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  • How to correctly create a virtual file system?

    - by Paul
    A task in my homework assignment asks me to create a virtual file system, mount it, and perform some operations on it. I am supposed to create a file of 10 MB whose bits are all set to 0, format it as ext3 and mount it. This is how I've done that: dd if=/dev/zero of=~/filesyst bs=10485760 count=1 sudo mkfs.ext3 ~/filesyst sudo mount –o loop ~/filesyst /media/fuse Even though I've used /dev/sero, the file i still full of gibberish characters (mostly at-signs). The permissions on /media/fuse are drw-rw-rw- (which are alright), but the permissions on the files inside it are something like this: d????????? ? ? ? ? ? lost+found -????????? ? ? ? ? ? secret_bin Where have I gone wrong?

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  • Do you leverage the benefits of the open-closed principle?

    - by Kaleb Pederson
    The open-closed principle (OCP) states that an object should be open for extension but closed for modification. I believe I understand it and use it in conjunction with SRP to create classes that do only one thing. And, I try to create many small methods that make it possible to extract out all the behavior controls into methods that may be extended or overridden in some subclass. Thus, I end up with classes that have many extension points, be it through: dependency injection and composition, events, delegation, etc. Consider the following a simple, extendable class: class PaycheckCalculator { // ... protected decimal GetOvertimeFactor() { return 2.0M; } } Now say, for example, that the OvertimeFactor changes to 1.5. Since the above class was designed to be extended, I can easily subclass and return a different OvertimeFactor. But... despite the class being designed for extension and adhering to OCP, I'll modify the single method in question, rather than subclassing and overridding the method in question and then re-wiring my objects in my IoC container. As a result I've violated part of what OCP attempts to accomplish. It feels like I'm just being lazy because the above is a bit easier. Am I misunderstanding OCP? Should I really be doing something different? Do you leverage the benefits of OCP differently? Update: based on the answers it looks like this contrived example is a poor one for a number of different reasons. The main intent of the example was to demonstrate that the class was designed to be extended by providing methods that when overridden would alter the behavior of public methods without the need for changing internal or private code. Still, I definitely misunderstood OCP.

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  • How can you predict the time it will take for two processes in two different machines in a cluster to communicate?

    - by Dokkat
    I am trying to develop a computing application which needs a lot of memory (500gb). Buying a single machine for that is overly expensive. I can, though, buy ~100 small instances on Digital Ocean or similar, divide the memory in blocks and use TCP to emulate shared memory between the instances. Now, my question is: how can I measure/predict the time it will take for two processes in two different machines like that to share information, in comparison to IPC and shared memory? Are there rules of thumb? I don't want exact values, but knowing more or less how much faster one is would be very helpful in visualising the feasibility of this approach.

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  • Alternatives to multiple sprite batches for achieving 2D particle system depth

    - by Ergwun
    In my 2D XNA game, I render all my sprites with a single sprite batch using SpriteSortMode.BackToFront and BlendState.AlphaBlend. I'm adding a particle system based on the App Hub particles sample. Since this uses SpriteSortMode.Deferred and BlendState.Additive, I will need to have two SpriteBatch.Begin / SpriteBatch.End pairs: one for 'regular' sprites, and one for particles. In my top-down shooter, If I want to have explosions appear under planes, but above the ground, then I believe I will have to have three Begin/End pairs, first to draw everything under the explosions, then to draw the explosions, then to draw everything above the explosions. If I want to have particle effects at multiple different depths, then I'm going to need even more Begin/Endpairs. This is all easy to code, but I'm wondering if there is an alternative way to handle this?

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  • How should I organise classes for a space simulator?

    - by Peteyslatts
    I have pretty much taught myself everything I know about programming, so while I know how to teach myself (books, internet and reading API's), I'm finding that there hasn't been a whole lot in the way of good programming. I am finishing up learning the basics of XNA and I want to create a space simulator to test my knowledge. This isn't a full scale simulator, but just something that covers everything I learned. It's also going to be modular so I can build on it, after I get the basics down. One of the early features I want to implement is AI. And I want to take this into account as I'm designing my classes so I can minimize rewriting code. So my question: How should I design ship classes so that both the player and AI can use them? The only idea I have so far is: Create a ship class that contains stats, models, textures, collision data etc. The player and AI would then have the data for position, rotation, health, etc and would base their status off of the ship stats.

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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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  • What programming concept is used in Nokia Lumina City Lens application [closed]

    - by gowri
    I am totally impressed about the Nokia City Lens application. How does the Nokia Lumia City Lens app work? Nokia Lumia City Lens app detects shops, restaurants, etc. by scanning the visual environment. But how can it detect shops or anything by only scanning visual information? Because we need a 360 degree view to detect a location. Because we can't simply match visual information and get that data. The visuals will change proportionally with distance and angle. So how does this app match the location and retrieve the information? Can anyone explain the concept What technology or algorithm is used in this app?

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  • Document Management System

    - by rjayavrp
    Is there any Document Management System in Ubuntu? I tried Alfresco, RavenDB, Owl, Document Manager. Alfresco, RavenDB are heavy. More than my requirements. Owl having source issues. Document Manager im trying to install. Should keep data on the same machine as I am looking for more of internal purpose. Should allow to upload Zip files as well. If it extracts Zip it will be a great + Should allow to send email to preconfigured email addresses Should allow to upload data of size around 100MB at one go Should maintain history of documents also deleted documents Should allow role based document access. Should be Free :) It should not do any spoofing on data. Documents are confidential. Please share your knowledge. Thanks.

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  • How to track many in-game statistics

    - by Alex Schearer
    I am looking to track many in-game events, e.g. the score of each move, how many moves are taken, what types of moves, etc. A lot of stats can simply be tracked with a counter. In some cases I need to aggregate data in order to calculate the value (e.g. most common move). How are you tracking in-game stats for your games? How do you avoid creating a class with tens or hundreds of fields? How do you avoid littering the code with tracking invocations? How do you abstract the aggregate data so as to avoid rewriting it for each scenario?

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  • Where to start building a BaaS

    - by Wesley
    I'm building a Cloud Platform, and the next phase of design involves building an extensible BaaS back end. (see http://youtu.be/lNi-05-PyEw) The reason I think we can attempt this, is there are dozens of these kinds of extensible back end data proxy's popping up almost daily at this point, which tells me the enabling technology is there to build one from scratch in a few months. I'd like to start in the right area: What kind of Dev background should I look for? What kind of tech stack should I build on? What kind of costs can I expect in terms of man-hours, etc... I know there isn't one right answer here, but I think this is the right sub to post this in, and credit will go towards to most constructive answer.

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  • "The system is running in low graphics mode", unable to connect to the Internet

    - by Blah
    When I try to log onto Ubuntu, I get a notice that reads: The system is running in low graphics mode. I searched for a solution and there are a slew of answers. However, many of them seem to suggest reinstalling different things. After pressing Ctrl+Alt+F1 and getting to a terminal, I attempt commands like sudo apt-get install example. Upon doing so I get notices that say things such as could not resolve host which I am assuming means I'm not connected to the Internet. Since I can not connect to the Internet, none of these responses are helpful to me. What can I do?

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  • How should I load level data in java?

    - by Matthew G.
    I'm setting up my engine for a certain action/arcade game to have a set of commands that would look something like this. Set landscape to grass Create rocks at ... Create player at X, Y Set goal to "Get to point X Y" Spawn enemy at X, Y I'd then have each object knowing what it has to do, and acting on its own. I've been thinking about how to store this data. External data files could be parsed by a level class, and certain objects can be spawned through that. I could also create a base level class and extend it for each level, but that'd create a large amount of classes. Another idea is to have one level parser class, but have a case for each level. This would be extremely silly and bulky, but I mention it because I found that I did this at 2 AM last night. I'm finally getting why I have to plan out my inheritances, though. RIP project. I might be completely missing another option.

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  • 2D scene graph not transforming relative to parent

    - by Dr.Denis McCracleJizz
    I am currently in the process of coding my own 2D Scene graph, which is basically a port of flash's render engine. The problem I have right now is my rendering doesn't seem to be working properly. This code creates the localTransform property for each DisplayObject. Matrix m_transform = Matrix.CreateRotationZ(rotation) * Matrix.CreateScale(scaleX, scaleY, 1) * Matrix.CreateTranslation(new Vector3(x, y, z)); This is my render code. float dRotation; Vector2 dPosition, dScale; Matrix transform; transform = this.localTransform; if (parent != null) transform = localTransform * parent.localTransform; DecomposeMatrix(ref transform, out dPosition, out dRotation, out dScale); spriteBatch.Draw(this.texture, dPosition, null, Color.White, dRotation, new Vector2(originX, originY), dScale, SpriteEffects.None, 0.0f); Here is the result when I try to add the Stage then to the stage a First DisplayObjectContainer and then a second one. It may look fine but the problem lies in the fact that I add a first DisplayObjectContainer at (400,400) and the second one within it (that's the smallest one) at position (0,0). So he should be right over its parent but he gets render within the parent at the same position the parent has (400, 400) for some reason. It's just as if I double the parent's localMatrix and then render the second cat there. This is the code i use to loop through every childs. base.Draw(spriteBatch); foreach (DisplayObject childs in _childs) { childs.Draw(spriteBatch); }

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  • internal error message pops up after each time system is rebooted

    - by Biju
    I had installed ubuntu 12.04 using wubi. But each time i boot the system an internal error message pops up. As show below:- Executable path /usr/share/apport/apport-gpu-error-intel.py Package xserver-xorg-video-intel 2:2.17.0-1ubuntu4 Problem Type crash Apportversion 2.0.1-0ubuntu7 and so on.. I had earlier upgraded to ubuntu 12.04 from ubuntu 11.10. And encountered the same issue. Hence i uninstalled the OS and reinstalled using wubi. I had posted the same query in ubuntu.com/support (Question Number: 195525) But couldnt find a solution. I am using dell inspiron with intel pentium. Need ur help in resolving this issue. thanking u, Biju

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  • How to build a .Net app which runs on desktop and as a Windows Service

    - by Mike
    Ok, I hope this is not too much confusing (with my poor English). I want to build a small .Net 4.0 app which monitors several other applications on a Windows Server OR on a regular Windows PC. It will have a WPF GUI with a variety of graphical controls. The app will be used in the following scenarios: If installed on a PC it should run as a “normal” single Windows desktop app If installed on a Server, it should run as a Windows Service. To use/manage the app it must have the same WPF GUI as in scenario 1 and the GUI should be run on the Server or on a remote PC At the moment I consider to write the application logic and connect it to the WPF GUI using a self-hosted WCF Data Service IN BOTH SCENARIOS. Since I’m not a pro developer I suppose it’s possible that I've missed something ;-) Will this work? Are there other/better solutions? Any answer or comment is highly appreciated.

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  • System that splits passwords across two servers

    - by Burning the Codeigniter
    I stumbled upon this news article on BBC, RSA splits passwords in two to foil hackers' attacks tl;dr - a (randomized) password is split in half and is stored across two separate servers, to foil hackers that gained access to either server upon a security breach. Now the main question is, how would this kind of system would be made... codespeaking, for PHP which I commonly develop on my web applications, the database password is normally stored in a configuration file, i.e. config.php with the username and password, in that case it is understandable that the passwords can be stolen if the security was compromised. However when splitting and sending the other half to the other server, how would this go on when making a communication to the other server (keeping in mind with PHP) since the other server password would be stored in a configuration file, wouldn't it? In terms of security is to keep the other server password away from the main one, just exactly how would the main server communicate, without exposing any other password, apart from the first server. This certainly makes me think...

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  • Query something and return the reason if nothing has been found

    - by Daniel Hilgarth
    Assume I have a Query - as in CQS that is supposed to return a single value. Let's assume that the case that no value is found is not exceptional, so no exception will be thrown in this case. Instead, null is returned. However, if no value has been found, I need to act according to the reason why no value has been found. Assuming that the Query knows the reason, how would I communicate it to the caller of the Query? A simple solution would be not return the value directly but a container object that contains the value and the reason: public class QueryResult { public TValue Value { get; private set; } public TReason ReasonForNoValue { get; private set; } } But that feels clumsy, because if a value is found, ReasonForNoValue makes no sense and if no value has been found, Value makes no sense. What other options do I have to communicate the reason? What do you think of one event per reason? For reference: This is going to be implemented in C#.

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  • How to manage many mobile device users at server side?

    - by Rami
    I built a social Android application in which users can see other users around them by GPS location. At the beginning thing went well as I had low number of users, but now that I have increasing number of users (about 1500 +100 every day) it has revealed a major problem in my design. In my Google App Engine servlet I have static HashMap that holds all the users profiles objects, currently 1500 and this number will increase as more users register. Why I'm doing it? Every user that requests for the users around him compares his GPS with other users and checks if they are in his 10km radius. This happens every five minutes on average. Consequently, I can't get the users from db every time because GAE read/write operation quota will tear me apart. The problem with this design is? As the number of users increases, the Hashmap turns to null every 4-6 hours, I think that this time is getting shorter, but I'm not sure. I'm fixing this by reloading the users from the db every time I detect that it becomes null, but this causes DOS to my users for 30 sec, so I'm looking for better solution. I'm guessing that it happens because the size of the hashmap. Am I right? I have been advised to use a spatial database, but that means that I can't work with GAE any more and it means that I need to build my big server all over again and lose my existing DB. Is there something I can do with the existing tools? Thanks.

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  • Store VOD wmi data in a database directly or use CQRS?

    - by JD01
    I need to collect Video on demand bandwidth usage every few minutes (or maybe ever few seconds) and store this in a database so users can produce graphs on bandwidth usage over a period of time (few hours, days, weeks or even possibly months). So the sort of data that will be stored will be the number of users watching videos, current server bandwidth (Mb/s), multicast bit rate etc. I am wondering whether using CQRS would be a good approach with Event sourcing as I can then rebuild my objects to create different projections (I.e. different graphs/reports etc) but then again it seems like I am introducing complexity which might not be needed. Or would it be best to just put the data directly in a database (currently using PostGres) directly and query off that? Having thought about it, my table is a form of audit log anyway, so I don't think I need event sourcing at all. Any thoughts?

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

    - by BornToCode
    Background: I need to build a desktop application with some operations (CRUD and more) (=winforms), I need to make another application which will re-use some of the functions of the main application (=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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  • Technologies stack to create soccer game vizualization on web page [on hold]

    - by Lambrusco
    I want to create soccer game vizualization. What technologies will be best to create such one for web page? On input I have two teams with players. I have theory about their movements, the movement of the ball on field and so on. I just want to vizualize their movements. What will be the best technology stack? I mean programming languages (C++, Ruby, Java, PHP) and vizualization ways (Flash, HTML5, JS)

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  • How Byte loading/storing is implemented By the CPU?

    - by AlexDan
    I know that in 32bit machine, cpu read from memory 32bits at a time. since the registers in this case is 32bit in size too, I can understand how this works. What I don't understand is how the cpu implement load instructions of 1 byte. does it load the whole word where the single byte is located to the register, then perform some kind of "byte shifting", or does the cpu can load a single byte, in this case when does the byte masking happen, is it until the byte got loaded in the register, or it happen when byte is send through the data bus ? P.S. The cpu Im using is MIPS, the instructions Im talking about are: lb or lbu

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  • As a software architect, am I supposed to focus that much on analysing the logs and fixing other's bugs?

    - by Hatem81
    Since my graduation (late 2005) I was working for the same company as a c++ software engineer. A year ago I was promoted as a software architect but I have found myself involved more and more in qualification and fixing bugs, level 2 support. 50% of my time spent in Notepad++ analysing the software logs and trying to figure out what went wrong. 30% fixing other's bugs and the remaining (if any) reviewing developers spaghetti code. I started hating this product and thinking about an exit strategy out of this company. What do you think I can do in this situation? do you other software architect still fixing bugs in the code?

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  • Locomotion-system with irregular IK

    - by htaunay
    Im having some trouble with locomtions (Unity3D asset) IK feet placement. I wouldn't call it "very bad", but it definitely isn't as smooth as the Locomotion System Examples. The strangest behavior (that is probably linked to the problem) are the rendered foot markers that "guess" where the characters next step will be. In the demo, they are smooth and stable. However, in my project, they keep flickering, as if Locomotion changed its "guess" every frame, and sometimes, the automatic defined step is too close to the previous step, or sometimes, too distant, creating a very irregular pattern. The configuration is (apparently)Identical to the human example in the demo, so I guessing the problem is my model and/or animation. Problem is, I can't figure out was it is =S Has anyone experienced the same problem? I uploaded a video of the bug to help interpreting the issue (excuse the HORRIBLE quality, I was in a hurry).

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  • Object-based content management system

    - by Adam Maras
    I remember hearing within the last year or two about a content management system either being released or developed that was centralized around product/item information. I'm aware that there are several CMSes that have this capability, but this particular one was built specifically for that task. Also, I remember it winning some sort of award or recognition for upcoming software products. However, I can't for the life of me remember what this CMS was called or who was developing it. Does anyone know what package I'm talking about?

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