snake.java

// A boolean used to check if the game is ended
boolean gameover = false; 

// A general size used for the objective
// and snake head and tail
float s = 5;

// All the positions of the snake's head and tail
// snakePositions.get(0) => head
// snakePositions.get(n > 0) => tail
ArrayList<PVector> snakePositions = new ArrayList<PVector>();

// The direction of the snake
PVector snakeDirection = new PVector(1, 0);

// The position of the objective
PVector objPosition = new PVector(0, 0);

// A method used to check if two vectors overlaps
public boolean overlaps(PVector p1, PVector p2) {
  PVector c1 = new PVector(p1.x + s/2, p1.y + s/2);
  PVector c2 = new PVector(p2.x + s/2, p2.y + s/2);
  return PVector.dist(c1, c2) < s;
}

// A method used to randomize the position
// of a vector within the boundaries
public void randomize(PVector position, float a, float b) {
  position.x = random(a, b);
  position.y = random(a, b);
}

// A method used to end the game
public void endgame() {
  gameover = true;
  
  // Show a black screen
  background(0);
  // Set text color
  fill(255);
  // Show game over text
  text("Gameover", 10, 20); 
}

// A method used to reset the game
public void reset() {
  gameover = false;
  
  // Clear the positions
  snakePositions.clear();
  
  // Get screen center position
  PVector c = new PVector(width/2, height/2);
  
  // Add the snake's head
  snakePositions.add(c);
  
  // Randomize the position of the obj.
  randomize(objPosition, 0, width-s); 
}

void setup() {
  // Set the application's frame rate
  // Lower frame rate = slower movement
  // Higher frame rame = faster movement
  frameRate(15); 
  
  // Reset the game
  reset();
}

void draw() {
  // Set background color
  background(0);
  
  // If the game ended
  if (gameover) {
    // Wait 5 seconds
    delay(5000);
    // Reset the game    
    reset();
    return;
  }
  
  // Draw score
  fill(255);
  text("Score: " + (snakePositions.size()-1), 10, 20);
  
  // Set snake and objective 
  // fill and stroke color 
  fill(0);
  stroke(255);
  
  // Draw the objective
  rect(objPosition.x, objPosition.y, s, s);
  
  // Draw the snake
  for (int i = snakePositions.size() - 1; i > -1; i--) {

      // Get the current position
      PVector position = snakePositions.get(i);
      
      // If the position is the head
      if (i == 0) {
        // Move towards the direction
        position.x += snakeDirection.x * s;
        position.y += snakeDirection.y * s;
        
        // Check if the position is outside
        // the screen's borders
        // Horizontal
        if (position.x < 0) position.x = width;
        else if (position.x > width) position.x = 0;
        // Vertical
        if (position.y < 0) position.y = height;
        else if (position.y > height) position.y = 0;  
          
        // Check if the head overlaps with
        // the objective
        if (overlaps(position, objPosition)) {
          // Randomize the position of the obj.
          randomize(objPosition, 0, width-s);
          // Increase the snake's tail
          PVector last = snakePositions.get(snakePositions.size() - 1);
          PVector next = new PVector(last.x-(snakeDirection.x*s), last.y-(snakeDirection.x*s));
          snakePositions.add(next);
        }        
        
      } else {
        // Check if the tail overlaps with the head
        // Unless it's the point attached directly to the head
        if (i > 1 && overlaps(position, snakePositions.get(0))) {          
          endgame();
          break;
        } else {        
          // Get the position before
          PVector before = snakePositions.get(i - 1);         
          // Set the current element's position to the position before
          position.x = before.x;
          position.y = before.y;
        }        
      }
      
      // Display the point
      rect(position.x, position.y, s, s);
   }
}

void keyPressed() {
  if (key == 'a' && snakeDirection.x != 1) {
    snakeDirection.x = -1;
    snakeDirection.y = 0;
  }
  else if (key == 'd' && snakeDirection.x != -1) {
    snakeDirection.x = 1;
    snakeDirection.y = 0;
  }
  else if (key == 's' && snakeDirection.y != -1) {
    snakeDirection.x = 0;
    snakeDirection.y = 1;
  }
  else if (key == 'w' && snakeDirection.y != 1) {
    snakeDirection.x = 0;
    snakeDirection.y = -1;
  }
}