gravity.java

java编程的一些Applets例子。值得深入研究一下。

	hilightNearestLine();
	repaint();
    }

    // In edit mode, add a new Friend (enemy) to the world, sitting
    // on the line that is closest to the cursor.
    void addFriend() {
	if (lastLine == -1) return;
	planet.addFriend( lastLine );
	repaint();
    }

    // If the cursor moves to or past the edge of the screen,
    // automatically slide the virtual screen around to keep the cursor 
    // towards the middle.
    public void autoslide() {
	Point sp = screenCoords( new Point( (int)x, (int)y) );
	int tx = sp.x - size().width/4;
	if (tx>0) {
	    tx = sp.x - (size().width*3)/4;
	    if (tx<0)
	      tx = 0;
	}
	int ttx=tx;
	int ty = sp.y - size().height/4;
	int tty=ty;
	if (ty>0) {
	    ty = sp.y - (size().height*3)/4;
	    if (ty<0)
	      ty = 0;
	}
	translate( -tx, -ty );
    }

    // Check to see if things have hit each other.
    public void intersections() {
	boolean wereHit = intersectBullets();
	if (shield) {
		wereHit = false;
		playEffect( theyFireClip );
	}
	//wereHit = false;
	if (!exploded && (ship.intersectFigure( planet ) || wereHit)) {
	    playEffect( iSplodeClip );
	    exploded = true;
	    explodedTime = System.currentTimeMillis();
	    vx = vy = 0;
	    turnLeft = turnRight = engine = false;
	}
	if (exploded && (System.currentTimeMillis()-explodedTime)>3000) {
	    exploded = false;
	    x = startx;
	    y = starty;
	    shipang = (Math.PI*3)/2;
	    vx = vy = 0;
	}
    }

    // move the ship, move the bullets, remove really old
    // bullets, draw stuff, run the AI for the enemies,
    // check for hits, and automatically slide the virtual
    // screen.  In short, do everything.
    public void frame( double delta ) {
	//System.out.println( "Delta: " + delta );
	rotation( delta );
	move( delta );
	moveBullets( delta );
	ageBullets( delta );
	repaint();
	planet.fireBulletsMaybe( delta*buls_per_sec, x, y );
	intersections();
	autoslide();
    }

    // Rotate the ship.
    public void rotation( double delta ) {
	if (exploded) return;
	if (turnLeft)
	  shipang -= delta * rot_vel;
	else if (turnRight)
	  shipang += delta * rot_vel;
    }

    // Move the ship forward.
    public void move( double delta ) {
	if (exploded) return;
	if (engine) {
	    vx += delta * engineAccel * Math.cos( shipang );
	    vy += delta * engineAccel * Math.sin( shipang );
	}
	vy += delta * gravityAccel;
	x += delta * vx;
	y += delta * vy;
    }

    // Stop the ship hard.
    public void stopp() {
	vx = vy = 0;
    }

    // Fire a new bullet into the world, at (x,y), moving in
    // direction (vx,vy).
    void addBullet( double x, double y, double vx, double vy ) {
	if (n_buls >= max_buls) return;
	bulx[n_buls] = bullx[n_buls] = x;
	buly[n_buls] = bully[n_buls] = y;
	bulvx[n_buls] = vx;
	bulvy[n_buls] = vy;
	bulage[n_buls] = 0;
	n_buls++;
    }

    // for interface TakesABullet.
    public void take( double x, double y, double vx, double vy ) {
	addBullet( x, y, vx, vy );
    }

    // The player fires a bullet.
    void addShipBullet() {
	if (exploded) return;
	double s = Math.sin( shipang );
	double c = Math.cos( shipang );
	addBullet( x+c*((Ship.size*4)/3), y+s*((Ship.size*4)/3),
		  vx+bul_vel*c, vy+bul_vel*s );
    }

    // Remove a bullet from the world.
    void removeBullet( int i ) {
	n_buls--;
	bulx[i] = bulx[n_buls];
	buly[i] = buly[n_buls];
	bulvx[i] = bulvx[n_buls];
	bulvy[i] = bulvy[n_buls];
	bullx[i] = bullx[n_buls];
	bully[i] = bully[n_buls];
	bulage[i] = bulage[n_buls];
    }

    // Note the inevitable aging of the bullets.
    void ageBullets( double delta ) {
	for (int i=0; i<n_buls; ++i)
	  bulage[i] += delta;
	for (int i=0; i<n_buls; ++i) {
	    if (bulage[i] > max_bul_age)
	      removeBullet( i );
	}
    }

    // move each bullet ahead.
    void moveBullets( double delta ) {
	for (int i=0; i<n_buls; ++i) {
	    bullx[i] = bulx[i];
	    bully[i] = buly[i];
	    bulx[i] += delta * bulvx[i];
	    buly[i] += delta * bulvy[i];
	}
    }

    // Draw the bullets to a Graphics
    void renderBullets( Graphics g ) {
	for (int i=0; i<n_buls; ++i) {
	    //g.drawRect( (int)bulx[i], (int)buly[i], 1, 1 );
	    g.drawLine( (int)bulx[i], (int)buly[i],
		       (int)bullx[i], (int)bully[i] );
	}
    }

    // Check for intersection between any bullet and the player.
    // Returns true if player is hit.
    boolean intersectBullets() {
	boolean wereHit = false;
	int bline[][] = new int[2][2];
	for (int i=0; i<n_buls; ++i) {
	    bline[0][0] = (int)bulx[i];
	    bline[0][1] = (int)buly[i];
	    bline[1][0] = (int)bullx[i];
	    bline[1][1] = (int)bully[i];
	    if (planet.intersectLines( bline ))
	      removeBullet( i );
	    else
	      planet.intersectFriends( bline );
	    if (ship.intersectLines( bline ))
	      wereHit = true;
	}
	return wereHit;
    }

    // Turn edit mode on or off.
    // When on, turn the game heartbeat off (i.e. pause).
    void editmodeOnOff() {
	editmode = !editmode;
	if (editmode)
	  heartbeat.suspend();
	else
	  heartbeat.resume();
	repaint();
    }

    // Load the world from the URL 'world'.
    public void loadWorldFromNet() {
	try {
	    planet.read( new URL( getDocumentBase(), "world" ) ); 
	} catch( MalformedURLException e ) {
	    System.out.println( e );
	}
    }

    public boolean keyDown( Event evt, int key ) {
	switch( key ) {
	  case 'z': turnLeft = true; break;
	  case 'x': turnRight = true; break;
	  case '.': { engine = true; playEffect( thrustClip ); break; }
	  case ',': { addShipBullet(); playEffect( iFireClip ); break; }
	  case ' ': shield = true; break;
	  case 'e': editmodeOnOff(); break;
	  case '\t': stopp(); break;
	  case 'd': if (editmode) removeNearestLine(); break;
	  case 'a': if (editmode) addFriend(); break;
	  case 'S': if (editmode) planet.write( "world" ); repaint(); break;
	  case 'L': if (editmode) planet.read( "world" ); repaint(); break;
	  case 'l': if (editmode) loadWorldFromNet(); repaint(); break;
	}
	return true;
    }

    public boolean keyUp( Event evt, int key ) {
	switch( key ) {
	  case 'z': turnLeft = false; break;
	  case 'x': turnRight = false; break;
	  case '.': engine = false; break;
	  case ' ': shield = false; break;
	}
	return true;
    }

    public boolean mouseUp(Event e, int x, int y) {
	if (playing) {
	    stopSoundtrack(soundtrackClip);
	} else {
	    playSoundtrack(soundtrackClip);
	}
	return true;
    }

    public boolean mouseDown( Event evt, int x, int y ) {
	if (drawing) {
	    drawing = false;
	    planet.addLine( currentline[0][0], currentline[0][1],
		      currentline[1][0], currentline[1][1] );
	} else {
	    drawing = true;
	    currentline[1][0] = currentline[0][0] = x;
	    currentline[1][1] = currentline[0][1] = y;
	}
	repaint();
	return true;
    }
    public boolean mouseDrag( Event evt, int x, int y ) {
	if (editmode) {
	    mx = x;
	    my = y;
	    editStuff();
	}
	if (drawing) {
	    currentline[1][0] = x;
	    currentline[1][1] = y;
	    repaint();
	}
	return true;
    }
    public boolean mouseMove( Event evt, int x, int y ) {
	if (editmode) {
	    mx = x;
	    my = y;
	    editStuff();
	}
	if (drawing) {
	    currentline[1][0] = x;
	    currentline[1][1] = y;
	    repaint();
	}
	return true;
    }

    public void start() {
	playSoundtrack(soundtrackClip);
    }

    public void stop() {
	stopSoundtrack(soundtrackClip);
    }
}