{

static final int FRAME_WIDTH = 600;

static final int FRAME_HEIGHT = 800;

static final int WIDTH = 400;

static final int HEIGHT = 600;

static final int START_X = 100;

static final int START_Y = 100;

static final int MAX_SIGHT = 3000;

static final double SPEED = 2.0;

static final int TURN_BUFFER = 400;

static final int PASS_BUFFER = 200;

static final int NUM_TURNS = 50;

static final double BARRIER_PROB = .1;

static final int BARRIER_HEIGHT = 150;

static final int BARRIER_BUFFER = 3;

static final int START_MISSIONS = 10;

static final int MISSION_LENGTH = 20;

static final int MISSION_BUFFER = 5;

Screen screen;

double playerX, playerY, playerZ;

double turn;

int numMissions;

int neededMissions;

int missionBuffer;

int barrierBuffer;

int turnIndex;

Turn[] centerHinges;

boolean up, down, left, right;

boolean crashed;

Field(Screen screen_)

{

screen = screen_;

playerX = 0.0;

playerY = 500.0;

playerZ = 1.0;

turn = 0.0;

numMissions = 0;

neededMissions = START_MISSIONS;

turnIndex = 0;

centerHinges = new Turn[NUM_TURNS];

centerHinges[0] = centerHinges[1] = new Turn(0, 0, 0, 0);

for (int i = 2; i < NUM_TURNS; i++)

createTurn(i);

up = down = left = right = false;

crashed = false;

}

int playerX()

{

return (int)playerX;

}

int playerY()

{

return (int)playerY;

}

int playerZ()

{

return (int)playerZ;

}

Polygon region(int index)

{

Polygon region = new Polygon();

addPoint2D(region, leftHinge(index));

addPoint2D(region, leftHinge(index + 1));

addPoint2D(region, rightHinge(index + 1));

addPoint2D(region, rightHinge(index));

return region;

}

Point2D leftHinge(int index)

{

Turn turn = centerHinges[index];

double angle = (turn.angle + turn.prevAngle) / 2 + Math.PI / 2;

double x = turn.x - WIDTH / 2 * Math.sin(angle);

double z = turn.z - WIDTH / 2 * Math.cos(angle);

return new Point2D(x, z);

}

Point2D rightHinge(int index)

{

Turn turn = centerHinges[index];

double angle = (turn.angle + turn.prevAngle) / 2 + Math.PI / 2;

double x = turn.x + WIDTH / 2 * Math.sin(angle);

double z = turn.z + WIDTH / 2 * Math.cos(angle);

return new Point2D(x, z);

}

void act()

{

if (crashed) return;

if (missionBuffer == 0)

setMissions();

playerZ += SPEED * Math.cos(turn);

playerX += SPEED * Math.sin(turn);

if (!region(1).contains(playerX, playerZ))

{

for (int i = 0; i < NUM_TURNS - 1; i++)

centerHinges[i] = centerHinges[i + 1];

createTurn(NUM_TURNS - 1);

if (!region(1).contains(playerX, playerZ))

crash();

turnIndex++;

if (missionBuffer > 0)

missionBuffer--;

if (barrierBuffer > 0)

barrierBuffer--;

}

if (playerY + 100 >= centerHinges[3].barrierY

&& playerY + 100 <= centerHinges[3].barrierY + BARRIER_HEIGHT)

{

crash();

}

if (up && playerY > START_Y + 50)

playerY--;

if (down && playerY < START_Y + HEIGHT - 150)

playerY++;

if (left)

turn -= .005;

if (right)

turn += .005;

}

void crash()

{

crashed = true;

screen.showMessage(36, 300, "YOU LOSE.");

Soundtrack.play("explosion.wav");

}

private void createTurn(int index)

{

double dist = 100;

double newTurn = (index == NUM_TURNS - 1 && Math.random() < .1 ? Math.random() * 2 - 1 : 0);

Turn prev = centerHinges[index - 1];

double newX = prev.x + dist * Math.sin(prev.angle);

double newZ = prev.z + dist * Math.cos(prev.angle);

int barrierY = (index == NUM_TURNS - 1 && barrierBuffer == 0 && Math.random() < BARRIER_PROB ?

(int)(Math.random() * (HEIGHT - BARRIER_HEIGHT)) + START_Y : -1);

if (barrierY != -1)

barrierBuffer = BARRIER_BUFFER;

centerHinges[index] = new Turn(newX, newZ, prev.angle + newTurn, prev.angle, barrierY);

}

private void setMissions()

{

if (turnIndex == 0)

{

screen.showMessage(24, 40, "YOU NEED " + neededMissions + " MISSIONS");

missionBuffer = MISSION_BUFFER;

}

if ((turnIndex + 3) % MISSION_LENGTH == 0)

{

numMissions++;

screen.showMessage(24, 40, "YOU HAVE " + numMissions, "OUT OF " + neededMissions + " MISSIONS");

missionBuffer = MISSION_BUFFER;

}

if (Math.random() < .001 * Math.pow(.1, neededMissions - numMissions - 3))

{

neededMissions += 5;

screen.showMessage(24, 40, "THE NUMBER OF MISSIONS", "HAS BEEN RAISED TO " + neededMissions);

missionBuffer = MISSION_BUFFER;

}

}

private void addPoint2D(Polygon po, Point2D p)

{

po.addPoint((int)p.x, (int)p.z);

}

}