Introduction to programming class 12

Introduction to Programming
Class 12 – A Complete Game
Paul Brebner

Game design – car and traffic lights

Design
• Green car
• Drive it around
• Goal is to hit Green Traffic lights
• Once hit, green lights go RED
• Don’t hit RED lights again or gameover
• Don’t hit edge of screen of gameover
• Score for each green light hit
• Speed increases for each green light hit
• Display score in top left
• Display end of game message in middle

Variables (1)
color carColor = color(0,0,255); // blue for car
color targetColor = color(0,255,0); // green for GO!
color redColor = color(255,0,0); // red for danger
int moveX = 0; // -1, 0, or 1 for direction
int moveY = 0;
int carX = 0; // car x y location
int carY = 0;
int targetX = 0; // green light x y location
int targetY = 0;

Variables (2)
boolean newTarget = true; // create new target
int reds = 0; // current number of reds
int maxReds = 5; // max possible reds
int[] redX = new int[maxReds]; // red light array x locations
int[] redY = new int[maxReds]; // red light array y locations
int windowSize = 500; // screen size
boolean gameOver = false; // while true keep playing
PFont Font = createFont("Arial",20, true); // font for scores etc
int score = 0; // player score
float startSpeed = 2; // start speed in pixels
float speed = startSpeed; // car speed
int carSize = 10; // car size (width)
int lightSize = 10; // red and green light size (diameter)
int crashSize = carSize/2+lightSize/2; // how close car and light get before crash

Setup and draw
void setup()
{
size(windowSize, windowSize);
frameRate(25);
background(0);
rectMode(CENTER);
reset();
}
void draw()
{
runGame();
}

Divide program into functions
reset() used at start and end to set
variables to start values
void reset()
{
carX = width/2;
carY = height/2;
gameOver = false;
newTarget = true;
moveY = 0;
moveX = 0;
speed = startSpeed;
reds = 0;
score = 0;
}

Main actions of game
void runGame()
{
background(0);
if (gameOver)
{ // TODO Later
}
else
{
drawCar();
drawTarget();
drawReds();
carMove();
checkBoundary();
hitTarget();
hitReds();
scoreBoard();
}
}

Make empty functions
void drawCar()
{
}
etc

Fill in details
void drawCar()
{
fill(carColor);
rect(carX, carY, carSize, carSize);
}
// allow movement
void keyPressed()
{
if (keyCode == UP) { moveY = -1; moveX = 0; }
if (keyCode == DOWN) { moveY = 1; moveX = 0; }
if (keyCode == LEFT) { moveX = -1; moveY = 0; }
if (keyCode == RIGHT) { moveX = 1; moveY = 0; }
if (keyCode == 'R') { reset(); }
}

carMove()
void carMove()
{
carX += moveX*speed;
carY += moveY*speed;
}

drawTarget()
void drawTarget()
{
fill(targetColor);
if (newTarget) // if newTarget work out location for it
{
targetX = (int)random(lightSize, windowSize-lightSize);
targetY = (int)random(lightSize, windowSize-lightSize);
newTarget = false;
}
ellipse(targetX, targetY, lightSize, lightSize);
}

hitTarget() [simple]
void hitTarget()
{
if (dist(targetX, targetY, carX, carY) <= crashSize)
{
newTarget = true;
speed += 0.3;
score++;
}
}

scoreBoard()
void scoreBoard()
{
String s = "SCORE " + score + " SPEED " + speed;
textAlign(LEFT);
textFont(Font);
fill(237,149,0);
text(s,10,30,40);
}

checkBoundary()
void checkBoundary()
{
if (carX > ?|| carX < ? || carY > ?|| carY < ?)
gameOver = true;
}

checkBoundary()
void checkBoundary()
{
if (carX > windowSize || carX < 0 || carY > windowSize || carY < 0)
gameOver = true;
}

hitTarget() [full]
void hitTarget()
{
if (dist(targetX, targetY, carX, carY) <= crashSize)
{
newTarget = true;
speed += 0.3;
score++;
reds++;
if (reds >= maxReds) // no more room in array!
gameOver = true;
else
{
// new red where target was
redX[reds] = targetX;
redY[reds] = targetY;
}
}
}

hitReds()
void hitReds()
{
// Tricky! i < reds so you don't die immediately by hitting the green light that turned red
// What if it is i <= reds?
for (int i=0; i < reds; i++)
if (dist(carX, carY, redX[i], redY[i]) <= crashSize)
gameOver = true;
}

runGame()
code for gameOver == true
void runGame()
{
background(0);
if (gameOver)
{
scoreBoard();
String s = "Game over! You scored " + score;
textAlign(CENTER);
textFont(Font);
fill(100,200,50);
text(s,width/2,height/2,40);
}
else // code from before

Tricky version (V2)
void hitTarget()
{
float d = dist(targetX, targetY, carX, carY);
boolean hit = (d <= crashSize);
if (hit || (d < 100 && random(0,1) >= 0.99))
{
newTarget = true;
speed += 0.3;
reds++;
if (reds >= maxReds) // no more room in array!
gameOver = true;
else
{
// new red where target was
redX[reds] = targetX;
redY[reds] = targetY;
}
if (hit) score++;
}
}

Extensions
• Add a time limit to hit light then move it
• Give the red lights speed so they move around
• Need another 2 arrays for x and y speed
• As game progresses create new reds with higher speed

Introduction to programming class 12

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