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• GameState management hierarchical FSM vs stack based FSM

  - by user8363

  I'm reading a bit on Finite State Machines to handle game states (or screens). I would like to build a rather decent FSM that can handle multiple screens. e.g. while the game is running I want to be able to pop-up an ingame menu and when that happens the main screen must stop updating (the game is paused) but must still be visible in the background. However when I open an inventory pop-up the main screen must be visible and continue updating etc. I'm a bit confused about the difference in implementation and functionality between hierarchical FSM's and FSM's that handle a stack of states instead. Are they basically the same? Or are there important differences?

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• How does a search functionality fit in DDD with CQRS?

  - by Songo

  In Vaughn Vernon's book Implementing domain driven design and the accompanying sample application I found that he implemented a CQRS approach to the iddd_collaboration bounded context. He presents the following classes in the application service layer: CalendarApplicationService.java CalendarEntryApplicationService.java CalendarEntryQueryService.java CalendarQueryService.java I'm interested to know if an application will have a search page that feature numerous drop downs and check boxes with a smart text box to match different search patterns; How will you structure all that search logic? In a command service or a query service? Taking a look at the CalendarQueryService.java I can see that it has 2 methods for a huge query, but no logic at all to mix and match any search filters for example. I've heard that the application layer shouldn't have any business logic, so where will I construct my dynamic query? or maybe just clutter everything in the Query service?

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• DDD and filtering

  - by tikhop

  I am developing an app in ddd maner. So I have a complex domain model. Suppose I have a Fare object and Airline. Each Airline should contain several or much more Fares. My UI should represent Model (only small part of complex model) as a list of Airline, when the user select the Airline, I must show the list of Fares. User can filtering the Fares (by travel time, cost, etc.). What is the appropriate place for filtering Fares and Airlines? I am assuming that I should do it in ViewModel. Like: My domain model has wrapped with Service Layer - UI works with ViewModel - ViewModel obtain data from Service Layer filtering it and create DTO objects for UI. Or I'm wrong?

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• How would you gather client's data on Google App Engine without using Datastore/Backend Instances too much?

  - by ruslan

  I'm relatively new to StackExchange and not sure if it's appropriate place to ask design question. Site gives me a hint "The question you're asking appears subjective and is likely to be closed". Please let me know. Anyway.. One of the projects I'm working on is online survey engine. It's my first big commercial project on Google App Engine. I need your advice on how to collect stats and efficiently record them in DataStore without bankrupting me. Initial requirements are: After user finishes survey client sends list of pairs [ID (int) + PercentHit (double)]. This list shows how close answers of this user match predefined answers of reference answerers (which identified by IDs). I call them "target IDs". Creator of the survey wants to see aggregated % for given IDs for last hour, particular timeframe or from the beginning of the survey. Some surveys may have thousands of target/reference answerers. So I created entity public class HitsStatsDO implements Serializable { @Id transient private Long id; transient private Long version = (long) 0; transient private Long startDate; @Parent transient private Key parent; // fake parent which contains target id @Transient int targetId; private double avgPercent; private long hitCount; } But writing HitsStatsDO for each target from each user would give a lot of data. For instance I had a survey with 3000 targets which was answered by ~4 million people within one week with 300K people taking survey in first day. Even if we assume they were answering it evenly for 24 hours it would give us ~1040 writes/second. Obviously it hits concurrent writes limit of Datastore. I decided I'll collect data for one hour and save that, that's why there are avgPercent and hitCount in HitsStatsDO. GAE instances are stateless so I had to use dynamic backend instance. There I have something like this: // Contains stats for one hour private class Shard { ReadWriteLock lock = new ReentrantReadWriteLock(); Map<Integer, HitsStatsDO> map = new HashMap<Integer, HitsStatsDO>(); // Key is target ID public void saveToDatastore(); public void updateStats(Long startDate, Map<Integer, Double> hits); } and map with shard for current hour and previous hour (which doesn't stay here for long) private HashMap<Long, Shard> shards = new HashMap<Long, Shard>(); // Key is HitsStatsDO.startDate So once per hour I dump Shard for previous hour to Datastore. Plus I have class LifetimeStats which keeps Map<Integer, HitsStatsDO> in memcached where map-key is target ID. Also in my backend shutdown hook method I dump stats for unfinished hour to Datastore. There is only one major issue here - I have only ONE backend instance :) It raises following questions on which I'd like to hear your opinion: Can I do this without using backend instance ? What if one instance is not enough ? How can I split data between multiple dynamic backend instances? It hard because I don't know how many I have because Google creates new one as load increases. I know I can launch exact number of resident backend instances. But how many ? 2, 5, 10 ? What if I have no load at all for a week. Constantly running 10 backend instances is too expensive. What do I do with data from clients while backend instance is dead/restarting? Thank you very much in advance for your thoughts.

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• Webshop for digital goods with voucher / gift card system [duplicate]

  - by Kelzama

  This question already has an answer here: Which Ecommerce Script Should I Use? 1 answer I'm searching for a webshop which provides the following: The shop offers digital goods (like mp3) User can buy a voucher / gift card @Reseller (Or there is a code provided in the CD) User can enter his code @ webshop and gets the download (unregistered) User can enter his code @ webshop and download is added to his/her library (registered) optional: Resellers can buy codes from the Webshop I already tried prestashop as it looks quite nice. But it needs a lot of custom programming (and has a very strange voucher-system). Customer has to add the File into the basket and add the voucher at checkout. I want to skip that ;) Is there a Webshop (Or CMS + Plugin) which provides the things I need? (it could also be a CMS with a Storage/Folder Plugin (like joomla + K2) and a possibility to activate downloads via unique Codes.) Any ideas are highly appreciated :) Thanks in advance.

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• Component-based design: handling objects interaction

  - by Milo

  I'm not sure how exactly objects do things to other objects in a component based design. Say I have an Obj class. I do: Obj obj; obj.add(new Position()); obj.add(new Physics()); How could I then have another object not only move the ball but have those physics applied. I'm not looking for implementation details but rather abstractly how objects communicate. In an entity based design, you might just have: obj1.emitForceOn(obj2,5.0,0.0,0.0); Any article or explanation to get a better grasp on a component driven design and how to do basic things would be really helpful.

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• How to decide whether to implement an operation as Entity operation vs Service operation in Domain Driven Design?

  - by Louis Rhys

  I am reading Evans's Domain Driven Design. The book says that there are entity and there are services. If I were to implement an operation, how to decide whether I should add it as a method on an entity or do it in a service class? e.g. myEntity.DoStuff() or myService.DoStuffOn(myEntity)? Does it depend on whether other entities are involved? If it involves other entities, implement as service operation? But entities can have associations and can traverse it from there too right? Does it depend on stateless or not? But service can also access entities' variable, right? Like in do stuff myService.DoStuffOn, it can have code like if(myEntity.IsX) doSomething(); Which means that it will depend on the state? Or does it depend on complexity? How do you define complex operations?

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• Transmitting Form Data from the Client to the Web Server

  The steps involved in transmitting form data from the client to the web server User loads web form User enters data in to web form fields User clicks submit On submit page validates fields using JavaScript. If validation errors are found then the validation script stops the browser from canceling posting the data to the web server and displays error messages as needed If the form passes the data validation process then the browser will URL encode the values of every field and post it to the server.  The server reads the posted data from the query string and then again validates the data just to ensure data consistency and to prevent any non-validated data because JavaScript was turned off on the clients browser from being inserted in to a database or passed on to other process If the data passes the second validation check then the server side code will continue with the requested processes

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• Broad topics needed for teaching game development

  - by livingtech

  I am going to be doing a presentation on game development to an iPhone user group in the near(ish) future. My audience are iPhone developers, but not necessarily very experienced ones, and this is meant to be an introduction. My question is, what broad topics are needed to understand game development? I acknowledge that this is fairly subjective, but I really am hoping for a comprehensive list of high-level topics that apply to a broad enough swath of games that anyone interested in the topic SHOULD know about them. I would be ecstatic with some pointers to any resources that attempt to make a list such as this this. (I have looked, but my google-fu is failing me tonight.) Here's what I have so far: The Game Loop a sub-note about event driven games 2D Animation sprites/texture maps 3D Animation importance of frameworks modeling software Particles and particle effects hit detection AI Obviously I will not be covering all these topics with any depth, more like simply defining them so that after my talk, the audience will (hopefully) be able to wrap their heads around how any given game might be developed. What am I missing?

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• Use of Service Bus in a Pub-Sub Engine

  - by JoseK

  In one of our projects, we've built a Publisher - Subscriber Engine on Oracle Service Bus. The functionality being a series of events are published and subscribers (JMS queues) receive these whenever a new event is published. We are facing some technical issues now, performance-wise and hence an architectural review is underway. Now for my questions: Architecturally the ESB has to publish events into a DB and read from the DB which users wish to be notified, then push the event onto their respective queues. There is a high amount of DB interaction and the question is whether ESB should be having such high amount of interaction with the DB in the first place? Or should there have been some alternate component responsible for doing this. Alternately is there any non-DB approach in which we can store the events and subscribers? Where else can this application data be held within the ESB context?

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• Frames per Second and Updates per Second [on hold]

  - by matt murray

  So this is more a general resources question, as I am seeking knowledge on how best to conserve resources in a game (I am writing in Java, and please this is not a thread on what language I should write it in, I have already chosen Java) so that the updates and frames per second could be the highest they could be. In general I am just searching for any articles you may have, any personal experience, anything what so ever that could be of use to a pretty new Java game developer on the subject! Thanks in advance!

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• Programming is easy, Designing is hard

  - by Rachel

  I work as Programmer and I feel if design documents are properly in place and requirements are clearly specified than programming is not that difficult but when I think in terms of Designing a Software than it gives chills to me and I think its a very difficult part. I want to develop my Design Skills so, How should I go about it ? Are there any books, blogs, websites or other approaches that SO community can suggest ? Update: By Design I meant Design of overall Application or particular problem at hand and not UI Design.

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• How to design a scriptable communication emulator?

  - by Hawk

  Requirement: We need a tool that simulates a hardware device that communicates via RS232 or TCP/IP to allow us to test our main application which will communicate with the device. Current flow: User loads script Parse script into commands User runs script Execute commands Script / commands (simplified for discussion): Connect RS232 = RS232ConnectCommand Connect TCP/IP = TcpIpConnectCommand Send data = SendCommand Receive data = ReceiveCommand Disconnect = DisconnectCommand All commands implement the ICommand interface. The command runner simply executes a sequence of ICommand implementations sequentially thus ICommand must have an Execute exposure, pseudo code: void Execute(ICommunicator context) The Execute method takes a context argument which allows the command implementations to execute what they need to do. For instance SendCommand will call context.Send, etc. The problem RS232ConnectCommand and TcpIpConnectCommand needs to instantiate the context to be used by subsequent commands. How do you handle this elegantly? Solution 1: Change ICommand Execute method to: ICommunicator Execute(ICommunicator context) While it will work it seems like a code smell. All commands now need to return the context which for all commands except the connection ones will be the same context that is passed in. Solution 2: Create an ICommunicatorWrapper (ICommunicationBroker?) which follows the decorator pattern and decorates ICommunicator. It introduces a new exposure: void SetCommunicator(ICommunicator communicator) And ICommand is changed to use the wrapper: void Execute(ICommunicationWrapper context) Seems like a cleaner solution. Question Is this a good design? Am I on the right track?

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• What tools, libraries, or framework is needed to create a completely offline Javascript application?

  - by makerofthings7

  I am interested in creating a HTML application that can run as disconnected from the server as possible. Two examples of this include OWA in Exchange 2013 and to a lesser extent and the client available at www.ripple.com With the focus on OWA in Exchange 2013, what is needed to replicate the offline functionality available in a different application? A list technologies, frameworks, etc would be immensely helpful

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• Design Patterns and their most common uses for them [closed]

  - by cable729

  Possible Duplicate: What are some programming design patterns that are useful in game development? As I'm returning to game dev, I've realized that I've lost a lot of the knowledge I had before. So now I'm looking at design patterns that I can use for my next project. One design pattern that I've seen a lot is the 'composition method,' which uses actors and components. Is that the right name for it? I'd like to look more at this and see what the advantages/pitfalls are. So what design patterns are out there, and what are the advantages/disadvantages to them?

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• Multiple sites with the same codebase in Python

  - by Jimmy

  I am trying to run a large amount of sites which share about 90% of their code. They are simply designed to query an API and return the results. They will have a common userbase / database but will be configured slightly different and will have different CSS (perhaps even different templating). My initial idea was to run them as separate applications with a common library but I have read about the sites framework which would allow them to run from a single instance of Django which may help to reduce memory usage. https://docs.djangoproject.com/en/dev/ref/contrib/sites/ Is the site framework the right approach to a problem like this, and does it have real benefits over running separate applications? Initially I thought it was, but now I think otherwise. I have heard the following: Your SITE_ID is set in settings.py, so in order to have multiple sites, you need multiple settings.py configurations, which means multiple distinct processes/instances. You can of course share the code base between them, but each site will need a dedicated worker / WSGIDaemon to serve the site. This effectively removes any benefit of running multiple sites under one hood, if each site needs a UWSGI instance running. Alternative ideas of systems: https://github.com/iivvoo/django_layers https://github.com/shestera/django-multisite I don't know what route to be taking with this.

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• Scrum for Team System v3 RTM available

  - by Enrique Lima

  If you are using the Scrum for Team System (aka Conchango Scrum Template), it has hit RTM and it is available for download.  First you will need to register and then you will ne able to access the goods. There is also a very well laid out Getting Started with v3 guide, put together by Crispin Parker. Note:  Very important to know and consider, is the fact there is no upgrade or migration strategy laid out from v2.2.  So you are left to your own devices on that one.  There are plenty of discussions going on as far as making it happen.  Don’t get me wrong v2.2 work items will be present and you will be able to use them, just don’t expect the v3 template to trigger when  adding new work items. For now, get TFS in place, install the template and start fresh.  The Workbench should be released soon too, and that makes it a great component to this solution.

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• Should I incorporate exit cost into choosing a solution

  - by Mr Happy

  I'm currently choosing between two viable software designs/solutions. Solution 1 is easy to implement, but will lock some data in a propriaty format, and will be hard to change later. Solution 2 is hard to implement, but will be a lot easier to change later on. Should I go YAGNI on this or should I incorporate the exit cost in the decision making? Or asked differently, is the exit cost part of the TCO? I'm thinking of going back to the customer with this to ask wether or not he thinks the exit costs are relevant, but I'd like to know what the community thinks first. P.S. Is exit cost the correct term?

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• Game editor integration with the engine?

  - by Daniel

  What I am trying to figure out is what is the best way to integrate the editor(level, effects, model, etc...) in the most effective way? Now the first thing I thought would be to create the game engine(*) extremely modular. For example I took the example of game states. You could have multiple game states that all have their own update() and draw() methods among others. Each game state class would inherit from a base GameState class. This allows for a more modular approach and a useful one at that. Now would the most efficient approach be to implement the editor along with the modular engine, or create two different designs for both the game, and editor? I thought to take the game state example and extend it to window states, and well could be used for a lot more systems. Is there a better implementation of this design(game state) for use in other systems used in the engine? *: Now I know the term game engine is sorta irrelevant, and misused in many situations. What I am referring to as the "game engine" is the combination of the systems that the game must interact with for short. Also this is more of a theory / design question than an implementation. Even though both mix, i'd rather like to have a more general idea on how the editor is built in an efficient way and still using the same engine code as what the game uses. Thanks, Daniel P.S If you need more clarification or extra bits just leave a comment.

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• How to manage security of these self hosted web apis, to ensure that the request coming for accessing data is authenticated?

  - by Husrat Mehmood

  Let's pretend I am going to work on an enterprise application. Say I have 11 modules in the application and I would have to develop Dashboards for every role in the organization for whom I are going to develop application. We Decided to use Asp.Net Web Api and return json data from our apis. We are going to include 11 Self hosted web apis projects in our application (one self hosted web api) for every module. All 11 modules are connected to one Sql server 2012 Database. Then once api is ready we would have to create Business Dashboards (Based upon roles in Organization). So Now my web api client is Asp.Net Mvc application.Asp.Net mvc will consume those web apis. Here is the part for whom all explanation is done. How should I manage Security of all 11 self hosted web apis? How should I only authenticated request is coming? If I authenticate user by login and password and then redirect user to appropriate Dashboard designed for the role that user have and load data by consuming web apis. How should I ensure that the request coming for accessing data is authenticated?

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• Relationship between Repository and Unit of Work

  - by NullOrEmpty

  I am going to implement a repository, and I would like to use the UOW pattern since the consumer of the repository could do several operations, and I want to commit them at once. After read several articles about the matter, I still don't get how to relate this two elements, depending on the article it is being done in a way u other. Sometimes the UOW is something internal to the repository: public class Repository { UnitOfWork _uow; public Repository() { _uow = IoC.Get<UnitOfWork>(); } public void Save(Entity e) { _uow.Track(e); } public void SubmittChanges() { SaveInStorage(_uow.GetChanges()); } } And sometimes it is external: public class Repository { public void Save(Entity e, UnitOfWork uow) { uow.Track(e); } public void SubmittChanges(UnitOfWork uow) { SaveInStorage(uow.GetChanges()); } } Other times, is the UOW whom references the Repository public class UnitOfWork { Repository _repository; public UnitOfWork(Repository repository) { _repository = repository; } public void Save(Entity e) { this.Track(e); } public void SubmittChanges() { _repository.Save(this.GetChanges()); } } How are these two elements related? UOW tracks the elements that needs be changed, and repository contains the logic to persist those changes, but... who call who? Does the last make more sense? Also, who manages the connection? If several operations have to be done in the repository, I think using the same connection and even transaction is more sound, so maybe put the connection object inside the UOW and this one inside the repository makes sense as well. Cheers

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• "Waiting for Sound System to respond." error dialog

  - by Paulo Truta

  Hello guys. I'm having a nasty problem with the Sound Menu on my Ubuntu 10.10 Installation. What happens is that the sound control icon is blocked, and i can't control the master volume. If i try to get to the Sound Preferences i get a little Pop-Up Window saying: "Waiting for Sound System to respond...". Don't know what to do... Apart of that, sound works great. Thanks a lot ;) PS: I made 2 screenshot uploads. Hope it helps.

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• HD video editing system with Truecrypt

  - by Rob

  I'm looking to do hi-def video editing and transcoding on an unencrypted standard partition, with Truecrypt on the system partition for sensitive data. I'm aiming to keep certain data private but still have performance where needed. Goals: Maximum, unimpacted, performance possible for hi-def video editing, encryption of video not required Encrypt system partition, using Truecrypt, for web/email privacy, etc. in the event of loss In other words I want to selectively encrypt the hard drive - i.e. make the system partition encrypted but not impact the original maximum performance that would be available to me for hi-def/HD video editing. The thinking is to use an unencrypted partition for the video and set up video applications to point at that. Assuming that they would use that partition only for their workspace and not the encrypted system partition, then I should expect to not get any performance hit. Would I be correct? I guess it might depend on the application, if that app is hard-wired to use the system partition always for temporary storage during editing and transcoding, or if it has to be installed on the C: system partition always. So some real data on how various apps behave in the respect would be useful, e.g. Adobe, Cyberlink, Nero etc. etc. I have a Intel i7 Quad-core (8 threads) 1.6Ghz (up to 2.8Ghz turbo-boost) 4Gb, 7200rpm SATA, nvidia HP laptop. I've read the excellent posting about the general performance impact of truecrypt but the benchmarks weren't specific enough for my needs where I'm dealing with HD-video and using a non-encrypted partition to maintain max performance.

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• iOS chat application design, sending/relaying the message over to the end user

  - by AyBayBay

  I have a design question. Let us say you were tasked with building a chat application, specifically for iOS (iOS Chat Application). For simplicity let us say you can only chat with one person at a time (no group chat functionality). How then can you achieve sending a message directly to an end user from phone A to phone B? Obviously there is a web service layer with some API calls. One of the API calls available will be startChat(). After starting a chat, when you send a message, you make another async call, let us call it sendMessage() and pass in a string with your message. Once it goes to the web service layer, the message gets stored in a database. Here is where I am currently stuck. After the message gets sent to the web service layer, how do we then achieve sending/relaying the message over to the end user? Should the web server send out a message to the end user and notify them, or should each client call a receiveMessage() method periodically, and if the server side has some info for them it can then respond with that info? Finally, how can we handle the case in which the user you are trying to send a message to is offline? How can we make sure the end user gets the packet when he moves back to an area with signal?

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• Using an actor model versus a producer-consumer model?

  - by hewhocutsdown

  I'm doing some early-stage research towards architecting a new software application. Concurrency and multithreading will likely play a significant part, so I've been reading up on the various topics. The producer-consumer model, at least how it is expressed in Java, has some surface similarities but appears to be deeply dissimilar to the actor model in use with languages such as Erlang and Scala. I'm having trouble finding any good comparative data, or specific reasons to use or avoid the one or the other. Is the actor model even possible with Java or C#, or do you have do use one of the languages built for the purpose? Is there a third way?

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