This presentation is the second one of the Game Development for Nokia Asha Devices with Java ME training

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