The document outlines game development for Nokia Asha devices using Java ME, focusing on low-level UI APIs and canvas management. It covers important aspects such as event handling for keyboard and touchscreen devices, sprite management, and the game loop structure. Additionally, it includes coding examples for implementing graphical elements and capturing user input effectively.

1. Game Development for
Nokia Asha Devices
with Java ME
Marlon Luz - INdT
Nokia Developer Evangelist
@marlonluz

2. 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
Alert Form List TextBox GameCanvas

3. 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!
}

4. 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);
}
}

5. 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

6. 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);
}

7. 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

8. 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)

9. public class MyCanvas2 extends Canvas {
Events 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();
}
}

10. Sample
• Checkers Game

11. 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

12. Game API - Sample
GameCanvas Sprite
Sprite

13. 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();
}

14. Thread
• Thread

15. Sprites - Frames
{0,1,2,3,4,5,6,7,8,9,10,11,12}

16. Sprite
• Simplifies the Sprite management
Image image = Image.createImage(“mysprite.png”);
Sprite sprite = new Sprite(image, 5,5);
• Controls the Sprite movement
sprite.move(10,10);
• Checks collisions
sprite.collidesWith(otherSprite,false);
sprite.collidesWith(tiledLayer,false);
sprite.collidesWith(otherImage,20,20,false);
• Goes to the next frame of the sprite
Sprite.nextFrame();
• Controls transformations of the sprite
sprite.setTransform(Sprite.TRANS_ROT90);

17. 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;
}

18. Let’s code

19. Thanks
Marlon Luz
ext-marlon.luz@nokia.com
@marlonluz