects how easy it is to kill If the player is using a low powered weapon it will take longer to kill than if the player uses a high powered weapon Each successful hit to an enemy decreases its life by the weapon s power When the enemy s life goes to O the enemy is considered killed and removed from the playfield Some enemies have special events that run when they die For example defeating the mothership enemy in Level 3 will end the level 4 2 4 Sprit
14. itial location and sent across the specified path However during level execution objects could also place their own events into the scheduler For example in level 3 the large UFO enemy will periodically place new enemies onto the play field In addition since completion of the level depends on defeating this enemy it does not have a normal level end event Instead when the large UFO is defeated a level end event is added to the scheduler 5 Deployment 5 1 Java Web Start One of the problems involving Java applications is how to distribute the application True a JAR Java Archive file can be packaged and given out however it is not clear how to run these files There is no apparent difference to the end user between a JAR file that contains an application and one that merely contains class files or resources used by one Also it is difficult to provide updates since the user would have to look for a new version each time Previously applets were used The original Project Deep Space game ran as an applet However this was dependant on which browser and version of Java was used Some people had Sun s JRE installed but their browser was still using Microsoft s VM Also applets require the web browser to run and this might hinder performance of the browser while the applet is running 12 Applets are not as powerful as applications Applications can create their own dialogs or run in full screen mode For this reason
15. le first A security warning will come up at which point you should click yes to continue The security warning is necessary because the game uses full screen mode An alternate way is to use the included DeepSpace2 jar file With most installations of Java you can double click on this file and it will start From the command line you can use this command java jar DeepSpace2 jar B 2 Compilation This game can also be compiled from source If you have the source directory open it in your favorite IDE and compile it from there From the command line compilation is a little different since there are several different packages to compile Unfortunately there is no Ant build script available The command to compile the packages is javac classpath java enemies java levels java ships java weapons java if you are in the directory named DeepSpace2 where the sources are To run it afterwards you will also need to set the class path using the command java classpath DeepSpace2 GameManager B 3 Starting a game Once the game is started you will see the Deep Space 2 title screen See Figure 4 Press ESC to bring up the menu The menu can be brought up at any time during play 19 Figure 4 Title Screen From this screen you can either start a new game or quit The n button may also be used to start a new game but only from the title screen Once you start the game you ll
16. m 8 References 8 1 Software Java Development Kit http ava sun com Eclipse IDE http www eclipse org Audacity Sound Editor http audacity sourceforge net 16 8 2 API and Heferences Java2D http ava sun com products java media 2D Java Sound http 1ava sun com products 1ava media sound index jsp Java Web Start http ava sun com 2se 1 5 0 docs guide avaws Video Game Music http www vgmusic com Appendix A Function API A 1 Class Hierarchy Important classes used in this project were Sprite An object with an image attached to it It has basic components such as location x y velocity and destination for moving objects Shooter A subclass of Sprite that defines a moving object either player or enemy that has the capability to fire weapons In this case only the player object was using it Ship A subclass of Shooter that defines the player s ship It contains interfaces to be moved around by the player Gun This class is what Shooter objects use to fire weapons It contains information such as the bullets able to be fired the sound effects used and the rate of fire When firing a bullet it generates a Shot object and sends it to the top of the screen Shot A bullet fired by a Gun object this inherits from Sprite The main difference is its drawing model It is smoother than the player s object model since it typically only moves in a single direction E
17. maments that will increase your destructive capabilities Use these to wipe out all enemies in your path Good luck 22
18. mode Using bitmapped graphics seems to be much slower than dynamically generated graphics using the Java 2D API In both cases the data for the ship aliens bullets etc is either loaded from a file or generated with Java2D calls fillOval to draw ovals etc saved as a BufferedImage and then cached for later retrieval Despite their caching as similar images the performance improved noticeably when the generated graphics were used For the sky background level performance degraded largely when bitmapped images were used instead of generated graphics Even on a more powerful machine the entire game was slowed down by this degradation If time were less of a concern performance could be maximized by converting all graphics used to generated graphics However the time required to do this is prohibitive since instead of drawing them using a paint program they must be written down as a set of instructions tested debugged and modified 6 3 Performance Enhancements The performance of this application was improved in several ways One way was in reuse of objects In the first quarter s demo performance was degraded by the creation of many small objects A sprite cache and sound cache was created to cache images and sounds so they would not have to be reloaded constantly These are implemented using a hash map where keys strings would be matched to created images or sounds Increasing the heap size had a small improvement When
19. nemy An enemy that moves around the screen If it comes into contact with the player the player will take damage Fatal This is an interface used by Shot and Enemy This denotes any object capable of inflicting harmful damage 17 Level The base class of all levels A 2 Methods used This section only covers the more important methods Sprite checkintersects Checks to see if a sprite intersects any interesting sprites For shots it checks the enemies and for the enemies it checks the player Sprite intersect Sprite Called on the target sprite when hit Does nothing by default but can be overridden Shooter player enemy calls hit Powerups Player gains weapon Shooter hit Fatal Object is hit by a harmful bullet Calls damage to subtract the bullet s power Shooter damage int health Target loses life If life goes to O calls die Shooter die Enemy is removed from play and score is added If player is killed player loses a life Appendix B User Manual B 1 Installation Deep Space 2 requires the Java Runtime Environment JRE version 5 0 or above The latest version of the JRE can be installed from http ava sun com The easiest way to play is to run the program using Java Web Start which is included with the JRE Open the game URL 18 cs calstatela edu corona cs491 DeepSpace2 jnlp and the game will download automatically Your browser may require you to open the fi
20. oving faster than the frame rate The input loops are important too The player has several control listeners attached to it One listener checks the keyboard another the mouse and yet another checks for cheat codes The old system used in the first quarter was completely event driven When a key was pressed the ship would move in a particular direction This worked well enough to start however the keys had erratic repeat rates When a key is first pressed there is a slight pause before the repeat sets in With the improved version flags for each direction are set when the keys are pressed or released Then the input thread reads the flags periodically and moves the ship as appropriate This allows for a smoother control using the keyboard The mouse is slightly different The player can move the mouse quickly or slowly but it wouldn t be a good idea if the ship moved quickly along with the player s mouse pointer So the mouse s input loop checks the mouse position and slowly moves the player toward the current position Therefore if one uses the mouse to play it is recommended to move the mouse pointer more slowly 4 2 2 Player Ships The player has a ship object attached to it There are several methods that are usable to move the ship around the keyboard and the mouse Due to the way the keyboard handles input it s recommended to use the mouse for movement and the keyboard for firing There are several different
21. running the program using the verbose gc logging parameter the heap size would quickly pass the 4MB default size and hover slightly above there When the heap size was increased to 8MB performance was a little better at the beginning due to 15 less frequent garbage collection required However this only affected the beginning when the application is first loaded since later the JVM would automatically increase the heap size itself 6 4 Analysis This game works a lot faster on a more powerful computer Perhaps it is due to non optimized programming or the Java platform itself however additional overhead seems to be required when playing this game A relatively fast computer is recommended On the Linux platform performance is much slower There are vendor specific modules for the video card I was using however they were not available for the particular kernel I had and since they were not open source I could not compile them myself Therefore I used the standard drivers Performance on this system was much slower even slower than the Pentium II system However the Java sound capabilities were not affected 7 Conclusion This project shows that the Java platform has matured enough to allow development for high speed games where previously it did not However there is still enough overhead that the game does not run very fast on older computers Improvements in the game s design can be made to help alleviate this proble
22. the Java2D API was introduced which made graphics development easier so it would be interesting to see how well game development would be using this improved interface Deep Space 2 also uses the Java Sound library to provide background music and sound for the game Using multiple sound clips many different sound effects can be played simultaneously along with background music with little performance penalty The newest version of Java Java 5 introduced several new features Many of the new language constructs such as generics and improved for loops made programming the more tedious and often repeated portions easier However due to these improved constructs there were some incompatibilities with Java 1 4 Since it would be cumbersome to maintain compatibility with both platforms the Java 5 methods were chosen and thus Java 5 was used as the minimum required version for this project Java 5 was also chosen due to the library improvements The new PriorityQueue class allows for efficient scheduling and the improvements to the Java Sound API make sound programming easier 3 System Architecture 3 1 Hardware Configuration There were two main machines used in this project for development and testing e Computer I Pentium II 400 MHz Windows XP e Computer II AMD Athlon 64 3400 2 2 GHz Windows XP amp Linux It has also been tested on various other machines but not extensively Since many computers at school are
23. tion Additionally an icon can be displayed which will be shown while launching the application The JAR files required for the application are given in the resources section When the Java Web Start launcher starts it checks online to see if newer versions of these files exist If so then only the ones that have changed are downloaded In the Deep Space 2 game the images and sounds are placed in separate JAR files This way if a change to the code is made the resources will not have to be downloaded again 5 1 2 Security One additional feature is the security requirement specified in the JNLP file Since Deep Space 2 requires full screen mode the application must be run in secure mode If it is not security exceptions will be thrown at run time In order for the application to run the JAR files must be signed with a security certificate These are generated using the keytool and jarsigner applications included with the JDK 6 Performance Evaluation 6 1 Experimental Setup This game was run on the two different computers mentioned in section 3 The native modes for each were one at 1280x1024 the other at 1280x800 Both the native resolutions and the game s recommended resolution of 800x600 were used 14 6 2 Experimental Results The older computer run way too slow at 1280x1024 however performance was acceptable when the resolution was lowered The more powerful computer performed much faster in either graphics
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