Molde University College INF 245 Fall 2007 OBø 1 INF245 Mobile applications Games Programming using...

Molde University College INF 245 Fall 2007 OBø

1

INF245 Mobile applications Games Programming

using MIDP

H 2007

Ola Bø


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)


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


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


5

Action games

Animation/Simulation partly controlled by user

One or more mobing objects ”Natural movements” Collisions


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


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


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


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. }}


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


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. }}


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)


13

Update positions 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

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

If accelerated motion you shoud addvx=ax+v0xxy=ay+v0yax is acceleration in x-directionay is acceleration in y-direction


14

Updating positions using fractions

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

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;


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.


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


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


19

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


20

Tiled Layer

source: Jonathan Knudsen


21

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


22

MIDP 2.0

Polled keyboard makes one loop possible Better control over painting timing Sprites with collision detection


23

MIDP 2.0 Game Canvas Game Loop


24

javax.microedition.lcdui.game

Layer

paint()setVisible()

(from game)

LayerManager

append()getLayerAt()insert()paint()remove()

(from game)

-component[]

GameCanvas

GameCanvas()getGraphics()flushGraphics()getKeyStates()paint()

(from game)

Sprite

collidesWith()defineCollisionRectangle()defineReferencePixel()paint()setFrame()setFrameSequence()setImage()setRefPixelPosition()

(from game)

TiledLayer

createAnimatedTile()paint()setCell()setStaticTileSet()

(from game)

Canvas(from lcdui)


25

Sound

Sound can be controlled using the multimedia API - JSR 135

Use of vibration? Use of camera


26

Other possibilities and limitations 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


27

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


28

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


29

Final Questions

What kinds of desktop games you know of might be fun played on a mobile platform?


30

Sources Papers

Jonathan Knudsen: Creating 2D Action Games with the Game APIhttp://developers.sun.com/techtopics/mobility/midp/articles/game/

Bill Day: Wireless Game Development Now and Future http://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

http://developers.sun.com/techtopics/mobility/midp/articles/game/

http://developers.sun.com/events/techdays/presentations/brazil/WirelessGameDevelopment.pdf

http://developers.sun.com/events/techdays/presentations/brazil/WirelessGameDevelopment.pdf

http://developers.sun.com/mobility/midp/articles/gamepart1/









Date post:	18-Dec-2015
Category:	Documents
Upload:	silvia-long
View:	213 times
Download:	0 times

Molde University College INF 245 Fall 2007 OBø 1 INF245 Mobile applications Games Programming using...

Documents