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• What should a developer know before building a public web site?

  - by Joel Coehoorn

  What things should a programmer implementing the technical details of a web site address before making the site public? If Jeff Atwood can forget about HttpOnly cookies, sitemaps, and cross-site request forgeries all in the same site, what important thing could I be forgetting as well? I'm thinking about this from a web developer's perspective, such that someone else is creating the actual design and content for the site. So while usability and content may be more important than the platform, you the programmer have little say in that. What you do need to worry about is that your implementation of the platform is stable, performs well, is secure, and meets any other business goals (like not cost too much, take too long to build, and rank as well with Google as the content supports). Think of this from the perspective of a developer who's done some work for intranet-type applications in a fairly trusted environment, and is about to have his first shot and putting out a potentially popular site for the entire big bad world wide web. Also: I'm looking for something more specific than just a vague "web standards" response. I mean, HTML, JavaScript, and CSS over HTTP are pretty much a given, especially when I've already specified that you're a professional web developer. So going beyond that, Which standards? In what circumstances, and why? Provide a link to the standard's specification. This question is community wiki, so please feel free to edit that answer to add links to good articles that will help explain or teach each particular point. To search in only the answers from this question, use the inquestion:this option.

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• The NEW MySQL for Developers Course

  - by Antoinette O'Sullivan

  Just Released - The new MySQL for Developers training course.  This 5 day course covers everything a developer needs to know when planning, designing and implementing applications using MySQL, with realistic examples using languages such as Java and PHP. This course gives an in-depth coverage of statements that access and modify data, and shows the student how to design and create other MySQL objects such as triggers, views, and stored procedures. You can take this course: From your desk as a live virtual offering. There are over 800 events on the schedule so you should find one in a timezone near you. The virtual events are also delivered in many languages including English, German, Korean, Latin American Spanish, ... In a classroom. Here is a sample of events on the schedule:  Location  Date  Delivery Language  Prague, Czech Republic 8 October 2012 Czech  Warsaw, Poland 5 November 2012 Polish  Wien, Austria  12 November 2012 German  London, England 15 October 2012 English  Bern, Switzerland  11 April 2013 German  Zurich, Switzerland 14 November 2012 German  Milan, Italy 19 November 2012  Italian  Rome, Italy  15 October 2012  Italian  Gummersbach, Germany  11 February 2013 German  Hamburg, Germany  12 November 2012  German Munich, Germany  10 June 2013  German  Lisbon, Portugal 26 November 2012 European Portuguese  Porto, Portugal 18 February 2013 European Portuguese  Nairobi, Kenya  19 November 2012  English  Madrid, Spain  10 December 2012  Spanish Petaling Jaya, Malaysia  15 October 2012  English  Bangkok, Thailand  29 October 2012  English For further information on the Authentic MySQL Curriculum, to register for an event or express interest in an additional event, go to http://oracle.com/education/mysql.

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• How exactly is an Abstract Syntax Tree created?

  - by Howcan

  I think I understand the goal of an AST, and I've build a couple of tree structures before, but never an AST. I'm mostly confused because the nodes are text and not number, so I can't think of a nice way to input a token/string as I'm parsing some code. For example, when I looked at diagrams of AST's, the variable and its value were leaf nodes to an equal sign. This makes perfect sense to me, but how would I go about implementing this? I guess I can do it case by case, so that when I stumble upon an "=" I use that as a node, and add the value parsed before the "=" as the leaf. It just seems wrong, because I'd probably have to make cases for tons and tons of things, depending on the syntax. And then I came upon another problem, how is the tree traversed? Do I go all the way down the height, and go back up a node when I hit the bottom, and do the same for it's neighbor? I've seen tons of diagrams on ASTs, but I couldn't find a fairly simple example of one in code, which would probably help.

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• Why don't C++ Game Developers use the boost library?

  - by James

  So if you spend any time viewing / answering questions over on Stack Overflow under the C++ tag, you will quickly notice that just about everybody uses the boost library; some would even say that if you aren't using it, you're not writing "real' C++ (I disagree, but that's not the point). But then there is the game industry, which is well known for using C++ and not using boost. I can't help but wonder why that is. I don't care to use boost because I write games (now) as a hobby, and part of that hobby is implementing what I need when I am able to and using off-the-shelf libraries when I can't. But that is just me. Why don't game developers, in general, use the boost library? Is it performance or memory concerns? Style? Something Else? I was about to ask this on stack overflow, but I figured the question is better asked here. EDIT : I realize I can't speak for all game programmers and I haven't seen all game projects, so I can't say game developers never use boost; this is simply my experience. Allow me to edit my question to also ask, if you do use boost, why did you choose to use it?

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• Distributed Development Tools -- (Version control and Project Management)

  - by Macy Abbey

  I've recently become responsible for choosing which source control and project management software to use for a company that employs me. Currently it uses Jira (project management) and Subversion (version control). I know there are many other options out there -- the ones I know about are all in this article http://mashable.com/2010/07/14/distributed-developer-teams/ . I'm leaning towards recommending they just stay with what they have as it seems workable and any change would have to be worth the cost of switching to say github/basecamp or some other solution. Some details on the team: It's a distributed development shop. Meetings of the whole team in one room are rare. It's currently a very small development team (three developers). The project management software is used by developers and a product manager or two. What are you experiences with version control and project management web applications? Are there any you would recommend and you think are worth the switching cost of time to learn new services / implementing the change? Edit: After educating myself further on the options it appears DVCS offer powerful benefits that may be worth investing in now as opposed to later in the company's lifetime when the switching cost is higher: I'm a Subversion geek, why I should consider or not consider Mercurial or Git or any other DVCS?

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• How to really master ASP.NET MVC?

  - by user1620696

  Some years ago I've worked with web development just using PHP without focus on object orientation and so on. When I knew a little bit about it, and the benefits it brings, I've started moving to ASP.NET MVC. First, I've studied C# in the book Visual C# Step by Step. I've found it a good book for a beginner, and I could learn a lot of this new language with it. Now, when I've came to study ASP.NET MVC, I hadn't so much luck. I've studied on some books that explained MVC well and so on, but then started just saying: "do that, and now that, and then that", and I feel I couldn't really master ASP.NET MVC. I feel this, because when I was reading, I knew how to do the things the book taught, like implementing DI with Ninject and so on, but some time later, without looking at it for some time, I couldn't do it by myself. What I'm trying to say, is that usually I don't know where to start, how to do things in this framework and so on. How can I really master ASP.NET MVC? There is some book, some tutorial series, anything, that can really help with that? I'm pretty happy with the .NET framework, my problem isn't it, my only problem is working with the MVC framework, and applying the techniques from object orientation there. I don't know if this question is on-topic here, but I'm really just looking for some good references, to become better with this framework.

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• Progress bar in Super Hexagon using OpenGL ES 2 (Android)

  - by user16547

  I'm wondering how the progress bar in Super Hexagon was made. (see image, top left) Actually I am not very sure how to implement a progress bar at all using OpenGL ES 2 on Android, but I am asking specifically about the one used in Super Hexagon because it seems to me less straightforward / obvious than others: the bar changes its colour during game play. I think one possibility is to use the built-in Android progress bar. I can see from some Stackoverflow questions that you can change the default blue colour to whatever you want, but I'm not sure whether you can update it during the game play. The other possibility I can think of for implementing a progress bar is to have a small texture that starts with a scale of 0 and that you keep scaling until it reaches the maximum size, representing 100%. But this suffers from the same problem as before: you'll not be able to update the colour of the texture during run-time. It's fixed. So what's the best way to approach this problem? *I'm assuming he didn't use a particular library, although if he did, it would be interesting to know. I'm interested in a pure OpenGL ES 2 + Android solution.

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• Best practices: Ajax and server side scripting with stored procedures

  - by Luka Milani

  I need to rebuild an old huge website and probably to port everyting to ASP.NET and jQuery and I would like to ask for some suggestion and tips. Actually the website uses: Ajax (client site with prototype.js) ASP (vb script server side) SQL Server 2005 IIS 7 as web server This website uses hundred of stored procedures and the requests are made by an ajax call and only 1 ASP page that contain an huge select case Shortly an example: JAVASCRIPT + PROTOTYPE: var data = { action: 'NEWS', callback: 'doNews', param1: $('text_example').value, ......: ..........}; AjaxGet(data); // perform a call using another function + prototype SERVER SIDE ASP: <% ...... select case request("Action") case "NEWS" With cmmDB .ActiveConnection = Conn .CommandText = "sp_NEWS_TO_CALL_for_example" .CommandType = adCmdStoredProc Set par0DB = .CreateParameter("Param1", adVarchar, adParamInput,6) Set par1DB = .CreateParameter(".....", adInteger, adParamInput) ' ........ ' can be more parameters .Parameters.Append par0DB .Parameters.Append par1DB par0DB.Value = request("Param1") par1DB.Value = request(".....") set rs=cmmDB.execute RecodsetToJSON rs, jsa ' create JSON response using a sub End With .... %> So as you can see I have an ASP page that has a lot of CASE and this page answers to all the ajax request in the site. My question are: Instead of having many CASES is it possible to create dynamic vb code that parses the ajax request and creates dynamically the call to the desired SP (also implementing the parameters passed by JS)? What is the best approach to handle situations like this, by using the advantages of .Net + protoype or jQuery? How the big sites handle situation like this? Do they do it by creating 1 page for request? Thanks in advance for suggestion, direction and tips.

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• How can I discourage the use of Access?

  - by Greg Buehler

  Lets pretend that a very large company (revenue numbers with more than 8 figures) is looking to do a refresh on a software system, particularly the dashboard used by employees. This system was originally put together in the early 1990's to handle inventory tracking and storage across a variety of facilities (10+). Since this large company is now in the process of implementing some of these inventory processes with SAP they are in need of a major refresh. The existing system: Microsoft Access project performs dashboard duties Unique shipping/receiving configurations at different facilities require unique forms and queries within the Access project Uses 3rd party libraries referenced by Access to directly interface with at control system (read: motors, conveyors, and counters) Individual SQL Server 2000 instances (some traces of pre-update SQL Server 6.0 documents) at each facility The Issue: This system started as a home brewed inventory tracking scheme with a single internal sponsor who is still in charge of the technical direction. The original sponsor prescribing the desired deliverables that are being called for in the current RFP. The RFP describes a system based around a single Access project. Any suggestion that Access is ill suited for a project of this scope are shot down under the reasoning that "it works for the scope now". Are there any case studies, notices, or statements that can be used to disuade this potential customer from repeating their mistake? Does Microsoft make any statements directly about when it is highly recommended to ditch Access?

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• How can Highscores be more meaningful and engaging?

  - by Anselm Eickhoff

  I'm developing a casual Android game in which the player's success can very easily be represented by a number (I'm not more specific because I'm interested in the topic in general). Although I myself am not a highscore person at all, I was thinking of implementing a highscore for that game, but I see at least 2 problems in the classical leaderboard approach: very soon the highscore will be dominated by hardcore players, leaving no chance for beginners, who are then frustrated. This is very severe especially in casual games. there is no direct reward for being a loyal player who plays the game over and over again My current idea is to "reset" the highscore every 24 hours (for example) and each day nominate the "player of the day" who then gets a "star". Then there would be some kind of meta-highscore of players with the most stars. That way even beginners might have a chance to be "player of the day" once and continued or repeated play is rewarded much more. The idea is still very rough and there are many problems in the details and the technical implementation but I have a feeling it is a step in the right direction. Do you have creative and new ideas on how to implement highscores? Which games are doing this well / what types of highscores do you find most engaging?

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• What kind of physics to choose for our arcade 3D MMO?

  - by Nick

  We're creating an action MMO using Three.js (WebGL) with an arcadish feel, and implementing physics for it has been a pain in the butt. Our game has a terrain where the character will walk on, and in the future 3D objects (a house, a tree, etc) that will have collisions. In terms of complexity, the physics engine should be like World of Warcraft. We don't need friction, bouncing behaviour or anything more complex like joints, etc. Just gravity. I have managed to implement terrain physics so far by casting a ray downwards, but it does not take into account possible 3D objects. Note that these 3D objects need to have convex collisions, so our artists create a 3D house and the player can walk inside but can't walk through the walls. How do I implement proper collision detection with 3D objects like in World of Warcraft? Do I need an advanced physics engine? I read about Physijs which looks cool, but I fear that it may be overkill to implement that for our game. Also, how does WoW do it? Do they have a separate raycasting system for the terrain? Or do they treat the terrain like any other convex mesh? A screenshot of our game so far:

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• Empty interface to combine multiple interfaces

  - by user1109519

  Suppose you have two interfaces: interface Readable { public void read(); } interface Writable { public void write(); } In some cases the implementing objects can only support one of these but in a lot of cases the implementations will support both interfaces. The people who use the interfaces will have to do something like: // can't write to it without explicit casting Readable myObject = new MyObject(); // can't read from it without explicit casting Writable myObject = new MyObject(); // tight coupling to actual implementation MyObject myObject = new MyObject(); None of these options is terribly convenient, even more so when considering that you want this as a method parameter. One solution would be to declare a wrapping interface: interface TheWholeShabam extends Readable, Writable {} But this has one specific problem: all implementations that support both Readable and Writable have to implement TheWholeShabam if they want to be compatible with people using the interface. Even though it offers nothing apart from the guaranteed presence of both interfaces. Is there a clean solution to this problem or should I go for the wrapper interface? UPDATE It is in fact often necessary to have an object that is both readable and writable so simply seperating the concerns in the arguments is not always a clean solution. UPDATE2 (extracted as answer so it's easier to comment on) UPDATE3 Please beware that the primary usecase for this is not streams (although they too must be supported). Streams make a very specific distinction between input and output and there is a clear separation of responsibilities. Rather, think of something like a bytebuffer where you need one object you can write to and read from, one object that has a very specific state attached to it. These objects exist because they are very useful for some things like asynchronous I/O, encodings,...

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• Book Review: Professional ASP.Net MVC4

  - by Sam Abraham

  The past few weeks have been particularly busy as I continue to dedicate a bigger portion of my free time to refreshing my memory and enhancing my knowledge of best practices pertaining to technologies we plan on using for a major upcoming project. In this blog post, I will be providing a brief overview of my latest reading “Professional ASP.Net MVC4” by Jon Galloway, Phil Haack, Brad Wilson and K. Scott Allen. This book is a must read for web developers looking to enhance their MVC expertise with best practices and tips shared from recognized industry experts. This book takes the reader on a 16-chapter long journey towards being a better ASP.NET MVC developer with chapter 16 putting all information covered in practical context by dissecting the implementation of Nuget.org, a real-life open-source, ASP.NET MVC project.  All code samples referenced in this book are conveniently accessible via NuGet, a free, open-source Library package manager that installs as a Visual Studio Extension. Chapters 2, 3 and 4 thoroughly cover MVC’s various components: Controllers “C”, Views “V” and Models “M” respectively. Chapter 5 covers additional extension methods (Helpers) provided to speed and ease the use of common HTML elements such as forms, textboxes, grids, to name a few… Chapter 6 tackles built-in validation while providing examples and use cases on implementing custom validation that plugs into the MVC framework. Chapters 7 thru 13 discusses the latest on Membership, Ajax, Routing, NuGet and the ASP.Net Web API. Chapters 12 (Dependency Injection) and 13 (Unit Testing) demonstrate a big competitive advantage of MVC with its ease of test-ability and plug-ability. Chapters 14 and 15 targets the advanced developer showcasing how to extend MVC to customize and replace every piece in the framework.In conclusion, I strongly recommend Professional ASP.NET MVC 4 as an excellent read for both developers already using MVC as well as those getting started with the framework.   Many thanks to the Wiley/Wrox User Group Program for their support of our West Palm Beach Developers’ Group.  You can access my reviews of books I recently read: Professional ASP.NET Design Patterns Professional WCF 4.0 Inside Windows Communication Foundation Inside Microsoft SQL Server 2008 series

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• Everything has an Interface [closed]

  - by Shane

  Possible Duplicate: Do I need to use an interface when only one class will ever implement it? I am taking over a project where every single real class is implementing an Interface. The vast majority of these interfaces are implemented by a single class that share a similar name and the exact same methods (ex: MyCar and MyCarImpl). Almost no 2 classes in the project implement more than the interface that shares its name. I know the general recommendation is to code to an interface rather than an implementation, but isn't this taking it a bit too far? The system might be more flexible in that it is easier to add a new class that behaves very much like an existing class. However, it is significantly harder to parse through the code and method changes now require 2 edits instead of 1. Personally, I normally only create interfaces when there is a need for multiple classes to have the same behavior. I subscribe to YAGNI, so I don't create something unless I see a real need for it. Am I doing it all wrong or is this project going way overboard?

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• Demantra Implementation Tip Windows and Unix or Linux

  - by user702295

  Hello!  Are you implementing using a third party or consulting resources?   Recently we have seen some cases where customers no longer have a windows installation.  After the initial install and configuration, once the instance has gone live, the windows install is either deleted or most likely no longer with the customer as the same was installed on the implementers' laptop to start with. As a result when support comes back requesting the customer to apply a patch and/or upgrade they do not have a windows installation.  This has started happening after Oracle Demantra gave them the option to configure the engine on Unix.  Workaround: It is advisable that the customer keep their Windows installation intact for further patching and/or upgrade.  It is aslo possible that the implementer had installed Demantra on his Windows box and you do not have access to it any more.  It is possible that with the web and engine on Unix, and the silent installer having downloaded all the executable for Business Modeler, to work on the User's client machine, you may no longer need the windows install. I have not tested the above 

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• Sorting objects before rendering

  - by dreta

  I'm trying to implement a scene graph and in all the articles i've come across there is talk about object sorting. So you'd sort your objects by "material" for example. Now untill i sat down and started implementing it, i kind of took this for granted, because it made sense. But now i'm wondering what does sorting actually change? In my engine, i have a manager for UBOs, i use those to store data that'll be shared between programs, at the moment that only involves time, camera and projection matrices and lights (i'm not worrying about managing which lights affect which objects ATM). Now for each model i have to change the model to world matrix uniform, no sorting is going to change that. So is the jump from changing this matrix to also setting a material for each object that bad? I vaguely remember reading somewhere that each time you change something in the pipeline, it has to get flushed and that can cause performance issues. But for each drawing call i'm setting up a model to world matrix anyway, so what sense does it make to ever be concerned about this? BTW is there any information about whether changing a uniform and calling glBufferSubData is more (or less) expensive.

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• Clean MVC design when there is viewer latency

  - by Tony Suffolk 66

  It isn't clear if this question has already been answered, so apologies in advance if this is a duplicate : I am implementing a game and trying to design around a clean MVC pattern - so my Control plane will implement the rules of the game (but not how the game is displayed), and the View plane implements how the game is displayed, and user iteraction - i.e. what game items or controls the user has activated. The challenge that I have is this : In my game the Control Plane can move game items more or less instaneously (The decision about what item to place where - and some of the initial consequences of that placement are reasonably trivial to calculate), but I want to design the Control Plane so that the View plane can display these movements either instaneously or using movement animations. The other complication is that player interaction must be locked out while those game items are moving (similar to chess - you can't attack an opposing piece as it moves past one of your pieces) So do I : Implement all the logic in the Control Plane asynchronously - and separate the descision making from the actions - so the Control plane decides piece 'A' needs to move to a given place - tells the view plane, and but does not implement the move in data until the view plane informs the control plane that the move/animation is complete. A lot of interlock points between the two layers. Implement all the control plane logic in one place - decisions and movement (keeping track of what moved where), and pass all the movements in one go to the View plane to do with what it will. Control Plane is almost fire and forget here. A hybrid of 1 & 2 - The control plane implements all the moves in a temporary data store - but maintains a second store which reflects what is actually visible to the viewer, based on calls and feedback from the View plane. All 3 are relatively easy to implement (target language is python), but having never done a clean MVC pattern with view latency before - I am not sure which design is best

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• When must I turn my business idea into a formal Company? [closed]

  - by Sony Santos

  I'm a programmer, I have an idea, I know how to implement it, it will be a website, and that site will be my business. My question is very basic: where in timeline must I register my business as an official Company (ie, according Government laws)? Here there are some options to debate or to help answer me: Now - or as soon as I have the idea; When looking for investors (e.g., when a prototype or business plan is ready); When implementing the website; At site's launch; I must launch the website as a personal informal business and, when the business gets success and turns into a more solid and self-running one, only then I must formalize it; It doesn't matter; I can create the company when I want. Nobody talks about that. If I just have an idea, must I run into an office to create a Company? I don't think so. When I'll look for investors, the Company must to pre-exist? Or will the Company be formed with the investor? I'm looking for a generic, country-independent answer, but may the answer for your country can be useful to me. I'm Brazilian, and I believe that the country doesn't matter to this question. (Sorry if this is off-topic, but I coudn't find a batter stackexchange site to ask this.)

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• Data classes: getters and setters or different method design

  - by Frog

  I've been trying to design an interface for a data class I'm writing. This class stores styles for characters, for example whether the character is bold, italic or underlined. But also the font-size and the font-family. So it has different types of member variables. The easiest way to implement this would be to add getters and setters for every member variable, but this just feels wrong to me. It feels way more logical (and more OOP) to call style.format(BOLD, true) instead of style.setBold(true). So to use logical methods insteads of getters/setters. But I am facing two problems while implementing these methods: I would need a big switch statement with all member variables, since you can't access a variable by the contents of a string in C++. Moreover, you can't overload by return type, which means you can't write one getter like style.getFormatting(BOLD) (I know there are some tricks to do this, but these don't allow for parameters, which I would obviously need). However, if I would implement getters and setters, there are also issues. I would have to duplicate quite some code because styles can also have a parent styles, which means the getters have to look not only at the member variables of this style, but also at the variables of the parent styles. Because I wasn't able to figure out how to do this, I decided to ask a question a couple of weeks ago. See Object Oriented Programming: getters/setters or logical names. But in that question I didn't stress it would be just a data object and that I'm not making a text rendering engine, which was the reason one of the people that answered suggested I ask another question while making that clear (because his solution, the decorator pattern, isn't suitable for my problem). So please note that I'm not creating my own text rendering engine, I just use these classes to store data. Because I still haven't been able to find a solution to this problem I'd like to ask this question again: how would you design a styles class like this? And why would you do that? Thanks on forehand!

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• Any good reason open files in text mode?

  - by Tinctorius

  (Almost-)POSIX-compliant operating systems and Windows are known to distinguish between 'binary mode' and 'text mode' file I/O. While the former mode doesn't transform any data between the actual file or stream and the application, the latter 'translates' the contents to some standard format in a platform-specific manner: line endings are transparently translated to '\n' in C, and some platforms (CP/M, DOS and Windows) cut off a file when a byte with value 0x1A is found. These transformations seem a little useless to me. People share files between computers with different operating systems. Text mode would cause some data to be handled differently across some platforms, so when this matters, one would probably use binary mode instead. As an example: while Windows uses the sequence CR LF to end a line in text mode, UNIX text mode will not treat CR as part of the line ending sequence. Applications would have to filter that noise themselves. Older Mac versions only use CR in text mode as line endings, so neither UNIX nor Windows would understand its files. If this matters, a portable application would probably implement the parsing by itself instead of using text mode. Implementing newline interpretation in the parser might also remove some overhead of using text mode, as buffers would need to be rewritten (and possibly resized) before returning to the application, while this may be less efficient than when it would happen in the application instead. So, my question is: is there any good reason to still rely on the host OS to translate line endings and file truncation?

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• Relation between developers and clients

  - by guiman

  Hi everyone, i've been facing a situation at work and i would like to share it with you and tell me: Did you had to do it to? Should a developer be in direct contact wit the client? Or there should be an "adapter" guy that translates client needs in pseudo formal requirements understandable to us? I'm currently working in a small company that its taking care of implementing lots of systems, most of them for goverment institutions, in witch it generally means taking software developted 20 years ago and refurbish them so fit up-to-date needs. The clients generally are very used to them and tend to discourage change (they are in their 50s 60s give or take, so not technologie-friendly in general). As you can imagine, dev-team in most cases starts taking care of relation with clients, generating the documentation needed in this cases (CU usually), assisting to weekly meets to see improvements with clients. As for experience, this is a gold mine for me, because gives a nice perspective on all the aspects of software development, but also some problems rise because, if developers come from mars then client are from venus. So there is a fine gap on the vocabulary/experience/capability-to-interpret-needs that generates an noice in the communication, and some times affecting the final product.

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• How to keep background requests in sequence

  - by Jason Lewis

  I'm faced with implementing interfaces for some rather archaic systems, for handling online deposits to stored value accounts (think campus card accounts for students). Here's my dilemma: stage 1 of the process involves passing the user off to a thrid-party site for the credit card transaction, like old-school PayPal. Step two involves using a proprietary protocol for communicating with a legacy system for conducting the actual deposit. Step two requires that each transaction have a unique sequence number, and that the requests' seqnums are in order. Since we're logging each transaction in Postgres, my first thought was to take a number from a sequence in the DB, guaranteeing uniqueness. But since we're dealing with web requests that might come in near-simultaneously, and since latency with the return from the off-ste payment processor is beyond our control, there's always the chance for a race condition in the order of requests passed back to the proprietary system, and if the seqnums are out of order, the request fails silently (brilliant, right?). I thought about enqueuing the requests in Redis and using Resque workers to process them (single worker, single process, so they are processed in order), but we need to be able to give the user feedback as to whether the transaction was processed successfully, so this seems less feasible to me. I've tried to make this application handle concurrency well (as much as possible for a Ruby on Rails app), but now we're in a situation where we have to interact with a system that is designed to be single process, single threaded, and sequential. If it at least gave an "out of order" error, I could just increment (or take the next value off the sequence), but it's designed to fail silently in the event of ANY error. We are handling timeouts in a way that blocks on I/O, but since the application uses multiple workers (Unicorn), that's no guarantee. Any ideas/suggestions would be appreciated.

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• D3DXMatrixDecompose gives different quaternion than D3DXQuaternionRotationMatrix

  - by Fraser

  In trying to solve this problem, I tracked down the problem to the conversion of the rotation matrix to quaternion. In particular, consider the following matrix: -0.02099178 0.9997436 -0.008475631 0 0.995325 0.02009799 -0.09446743 0 0.09427284 0.01041905 0.9954919 0 0 0 0 1 SlimDX.Quaternion.RotationMatrix (which calls D3DXQuaternionRotationMatrix gives a different answer than SlimDX.Matrix.Decompose (which uses D3DXMatrixDecompose). The answers they give (after being normalized) are: X Y Z W Quaternion.RotationMatrix -0.05244324 0.05137424 0.002209336 0.9972991 Matrix.Decompose 0.6989997 0.7135442 -0.03674842 -0.03006023 Which are totally different (note the signs of X, Z, and W are different). Note that these aren't q/-q (two quaternions that represent the same rotation); they face completely different directions. I've noticed that with matrices for rotations very close to that one (successive frames in the animation) that the Matrix.Decompose version gives a solution that flips around wildly and occasionally goes into the desired position, while the Quaternion.RotationMatrix version gives solutions that are stable but go in the wrong direction. This is only for the right arm in my animation -- for the left arm, both functions give the correct solution, which is the same quaternion within error tolerances. This makes me think that there's some sort of numeric instability or weird stuff with signs going on. I tried implementing this and then this, but both gave me a completely incorrect solution (even for the matricies where the SlimDX ones were working correctly) -- maybe the rows and columns are flipped?

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• Flixel: doesn't light tile up

  - by Arno

  i'm creating a game with flixel, and I want to have a effect when you mouse over a tile, I tried implementing it, and this is what it gives: public class GameState extends FlxState { private var block:EmptyBlock; public function GameState() { } override public function create():void { for (var i:Number = 0; i < 30; i++) { block = new EmptyBlock(i, 20); block.create(); } } override public function update():void { block.update(); super.update(); } } } GameState class and here is the EmptyBlock class: public class EmptyBlock { private var x:int; private var y:int; private var row:FlxRect public function EmptyBlock(x:int, y:int ) { this.x = x; this.y = y; } public function create():void { row = new FlxRect(x, y, 32, 32); trace ("Created block at" + x + y); } public function update():void { if (FlxG.mouse.screenX == row.x) { if (FlxG.mouse.screenY == row.y) { var outline:FlxSprite = new FlxSprite(row.x, row.y).makeGraphic(row.width, row.height, 0x002525); } } } } }

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• Count function on tree structure (non-binary)

  - by Spevy

  I am implementing a tree Data structure in c# based (largely on Dan Vanderboom's Generic implementation). I am now considering approach on handling a Count property which Dan does not implement. The obvious and easy way would be to use a recursive call which Traverses the tree happily adding up nodes (or iteratively traversing the tree with a Queue and counting nodes if you prefer). It just seems expensive. (I also may want to lazy load some of my nodes down the road). I could maintain a count at the root node. All children would traverse up to and/or hold a reference to the root, and update a internally settable count property on changes. This would push the iteration problem to when ever I want to break off a branch or clear all children below a given node. Generally less expensive, and puts the heavy lifting what I think will be less frequently called functions. Seems a little brute force, and that usually means exception cases I haven't thought of yet, or bugs if you prefer. Does anyone have an example of an implementation which keeps a count for an Unbalanced and/or non-binary tree structure rather than counting on the fly? Don't worry about the lazy load, or language. I am sure I can adjust the example to fit my specific needs. EDIT: I am curious about an example, rather than instructions or discussion. I know this is not technically difficult...

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