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INF245 Mobile applications Games Programming using MIDP

INF245 Mobile applications Games Programming using MIDP. H 2007 Ola Bø. First some business information (source Gaute Godager, Funcom 2004). The market for mobile games 175 000 000 active players Ordinary games (not mobile) Development cost 10-250 MNOK

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INF245 Mobile applications Games Programming using MIDP

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  1. INF245 Mobile applicationsGames Programming using MIDP H 2007 Ola Bø Molde University College INF 245 Fall 2007 OBø

  2. First some business information (source Gaute Godager, Funcom 2004) • The market for mobile games 175 000 000 active players • Ordinary games (not mobile) • Development cost 10-250 MNOK • Developed by teams with three groups of personnel • Programmers • Artist/Gaphics • Desinger • For games distributed through shops profits are divided • Developer 10-20 % • Distributor 30 % • Publisher the rest • 5 % of the titles makes 80% of the money (200 GNOK) Molde University College INF 245 Fall 2007 OBø

  3. Many kinds of games • Graphics- or text-based games • One or more playyers • On one unit or networked • Build upon board games? • Action games Molde University College INF 245 Fall 2007 OBø

  4. Levels of networking in mobile gaming (Powers 2006) • Single player with community features (global high-score, tournaments, chat) • Turn based games(chess, checkers,...) • On-line multiplayer Molde University College INF 245 Fall 2007 OBø

  5. Action games • Animation/Simulation partly controlled by user • One or more mobing objects • ”Natural movements” • Collisions Molde University College INF 245 Fall 2007 OBø

  6. Action games • Program must handle • Input from user • Interpret keypresses to control movement • Movement • Smooth motion of objects • Handle collisions • Display • Update screen • Background and foreground graphics • Cinema: 24 frames per second • We need at leas same frame rate to avoid jerky movements Molde University College INF 245 Fall 2007 OBø

  7. Action games in MIDP 1.0 • Keyboard input results in keyPressed being called • All objects in movement must get new positions for every time screen is redrawn • Object is removed from old position • Object is drawn in new position • Paint must be called often enough • Loop calling repaint • Loop must run at least 24 timer per s • Code must be quick enough Molde University College INF 245 Fall 2007 OBø

  8. Aksjonsspill i MIDP 1.0 • Input fra brukeren kommer i form av keyPressed() kall • Alle objekter i jevn bevegelse må få oppdatert posisjon for hver gang skjermen tegnes på nytt • Objektet må fjernes fra gammel posisjon • Objektet tegnes i ny posisjon • Vi må sørge for at Paint kalles tilstrekkelig ofte • Loop som kaller rePaint() • Loopen må kjøres minst 24 ganger per sekund • Koden må være rask nok Molde University College INF 245 Fall 2007 OBø

  9. public void GameBoard extends Canvas implements Runnable { public void run() { while (true) { // Update positions // Handle collisions repaint(); // Wait until time for next update. } } public void paint(Graphics g) { // Draw what needs to be drawn } protected void keyPressed(int keyCode) { // Handle input from user. } } Molde University College INF 245 Fall 2007 OBø

  10. Time control • Smooth movement demands continual update • Cinema: 24 frames per second • 25 fps corresponds to a repaint every 1000ms/25fps=40 ms • TICKTIME=40ms • Use System.currentTimeMillis() • Register startTime and endTime for each recalculation. • Sleep away the remaining time using Thread.sleep(40-(endTime-startTime) to obtain constant time per frame. • Use rePaint() to order screen update for each frame Molde University College INF 245 Fall 2007 OBø

  11. public void GameBoard extends Canvas implements Runnable { public void run() { while (true) {//Game loop startTime=System.currentTimeMillis(); // Update positions // Handle collisions endTime=System.currentTimeMillis(); // Wait until time for next update. Thread.sleep(TICKTIME-(endTime-startTime); repaint(); } } public void paint(Graphics g) { // Draw what needs to be drawn } protected void keyPressed(int keyCode) { // Handle input from user. } } Molde University College INF 245 Fall 2007 OBø

  12. Input from the user • keyCode parameter contains code for key pressed • getGameAction interprets the key code • I the exampe over, the input results in the racket being moved to the left or to the right, (but not out of the board) Molde University College INF 245 Fall 2007 OBø

  13. Update positions sx is the x-coordinate of the objectsy is the y-coordinate of the objectvx is the speed of the object in the x-directions0x is previous x-coordinatet is time • Objects moving with constant speed • sx=vx*t+s0x • sy=vy*t+s0y • Simplifications • If vx (and vy) is movement per frame time • Then the next position can be calculated like this • sx=s0x+vx • sy=s0y+vy • Speed and acceleration can be fractions • Problem: • You may not have floating point arithmetics • Floating point may be too slow If accelerated motion you shoud add vx=ax+v0x xy=ay+v0y ax is acceleration in x-direction ay is acceleration in y-direction Molde University College INF 245 Fall 2007 OBø

  14. Updating positions using fractions sxold=sx; int sx0=sxold*1000+sxr;//sx0 i thousandth included old rest int sxq=vx+sx0; //new x in thousandt sx=sxq/1000; //back to integers sxr=sxq%1000; //new rest syold=sy; int sy0=syold*1000+syr; int syq=vy+sy0; sy=syq/1000; syr=syq%1000; But / % and * takes a long time and can result in jerky animations CLDC 1.1 have floating point, but that is slow too Using round number in the binary system and binary operations << to multiply>> to divide& to find the restcan speed things up Molde University College INF 245 Fall 2007 OBø

  15. Quicker calculations using binary arithmetics All calculations are fractions with 2^7=128 as denominator to improve precision when compared to integer numbers uses the following ultra quick operations <<7 to multiply by 128 >>7 to divide by 128 &0x3f to find rests >> << &-operations are quicker than * / og %. How much quicker? Can be determined experimentally. Molde University College INF 245 Fall 2007 OBø

  16. Collision handlingBall should not go through walls Ball rebounds. Ballen changes direction left is position for left wallBALLR is ball radius sx is x-coordinate for ball center Add point Accelerates to simulate gravitation Molde University College INF 245 Fall 2007 OBø

  17. Paint() • Mobing objects must first be deleted in old position before being redrawn • Can be avoided by double-buffering and drawing everything for each repaint. • Do not redraw more than necessary • Only redraw what has changed since last redraw. • If showNotify() has been called all should be redrawn • Complex drawing operations can be replaced by copying a picture of the drawing • Find five improvements in code on next page Molde University College INF 245 Fall 2007 OBø

  18. MIDP 2.0javax.microedition.lcdui.game • Layers • Layers over each other. z=0 is the bottom layer • TileLayer with tiles • The tiles are fetched from a picture-file using a tilenr • A sprite is a layer animating an object • The pictures of the animation are fetched from file and displayed in a programmable order • Layers and sprites are an old invention used on game consoles of the eighties. They can be used on mobile devices today even if mobile devices have better capacity • Transparency-handling Molde University College INF 245 Fall 2007 OBø

  19. Tiled Layer source: Jonathan Knudsen Molde University College INF 245 Fall 2007 OBø

  20. Sprites • A partly transparent two-dimensional animation shown in a plan in a threedimensional scene (source: Wikipedia) • May be rotated in the plane • Always seen from the same side • Can overlap and be overlapped by other objects • Stored as a picture series shown in quick succession • The application can control where in the picture series animation should start and which way to go Molde University College INF 245 Fall 2007 OBø

  21. MIDP 2.0 • Polled keyboard makes one loop possible • Better control over painting timing • Sprites with collision detection Molde University College INF 245 Fall 2007 OBø

  22. MIDP 2.0 Game Canvas Game Loop Molde University College INF 245 Fall 2007 OBø

  23. javax.microedition.lcdui.game Molde University College INF 245 Fall 2007 OBø

  24. Sound • Sound can be controlled using the multimedia API - JSR 135 • Use of vibration? • Use of camera Molde University College INF 245 Fall 2007 OBø

  25. 3D 3D API JSR 184 Speed problems Slow game and 3D apis reported one some platforms Program size problem May be alleviated using obfuscation Networking problems Latency (Powers 2006) seconds over WWAN Bandwidth The usual suspects Screen Input devices Heterogeneity Mobile context of use Other possibilities and limitations Molde University College INF 245 Fall 2007 OBø

  26. Multiplayer demands communications • Possible solutions • Bluetooth • +low cost +social • -short range - limited number of participants - setup • WWAN • + range + can support many participants • - cost - latency time - unpredictable bandwdth • - handling of users – may need lobby to meet • SMS • + simplicity + availability • - - cost - - latency time Molde University College INF 245 Fall 2007 OBø

  27. Alternatives to J2ME • “Native” gaming-applications • Programmer must learn the platform • Code might run faster • Code might use more of the platform capabilities • Separate version for each platform • Dedicated gaming platforms – Mophun Molde University College INF 245 Fall 2007 OBø

  28. Final Questions • What kinds of desktop games you know of might be fun played on a mobile platform? Molde University College INF 245 Fall 2007 OBø

  29. Sources • Papers • Jonathan Knudsen: Creating 2D Action Games with the Game API http://developers.sun.com/techtopics/mobility/midp/articles/game/ • Bill Day: Wireless Game Development Now and Futurehttp://developers.sun.com/events/techdays/presentations/brazil/WirelessGameDevelopment.pdf • Developers Training Material: Optimizing Your J2ME Applications for the Sony Ericsson T 610 Z600 • Michael Powers(2006) Mobile Online Games articles series. http://developers.sun.com/mobility/midp/articles/gamepart1/http://developers.sun.com/mobility/midp/articles/gamepart2/http://developers.sun.com/mobility/midp/articles/gamepart3/ • Book • Martin J. Wells: J2ME Game Programming • Recommended if you are interested in programming action-games Molde University College INF 245 Fall 2007 OBø

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