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  • How to verify the Liskov substitution principle in an inheritance hierarchy?

    - by Songo
    Inspired by this answer: Liskov Substitution Principle requires that Preconditions cannot be strengthened in a subtype. Postconditions cannot be weakened in a subtype. Invariants of the supertype must be preserved in a subtype. History constraint (the "history rule"). Objects are regarded as being modifiable only through their methods (encapsulation). Since subtypes may introduce methods that are not present in the supertype, the introduction of these methods may allow state changes in the subtype that are not permissible in the supertype. The history constraint prohibits this. I was hoping if someone would post a class hierarchy that violates these 4 points and how to solve them accordingly. I'm looking for an elaborate explanation for educational purposes on how to identify each of the 4 points in the hierarchy and the best way to fix it. Note: I was hoping to post a code sample for people to work on, but the question itself is about how to identify the faulty hierarchies :)

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  • Implementing invisible bones

    - by DeadMG
    I suddenly have the feeling that I have absolutely no idea how to implement invisible objects/bones. Right now, I use hardware instancing to store the world matrix of every bone in a vertex buffer, and then send them all to the pipeline. But when dealing with frustrum culling, or having them set to invisible by my simulation for other reasons, means that some of them will be randomly invisible. Does this mean I effectively need to re-fill the buffer from scratch every frame with only the visible unit's matrices? This seems to me like it would involve a lot of wasted bandwidth.

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  • What alternatives exist of how an agent can follow the path calculated by a path-finding algorithm?

    - by momboco
    What alternatives exist of how an agent can follow the path calculated by a path-finding algorithm? I've seen that the most easy form is go to one point and when the agent has reached this point, discard it and go to the next point. I think that this approach has problems when the game has physics with dynamic objects that can block the travel between point A and point B, then the agent is taken from his original trayectory and sometimes go to the last destiny point is not the most natural behavior. In the literature always I have read that the path is only a suggestion of where the agent has to go, but I don't know how this suggested path must be followed. Thanks.

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  • What happened this type of naming convention?

    - by Smith
    I have read so many docs about naming conventions, most recommending both Pascal and Camel naming conventions. Well, I agree to this, its ok. This might not be pleasing to some, but I am just trying to get you opinion why you name you objects and classes in a certain way. What happened to this type of naming conventions, or why are they bad? I want to name a struct, and i prefix it with struct. My reason, so that in IntelliSense, I see all the struct in one place, and anywhere I see the struct prefix, I know it's a struct: structPerson structPosition anothe example is the enum, although I may not prefix it with "enum", but maybe with "enm": enmFruits enmSex again my reason is so that in IntelliSense, I see all my enums in one place. Because, .NET has so many built in data structures, I think this helps me do less searching. Please I used .NET in this example, but I welcome language agnostic answers.

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  • What do you do when your naming convention clashes with your language?

    - by Jon Purdy
    Okay, this is one of those little things that always bugged me. I typically don't abbreviate identifiers, and the only time I use a short identifier (e.g., i) is for a tight loop. So it irritates me when I'm working in C++ and I have a variable that needs to be named operator or class and I have to work around it or use an abbreviation, because it ends up sticking out. Caveat: this may happen to me disproportionately often because I work a lot in programming language design, where domain objects may mirror concepts in the host language and inadvertently cause clashes. How would you deal with this? Abbreviate? (op) Misspell? (klass) Something else? (operator_)

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  • How do you navigate and refactor code written in a dynamic language?

    - by Philippe Beaudoin
    I love that writing Python, Ruby or Javascript requires so little boilerplate. I love simple functional constructs. I love the clean and simple syntax. However, there are three things I'm really bad at when developing a large software in a dynamic language: Navigating the code Identifying the interfaces of the objects I'm using Refactoring efficiently I have been trying simple editors (i.e. Vim) as well as IDE (Eclipse + PyDev) but in both cases I feel like I have to commit a lot more to memory and/or to constantly "grep" and read through the code to identify the interfaces. As for refactoring, for example changing method names, it becomes hugely dependent on the quality of my unit tests. And if I try to isolate my unit tests by "cutting them off" the rest of the application, then there is no guarantee that my stub's interface stays up to date with the object I'm stubbing. I'm sure there are workarounds for these problems. How do you work efficiently in Python, Ruby or Javascript?

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  • Document Link about Database Features on Exadata

    - by Bandari Huang
    DBFS on Exadata Exadata MAA Best Practices Series - Using DBFS on Exadata  (Internal Only) Oracle® DatabaseSecureFiles and Large Objects Developer's Guide 11g Release 2 (11.2) E18294-01 Configuring a Database for DBFS on Oracle Database Machine [ID 1191144.1] Configuring DBFS on Oracle Database Machine [ID 1054431.1] Oracle Sun Database Machine Setup/Configuration Best Practices [ID 1274318.1] - Verify DBFS Instance Database Initialization Parameters    DBRM on Exadata Exadata MAA Best Practices Series - Benefits and use cases with Resource Manager, Instance Caging, IORM  (Internal Only) Oracle® Database Administrator's Guide 11g Release 2 (11.2) E25494-02    

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  • Windows 7 Service Pack 1 is Released: But Should You Install It?

    - by The Geek
    Microsoft has just released the final version of Service Pack 1 for Windows 7, but should you drop everything and go through the process of installing it? Where can you get it? We’ve got the answers for you. If you’ve never installed a service pack before, it’s just a big collection of fixes and changes for your operating system, bundled into a big fat download to make it more convenient if you reinstall—if you’ve kept Windows updated, it should have most of the fixes already installed through Windows Update Latest Features How-To Geek ETC How To Make Hundreds of Complex Photo Edits in Seconds With Photoshop Actions How to Enable User-Specific Wireless Networks in Windows 7 How to Use Google Chrome as Your Default PDF Reader (the Easy Way) How To Remove People and Objects From Photographs In Photoshop Ask How-To Geek: How Can I Monitor My Bandwidth Usage? Internet Explorer 9 RC Now Available: Here’s the Most Interesting New Stuff Never Call Me at Work [Humorous Star Wars Video] Add an Image Properties Listing to the Context Menu in Chrome and Iron Add an Easy to View Notification Badge to Tabs in Firefox SpellBook Parks Bookmarklets in Chrome’s Context Menu Drag2Up Brings Multi-Source Drag and Drop Uploading to Firefox Enchanted Swing in the Forest Wallpaper

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  • vector collision on polygon in 3d space detection/testing?

    - by LRFLEW
    In the 3d fps in java I'm working on, I need a bullet to be fired and to tell if it hit someone. All visual objects in the game are defined through OpenGL, so the object it can be colliding with can be any drawable polygon (although they will most likely be triangles and rectangles anyways). The bullet is not an object, but will be treated as a vector that instantaneously moves all the way across the map (like the snipper riffle in Halo). What's the best way to detect/test collisions with the polygon and the vector. I have access to OpenCL, however I have absolutely no experience with it. I am very early in the developmental stage, so if you think there's a better way of going about this, feel free to tell me (I barley have a player model to collide with anyways, so I'm flexible with it). Thanks

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  • How are components properly instantiated and used in XNA 4.0?

    - by Christopher Horenstein
    I am creating a simple input component to hold on to actions and key states, and a short history of the last ten or so states. The idea is that everything that is interested in input will ask this component for the latest input, and I am wondering where I should create it. I am also wondering how I should create components that are specific to my game objects - I envision them as variables, but then how do their Update/Draw methods get called? What I'm trying to ask is, what are the best practices for adding components to the proper collections? Right now I've added my input component in the main Game class that XNA creates when everything is first initialized, saying something along the lines of this.Components.Add(new InputComponent(this)), which looks a little odd to me, and I'd still want to hang onto that reference so I can ask it things. An answer to my input component's dilemma is great, but also I'm guessing there is a right way to do this in general in XNA.

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  • How to render a retro-like pixel graphics from 3d models?

    - by momijigari
    I was wondering if there's a possibility to render a retro-pixel-like graphics from 3d model in real time? I'm talking about the Starfarer-like graphics. I know it's hand drawn, and it's 2d. But if I need a 3d objects with the same aesthetics? I'm currently working with Flash. But I don't need any ready-solutions, I just want to understand the principle from any other platform if there is one. So if anybody met anything like this I would appreciate your help. (If it's not possible to do in real time, I could at least pre-render a sequence of sprites. It would be much better than creating hundreds of hand-drawn ones)

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  • What causes the iOS OpenGLES driver to allocate extra memory?

    - by Martin Linklater
    I'm trying to optimize the memory usage of our iOS game and I'm puzzled about when/why the iOS GLES driver allocates extra memory at runtime... When I run our game through Instruments with the OpenGL ES Driver instrument the gartUsedBytes value can fluctuate quite wildly. We preload all our textures and build the buffer objects up front, so it's not the game engine requesting extra memory from GL. Currently we are manually requesting around 50MB of GL memory, yet the gartUsedBytes value sits at around 90MB most of the time, peaking at 125MB from time to time. It seems to be linked to what you are rendering that frame - our PVS only submits VBO's for visible meshes. Can anyone shed some light on what the driver is doing in the background ? Like I said earlier, all our game engine allocations are done on level load, so in theory there shouldn't be any fluctuation on GL memory usage while the level is running. Thanks.

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  • Could you give me an example of how to attach an object in Deleted state – I keep getting an exception [migrated]

    - by carewithl
    From MSDN : An object in the Deleted state can only be attached when the ObjectStateManager is already tracking the relationship instance. Could you give me an example of how to attach an object in the Deleted state. I tried the following and got "System.InvalidOperationException: The object being attached is in an added or deleted state. Relationships cannot be created for objects in this state". var contact = context.Contacts.First(); Console.WriteLine(contact.Addresses.Count()); // 2 var address = contact.Addresses.First(); context.Addresses.DeleteObject(address); contact.Addresses.Attach(address); // InvalidOperationException thank you

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  • Breaking up a large PHP object used to abstract the database. Best practices?

    - by John Kershaw
    Two years ago it was thought a single object with functions such as $database->get_user_from_id($ID) would be a good idea. The functions return objects (not arrays), and the front-end code never worries about the database. This was great, until we started growing the database. There's now 30+ tables, and around 150 functions in the database object. It's getting impractical and unmanageable and I'm going to be breaking it up. What is a good solution to this problem? The project is large, so there's a limit to the extent I can change things. My current plan is to extend the current object for each table, then have the database object contain these. So, the above example would turn into (assume "user" is a table) $database->user->get_user_from_id($ID). Instead of one large file, we would have a file for every table.

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  • Data Source Security Part 5

    - by Steve Felts
    If you read through the first four parts of this series on data source security, you should be an expert on this focus area.  There is one more small topic to cover related to WebLogic Resource permissions.  After that comes the test, I mean example, to see with a real set of configuration parameters what the results are with some concrete values. WebLogic Resource Permissions All of the discussion so far has been about database credentials that are (eventually) used on the database side.  WLS has resource credentials to control what WLS users are allowed to access JDBC resources.  These can be defined on the Policies tab on the Security tab associated with the data source.  There are four permissions: “reserve” (get a new connection), “admin”, “shrink”, and reset (plus the all-inclusive “ALL”); we will focus on “reserve” here because we are talking about getting connections.  By default, JDBC resource permissions are completely open – anyone can do anything.  As soon as you add one policy for a permission, then all other users are restricted.  For example, if I add a policy so that “weblogic” can reserve a connection, then all other users will fail to reserve connections unless they are also explicitly added.  The validation is done for WLS user credentials only, not database user credentials.  Configuration of resources in general is described at “Create policies for resource instances” http://docs.oracle.com/cd/E24329_01/apirefs.1211/e24401/taskhelp/security/CreatePoliciesForResourceInstances.html.  This feature can be very useful to restrict what code and users can get to your database. There are the three use cases: API Use database credentials User for permission checking getConnection() True or false Current WLS user getConnection(user,password) False User/password from API getConnection(user,password) True Current WLS user If a simple getConnection() is used or database credentials are enabled, the current user that is authenticated to the WLS system is checked. If database credentials are not enabled, then the user and password on the API are used. Example The following is an actual example of the interactions between identity-based-connection-pooling-enabled, oracle-proxy-session, and use-database-credentials. On the database side, the following objects are configured.- Database users scott; jdbcqa; jdbcqa3- Permission for proxy: alter user jdbcqa3 grant connect through jdbcqa;- Permission for proxy: alter user jdbcqa grant connect through jdbcqa; The following WebLogic Data Source objects are configured.- Users weblogic, wluser- Credential mapping “weblogic” to “scott”- Credential mapping "wluser" to "jdbcqa3"- Data source descriptor configured with user “jdbcqa”- All tests are run with Set Client ID set to true (more about that below).- All tests are run with oracle-proxy-session set to false (more about that below). The test program:- Runs in servlet- Authenticates to WLS as user “weblogic” Use DB Credentials Identity based getConnection(scott,***) getConnection(weblogic,***) getConnection(jdbcqa3,***) getConnection()  true  true Identity scottClient weblogicProxy null weblogic fails - not a db user User jdbcqa3Client weblogicProxy null Default user jdbcqaClient weblogicProxy null  false  true scott fails - not a WLS user User scottClient scottProxy null jdbcqa3 fails - not a WLS user User scottClient scottProxy null  true  false Proxy for scott fails weblogic fails - not a db user User jdbcqa3Client weblogicProxy jdbcqa Default user jdbcqaClient weblogicProxy null  false  false scott fails - not a WLS user Default user jdbcqaClient scottProxy null jdbcqa3 fails - not a WLS user Default user jdbcqaClient scottProxy null If Set Client ID is set to false, all cases would have Client set to null. If this was not an Oracle thin driver, the one case with the non-null Proxy in the above table would throw an exception because proxy session is only supported, implicitly or explicitly, with the Oracle thin driver. When oracle-proxy-session is set to true, the only cases that will pass (with a proxy of "jdbcqa") are the following.1. Setting use-database-credentials to true and doing getConnection(jdbcqa3,…) or getConnection().2. Setting use-database-credentials to false and doing getConnection(wluser, …) or getConnection(). Summary There are many options to choose from for data source security.  Considerations include the number and volatility of WLS and Database users, the granularity of data access, the depth of the security identity (property on the connection or a real user), performance, coordination of various components in the software stack, and driver capabilities.  Now that you have the big picture (remember that table in part 1), you can make a more informed choice.

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  • Why is JavaScript not used for classical application development (compiled software)?

    - by Jose Faeti
    During my years of web development with JavaScript, I come to the conclusion that it's an incredible powerful language, and you can do amazing things with it. It offers a rich set of features, like: Dynamic typing First-class functions Nested functions Closures Functions as methods Functions as Object constructors Prototype-based Objects-based (almost everything is an object) Regex Array and Object literals It seems to me that almost everything can be achieved with this kind of language, you can also emulate OO programming, since it provides great freedom and many different coding styles. With more software-oriented custom functionalities (I/O, FileSystem, Input devices, etc.) I think it will be great to develop applications with. Though, as far as I know, it's only used in web development or in existing softwares as a scripting language only. Only recently, maybe thanks to the V8 Engine, it's been used more for other kind of tasks (see node.js for example). Why until now it's only be relegated only to web development? What is keeping it away from software development?

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  • Recordings Available - Features & Functions Forms Module

    - by MHundal
    ETPM provides robust Forms functionality that allows implementations to configure Registration & Tax Forms, configure Form Rules and process the Forms.  The Forms Definition allows for defining the Form Sections and Form Lines.  The Forms Generator uses the Forms Definition details to create the necessary Business Objects, Application Security and User Interfaces to allow interaction with the Forms.  Form Rules are used for validation of the Form Line details and creating entities in the system (creating taxpayers, accounts, financial transactions, etc...). The following recordings provide an overview of the Forms Definition Process, Form Rules and other important concepts part of the Forms Module. Forms Module Overview:  https://oracletalk.webex.com/oracletalk/ldr.php?AT=pb&SP=MC&rID=66851417&rKey=7de22df4978e7974 Forms Configuration Overview:  https://oracletalk.webex.com/oracletalk/ldr.php?AT=pb&SP=MC&rID=66964342&rKey=ea564cfd701bb32d Form Rules Overview:  https://oracletalk.webex.com/oracletalk/ldr.php?AT=pb&SP=MC&rID=66966652&rKey=2e02c1e28e058d70  

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  • How should I access frame buttons from a controller in an MVC approach?

    - by Loris
    I'm developing an italian card game using the mvc pattern. I have the class GameFrame that contains the view. The user's card are buttons (JButton objects). I have 3 controllers: GameController: to control the game in general. Contains the game loop. HumanPlayerController: to control the user input ComputerPlayerController: contains the AI of the computer PlayerController: is an interface with the makeTurn() method. It's implemented by HumanP.C. and ComputerP.C. HumanPlayerController implements ActionListener too. But what is the right way to access to the GameFrame buttons? I need it for understand which card was chosen. GameFrame and HumanPlayerController are in different packages. Should i make the JButtons public?

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  • Should actors in a game be responsible for drawing themselves?

    - by alex
    I am very new to game development, but not to programming. I am (again) playing around with a Pong type game using JavaScript's canvas element. I have created a Paddle object which has the following properties... width height x y colour I also have a Pong object which has properties such as... width height backgroundColour draw(). The draw() method currently is resetting the canvas and that is where a question came up. Should the Paddle object have a draw() method responsible for its drawing, or should the draw() of the Pong object be responsible for drawing its actors (I assume that is the correct term, please correct me if I'm incorrect). I figured that it would be advantagous for the Paddle to draw itself, as I instantiate two objects, Player and Enemy. If it were not in the Pong's draw(), I'd need to write similar code twice. What is the best practice here? Thanks.

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  • What is a good practice for 2D scene graph partitioning for culling?

    - by DevilWithin
    I need to know an efficient way to cull the scene graph objects, to render exclusively the ones in the view, and as fast as possible. I am thinking of doing it the following way, having in each object a local boundingbox which holds the object bounds, and a global boundingbox which holds the bounds of the object and all children. When a camera is moved, the render list is updated by traversing the global boundingboxes. When only the object is being moved, it tries to enlarge or shrink the ancestors global boundingboxes, and in the end updating or not the renderlist. What do you think of this approach? Do you think it will provide a fast and efficient culling? Also, because the render list is a contiguous list, it could accelerate the rendering, right? Any further tips for a 2D scene graphs are highly appreciated!

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  • Grid based collision - How many cells?

    - by Fibericon
    The game I'm creating is a bullet hell game, so there can be quite a few objects on the screen at any given time. It probably maxes out at about 40 enemies and 200 or so bullets. That being said, I'm splitting up the playing field into a grid for my collision checking. Right now, it's only 8 cells. How many would be optimal? I'm worried that if I use too many, I'll be wasting CPU power. My main concern is processing power, to make the game run smoothly. RAM is not a big concern for me.

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  • Difference between Sound and Music

    - by Southpaw Hare
    What are the key differences between the Sound and Music classes in Pygame? What are the limitations of each? In what situation would one use one or the other? Is there a benefit to using them in an unintuitive way such as using Sound objects to play music files or visa-versa? Are there specifically issues with channel limitations, and do one or both have the potential to be dropped from their channel unreliably? What are the risks of playing music as a Sound?

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  • Dynamic navigation mesh changes

    - by Nairou
    I'm currently trying to convert from grids to navigation meshes for pathfinding, since grids are either too coarse for accurate navigation, or too fine to be useful for object tracking. While my map is fairly static, and the navigation mesh could be created in advance, this is somewhat of a tower defense game, where objects can be placed to block paths, so I need a way to recalculate portions of the navigation mesh to allow pathing around them. Is there any existing documentation on good ways to do this? I'm still very new to navigation meshes, so the prospect of modifying them to cut or fill holes sounds daunting.

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  • In OpenGl ES 2, should I allocate multiple transformation matrices?

    - by thm4ter
    In OpenGl ES 2, should I declare just one transformation matrix, and share it across all objects or should I declare a transformation matrix in each object that needs it? for clarification... something like this: public class someclass{ public static float[16] transMatrix = new float[16]; ... public static void translate(int x, int y){ //do translation here } } public class someotherclass{ ... void draw(GL10 unused){ someclass.translate(10,10); //draw } } verses something like this: public class obj1{ public static float[16] transMatrix = new float[16]; ... void draw(GL10 unused){ //translate //draw } } public class obj2{ public static float[16] transMatrix = new float[16]; ... void draw(GL10 unused){ //translate //draw } }

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  • What is an acceptable GC frequency for a SlimDX/Windows/.NET game?

    - by Rei Miyasaka
    I understand that the Windows GC is much better than the Xbox/WP7 GC, being that it's generational and multithreaded -- so I don't need to worry quite as much about avoiding memory allocation. SlimDX even has some unavoidable functions that generate some amount of garbage (specifically, MapSubresource creates DataBoxes), yet people don't seem to be too upset about it. I'd like to use some functional paradigms to write my code too, which also means creating objects like closures and monads. I know premature optimization isn't a good thing, but are there rules of thumb or metrics that I can follow to know whether I need to cut down on allocations? Is, say, one gen 0 GC per frame too much? One thing that has me stumped is object promotions. Gen 0 GCs will supposedly finish within a millisecond or two, but if I'm understanding correctly, it's the gen 1 and 2 promotions that start to hurt. I'm not too sure how I can predict/prevent these.

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