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Lesson-4.html
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Lesson-4.html
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<!DOCTYPE html>
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<title>Snake Game-Phaser</title>
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<span class="text-highlight">Game Development</span>
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<h1 class="doc-title"><i class="icon fa fa-paper-plane"></i>Game Development</h1>
<div class="meta"><i class="fa fa-clock-o"></i> Snake Game using Phaser</div>
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<section id="introduction-section" class="doc-section">
<h2 class="section-title">Collision Detection</h2>
<div class="section-block">
<p>A game in which the snake is roaming freely in the playing field is not much fun. We need to detect when the snake comes in contact with a wall, an apple or itself. This is called collision detection.<br></p>
<p>This is usually done by using a physics engine, of which the Phaser framework supports a few. But they are too complex for a simple game like this. We will instead do our own collision detection by comparing coordinates.<br></p>
<p>In the update function, after the code for moving the snake, we call a number of methods. They will compare coordinates to tell us if a collision has occurred.</p>
<pre><code class="language-markup">
update: function() {
// Snake movement
// ...
// End of snake movement
// Increase length of snake if an apple had been eaten.
// Create a block in the back of the snake with the old position of the previous last block
// (it has moved now along with the rest of the snake).
if(addNew){
snake.unshift(game.add.sprite(oldLastCellx, oldLastCelly, 'snake'));
addNew = false;
}
// Check for apple collision.
this.appleCollision();
// Check for collision with self. Parameter is the head of the snake.
this.selfCollision(firstCell);
// Check with collision with wall. Parameter is the head of the snake.
this.wallCollision(firstCell);
}
},
appleCollision: function() {
// Check if any part of the snake is overlapping the apple.
// This is needed if the apple spawns inside of the snake.
for(var i = 0; i < snake.length; i++){
if(snake[i].x == apple.x && snake[i].y == apple.y){
// Next time the snake moves, a new block will be added to its length.
addNew = true;
// Destroy the old apple.
apple.destroy();
// Make a new one.
this.generateApple();
// Increase score.
score++;
// Refresh scoreboard.
scoreTextValue.text = score.toString();
}
}
},
selfCollision: function(head) {
// Check if the head of the snake overlaps with any part of the snake.
for(var i = 0; i < snake.length - 1; i++){
if(head.x == snake[i].x && head.y == snake[i].y){
// If so, go to game over screen.
game.state.start('Game_Over');
}
}
},
wallCollision: function(head) {
// Check if the head of the snake is in the boundaries of the game field.
if(head.x >= 600 || head.x < 0 || head.y >= 450 || head.y < 0){
// If it's not in, we've hit a wall. Go to game over screen.
game.state.start('Game_Over');
}
}
</code></pre>
<p>When the snake collides with the apple we increase the score and the length of the snake. But when a collision with the wall or the snake body occurs, we should end the game. To do this, we need to make the <b>Game_Over</b> state. Again, we need to register it with main.js. Add this line near the bottom of that file:</p>
<p><b>main.js</b></p>
<pre><code class="language-markup">
game.state.add('Game_Over', Game_Over);
</code>
</pre>
<p>And the state itself:</p>
<p><b>game_over.js</b></p>
<pre><code class="language-markup">
var Game_Over = {
preload : function() {
// Load the needed image for this game screen.
game.load.image('gameover', './assets/images/gameover.png');
},
create : function() {
// Create button to start game like in Menu.
this.add.button(0, 0, 'gameover', this.startGame, this);
// Add text with information about the score from last game.
game.add.text(235, 350, "LAST SCORE", { font: "bold 16px sans-serif", fill: "#46c0f9", align: "center"});
game.add.text(350, 348, score.toString(), { font: "bold 20px sans-serif", fill: "#fff", align: "center" });
},
startGame: function () {
// Change the state back to Game.
this.state.start('Game');
}
};
</code>
</pre>
<P><b>That's it our Snake Game is Ready!!</b></P>
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<li><a href="Game-Development.html">Intro & Setup</a></li>
<li><a href="Lesson-1.html">Loading an Image</a></li>
<li><a href="Lesson-2.html">Drawing the Snake</a></li>
<li><a href="Lesson-3.html">Movement and Control</a></li>
<li><a href="Lesson-4.html">Collision Detection</a></li>
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