4. Using
Graphics
• Class:
javax.microedition.lcdui.Canvas
• Create
a
subclass:
– class MyCanvas extends Canvas
• Canvas-‐class
has
only
one
abstract
method:
– paint(graphics g)
• It
is
possible
to
override
methods
that
deal
with
events
5. Simple
Example
class MyCanvas extends Canvas {
public void paint(Graphics g){
// draw
}
}
class MyMidlet extends MIDlet{
public void startApp(){
MyCanvas mycanvas = new MyCanvas();
Display.getDisplay(this).setCurrent(mycanvas);
}
}
6. Repain%ng
• You
never
call
the
paint()
method.
• Instead
of
you
use
repaint():
– By
using
this
method,
you
ask
the
framework
to
repaint
the
canvas
– Framework
decides
when
is
the
best
%me
to
repaint
the
canvas
• There
is
a
also:
– repaint(int x, int y, int width, int
height)
11. Game
API
• It
is
easy
to
handle
anima%on
and
graphics
with
the
Game
API
• All
the
classes
can
be
found
from
javax.microedition.lcdui.game.*;
12. GameCanvas
• Using
the
tradi%onal
Canvas-‐class
– You
inherit
the
Canvas
and
override
paint-‐method.
– repaint()
– Event
handling
is
done
by
using
methods
like
keypressed,
keyreleased
• Using
the
GameCanvas-‐class
– You
inherit
the
GameCanvas-‐class
– There
is
no
need
for
paint-‐method,
you
can
draw
anywhere!
– flushGraphics()
– Two
ways
of
doing
event
handling!
13. Example
of
GameCanvas
Usage
class MyCanvas extends GameCanvas {
public void anymethod(){
Graphics g = getGraphics();
// some drawing
flushGraphics()
}
}
14. Handling
Events
• Constructor
of
GameCanvas
– protected GameCanvas(boolean
suppressKeyEvents)
• You
have
to
call
this
constructor
in
you
own
GameCanvas
class..
– =>
You
have
to
give
a
boolean
value..
– true:
use
only
GameCanvases
own
event
handling
– false:
in
addi4on
to
GameCanvases
own
event
handling
use
Canvases
event
handling
15. GameCanvas
Usage
class MyCanvas extends GameCanvas {
public MyCanvas() {
// Let's use Game Canvas event handling!
super(true);
}
public void anymethod() {
// drawing..
}
}
16. Event
Handling
• You
can
ask
which
bu]on
is
pressed
(GameCanvas
Event
Handling)
– public int getKeyStates()
• Bit-‐finals
of
GameCanvas
– UP_PRESSED, DOWN_PRESSED, LEFT_PRESSED,
RIGHT_PRESSED, FIRE_PRESSED,
GAME_A_PRESSED, GAME_B_PRESSED,
GAME_C_PRESSED, GAME_D_PRESSED
17. GameCanvas
Example
3
class MyCanvas extends GameCanvas implements Runnable {
public MyCanvas() {
super(true);
Thread thread = new Thread(this);
thread.start();
}
public void run() {
while(true) {
int ks = getKeyStates();
if ((ks & UP_PRESSED) != 0)
moveUp();
else if((ks & DOWN_PRESSED) != 0)
moveDown();
// Drawing...
}
}
}
18. Touch
class MyCanvas extends GameCanvas implements Runnable {
public MyCanvas() {
super(true);
Thread thread = new Thread(this);
thread.start();
}
public void run() {
while(true) {
doSomething();
}
}
public void pointerPressed(int x, int y) { .. }
public void pointerReleased(int x, int y) { .. }
public void pointerDragged(int x, int y) { .. }
}
19. GameLoop
and
FPS
class MyCanvas extends GameCanvas implements Runnable {
public MyCanvas() {
super(true);
Thread thread = new Thread(this);
thread.start();
}
public void run() {
// THIS WILL LOOP AS FAST AS IT CAN!
while(true) {
doSomething();
}
}
}
20. GameLoop
and
FPS
class MyCanvas extends GameCanvas implements Runnable {
private int fps = 1;
public MyCanvas() {
super(true);
Thread thread = new Thread(this);
thread.start();
}
public void run() {
// Now iteration is 1 frames per sec
while(true) {
doSomething();
try {
Thread.sleep(1000 / fps);
} catch (InterruptedException e) { .. }
}
}
}
21. GameLoop
and
FPS
class MyCanvas extends GameCanvas implements Runnable {
private int fps = 30;
public MyCanvas() {
super(true);
Thread thread = new Thread(this);
thread.start();
}
public void run() {
// Problem, what if the mobile phone can keep up with the pace?
while(true) {
// This takes second…
doSomethingHeavyAndMagical3DStuff();
try {
Thread.sleep(1000 / fps); // and after the second, we will wait more!
} catch (InterruptedException e) { .. }
}
}
}
22. class MyCanvas extends GameCanvas implements Runnable {
private int fps = 30;
public
long
long
long
long
void run() {
time = 0;
elapsedTime = 0;
interval = 0;
sleepTime = 0;
while(true) {
// Get current time
time = System.currentTimeMillis();
doSomethingHeavyAndMagical3DStuff();
// Elapsed time
elapsedTime = System.currentTimeMillis() - time;
// Do we need to sleep?
sleepTime = 0;
// If elapsed time was 100 millisecs, then
//
1000 / 30 - 100 = -66,66. Sleep is not needed (= 0)!
// If elapsed time was 1 millisecs, then sleepTime:
//
1000 / 30 - 1 = 32,333.
// If elapsed time was 20 millisecs, then sleepTime:
//
1000 / 30 - 20 = 13,333..
interval = (int) ((1000.0 / fps) - elapsedTime);
if(interval > 0) {
sleepTime = interval;
}
try {
}
}
}
Thread.sleep(sleepTime);
} catch (InterruptedException e) { }
23. Layers
• You
can
use
layers
with
the
Game
canvas.
• For
example:
– background-‐layer
(bo]om)
– car-‐layer
(front
of
the
background)
• javax.microedition.lcdui.game.Layer
24. Layer-‐class
• Layer
class
is
abstract
and
it
has
two
concrete
subclasses:
1)
TiledLayer,
2)
Sprite
• Layer's
methods
– int getX()
– int getY()
– int getWidth()
– int getHeight()
– void setPosition(..)
– move(..)
25. Class
Diagram
{abstract}
Layer
int
getX()
int
getY()
int
getWidth()
int
getHeight()
void
setPosi%on(..)
move(..)
Sprite
TiledLayer
26. Mastering
the
layers
• Every
layer
(Sprite
or
TiledLayer)
is
put
into
a
LayerManager.
The
LayerManager is
eventually
drawn
to
the
screen.
• LayerManager's
methods
– append(Layer l)
– insert(Layer l, int i)
– Layer getLayer(int i)
– paint(..)
27. Class
Diagram
LayerManager
{abstract}
Layer
append(Layer
l)
insert(Layer
l,
int
i)
Layer
getLayer(int
i)
paint(..)
int
getX()
*
int
getY()
int
getWidth()
int
getHeight()
void
setPosi%on(..)
move(..)
Sprite
TiledLayer
29. Sprite
-‐
class
• Sprite
classes
constructors:
– public Sprite(Image i)
– public Sprite(Image i, int framewidth,
int frameheight)
30. Example
of
Using
Sprite
and
LayoutManager
LayerManager l = new LayerManager();
Sprite s = new Sprite(myimage);
s.setPosition(50,50);
l.append(s);
Graphics g = getGraphics();
l.paint(g,0,0);
flushGraphics();
31. Sprite
anima%on
• Make
one
image-‐file,
which
contains
all
the
frames
• In
the
Sprite's
constructor
you
define
one
frame's
height
and
width
• ASer
that
you
can
use
Sprite's
nextFrame()
method
32. Example
Sprite x = new Sprite(image, 540/18, 30);
layermanager.append(x);
.
.
x.nextFrame();
33. With
Threads..
public void run() {!
while(true){!
int ks = getKeyStates();!
if((ks & RIGHT_PRESSED) != 0){!
mysprite.move(3,0);!
mysprite.nextFrame();!
}!
}!
}!
34. Influencing
frames
• Changing
sequence
– int sequence [] = {0, 15, 17};
– mysprite.setFrameSequence(sequence)
• Jumping
to
another
frame
– mysprite.setFrame(10);
35. Transforma%on
• It
is
possible
to
transform
the
sprite
– public void setTransform(int transform)
• Finals
– TRANS_NONE
– TRANS_ROT90
– TRANS_MIRROR
– ..
see
the
api
• In
prac%ce
– mysprite.setTransform(Sprite.TRANS_MIRROR)
38. Collisions
• Sprite
– collidesWith(Sprite s, boolean pixelLevel)
– collidesWith(TiledLayer s, boolean pixelLevel)
– collidesWith(Image s, int x, int y, boolean pixelLevel)
• PixelLevel
– The
rect
of
the
sprite
or
the
"real
pixels"
39. Example
Sprite x = new Sprite(...);
Sprite y = new Sprite(...);
if(x.collidesWith(y, true)){
// CRASH!
}
40. TiledLayer
• A
TiledLayer
is
a
visual
element
composed
of
a
grid
of
cells
that
can
be
filled
with
a
set
of
%le
images.
• Rows
and
Columns
– TiledLayer(int columns, int rows, Image
i, int tileWidth, int tileHeight);
41. Example
TiledLayer a = new TiledLayer(4,2, picture, 32, 32);
a.setCell(0,1,1); a.setCell(1,1,1), a.setCell(2,1,1);
a.setCell(3,1,1);
a.setCell(1,0,2);
a.setCell(2,0,3);
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