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

  - by ruslan

  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?

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• Rendering order in an Entity System

  - by Daedalus

  Say I use a basic ES approach, and also inside Systems I hold lists of all entities that Systems are required to process. How do I maintain this list of entities in desired rendering order, i.e. for a dumb 2D RenderingSystem? I saw this discussion, and what they suggest is to do something like Z ordering - what I would probably do is just to store a "layer" int in DrawableComponent and then, inside RenderingSystem, just sort entities by mentioned "layer" whenever the entity list for RenderingSystem changes. They also say we could just delete and recreate the entity whenever we want it on the top, but it seems too inflexible to me. How is this problem usually solved?

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• MQTT, GWT, ActiveMQ stack to bring jms to the browser

  - by scphantm

  I am in the preliminary stages of architecting a legacy replacement project. They already have sub half second performance on their green screens and they want the same on their web app. We have a 390 mainframe that can handle anything we throw at it but they don't have a good jvm for it, so we have two tiers of websphere servers between the mainframe and the browser, The ui server, and the bl server. For the ui, I'm leaning towards GWT. But one thing that I think would seal the deal is to add messaging capabilities to the browser. The idea is say you click on a link that displays a second panel of information, instead of the classic GWT where it triggers a GWT-RPC call to the ui server, the ui server routs it to the bl server, the bl sends it to the mainframe and back out, it drops an MQTT message directly to the bl server or directly to the mainframe. Say writes go to the bl, reads go to the mainframe. This is an easy enough thing in classic jms because you can issue a message that has an expected response. Then have your callback ready to get the resonse. But from what I'm reading so far. It looks like mqtt doesn't have that. It looks like it's strictly fire and forget, which would make it really tough to come up with a way to get a response back to the workstation that called it. Am I right here? Has anyone tried this stack before with gwt.

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• How to design a separated tutorial mode?

  - by Sylpheed

  I'm working on a "social" game that's about 90% completion. One of the remaining features is the tutorial mode. Basically, the tutorial mode will restrict the user to access some parts of UI and limit the features (like store items). The tutorial will only progress if a certain event is triggered, specifically following the tutorial. The code is ready and we already have an "almost" working game. The problem is I haven't foreseen the tutorial mode while I was doing those 90%. My requirement is there shouldn't be any loading/transition from tutorial mode to normal mode. This means I have to pick up the progress from the tutorial (no re-rendering of assets and stuff). How should I design this in a way where I won't touch anything from my old code? I want it to be as easy as just plugging it in. I don't want to jam the tutorial in my old code since this will lead to many bugs.

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• What makes games responsive to user input?

  - by zaftcoAgeiha

  Many games have been praised for its responsive gameplay, where each user action input correspond to a quick and precise character movement (eg: super meat boy, shank...) What makes those games responsive? and what prevents other games from achieving the same? How much of it is due to the game framework used to queue mouse/keyboard events and render/update the game and how much is attributed to better coding?

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• Is 2 lines of push/pop code for each pre-draw-state too many?

  - by Griffin

  I'm trying to simplify vector graphics management in XNA; currently by incorporating state preservation. 2X lines of push/pop code for X states feels like too many, and it just feels wrong to have 2 lines of code that look identical except for one being push() and the other being pop(). The goal is to eradicate this repetitiveness,and I hoped to do so by creating an interface in which a client can give class/struct refs in which he wants restored after the rendering calls. Also note that many beginner-programmers will be using this, so forcing lambda expressions or other advanced C# features to be used in client code is not a good idea. I attempted to accomplish my goal by using Daniel Earwicker's Ptr class: public class Ptr<T> { Func<T> getter; Action<T> setter; public Ptr(Func<T> g, Action<T> s) { getter = g; setter = s; } public T Deref { get { return getter(); } set { setter(value); } } } an extension method: //doesn't work for structs since this is just syntatic sugar public static Ptr<T> GetPtr <T> (this T obj) { return new Ptr<T>( ()=> obj, v=> obj=v ); } and a Push Function: //returns a Pop Action for later calling public static Action Push <T> (ref T structure) where T: struct { T pushedValue = structure; //copies the struct data Ptr<T> p = structure.GetPtr(); return new Action( ()=> {p.Deref = pushedValue;} ); } However this doesn't work as stated in the code. How might I accomplish my goal? Example of code to be refactored: protected override void RenderLocally (GraphicsDevice device) { if (!(bool)isCompiled) {Compile();} //TODO: make sure state settings don't implicitly delete any buffers/resources RasterizerState oldRasterState = device.RasterizerState; DepthFormat oldFormat = device.PresentationParameters.DepthStencilFormat; DepthStencilState oldBufferState = device.DepthStencilState; { //Rendering code } device.RasterizerState = oldRasterState; device.DepthStencilState = oldBufferState; device.PresentationParameters.DepthStencilFormat = oldFormat; }

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• Multi-Threaded Pipelined Game Engine Data Synchronization Questions

  - by Douglas

  Let's say I'm setting up a worker pool based game engine with pipelining. Let's say I have 4 stages in my pipeline as such: Stage 1: Physics Stage 2: AI/Input Stage 3: Game Logic Stage 4: Rendering Now let's say that the physics detects a collision between a bullet and a character in stage 1. Two frames later the game logic may choose to remove that bullet from the simulation, however none of the other copies of the data for the other pipeline stages will get this information. How is this sort of thing and other things like it get handled? Do you generally make changes like this to every pipeline stage's data at the end of a frame?

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• Best approach to designing multi-client applications

  - by Tomh

  Hi, I was wondering how you guys start out if you need to design a multi-client project where multiple clients can interact with a server. In specific how do you go about dealing with different states and message handling, how do you start designing and considering all these cases? For example a video webchat application where it is possible that you call another client, while that client is already in a call, or is stuck in a modal dialog such that the calling dialog does not come through.

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• Building a template engine - starting point

  - by Anirudh

  We're building a Django-based project with a template component. This component will be separate from the project as such and can be Django/Python, Node, Java or whatever works. The template has to be rendered into HTML. The templates will contain references to objects with properties that are defined in the DB, say, a Bus. For eg, it could be something like [object type="vehicle" weight="heavy"] and it would have to pull a random object from the DB fulfilling the criteria : type="vehicle" weight="heavy" (bus/truck/jet) and then substitute that tag with an image, say, of a Bus. Also it would have to be able to handle some processing. Eg: What is [X type="integer" lte="10"] + [Y type="integer" lte="10"] [option X+Y correct_ans="true"] [option X-Y correct_ans="false"] [option X+y+1 correct_ans="false"] The engine would be expected to fill in a random integer value <= 10 for X and Y and show radioboxes for each of the options. Would also have to store the fact that the first option is the correct answer. Does it to make sense to write something from the scratch? Or is it better to use an existing templating system (like Django's own templating system) as a starting point? Any suggestions on how I can approach this?

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• Upcoming Database Design Pre-Cons

  - by drsql

  In July and October, I will be doing my "How To Design a Relational Database" full day conference in two places. First on July 26 for the East Iowa SQL Saturday , and then for the big daddy SQLPASS Summit in Charlotte, NC on October 14. You can see the entire abstract here on the SQL PASS site. It is essentially the same concept as last year, but this year I am making a few big changes to really give the people what they have desired (and am truly glad to have a swing at it several months...(read more)

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• About shared (static) Members and its behavior

  - by Allende

  I just realized that I can access shared members from instances of classes (probably this is not correct, but compile and run), and also learn/discover that, I can modify shared members, then create a new instance and access the new value of the shared member. My question is, what happens to the shared members, when it comes back to the "default" value (class declaration), how dangerous is it do this ? is it totally bad ? is it valid in some cases ?. If you want to test my point here is the code (console project vb.net) that I used to test shared members, as you can see/compile/run, the shared member "x" of the class "Hello" has default value string "Default", but at runtime it changes it, and after creating a new object of that class, this object has the new value of the shared member. Module Module1 Public Class hello Public Shared x As String = "Default" Public Sub New() End Sub End Class Sub Main() Console.WriteLine("hello.x=" & hello.x) Dim obj As New hello() Console.WriteLine("obj.x=" & obj.x) obj.x = "Default shared memeber, modified in object" Console.WriteLine("obj.x=" & obj.x) hello.x = "Defaul shared member, modified in class" Console.WriteLine("hello.x=" & hello.x) Dim obj2 As New hello() Console.WriteLine("obj2.x=" & obj2.x) Console.ReadLine() End Sub End Module UPDATE: First at all, thanks to everyone, each answer give feedback, I suppose, by respect I should choose one as "the answer", I don't want to be offensive to anyone, so please don't take it so bad if I didn't choose you answer.

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• Designing a "Grid" like object that contains game objects

  - by liortal

  I am working on a 2D game, where there's a game "board" on which other game objects are placed. This this is 2D, my starting point was to design a class that will internally use a 2d array for the actual stored game objects. This class could be simply accessed by 2 indices: (i, j) to get game objects on it. My problem is that i have no idea how to make the game "board" "propagate" its data onto its children. Design questions i ran into are: Should the children placed on the board have display properties such as size, screen position? Should the board itself dictate this information? How to update children in case the board changes some of its properties? (position, etc). Should the board be aware of the types of objects stored in it ? I have no idea how similar things such as WPF or other UI frameworks go about organizing a "container like" object that can arrange or apply certain UI properties to its children.

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• Techniques for separating game model from presentation

  - by liortal

  I am creating a simple 2D game using XNA. The elements that make up the game world are what i refer to as the "model". For instance, in a board game, i would have a GameBoard class that stores information about the board. This information could be things such as: Location Size Details about cells on the board (occupied/not occupied) etc This object should either know how to draw itself, or describe how to draw itself to some other entity (renderer) in order to be displayed. I believe that since the board only contains the data+logic for things regarding it or cells on it, it should not provide the logic of how to draw things (separation of concerns). How can i achieve a good partitioning and easily allow some other entity to draw it properly? My motivations for doing so are: Allow multiple "implementations" of presentation for a single game entity Easier porting to other environments where the presentation code is not available (for example - porting my code to Unity or other game technology that does not rely on XNA).

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• multi-clients web application,should I use custom user controls or a common user control

  - by ValidfroM

  Say my company is going to build a complicated asp.net web form education system. One of the module is web based registration. To make it flexiable, we decide to use user control(ascx) with rule-engine (work flow) regulating all business logic behide them. Thus in future,for different clients, we can simply config basic existing rules or adding new rules.(Rules stored in db or XML per client). Now the question is how to deal with the user controls (ascx)? My opinion is for different client build diffrent user control from scratch. other voice is like reuse existing user controls.

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• Is component-based design an architectural pattern or design pattern?

  - by xEnOn

  When using the component-based paradigm in game development with engines like Unity, is component-based design an architectural pattern, or a design pattern? Can I even say that component-based design is my "main" architectural pattern for my game? I see architectural patterns as being more high-level than design pattern. The component-based design in game development's context (like with Unity engine) seems to fit as an architectural pattern to me. However, on some sites, I read that component-based design is a behavioural pattern, much like other behavioural design patterns, and not so much like an architectural pattern like MVC.

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• Structure of a correctly implemented JTable with TableModel and Listeners?

  - by bamboocha

  I am pretty new to Java and its JTables and this is where I am struggling at the moment. I need to create a GUI which shows me results of a sql query like SELECT * FROM tblPeople WHERE name='Doe'. My idea was to create a a JFrame which displays a JTable with all found records. Besides this, I need to also implement some code to handle when a user is double clicking a record or selecting it by using his arrow keys (additional feature: pressing 12(e.g.) should select the 12th record). What is the best way to structure my program (what classes do I need and especially where do I store my logic)? I came up with structuring it the following way: Main.java ("view") SQLConnection.java PeopleTableModel.java (only stores and returns data given by the passed ResultSet, "model" inherits from DefaultTableModel) PeopleTable.java (stores basically all my logic including KeyListener and MouseListener, "controller", inherits from JTable) Are there better ways to achieve my goals? If so, what are they?

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• Develop for Desktop and mobile use?

  - by ran2

  I am in the very beginning of developing an app / desktop program. I want it to be cross-platform and possibly also as a tablet version (preferably Android Icecream sandwich). Note that I need to run it offline. I thought about the following approaches: ADOBE Air, since I do not need much performance. Plus I did some web programming in the past which might be of some use. Afaik it would run on OS X and Windows and should run on mobile OSes, too. Qt. Found some nice Qt based desktop recently and read it also works on android. Plus I like the SDK. HTML5 / JS. Again my web background should help me here. I wont need no sever side scripts, thus it should work without installing anything but a browser. How easy could this be converted into an Android app? There might be a plethora of other (better) ways to do it, but I haven't thought of them yet. Can you help out? How would you create such an application. Would it be better to do some pure desktop client and then create tablet versions? Would you rather start to create a website and worry later on how to turn into an app?

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• Digital "Post It" notes for organizing content of sites/pages

  - by Alex

  We're restructuring our old intranet into a new one and are going through each site to find content and use our new standard structure/look-and-feel. Do you recommend a tool where you can do "digital Post-It" notes? It would provide a way to type some items on a "card" and be able to move it around and organize it quickly. Also, if you know of tools in general for this kind of task, please advise. Thank you.

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• Leveraging Code Across Platforms in Ever Bigger Games

  - by ashes999

  Summary: The same way that I continually build complex engines and libraries within a single platform and technology to allow me to build increasingly bigger and better games, how to continue this when development crosses into different platforms? If I switch platforms, how do I leverage past code and experiences? Games are hard to build. Big games are even harder to build. I've decided that to be able to make big games, I need to start building smaller games, and building up an asset base of code, assets (graphics, sounds), tools, and most importantly, game engines, so that I can eventually get there. One game at a time. Let me give an analogy. To build an MMO 3D RPG, I would approach this by building and releasing small games with increasingly more features. This could entail, for example: A simple 2D game A tile-based game A game with RPG elements (items, equipment, monsters, battle) A full-fledged RPG A 3D RPG The problem now is if I have to change platforms or tools, I don't know how to leverage past code-bases (and experience) to start with a mature product. Right now, I'm writing Silverlight (FlatRedBall) games. Let's say I stick with this for ten years, and then suddenly decide to write a PS6 game, which is in a different programming language entirely. Granted, I have ten years of game-development experience (and correspondingly ten years of professional software development experience from my day job) to back me up. But I would still like some way to transplant that 2D RPG engine into the new programming language, or else leverage it somehow. Is this even possible? What are my options?

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• Service Layer - how broad should it be, and should it be used also on the local application?

  - by BornToCode

  Background: I need to build a main application with some operations (CRUD and more) (-in winforms), I need to make another application which will re-use some of the functions of the main application (-in webforms). I understood that using service layer is the best approach here. If I understood correctly the service should be calling the function on the BL layer (correct me if I'm wrong) The dilemma: In my main winform UI - should I call the functions from the BL, or from the service? (please explain why) Should I create a service for every single function on the BL even if I need some of the functions only in one UI? for example - should I create services for all the CRUD operations, even though I need to re-use only update operation in the webform? YOUR HELP IS MUCH APPRECIATED

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• Structuring game world entities and their rendering objects

  - by keithjgrant

  I'm putting together a simple 2d tile-based game. I'm finding myself spinning circles on some design decisions, and I think I'm in danger of over-engineering. After all, the game is simple enough that I had a working prototype inside of four hours with fewer than ten classes, it just wasn't scalable or flexible enough for a polished game. My question is about how to structure flow of control between game entity objects and their rendering objects. Should each renderer have a reference to their entity or vice-versa? Or both? Should the entity be in control of calling the render() method, or be completely oblivious? I know there are several valid approaches here, but I'm kind of feeling decision paralysis. What are the pros and cons of each approach?

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• How would you represent an object that can be of multiple types, when storing it as a document in MongoDB?

  - by blueberryfields

  Somewhat related to this question, say that I have an object category which, depending on which type of object I have, has different restrictions on what it contains. (if you can reword the previous sentence to make more sense I'd appreciate it) For example var SomeSchema = new Schema({ _id: ObjectID, [... large number of common fields ...] type: //Restricted somehow to members of a fixed array data: //depending on type, this might be restricted - sometimes an integer, sometimes array, etc... }); What's the idiosyncratic method for defining this type of schema? Is it appropriate to define a single schema, and handle the types inside of it's members, or am I better off with separate schema for each type?

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• Making Class Diagram for MVC Pattern Project

  - by iMohammad

  I have a question about making a class diagram for an MVC based college senior project. If we have 2 actors of users in my system, lets say Undergrad and Graduate students are the children of abstract class called User. (Generalisation) Each actor has his own features. My question, in such case, do we need to have these two actors in separate classes which inherits from the abstract class User? even though, I'm going to implement them as roles using one Model called User Model ? I think you can see my confusion here. I code using MVC pattern, but I've never made a class diagram for this pattern. Thank you in advance!

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• How should I handle using two databases with a legacy PHP application?

  - by Toby Allen

  I have a legacy PHP application that was written in 2004 and uses MSSQL as a database backend. At this stage MSSQL is still supported by PHP but only just via a Microsoft driver. I have looked at converting to mysql via automated tools, which work quite well, but I have quite complex views which need a lot of individual work to convert. I don't have a great deal of time to do this. Many tools I wish to use and frameworks I would like to move the application to, don't support MSSQL, so I was considering adding new features using a new mysql database and wondered if anyone had opinions on the pros and cons of using two seperate database backends in a single application?

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• How do I design a game framework for fast reaction to user input?

  - by Miro

  I've played some games at cca 30 fps and some of them had low reaction time - cca 0.1sec. I hadn't knew why. Now when I'm designing my framework for crossplatform game, I know why. Probably they've been preparing new frame during rendering the previous. RENDER 1 | RENDER 2 | RENDER 3 | RENDER 4 PREPARE 2 | PREPARE 3 | PREPARE 4 | PREPARE 5 I see first frame when second frame is being rendered and third frame being prepared. If I react in that time to 1st frame it will result in forth frame. So it takes 3/FPS seconds to appear results. In 30 fps it would be 100ms, what is quite bad. So i'm wondering what should I design my framework to response to user interaction quickly?

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