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GameEngine.js
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303 lines (264 loc) · 11 KB
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function GameEngine(gameCanvas, imageCache) {
// Store the parameters passed in here in case we need them later.
var theCanvas = gameCanvas;
var theImages = imageCache;
var canvasHeight = theCanvas.clientHeight,
canvasWidth = theCanvas.clientWidth;
var MOVE_PIXELS = 3;
var BULLET_SPEED = 5;
var KEY_REPEAT_DELAY = 250; // Milliseconds between registered keypresses
// Get the drawing context that we're going to use to draw on our game surface.
var drawCtx = theCanvas.getContext("2d");
// The game will need a game clock - so create it here.
var gameClock = new GameClock();
var playerSprite = createPlayerSprite();
// Interrogate the playersprite to find out it's width and height.
var playerWidth = playerSprite.getSize().w;
var playerHeight = playerSprite.getSize().h;
// We're going to have a lot of enemy sprites so array
var enemies = [];
// Just like the enemies, we can have a lot of bullets on screen.
// Manage these here.
var bullets = [];
// Manage explosions
var explosions = [];
// keep track of the start time so that we can determine how long the game has been running.
var gameStartTime = 0;
var ENEMY_ADDITION_INCREMENT = 0.05;// Every time we ratchet up the level this specifies how much we increment by
var initialAdditionRate = 0.05; // Initial rate for adding enemies.
var MS_PER_INCREMENT = 15000; // Ratchet up the level every 15secs.
var MAX_ENEMIES = 100;
// We only need to create the pattern once so do it when we initialise the game engine.
var pattern = drawCtx.createPattern(imageCache.get('images/terrain.png'),"repeat");
// The fill style isn't going to change throughout our game.
drawCtx.fillStyle = pattern;
// An array that we use to store a set of callbacks for events
var scoreEventListeners = [];
// Add an array for done listeners
var playerDestroyedListeners = [];
var keyStatusMap = {};
var keyHitTime = {};
function setKeyStatus(keyEvent, status) {
switch( keyEvent.keyCode ) {
case 32: // Space key
keyStatusMap["SPACE"] = status;
break;
case 37: // Left key
keyStatusMap["LEFT"] = status;
break;
case 38: // Up key
keyStatusMap["UP"] = status;
break;
case 39: // Right key
keyStatusMap["RIGHT"] = status;
break;
case 40: // DOWN key
keyStatusMap["DOWN"] = status;
break;
}
}
this.addScoreListener = function(listener) {
scoreEventListeners.push(listener);
}
this.removeScoreListener = function(listener) {
for(var ix = 0; ix< scoreEventListeners.length; ix++ ) {
if ( scoreEventListeners[ix] === listener ) {
scoreEventListeners.split(ix,1);
break;
}
}
}
function notifyScoreUpdate( score ) {
var scoreEvent = { score: score };
scoreEventListeners.forEach(function(listener) {
listener(scoreEvent);
});
}
this.addPlayerDestroyedListener = function(listener) {
playerDestroyedListeners.push(listener);
}
function notifyPlayerDestroyedListeners() {
playerDestroyedListeners.forEach(function(listener) {
listener();
});
}
this.init = function() {
gameStartTime = Date.now()
$(document).keydown(function(keyEvent) {
setKeyStatus(keyEvent,true);
});
$(document).keyup(function(keyEvent) {
setKeyStatus(keyEvent,false);
});
enemies.push(createEnemySprite());
gameClock.registerStep(function(framesElapsed,curFrameNo) {
Array.prototype.push.apply(enemies,addEnemies());
if ( !playerSprite.isDone() ) {
checkPlayerActions(framesElapsed);
}
drawCtx.fillRect(0,0,theCanvas.width, theCanvas.height);
playerSprite.update(framesElapsed);
playerSprite.render(drawCtx);
var ix = 0;
// Turn forEach statment below into code for the below loop so that we can
// remove completed sprites from the array as we process it.
renderSprites(enemies, framesElapsed);
if ( bullets.length > 0 ) {
renderSprites(bullets, framesElapsed);
}
if ( explosions.length > 0 ) {
renderSprites(explosions,framesElapsed);
}
enemies.forEach(function(nme){
bullets.forEach(function(bullet) {
if ( overlap(bullet, nme) ) {
bullet.setDone(true);
nme.setDone(true);
explosions.push(createExplosionAt(bullet.getPosition().top, bullet.getPosition().left));
notifyScoreUpdate(10);
}
});
if ( !playerSprite.isDone() && overlap(playerSprite,nme) ) {
playerSprite.setDone(true);
explosions.push(createExplosionAt(playerSprite.getPosition().top, playerSprite.getPosition().left));
notifyPlayerDestroyedListeners();
}
});
});
gameClock.start();
}
// Calculates when to add another enemy and returns an array of enemies that were created.
function addEnemies() {
var elapsedTimeMillis = Date.now() - gameStartTime;
// Our current difficulty level is based on the number MS Increments that have elapsed since the game started which would be elapsedTime/MS_PER_INCREMENT.
// Current difficulty level is that value multipled by the ENEMY_ADDITION_INCREMENT.
// And then we add the initial difficulty level.
// initialAdditionRate + (ENEMY_ADDITION_INCREMENT * elapedTimeMillis/MS_PER_INCREMENT)
// We use Math.floor to make sure that elapsedTimeMillis/MS_PER_INCERMENT always returns an integer.
// currentLevel is going to go 0.05, 0.10, 0.15, 0.20 ... 1.00
// We want to limit it to a max of 1 so surround it by a call to Math.min
var currentLevel = Math.min(initialAdditionRate + ( ENEMY_ADDITION_INCREMENT * Math.floor(elapsedTimeMillis / MS_PER_INCREMENT)),1);
var currentMaxEnemies = Math.floor(MAX_ENEMIES * currentLevel);
var numToCreate = currentMaxEnemies - enemies.length;
if (numToCreate < 0) numToCreate = 0;
var newEnemies = [];
while(numToCreate-- > 0) {
newEnemies.push(createEnemySprite());
}
return newEnemies;
}
// This function is used to detect overlaps between sprites. Returns true if the sprites overlap and false
// otherwise.
function overlap( s1, s2 ) {
// For simplicity we calculate the lines surrounding each of the sprites.
var s1_lines = { top : s1.getPosition().top, bottom: s1.getPosition().top+s1.getSize().h,
left: s1.getPosition().left, right: s1.getPosition().left + s1.getSize().w };
var s2_lines = { top : s2.getPosition().top, bottom: s2.getPosition().top+s2.getSize().h,
left: s2.getPosition().left, right: s2.getPosition().left + s2.getSize().w };
// Check top left & right corners of s1 against 4 sides of s2
return ((s1_lines.top >= s2_lines.top && s1_lines.top <= s2_lines.bottom &&
((s1_lines.left >= s2_lines.left && s1_lines.left <= s2_lines.right) ||
(s1_lines.right >= s2_lines.left && s1_lines.right <= s2_lines.right))) ||
// Check bottom left & rihgt corners of s1 against 4 sides of s2
(s1_lines.bottom >= s2_lines.top && s1_lines.bottom <= s2_lines.bottom &&
((s1_lines.left >= s2_lines.left && s1_lines.left <= s2_lines.right) ||
(s1_lines.right >= s2_lines.left && s1_lines.right <= s2_lines.right))));
}
// For each set of sprites that we need to render we
function renderSprites(spriteArray, framesElapsed) {
for( var ix = 0; ix < spriteArray.length; ix++ ) {
var s = spriteArray[ix];
s.update(framesElapsed);
s.render(drawCtx);
// Now we test to see if the sprite is still visible and if not
// we remove from the array so we no longer have to manage it.
if ( s.isDone() ) {
// Note post-decrement of ix - returns the current value of ix to the
// splice method call and then decrements ix
spriteArray.splice(ix--,1);
// If we didn't decrement ix, then it would skip evaluation of the next
// element of the sprites array.
}
}
}
function checkPlayerActions(framesElapsed) {
var currentPlayerPos = playerSprite.getPosition();
if ( keyStatusMap["LEFT"] ) {
playerSprite.setPosition(currentPlayerPos.top,
Math.max(0,
currentPlayerPos.left-(MOVE_PIXELS*framesElapsed)));
}
if ( keyStatusMap["RIGHT"] ) {
playerSprite.setPosition(currentPlayerPos.top,
Math.min(
canvasWidth-playerWidth,
currentPlayerPos.left+(MOVE_PIXELS*framesElapsed)));
}
if ( keyStatusMap["UP"] ) {
playerSprite.setPosition(
Math.max(0,currentPlayerPos.top-(MOVE_PIXELS*framesElapsed)),
currentPlayerPos.left);
}
if ( keyStatusMap["DOWN"] ) {
playerSprite.setPosition(
Math.min(canvasHeight-playerHeight,
currentPlayerPos.top+(MOVE_PIXELS*framesElapsed)),
currentPlayerPos.left);
}
if ( keyStatusMap["SPACE"] && checkKeyHitDelay("SPACE", KEY_REPEAT_DELAY)) {
// Create the bullet sprites.
bullets = bullets.concat(createBulletSprites());
}
}
// This function returns a value of true or false depending on whether the required period has elapsed since the last time
// a keypress was recognised.
function checkKeyHitDelay(keyName, delay) {
// See if we have recorded a hit time for this key already - if not then set the hist time as zero.
var lastHit = keyHitTime[keyName] ? keyHitTime[keyName] : 0;
// What time is it now,
var curTime = Date.now();
// Does the elapsed time exceed the required delay time.
if ( curTime-lastHit >= delay ) {
// If it does then update the key hit time ...
keyHitTime[keyName] = curTime;
// and return true
return true;
}
// Otherwise disregard this key press.
return false;
}
function createEnemySprite() {
var s = new AutoSprite(-1.66,'horizontal',imageCache.get('images/sprites.png'),0,78,80,39,10,[0,1,2,3,2,1],'horizontal');
var left = canvasWidth - 5; // Left most part of sprite is 5px from RHS
var top = Math.min(Math.random()*canvasHeight,
canvasHeight - s.getSize().h);
s.setPosition(top,left);
s['getType'] = function() {return "ENEMY";};
return s;
}
function createPlayerSprite() {
var s = new Sprite(imageCache.get('images/sprites.png'),5,0,39,25,10,[0,1]);
var top = Math.floor((canvasHeight - 39)/2);
s.setPosition(top,0);
s['getType'] = function() {return "PLAYER";};
return s;
}
function createBulletSprites() {
var spos = playerSprite.getPosition();
var ssize = playerSprite.getSize();
var forward = new AutoSprite(BULLET_SPEED, 'horizontal', imageCache.get('images/sprites.png'),0,39,17,7,0,[0],null,false);
forward.setPosition( spos.top + (ssize.h/2) - (forward.getSize().h/2),
spos.left + ssize.w);
var down = new AutoSprite(BULLET_SPEED,'vertical',imageCache.get('images/sprites.png'),0,60,9,5,0,[0],null,false);
down.setPosition(spos.top+ssize.h, spos.left + (ssize.w/2) - (down.getSize().w/2) );
var up = new AutoSprite(-BULLET_SPEED,'vertical',imageCache.get('images/sprites.png'),0,50,9,5,0,[0],null,false);
up.setPosition( spos.top, spos.left + (ssize.w/2) - (up.getSize().w/2) );
forward['getType'] = up['getType'] = down['getType'] = function() {return "BULLET";};
return [forward,up,down];
}
function createExplosionAt( top, left ) {
var boom = new Sprite(imageCache.get("images/sprites.png"),116,0,39,39,4,[0,1,2,3,4,5,6,7,8,9,10,11],'horizontal',true);
boom.setPosition(top,left);
return boom;
}
}