Game Development for Nokia Asha Devices with Java ME

Marlon Luz - INdTNokia Developer Evangelist

@marlonluz

Low-Level UI API• GUI to have control over each pixel in the screen

• Portable among MIDP devices when in the same screen resolution

Displayable

Screen Canvas

TextBoxAlert Form List GameCanvas

Canvas• Canvas is a subclass of Displayable class

• Have to extend the Canvas class•public class Tela extends Canvas {•}

• Overwrite the paint() method• protected void paint(Graphics g) {• // do some painting!• }

Drawing on the screen• import javax.microedition.lcdui.*;

• class MyCanvas extends Canvas {• public MyCanvas() {• super();• super.setFullScreenMode(true);• }

• public void paint(Graphics g) {• g.setColor(255, 255, 0);• g.fillRect(0, 0, getWidth(),• getHeight());• g.setColor(0, 0, 0);• g.drawString("Hello There", • getWidth() / 2, 0, • Graphics.TOP | Graphics.HCENTER);• }• }

Fonts• The Font class can be used to control the way text appears on the Canvas• Atributtes:

• Style• Size• Face

• Fonts usam âncoras com as coordenadas (x,y) para decidir ontem serão desenhadas

Fonts• public void paint(Graphics g) {• Font f =

Font.getFont(Font.FACE_PROPORTIONAL, •

Font.STYLE_UNDERLINED, •

Font.SIZE_LARGE);• g.setFont(f);• g.drawString("System Font", • getWidth()/2, getHeight()/2, • Graphics.TOP | Graphics.HCENTER);• }

Events• The developer is resposible to manage all input events

• Input events are throw when:• A key is pressed ( for keyboard enabled devices)• The screen is touched (for touchscreen devices)• A command is chosen

Events• For keyboard enabled devices use the following methods to capture key events:• keyPressed(int keyCode)• keyReleased(int keyCode)• keyRepeated(int keyCode)

• For touchscreen enabled devices use the following methods to capture touch events:• pointerPressed(int x, int y)• pointerReleased(int x, int y)• pointerDragged(int x, int y)

Events•public class MyCanvas2 extends Canvas {

int x,y; boolean firstTime = true; boolean userHasTouched = false;

public void paint(Graphics g) { if (firstTime) { g.setColor(255, 255, 0); g.fillRect(0, 0, getWidth(), getHeight()); firstTime = false; } if (userHasTouched) { g.setColor(0, 0, 0); g.fillArc(x, y, 5, 5, 0, 360); userHasTouched = false; } } protected void pointerPressed(int x, int y) { this.x = x; this.y = y; userHasTouched = true; repaint(); } }

Sample• Checkers Game

Game API• javax.microedition.lcdui.game package

• Help to develop games quickly and help to reduce the size of the JAR file

• Layers usage to create visual elements, for exemple:• Layer 1 – Background• Layer 2 – Enemy • Layer 3 – Player

Game API - SampleGameCanvas

Sprite

Sprite

Game loop•Game loop is responible to:• Handle player events• Update game logics• Repaint the screen scene• It runs inside a separeted thread

Graphics g = getGraphics();

while (isRunning) {

sleep();

update();

checkColisions();

layerManager.paint(g,0,0);

flushGraphics();

}

Thread• Thread

Sprites - Frames

{0,1,2,3,4,5,6,7,8,9,10,11,12}

Sprite• Simplifies the Sprite management

Image image = Image.createImage(“mysprite.png”);

Sprite sprite = new Sprite(image, 5,5);

• Controls the Sprite movementsprite.move(10,10);

• Checks collisionssprite.collidesWith(otherSprite,false);

sprite.collidesWith(tiledLayer,false);

sprite.collidesWith(otherImage,20,20,false);

• Goes to the next frame of the spriteSprite.nextFrame();

• Controls transformations of the spritesprite.setTransform(Sprite.TRANS_ROT90);

Player inputs•We have to get finger position

• The method pointerPressed(int x, int y) is called when the player touch the finger on the screen

• The method pointerDragged(int x, int y) is called when the player drags the finger on the screen

• The method pointerReleased(int x, int y) is called when the player takes the finger from the screen

protected void pointerPressed(int x, int y) { move = true; moveTO_Y = y;}

Let’s code

Marlon Luzext-marlon.luz@nokia.com

@marlonluz

Thanks