Listing 3. JumpCanvas.java
package net.frog_parrot.jump;
import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;
/**
* This class is the display of the game.
*
* @author Carol Hamer
*/
public class JumpCanvas extends javax.microedition.lcdui.game.GameCanvas {
//---------------------------------------------------------
// Dimension fields
// (constant after initialization)
/**
* The height of the green region below the ground.
*/
static final int GROUND_HEIGHT = 32;
/**
* A screen dimension.
*/
static final int CORNER_X = 0;
/**
* A screen dimension.
*/
static final int CORNER_Y = 0;
/**
* A screen dimension.
*/
static int DISP_WIDTH;
/**
* A screen dimension.
*/
static int DISP_HEIGHT;
/**
* A font dimension.
*/
static int FONT_HEIGHT;
/**
* The default font.
*/
static Font FONT;
/**
* A font dimension.
*/
static int SCORE_WIDTH;
/**
* The width of the string that displays the time,
* saved for placement of time display.
*/
static int TIME_WIDTH;
/**
* Color constant
*/
public static final int BLACK = 0;
/**
* Color constant
*/
public static final int WHITE = 0xffffff;
//---------------------------------------------------------
// Game object fields
/**
* A handle to the display.
*/
private Display myDisplay;
/**
* A handle to the MIDlet object (to keep track of buttons).
*/
private Jump myJump;
/**
* The LayerManager that handles the game graphics.
*/
private JumpManager myManager;
/**
* Whether the game has ended.
*/
private boolean myGameOver;
/**
* The player's score.
*/
private int myScore = 0;
/**
* How many ticks you start with.
*/
private int myInitialGameTicks = 950;
/**
* This is saved to determine if the time string needs
* to be recomputed.
*/
private int myOldGameTicks = myInitialGameTicks;
/**
* The number of game ticks that have passed.
*/
private int myGameTicks = myOldGameTicks;
/**
* You save the time string to avoid recreating it
* unnecessarily.
*/
private static String myInitialString = "1:00";
/**
* You save the time string to avoid recreating it
* unnecessarily.
*/
private String myTimeString = myInitialString;
//-----------------------------------------------------
// Gets/sets
/**
* This is called when the game ends.
*/
void setGameOver() {
myGameOver = true;
myJump.pauseApp();
}
//-----------------------------------------------------
// Initialization and game state changes
/**
* Constructor sets the data, performs dimension calculations,
* and creates the graphical objects.
*/
public JumpCanvas(Jump midlet) throws Exception {
super(false);
myDisplay = Display.getDisplay(midlet);
myJump = midlet;
// Calculate the dimensions.
DISP_WIDTH = getWidth();
DISP_HEIGHT = getHeight();
Display disp = Display.getDisplay(myJump);
if(disp.numColors() < 256) {
throw(new Exception("game requires 256 shades"));
}
if((DISP_WIDTH < 150) || (DISP_HEIGHT < 170)) {
throw(new Exception("Screen too small"));
}
if((DISP_WIDTH > 250) || (DISP_HEIGHT > 250)) {
throw(new Exception("Screen too large"));
}
FONT = getGraphics().getFont();
FONT_HEIGHT = FONT.getHeight();
SCORE_WIDTH = FONT.stringWidth("Score: 000");
TIME_WIDTH = FONT.stringWidth("Time: " + myInitialString);
if(myManager == null) {
myManager = new JumpManager(CORNER_X, CORNER_Y + FONT_HEIGHT*2,
DISP_WIDTH, DISP_HEIGHT - FONT_HEIGHT*2 - GROUND_HEIGHT);
}
}
/**
* This is called as soon as the application begins.
*/
void start() {
myGameOver = false;
myDisplay.setCurrent(this);
repaint();
}
/**
* Sets all variables back to their initial positions.
*/
void reset() {
myManager.reset();
myScore = 0;
myGameOver = false;
myGameTicks = myInitialGameTicks;
myOldGameTicks = myInitialGameTicks;
repaint();
}
/**
* Clears the key states.
*/
void flushKeys() {
getKeyStates();
}
/**
* This version of the game does not deal with what happens
* when the game is hidden, so I hope it won't be hidden...
* see the version in the next chapter for how to implement
* hideNotify and showNotify.
*/
protected void hideNotify() {}
/**
* This version of the game does not deal with what happens
* when the game is hidden, so I hope it won't be hidden...
* see the version in the next chapter for how to implement
* hideNotify and showNotify.
*/
protected void showNotify() {}
//-------------------------------------------------------
// Graphics methods
/**
* Paint the game graphic on the screen.
*/
public void paint(Graphics g) {
// Clear the screen:
g.setColor(WHITE);
g.fillRect(CORNER_X, CORNER_Y, DISP_WIDTH, DISP_HEIGHT);
// Color the grass green:
g.setColor(0, 255, 0);
g.fillRect(CORNER_X, CORNER_Y + DISP_HEIGHT - GROUND_HEIGHT,
DISP_WIDTH, DISP_HEIGHT);
// Paint the layer manager:
try {
myManager.paint(g);
} catch(Exception e) {
myJump.errorMsg(e);
}
// Draw the time and score:
g.setColor(BLACK);
g.setFont(FONT);
g.drawString("Score: " + myScore, (DISP_WIDTH - SCORE_WIDTH)/2,
DISP_HEIGHT + 5 - GROUND_HEIGHT, g.TOP|g.LEFT);
g.drawString("Time: " + formatTime(),
(DISP_WIDTH - TIME_WIDTH)/2, CORNER_Y + FONT_HEIGHT, g.TOP|g.LEFT);
// Write game over if the game is over:
if(myGameOver) {
myJump.setNewCommand();
// Clear the top region:
g.setColor(WHITE);
g.fillRect(CORNER_X, CORNER_Y, DISP_WIDTH, FONT_HEIGHT*2 + 1);
int goWidth = FONT.stringWidth("Game Over");
g.setColor(BLACK);
g.setFont(FONT);
g.drawString("Game Over", (DISP_WIDTH - goWidth)/2,
CORNER_Y + FONT_HEIGHT, g.TOP|g.LEFT);
}
}
/**
* A simple utility to make the number of ticks look like a time.
*/
public String formatTime() {
if((myGameTicks / 16) + 1 != myOldGameTicks) {
myTimeString = "";
myOldGameTicks = (myGameTicks / 16) + 1;
int smallPart = myOldGameTicks % 60;
int bigPart = myOldGameTicks / 60;
myTimeString += bigPart + ":";
if(smallPart / 10 < 1) {
myTimeString += "0";
}
myTimeString += smallPart;
}
return(myTimeString);
}
//-------------------------------------------------------
// Game movements
/**
* Tell the layer manager to advance the layers and then
* update the display.
*/
void advance() {
myGameTicks--;
myScore += myManager.advance(myGameTicks);
if(myGameTicks == 0) {
setGameOver();
}
// Paint the display.
try {
paint(getGraphics());
flushGraphics();
} catch(Exception e) {
myJump.errorMsg(e);
}
}
/**
* Respond to keystrokes.
*/
public void checkKeys() {
if(! myGameOver) {
int keyState = getKeyStates();
if((keyState & LEFT_PRESSED) != 0) {
myManager.setLeft(true);
}
if((keyState & RIGHT_PRESSED) != 0) {
myManager.setLeft(false);
}
if((keyState & UP_PRESSED) != 0) {
myManager.jump();
}
}
}
}
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