FlappyBirdサンプルのソースは下記となります。

https://github.com/gscalzo/FlappySwift

AppDelegate.swiftなどもあり、ファイル数は5つくらいのSwiftファイルとなっています。全体の動きをつかむのも難しくなさそうです。

コードをいくら見ていても実際に自分が作りたいものとは厚くて高い壁があるものです。実際に動くソースを見て、そこから学んでいくのはいかがでしょう。

FlappySwiftはiOS用、MIT Licenseのオープンソース・ソフトウェアです。

GameScene.swift 一部抜粋
{{{
//
// GameScene.swift
// FlappyBird
//
// Created by Nate Murray on 6/2/14.
// Copyright (c) 2014 Fullstack.io. All rights reserved.
//

import SpriteKit

class GameScene: SKScene {
var bird = SKSpriteNode()
var skyColor = SKColor()
var verticalPipeGap = 150.0
var pipeTextureUp = SKTexture()
var pipeTextureDown = SKTexture()
var movePipesAndRemove = SKAction()

override func didMoveToView(view: SKView) {
// setup physics
self.physicsWorld.gravity = CGVectorMake( 0.0, -5.0 )

// setup background color
skyColor = SKColor(red: 81.0/255.0, green: 192.0/255.0, blue: 201.0/255.0, alpha: 1.0)
self.backgroundColor = skyColor

// ground
var groundTexture = SKTexture(imageNamed: "land")
groundTexture.filteringMode = SKTextureFilteringMode.Nearest

var moveGroundSprite = SKAction.moveByX(-groundTexture.size().width * 2.0, y: 0, duration: NSTimeInterval(0.02 * groundTexture.size().width * 2.0))
var resetGroundSprite = SKAction.moveByX(groundTexture.size().width * 2.0, y: 0, duration: 0.0)
var moveGroundSpritesForever = SKAction.repeatActionForever(SKAction.sequence([moveGroundSprite,resetGroundSprite]))

for var i:CGFloat = 0; i < 2.0 + self.frame.size.width / ( groundTexture.size().width * 2.0 ); ++i {
var sprite = SKSpriteNode(texture: groundTexture)
sprite.setScale(2.0)
sprite.position = CGPointMake(i * sprite.size.width, sprite.size.height / 2.0)
sprite.runAction(moveGroundSpritesForever)
self.addChild(sprite)
}

// skyline
var skyTexture = SKTexture(imageNamed: "sky")
skyTexture.filteringMode = SKTextureFilteringMode.Nearest

var moveSkySprite = SKAction.moveByX(-skyTexture.size().width * 2.0, y: 0, duration: NSTimeInterval(0.1 * skyTexture.size().width * 2.0))
var resetSkySprite = SKAction.moveByX(skyTexture.size().width * 2.0, y: 0, duration: 0.0)
var moveSkySpritesForever = SKAction.repeatActionForever(SKAction.sequence([moveSkySprite,resetSkySprite]))

for var i:CGFloat = 0; i < 2.0 + self.frame.size.width / ( skyTexture.size().width * 2.0 ); ++i {
var sprite = SKSpriteNode(texture: skyTexture)
sprite.setScale(2.0)
sprite.zPosition = -20;
sprite.position = CGPointMake(i * sprite.size.width, sprite.size.height / 2.0 + groundTexture.size().height * 2.0)
sprite.runAction(moveSkySpritesForever)
self.addChild(sprite)
}

・・・
}}}