Justin Weaver - CS470
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1. However the reaction typically involves an change of Velocity and usually direction If the resulting bounce is unable to separate the two objects in the next Tick handler s Update call then the collision will be detected again and reacted to again As you might imagine this can result in an amusing rapid fire ping pong effect However this is not particularly desirable behavior for my space ships Thus the list is maintained so that if a collision is detected more than one the reaction will be bypassed To keep it current the list is pruned each tick when the collision checks happen 5 4 3 Ships Being Damaged by Their Own Bullets a k a Et tu Brute top In the course of testing the near final versions of the game I came across a gameplay bug that occurred often enough to be detrimental to the overall experience A player could fire a shot shortly before dying respawn and get damaged by their own bouncing bullet This was due to the fact that each Bullet class was linked via reference to its creating ship If the ship was destroyed then the player would receive a new ship which the bullet wouldn t recognize It was a simple fix I simply associated each bullet with its Player rather than its Ship This was OrbitClash My First Video Game J Weaver Page 14 of 19 really the point in the program s evolution that I decided to make a Player class it was an idea I had considered but this was the last straw 52. OrbitClash My First Video Game Project Write up Author Justin Weaver Date Apr 28th 2011 Instructor Kenrick Mock UAA Computer Science Department OrbitClash My First Video Game J Weaver Page 1 of 19 Table of Contents ABSAGE eee eee enn AA AN 2 ShipCreationEffect Classes 11 MINKOAICUION O AA 2 AS Algorithms e AA 11 PLO AA AA 2 LTC ollision D amp cction NU 11 3 REGUE AA AA eee 2 5 The Development Process ee 12 SFIS YStCMIMaNG GUINGMI CIS eee 2 5 1 The Spike Project A K A The Early Start 22 Gameplay Description eee ee PA SA AA E ee E A NT jie 3 Pro grim s DAVAO cere Serene a 3 5 2 Ship Rotation Sprite Sheets vs Real Time 3d Playe Onno aa ae reer a 3 STNG Tall ere AA eee AA 2 A MOG SIO GP NA 4 5 3 Ship Graphics Sound and Fonts 13 4 1 Simple Directmedia Layer SDL 4 5 4 Testing and Debugging eens 13 4 1 1 Surfaces Sprites and Animated_ 5 4 1 Animated Sprites and Collision DPIMES A eee oe eee 4 Detect on ZA eee ee 13 Hale EVE AIS a ones 4 542 Stop the Bouncing ee ere 13 LT Parc ko a AA ae eee 4 5 4 3 Ships Being Damaged by Their Own TA SOUS sence eee ee eee ee eee 5 B llets a k a El U teen AA 13 AEE one e meen ee meee 5 5 4 4 Max Bullets Exploit a k a Suicide ADE e O AA 5 t Rekbad icki a re eee 14 4 2 1 The Configuration Static Class 5 5 4 5 Framerate Independent Movement and_ 422 The sprhitesheet Glass ee aa 5 Predictive Col konek 14 4 2 3
3. particle system Note that the speed limit manipulator is not added to the main particle system but is run manually as noted above Ideally nearly all handling of collision detection and reaction would be better if it were abstracted from the main game class However due to time constraints I Planet SolidEntty top Y IDisposable OrbitClash 35 Class Fields Eu boundaryManipulator ParticleBoundary Eu gravityManipulator GravityWell fe particle5ystem ParticleSystem Pa speedLimitManipulator SpeedLimit Properties E Title get string Methods Gol void av KeyboardDown object sender KeyboardEventArgs e void a KeyboardUp object sender KeyboardEventArgs e void Y OrbitClash a Quit object sender QuitEventArgs e void av Tickfobject sender TickEventArgs e void Ja planet Disposable tt Class IDisposable a player2 la a playerl al Player 89 Class decided that making that change in an already working system just wasn t worth it OrbitClash My First Video Game J Weaver Page 10 of 19 4 2 8 1 The Tick Handler top In a bare bones fashion the Tick handler looks something like this Update all the particles in the universe by running each manipulator in the system on the list of particles and then updating their x position cocrdinates according to their resulting velocity property a
4. 4 4 Max Bullets Exploit a k a Suicide to Reload Trick top Another issue I discovered while testing was more of an exploit than a bug The count of live bullets 1s tallied at the cannon level and bullets persist even after a player s death I feel this adds a fun element So a player could have more than the maximum number of live bullets by firing off a rapid barrage quickly dying and then firing more To fix this I could simply move the counting of live bullets from the Cannon class to the Player class However it s hardly a serious issue and I just didn t get around to fixing it However I did add it to my Future Work list below 5 4 5 Framerate Independent Movement and Predictive Collision Detection top Ideally I would add support for framerate independent movement which moves a particle according to the amount of time that has passed since the Tick handler was last called rather than a static distance per Tick Itis possible to do but SDL NET clearly wasn t designed with framerate independent movement in mind Implementing it would mean discarding SDL NET s ParticleSystem almost entirely since theirs 1s designed to progress only in non fractional units Additionally framerate independent movement would necessitate some form of predictive collision detection If a SolidEntity can move more than one unit in a Tick we need to know if it will cross paths 1 e collide with another object otherwise we could
5. Main Page Web Accessed 01 Feb 2011 lt http cs sdl sourceforge net gt R5 GNU GNU General Public License GPL Web Accessed 18 Apr 2011 lt http www gnu org licenses gpl html gt R6 GNU GNU Lesser General Public License LGPL Web Accessed 18 Apr 2011 lt http www gnu org licenses lgpl html gt R7 JVI il I Ship Graphics Web Accessed 18 Apr 2011 lt http gmc yoyogames com index php showtopic 159419 gt R8 Christian Hollingsworth Planet Graphic Web Accessed 18 Apr 2011 lt http www flickr com photos smartboydesigns 3797823072 gt R9 Creative Commons Attribution 3 0 License Web Accessed 18 Apr 2011 lt http creativecommons org licenses by 3 0 gt R10 SoundBible Web Accessed 18 Apr 2011 lt http soundbible com gt R11 Creative Commons Sampling Plus 1 0 License Web Accessed 18 Apr 2011 OrbitClash My First Video Game J Weaver Page 19 of 19 lt http creativecommons org licenses sampling 1 0 gt e R12 Matt McInerney Orbitron Font Web Accessed 26 Apr 2011 lt http theleagueofmoveabletype com fonts 12 orbitron gt e R13 Nicolas Spalinger amp Victor Gaultney SIL Open Font License 1 1 Web Accessed 18 Apr 2011 lt http scripts sil org OFL gt 8 1 Useful Tools top e Audacity The Free Cross Platform Sound Editor lt http audacity sourceforge net gt The Gimp The GNU Image Manipulation Program lt http
6. and how to handle them OrbitClash s keypress event handlers merely set flags which are later read and processed in the Tick handler Most of the action takes place in the Tick handler which updates the states of all the particles in the universe and then draws them to the screen 4 1 3 Particles top SDL NET note the wrapper provides a particle engine that allows an instance of the Particle class to be created from a variety of different objects like a Sprite for example The ParticleSystem class consists of a list of particles and a list of particle manipulators A OrbitClash My First Video Game J Weaver Page 5 of 19 particle manipulator is a class that implements the IParticleManipulator interface which forces the programmer to provide an operation Manipulate that takes a list of particles and performs some arbitrary task on them Particles behave according to their Velocity property The Velocity property contains an abstract data type called a Vector which is composed of a 3 dimensional origin point a direction and a length In the Tick handler the ParticleSystem s Update and Refresh operations are called to send Particles flying around the screen A call to Update runs each particle manipulator in the system on every Particle in the system and updates each particle s position according to its Velocity Each particle has a Life property that ticks down incrementally each time Update 1s called If Life rea
7. the advantage of total creative control However it also left me with no starting direction The gaming industry is currently booming so some rudimentary knowledge of game programming could be handy With that in mind I decided to make my first video game 2 Overview When I was young and dinosaurs roamed the Earth one of my favorite casual games was Spacewar Hifustration 1 To be completely honest I don t remember the name of the game because it was actually just a clone of Spacewar for my beloved Amiga 500 So embodied in this game is my attempt to recreate the essence of that childhood memory 3 Requirements ma Illustration 1 A Spacewar clone 3 1 System Requirements top The game must run on the Microsoft NET 4 0 framework e The game must accommodate 2 players at one keyboard e The game must have good graphics sound effects and gameplay as determined by the client Obviously this type of evaluation is quite qualitative However since I am my own client I have the advantage of a constant feedback loop Thus a qualitative measurement of success is sufficient for the purposes of this project 3 2 Gameplay Description top e The game is a top down 2 dimensional non scrolling spaceship action shooter wherein two players duel to the death e Each player controls a small spaceship which is equipped with a shield limited a front facing cannon see next point and two front and rea
8. the entity in question and the entity specified as a parameter In OrbitClash the Planet Ship and Bullet classes all extend the SolidEntity abstract class 4 2 4 The Ship Cannon and Thruster Classes top SolidEntity eR Abstract Class Particle5prite j Properties pam Alive get 1 bool En Center get Point Methods Y Collision SolidEntity otherSolidEntity bool SolidEntity Sprite sprite SolidEntity Sprite sprite float x float y Vector vector int life Y IDisposable Planet Bullet z Class Class Solid Entity Solid Entity Y IDisposable Ship E Class Solid Entity top The ship class extends the SolidEntity class and 1s therefore also a ParticleSprite It carries with it two Thruster class instances forward and reverse and a Cannon instance It abstracts operations on the thrusters and cannon by keeping those data structures private and passing some requests directly to them e g the AmmoCount property The Ship s Die operation causes the ship to turn off its thrusters disable its weapons and set it s particle s Life property to 0 this effectively makes the ship hidden and inactive OrbitClash My First Video Game J Weaver Page 7 of 19 The BeginRotateLeft BeginRotateRight and EndRotate operations control the ship s sprite sheet animation The Thruster class extends the ParticleSystem class and contains a ParticlePixelEmitter which creates the engine exh
9. The SolidEntity Class 6 34O punzalan 14 4 2 4 The Ship Cannon and Thruster 23 Woik Breakdo wi AA AA AA 14 CASE AA nes eee O E E E E E E E E EN A 15 4 See Bullet CASA aetna SE OM ING SUITS AA AA ee eee Renee 15 Ao lhe Planei Cas aa 8 6 Eid ero ORAM pee ee es ee ere ees 15 4 2 7 The SpeedLimit and GravityWell 6 2 Rortormance ee AA ea AA 16 Classes Particle Manipulators 8 oo EG NG Reene oo ecemocenosusne eaconoreoneuensdosne 16 4 2 8 The OrbitClash Class and the Tick Gs Vidal eae AA ere ee 16 handle AA AA 9 63 2 Licensing Details 17 AL ell Wnt lick Handie ana 10 OA Wal SM IIS he eee ee gee 17 4 9he Player Class tee ee OSes SUA Te a O AA 18 4 2 10 The ScoreCard Class IRS S Re eree S a a AA ee eee 18 4 2 11 The ShipExplosionEffect and s User rook a eee eee 19 OrbitClash My First Video Game J Weaver Page 2 of 19 Abstract top OrbitClash is my first attempt at a video game The project was inspired by the classic game Spacewar It requires the Microsoft NET 4 0 framework to run When completed the game was released freely to the public under an open source license 1 Introduction top Whenever I do a project I always keep a couple of goals in mind learn something new and produce quality results For the purpose of this project I served as my own client I am a very motivated client with extremely high standards So I didn t make things easy on myself Being my own client gave me
10. ach is an extension of A55 ParticleCircleEmitier SDL NET s ParticleCircleEmitter class They each provide a single operation that Methods triggers their functionality at a specified Create Point position ParticleCircleEmrtter 4 ShipCreationEffect i IDisposable 3 ShipExplosionEffect Class Particlecircle Emitter screen position Each of these classes creates a simple burst of circle particles as defined in their respective sections of the configuration file An instance of each of these classes reside inside and are utilized by instances of the Player class E Methods Explode Point position ParticleCircleEmitter ShipExplosionEffect 4 3 Algorithms top 4 3 1 Collision Detection top One of the most interesting algorithms I wrote 1s the one that implements collision detection Collision detection 1s simply a method of recognizing when two particles come in contact collide One easy method of collision detection is to simply see if the rectangles of the sprites overlap OrbitClash My First Video Game J Weaver Page 12 of 19 However since most sprites come with transparent portions the rectangles may not tell the whole story Although simple rectangle detection may work fine in some scenarios for the purpose of my game I needed pixel level detection For pixel level collision detection the previously described rectangle check is done first because 1f the r
11. aust effect By not including the engine effects in the main particle system of the OrbitClash class I keep them from being effected by the manipulators attached with that system 1 e gravity screen edge bounce speed limit The Ship class provides Update and Render methods which are called from within OrbitClash s Tick handler Those methods simply call the operations by the same name within the Thruster class instances Thus the particles are all updated and rendered even though they do not exist in the game s main particle system i Disposable A Disposable 5 i 5 Cannon Ship E Class Class Solid Entity i F para E Properties a cannon T AmmoCount int E Ey LiveBulletCount int Hi ei psa T Power float Shields floa El Methods a Cannoni BeginForwardThruster void BeginReverseThruster void BeginRotateLeft void BeginRotateRight void Die void EndForwardThrusterl void EndReverseThruster void EndRotate void Firelannont Bullet Render void 5hipO Update bool PEE 86 OE St Fire Bullet Disposable a reverseThruster Thruster ml C i lass Particle5ystem gt io nd o forwardThruster bo E Fields fe particlePixelEmitter ParticlePixelEmitter Properties af ExhaustConeDegRange int ST Power float E Methods gt EndThrusterl void FireThruster void Thrusterl The Cannon class s Fire operation retu
12. ce property which is optionally applied to the background surface 1 e the star field depending on configuration settings The halo simply gives a visual representation of the limit of the reach of the gravitational force of the planet The gravitational force itself is applied via a particle manipulator Planet y Class Solid Entity Properties y Halo5urace Surface Methods which is discussed below Planet 4 2 7 The SpeedLimit and GravityWell Classes Particle Manipulators top IParticleManipulator The GravityWell and SpeedLimit classes F GravityWell are particle manipulators that implement Class SDL NET s IParticleManipulator interface ma d Manipulators are designed to be added to a Properties EE particle system which means they run of E T PA every particle in the main system each time EST Power get set float the main system s Update operation is ey Radius get set float called y p p l Methods GravityWell Point position float radius float power Optionally manipulators can be run Manipulate ParticleCollection particles void manually on a collection of particles by calling their Manipulate operation directly kaaa aaa Gravity Well draws all particles within Hr Radius distance of Position according to a SpeedLimit Class calculation that makes the drawing force TEER zero at the outer edge of the radius and maximal at the center of the well The
13. ches 0 the Particle is pruned from the system However if the lifespan 1s set to a negative value the particle lives forever or until it is killed by manually setting its Life to 0 The ParticleEmitter class which is also just a Particle itself emits a steady stream of particles in a configurable way The particle emitter was very handy for various important special effects I used particle pixel emitters for the thrusters of each ship s engine and particle circle emitters for the ship warping in and ship explosion effect 4 1 4 Sounds top Sounds are quite simple to use in SDL NET Each sound is loaded from an OGG Vorbis file other formats are supported e g MP3 WAV during the program s initialization The Thruster class holds the sounds for each ship s thruster The Cannon class carries the fire and dryfire sounds Since it handles all of the collision detection and reaction the main game class itself OrbitClash holds the collision sounds Asynchronous playback of each sound is initiated from the Tick handler 4 1 5 Fonts Text top SDL NET provides simple classes that are used to facilitate the loading of a font from a file and the rendering of a text string to a Surface The details are of little interest P IDisposable 4 2 Data Structures top SpriteSheet E Class 7 4 2 1 The Configuration Static Class top El Properties ET Animated5prite AnimatedSprite Ey Bitmap Bitmap Ey CurrentDirectionDeg int Ey Fir
14. e of the planet s gravity When a player is destroyed they simply respawn after a few seconds in a location that 1s on the opposite side of and a minimum safe distance from the planet from the other player Each player begins with three simple counters displayed o Kills a count of times the player destroyed other player Defeats a count of times the player was destroyed by other player Suicides a count of times the player hit the planet The game never ends it simply goes on until it is shut down 3 4 Player Controls top Player One Controls The Yellow Ship o Rotate left A o Rotate right D o Forward thruster W o Reverse thruster S o Fire cannon Left Control Player Two Controls The Red Ship o Rotate left Left Arrow o Rotate right Right Arrow o Forward thruster Up Arrow o Reverse thruster Down Arrow o Fire cannon Right Alt OrbitClash My First Video Game J Weaver Page 4 of 19 4 Design top Since I was completely new to game design and possessed only a limited understanding of graphics programming I decided to use a multimedia library called Simple Directmedia Layer SDL to facilitate the game s development SDL aids game development by simplifying the handling of animation physics sound and player input R3 4 1 Simple Directmedia Layer SDL top SDL is written in C but I used a wrapper called SdlDotNet which allows much of SDL s functionality to be used from w
15. ectangles aren t overlapping then there is no reason to do the more costly pixel level check If the full pixel check 1s necessary then we find the rectangle that contains the intersection of the two sprites and check each pixel within the rectangle If we find a location where two non transparent pixels overlap then we have a collision 5 The Development Process top I chose the name OrbitClash because it seemed appropriate to the game s concept and more importantly a Google search for orbit clash game didn t reveal any other video games with the same title 5 1 The Spike Project A K A The Early Start top I really had no idea how to make a game so I couldn t write a design document without doing a little programming work first So to familiarize myself with game programming I performed a Spike project My spike resulted in a simple program wherein two very primitive looking ships could be flung around the screen using the keyboard controls The ships bounced off the edges of the screen thanks to SDL NET s ParticleBoundary class which implements IParticleManipulator and keeps particles within a specified rectangular boundary However they still passed right through each other and the planet because I hadn t implemented collision detection yet The Spike was very helpful because of my inexperience and it was good quality work So I used the results of my spike as my first evolutionary prototype 5 2 Shi
16. force E EF Limit get set float becomes much more intense as the distance Methods from the center approaches zero The exact Manipulate ParticleCollection particles void description of the force calculation is the SpeedLimit float speedLimit gravity well s Power divided by the particle s distance from the center of the OrbitClash My First Video Game J Weaver Page 9 of 19 well as a percentage of the overall well radius squared The main OrbitClash class creates an instance of GravityWell and adds it to the main particle system SpeedLimit checks and caps the Length property of each particle s Vector The main OrbitClash class also creates an instance of the SpeedLimit class However it enforces the speed limit manipulator manually as described above to ensure that it is the last thing to update the particle system before the call to Render 4 2 8 The OrbitClash Class and the Tick handler The OrbitClash class 1s the main class of the program It handles events generated by SDL NET 1 e keypress tick quit maintains the primary game particle system and does the overseer work of detecting and reacting to collisions Naturally it also contains two instances of the Player class one for each player and a single instance of the Planet class It is also responsible for instantiating and adding the various particle manipulators used in the game 1 e boundary gravity to the
17. ill be more correct to implement framerate independent Toro movement and predictive collision detection l 6 3 Public Release top I published the game on GoogleCode The site contains a source code SVN repository as well as binary and source code archive downloads The game s homepage http orbitclash googlecode com ust 5 3 Installation 6 3 71 User Manual top Illustration 5 The OrbitClash homepage OrbitClash My First Video Game J Weaver Page 17 of 19 Operating the game is exceedingly simple However the OrbitClash user manual is included on the game s home page and in the ReadMe txt file bundled with each distribution I made a tactical decision not to duplicate it again in this document 6 3 2 Licensing Details top I chose the GNU General Public License GPL for OrbitClash because it is compatible with all of the licenses of the other resources used in this project and because it prevents my code from being used in some random closed source commercial product theoretically SDL and SDL NET are both licensed under the GNU Lesser General Public License LGPL IR Which is an open source GNU license commonly used with libraries The two ship graphics were created by JVI i I I who made them freely available under the conditions that they be attributed for their work and that they be notified via thread post when their work i
18. ithin the Microsoft NET framework s managed environment SDL NET uses NET s Interop services to access SDL s unmanaged resources which incurs a small overhead SDL is an event driven framework Consequently the game is built from a framework of abstract data types that are manipulated by a single main game class or controller in response to events generated by SDL 4 1 1 Surfaces Sprites and Animated Sprites top A Sprite 1s a two dimensional image or Surface often with a transparent background that can be quickly pasted into another Surface An animated sprite 1s designed not only to move around the screen but also to simultaneously play back a kind of flip book of sprites which are encapsulated in a sprite sheet A sprite sheet is really just a series of statically sized sequential motion capturing frames not unlike a strip of film During gameplay the ships in OrbitClash will not just move around the screen they will also be able to rotate So a sprite sheet was required to animate the rotation of each ship Other options were explored as I will discuss later but in the end I used sprite sheets 4 1 2 Events top Once the initial environment has been set up SDL is an event driven framework A framerate is assigned and SDL calls your own Tick handler for each refresh Additionally other handlers can be called in response to events like keypresses or application close The programmer chooses which events to attend
19. move one object through another Predictive detection would allow the program to notice and react to those collisions In the end I decided that the extra effort wasn t worth it I had made a decision at the start to use SDL NET so I felt it was right to use it as intended 5 4 6 Optimization top As I neared the end of the development phase I came to a shocking realization The game worked very smoothly on many machines but on my slower ones the game sometimes became unplayably slow I used a performance profiler to hone 1n on the slowdown points As it turns out the performance hit came from the fact that I had not converted the images I loaded from the disk into a uniform pixel format So the conversions were being done each time on the fly Once I made those simple changes the speed of the game greatly increased Even my lowly netbook can now maintain the game s set framerate of 30fps 5 5 Work Breakdown top I initially broke the development of the project into distinct phases of coding refactoring and testing I carefully separated each task and assigned a specific schedule to it However given the nature of evolutionary programming and the fact that I served as my own client I ended up adhering to a more informal system of short development cycles implementing testing and refactoring The project still reached completion at the planned time and there were no code like hell sessions involved The chart below is simplified f
20. myParticleSystem Update Check for and handle user input ProcessUserInput Local method I Check for and enforce collisions EnforceCollisions Local method Manually enforce speed limit manipulator to make sure it runs last speedLimiter Manipulate myParticleSystem Particles Render all the particles in the universe to the back buffer myParticlesystem Renden Video Screen Blit the InfoBar at the bottom of the screen to the back buffer DisplayInfoBar Local method Finally flip the back buffer onto the screen Video Screen Update 4 2 9 The Player Class top The Player class represents a real life player and contains a Ship and ScoreCard instance it also carries instances of the creation and explosion effect classes Its other job is to take user commands when its CheckKeyPresses and CheckKeyReleases operations are called by the main game class keypress event handlers and then execute those commands when the ProcessUserInput operation is called from within the main game class Tick handler P IDisposable Disposable Player A 2 ScoreCard ScoreCard ol Class gt Class F Properties DownKey get set Key DownKeylsDown get set bool i Disposable Fireki et set Ki F ka ai ey g z 5 z EY a Shi Ship FirekeyWasPressed get set bool IP Class LeftKey get set Key gt SolidEntity LeftKeylsDown get set bool i N
21. p Rotation Sprite Sheets vs Real Time Rendering top SDL does not provide an efficient method of rendering the ship rotation in real time The rotation would be done by the CPU rather than the graphics hardware Modern machines are fast and this would hardly be a killer However I wanted to do this right So I was faced with a choice learn OpenGL and do the rendering on the graphics hardware or make a sprite sheet and use SDL as I originally planned I opted to use a sprite sheet for a variety of reasons Mostly I did not want to add the extra complexity of learning OpenGL to my already busy agenda So I needed a sprite sheet showing the full 360 degrees of rotation for each ship I have been informed that automatically creating a sprite sheet of a rotating image 1s trivial in professional art software like Adobe Photoshop Unfortunately when free alternatives are elusive poor college students must make our own solutions So I whipped up a quick spinning sprite sheet creator of my own in C OrbitClash My First Video Game J Weaver Page 13 of 19 5 3 Ship Graphics Sound and Fonts top My original plan for making the ship graphics was to draw them by hand scan them and shrink them down to hide the defects However after a few less than spectacular attempts I located some free ship graphics to use I edited them for my needs ran them through my sprite sheet spinner program and made sure to give attribution to the arti
22. r facing thrusters unlimited e Each ship s cannon has unlimited capacity with the exception that there can be only 10 live bullets from each player in the universe at one time I imposed this rule rather than a lengthier OrbitClash My First Video Game J Weaver Page 3 of 19 cooldown between shots to make the game a little more challenging Note that the player that owns a bullet will never be harmed by it rather it would simply bounce off them Firing a ship s thruster accelerates the ship in its current direction When the thruster 1s not firing the ship continues on its trajectory unless affected by another force e g collision gravity etc Note that cannon bullets behave essentially the same way The entire game world consists of the fixed screen area only Ships and cannon bullets bounce back if they touch the edge of the screen However cannon bullets have a limited lifespan so they disappear fairly quickly At the center of the screen 1s a planet which exerts a gravitational pull on the ships and cannon bullets within a specified distance range Anything that touches the planet is instantly destroyed 3 3 Program Behavior top When the application starts up the game prompts Press the spacebar to begin When the game begins each ship begins on opposite sides of the screen with the planet between them Each ship s starting point is a safe distance from the planet so that they are outside the rang
23. rns a Bullet on success and null on failure The cannon may fail to fire if there are too many live bullets for that ship or if the cannon s cooldown period as specified in the configuration file has not elapsed To determine the number of live bullets the ship currently has in play the Cannon class maintains a list of the live bullets it has fired It provides the LiveBulletCount property which gets called each time a player attempts to fire their cannon When this occurs first it prunes its list of all bullets with Life of 0 then it returns the count of the number of items remaining in the list OrbitClash My First Video Game J Weaver 4 2 5 The Bullet Class The Bullet class 1s a SolidEntity that holds a reference back to the player that owns it The Power property indicates how much damage the bullet will do if it hits the opposing player s ship The Bullet class s constructor takes a variety of parameters including the bullet sprite the initial bullet Vector the bullet s Life and a reference to its owner The reference to owner is important because friendly bullets will merely bounce off a ship while hostile ones cause damage 4 2 6 The Planet Class top Page 8 of 19 top Bullet E Class Solid Entity r El Properties ET Owner Player paa Power float E Methods Bullet The Planet class is a SolidEntity that aside from encapsulating the P IDisposable planet image also contains the HaloSurfa
24. rom the chart in my original proposal OrbitClash My First Video Game J Weaver Page 15 of 19 Work Breakdown Writeup Estimated aaa Final Testing Estimated anes Refactoring Estimated Implementation Estimated MIs Writeup Actual EE Development Actual mE Semester CH KK 02 15 11 02 25 11 03 07 11 03 17 11 03 27 11 04 06 11 04 16 11 04 26 11 6 Results top I m quite satisfied with the results as a whole both as the client and the developer The game is very playable and fun However it would be nice to have a computer player to compete with since computer scientists often don t have real friends Check out the screen shots of the finished product below 6 1 Final Program top Illustration 2 The start up screen Kills 2 Kills O Defeats O feats O 9 Jicides o suicides Z Illustration 3 The ships in their initial positions OrbitClash My First Video Game J Weaver Page 16 of 19 i OrbitClash KillsS lt 4 ra IR KIS Defeats mhields s5 OCefeste 4 iicides 3 Bullets iicides 3 Illustration 4 An epic space battle 6 2 Performance top SDL NET uses Microsoft NET Interop services to call the unmanaged SDL libraries which incurs some overhead In spite of this the game does not put a significant strain on the system In fact its exact requirements are unknown but low enough that the maintainable frame rate isn t likely to be much of an issue However it would st
25. s used I did both The planet graphic was created by Christian Hollingsworth and licensed under the Creative Commons Attribution 3 0 license The sound effects I used were all obtained from SoundBible Most of the sounds were created by Mike Koenig and released under the Creative Commons Attribution 3 0 license For a comprehensive list see the Sound Attribution txt file in the Sounds directory of either the binary or source code distributions or OrbitClash The ship thruster sound was created by dobroride and released under the Creative Common Sampling Plus 1 0 license The ship warping in sound was created by snottyboy and released under the Creative Commons Attribution 3 0 license The only font I used is called Orbitron and it was created by Matt McInerney and released under the Open Font License I took special care to provide complete and specific licensing details in every distribution of the binary and source of the game so as to be sure not to violate any of the sub licenses 6 4 Wish List top e Tally live bullet count in the Player class instead of the Cannon class to prevent max bullet exploit e Graphic effects when bullet hits ship e Graphic effects when ship hit ship e Graphic effects of ship damage level e Configuration e Joystick support e Framerate independent movement amp predictive collision detection e Ability to pause unpause the game e Press H for instr
26. st in all deliverable and published materials including this paper below The planet graphic sounds and font that I used are all released under free licenses as detailed in the Licensing section of this paper below Everything not mentioned was created by me 5 4 Testing and Debugging top Since I was my own client I fell into regular loops of testing debugging and refactoring Along the way I faced a number of memorable educational and even amusing challenges 5 4 1 Animated Sprites and Collision Detection top The fact that the ship sprites are animated meant I had to take special considerations during the pixel level collision check I couldn t figure out why I was sometimes getting an exception during collisions I realized that the animation frame could change as the pixel level check was iterating through pixels To solve the problem I simply grabbed a reference to the appropriate frame as soon as I entered the pixel level checking method rather than dereferencing the animated sprite for its surface each time I needed it within the loop 5 4 2 Stop the Bouncing top Each instance of SolidEntity maintains a list of other SolidEntity objects it is currently colliding with This is useful because I do after the fact collision detection which means the objects are already overlapping when I detect the collision A collision triggers a reaction that varies depending on the types of objects involved 1 e planet ship bullet
27. stFrameShipDirectionDeg int 2 FrameSize Size Rotation PerFrameDeg int ih TransparentColor Color Methods SpriteSheet The configuration class contains many intricate settings OrbitClash some of which are described in this document However if you desire more specific details please see the comments in the Configuration cs file 4 2 2 The SpriteSheet Class top The SpriteSheet class is designed to hold information OrbitClash My First Video Game J Weaver Page 6 of 19 about a ship rotation animation Its constructor takes among other things the filename of the sprite sheet image to load as a parameter The class provides access to the entire image as well as configuration information like what direction the ship is facing in the first frame how many degrees the ship rotates in each frame the size of each frame in pixels and the color that will be treated as transparent Some of the information the class provides 1s dynamic For example the CurrentDirectionDeg property provides the current direction that the ship 1s facing by multiplying the degrees of rotation per frame by the index number of the current animation frame 4 2 3 The SolidEntity Class The SolidEntity abstract class extends the ParticleSprite class and is designed to facilitate collision detection between classes that further extend it The Collision operation returns true if a pixel level collision is detected between
28. uctions on main title screen e Give SolidEntity objects mass to make physics more realistic e Support higher resolutions OrbitClash My First Video Game J Weaver Page 18 of 19 e Network play e Power ups e Player profiles e Choice of ships w various specs e AI to play against e Installer for binary distribution 7 Summary top For this project I served as my own client so I found it sensible to use an evolutionary prototyping design methodology My goal was to develop a video game inspired by the classic game Spacewar The result is a very playable open source game I the client have declared the project a brilliant success As mentioned above to download the finished result visit http orbitclash googlecode com I learned a little bit about some very basic game programing graphics physics sound and player input along the way I also learned that collision detection is not as simple as it seems I feel like my work was a worthy introduction to the basic concepts of video game design 8 References top R1 Wikipedia contributors Spacewar Wikipedia The Free Encyclopedia 18 Jan 2011 lt http en wikipedia org wiki Spacewar gt Web 24 Jan 2011 R2 Microsoft Microsoft NET Framework Web Accessed 01 Feb 2011 lt http www microsoft com net gt R3 SDL Simple Directmedia Layer Web Accessed 01 Feb 2011 http www libsdl org R4 C SDL C SDL
29. umber get int IDisposable RightKey get set Key mg yg RightKeylsDown get set 3 bool AT CreationEffect il reationEffect Class ig ig tig liglig ig ig iy lg ig gy a 1 9er Sen 5 key b ParticleCircleEmitter UpKeylsDown get set boo ethods T IDisposable CheckKeyPresses Key key bool P ExplosionEffect ShipExplosionEffect 4 Class i p ParticleCircleEmitter ProcessUserlnput Bullet CheckKeyReleases Key key bool TZEZ OrbitClash My First Video Game J Weaver Page 11 of 19 4 2 10 The ScoreCard Class top The ScoreCard class holds statistical 1 sai inl information for a Player Its constructor ScoreCard A takes a player and a display position as Class parameters m d Properties The ScoreCard class will render itself to any surface passed to the Render operation in keeping with SDL NET conventions Eg Defeats get set 1 int Eg Kills get set int T Suicides get set int E Methods Refresh Surface surface void ScoreCard Player player Point displayPosition Stats Explanation e Kill killed the other player with bullets Defeat killed by the other player s bullets e Suicide killed by planetary impact 4 2 11 The ShipExplosionEffect and ShipCreationEffect Classes top o ck The ShipCreationEffect and j ShipExplosionEffect classes are very io t similar and e
30. www gimp org gt Tortoise SVN A Subversion client implemented as a windows shell extension lt http tortoisesvn tigris org gt
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