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• Use Enterprise Manager Cloud Control to monitor OBIEE 11.1.1.7.x Dashboards

  - by Torben Hein -Oracle

  (in via Senthil )  If your OBIEE 11.1.1.7.x is set up in the following way: The OBIEE repository is an Oracle Database and is set up as a data warehouse Usage tracking is enabled in OBIEE. ( For information on how to enable usage tracking in OBIEE, refer to the following link: Setting Up Usage Tracking in Oracle BI 11g ) The OBIEE instance is discovered in EM Cloud Control. ( For information on how to discover an OBIEE instance in Cloud Control, refer to the following link: Discovering Oracle Business Intelligence Instance and Oracle Essbase Targets ) The OBIEE repository is discovered in EM Cloud Control. ( For information on how to discover an Oracle database, refer to the following link: Discovering, Promoting, and Adding Database Targets ) then we've got news for you: KM Article:  OBIEE 11g: How To Diagnose Slowly Performing Dashboards using Enterprise Manager Cloud Control (Doc ID 1668236.1) takes you step by step through monitoring the SQL query performance behind your OBIEE dashboard. This Diagnostic approach ... .. will help you piece together information on BI dashboard performance, e.g. processing time from the different layers of the BI system including the repository. .. should enable you to get to the bottom of slow dashboards by using the wealth of information available in EM Cloud Control on OBIEE and Oracle DB. .. will NOT fix any performance issues on its own, but will help identify bottlenecks while processing dashboard requests. (layout and post: Torben, authorized: Lia)

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• Extreme Optimization – Numerical Algorithm Support

  - by JoshReuben

  Function Delegates Many calculations involve the repeated evaluation of one or more user-supplied functions eg Numerical integration. The EO MathLib provides delegate types for common function signatures and the FunctionFactory class can generate new delegates from existing ones. RealFunction delegate - takes one Double parameter – can encapsulate most of the static methods of the System.Math class, as well as the classes in the Extreme.Mathematics.SpecialFunctions namespace: var sin = new RealFunction(Math.Sin); var result = sin(1); BivariateRealFunction delegate - takes two Double parameters: var atan2 = new BivariateRealFunction (Math.Atan2); var result = atan2(1, 2); TrivariateRealFunction delegate – represents a function takes three Double arguments ParameterizedRealFunction delegate - represents a function taking one Integer and one Double argument that returns a real number. The Pow method implements such a function, but the arguments need order re-arrangement: static double Power(int exponent, double x) { return ElementaryFunctions.Pow(x, exponent); } ... var power = new ParameterizedRealFunction(Power); var result = power(6, 3.2); A ComplexFunction delegate - represents a function that takes an Extreme.Mathematics.DoubleComplex argument and also returns a complex number. MultivariateRealFunction delegate - represents a function that takes an Extreme.Mathematics.LinearAlgebra.Vector argument and returns a real number. MultivariateVectorFunction delegate - represents a function that takes a Vector argument and returns a Vector. FastMultivariateVectorFunction delegate - represents a function that takes an input Vector argument and an output Matrix argument – avoiding object construction  The FunctionFactory class RealFromBivariateRealFunction and RealFromParameterizedRealFunction helper methods - transform BivariateRealFunction or a ParameterizedRealFunction into a RealFunction delegate by fixing one of the arguments, and treating this as a new function of a single argument. var tenthPower = FunctionFactory.RealFromParameterizedRealFunction(power, 10); var result = tenthPower(x); Note: There is no direct way to do this programmatically in C# - in F# you have partial value functions where you supply a subset of the arguments (as a travelling closure) that the function expects. When you omit arguments, F# generates a new function that holds onto/remembers the arguments you passed in and "waits" for the other parameters to be supplied. let sumVals x y = x + y     let sumX = sumVals 10     // Note: no 2nd param supplied.     // sumX is a new function generated from partially applied sumVals.     // ie "sumX is a partial application of sumVals." let sum = sumX 20     // Invokes sumX, passing in expected int (parameter y from original)  val sumVals : int -> int -> int val sumX : (int -> int) val sum : int = 30 RealFunctionsToVectorFunction and RealFunctionsToFastVectorFunction helper methods - combines an array of delegates returning a real number or a vector into vector or matrix functions. The resulting vector function returns a vector whose components are the function values of the delegates in the array. var funcVector = FunctionFactory.RealFunctionsToVectorFunction(     new MultivariateRealFunction(myFunc1),     new MultivariateRealFunction(myFunc2));  The IterativeAlgorithm<T> abstract base class Iterative algorithms are common in numerical computing - a method is executed repeatedly until a certain condition is reached, approximating the result of a calculation with increasing accuracy until a certain threshold is reached. If the desired accuracy is achieved, the algorithm is said to converge. This base class is derived by many classes in the Extreme.Mathematics.EquationSolvers and Extreme.Mathematics.Optimization namespaces, as well as the ManagedIterativeAlgorithm class which contains a driver method that manages the iteration process.  The ConvergenceTest abstract base class This class is used to specify algorithm Termination , convergence and results - calculates an estimate for the error, and signals termination of the algorithm when the error is below a specified tolerance. Termination Criteria - specify the success condition as the difference between some quantity and its actual value is within a certain tolerance – 2 ways: absolute error - difference between the result and the actual value. relative error is the difference between the result and the actual value relative to the size of the result. Tolerance property - specify trade-off between accuracy and execution time. The lower the tolerance, the longer it will take for the algorithm to obtain a result within that tolerance. Most algorithms in the EO NumLib have a default value of MachineConstants.SqrtEpsilon - gives slightly less than 8 digits of accuracy. ConvergenceCriterion property - specify under what condition the algorithm is assumed to converge. Using the ConvergenceCriterion enum: WithinAbsoluteTolerance / WithinRelativeTolerance / WithinAnyTolerance / NumberOfIterations Active property - selectively ignore certain convergence tests Error property - returns the estimated error after a run MaxIterations / MaxEvaluations properties - Other Termination Criteria - If the algorithm cannot achieve the desired accuracy, the algorithm still has to end – according to an absolute boundary. Status property - indicates how the algorithm terminated - the AlgorithmStatus enum values:NoResult / Busy / Converged (ended normally - The desired accuracy has been achieved) / IterationLimitExceeded / EvaluationLimitExceeded / RoundOffError / BadFunction / Divergent / ConvergedToFalseSolution. After the iteration terminates, the Status should be inspected to verify that the algorithm terminated normally. Alternatively, you can set the ThrowExceptionOnFailure to true. Result property - returns the result of the algorithm. This property contains the best available estimate, even if the desired accuracy was not obtained. IterationsNeeded / EvaluationsNeeded properties - returns the number of iterations required to obtain the result, number of function evaluations.  Concrete Types of Convergence Test classes SimpleConvergenceTest class - test if a value is close to zero or very small compared to another value. VectorConvergenceTest class - test convergence of vectors. This class has two additional properties. The Norm property specifies which norm is to be used when calculating the size of the vector - the VectorConvergenceNorm enum values: EuclidianNorm / Maximum / SumOfAbsoluteValues. The ErrorMeasure property specifies how the error is to be measured – VectorConvergenceErrorMeasure enum values: Norm / Componentwise ConvergenceTestCollection class - represent a combination of tests. The Quantifier property is a ConvergenceTestQuantifier enum that specifies how the tests in the collection are to be combined: Any / All  The AlgorithmHelper Class inherits from IterativeAlgorithm<T> and exposes two methods for convergence testing. IsValueWithinTolerance<T> method - determines whether a value is close to another value to within an algorithm's requested tolerance. IsIntervalWithinTolerance<T> method - determines whether an interval is within an algorithm's requested tolerance.

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• How does TDD address interaction between objects?

  - by Gigi

  TDD proponents claim that it results in better design and decoupled objects. I can understand that writing tests first enforces the use of things like dependency injection, resulting in loosely coupled objects. However, TDD is based on unit tests - which test individual methods and not the integration between objects. And yet, TDD expects design to evolve from the tests themselves. So how can TDD possibly result in a better design at the integration (i.e. inter-object) level when the granularity it addresses is finer than that (individual methods)?

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• Is it bad to have an "Obsessive Refactoring Disorder"?

  - by Rachel

  I was reading this question and realized that could almost be me. I am fairly OCD about refactoring someone else's code when I see that I can improve it. For example, if the code contains duplicate methods to do the same thing with nothing more than a single parameter changing, I feel I have to remove all the copy/paste methods and replace it with one generic one. Is this bad? Should I try and stop? I try not to refactor unless I can actually make improvements to the code performance or readability, or if the person who did the code isn't following our standard naming conventions (I hate expecting a variable to be local because of the naming standard, only to discover it is a global variable which has been incorrectly named)

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• How do I overcome paralysis by analysis when coding?

  - by LuxuryMode

  When I start a new project, I often times immediately start thinking about the details of implementation. "Where am I gonna put the DataBaseHandler? How should I use it? Should classes that want to use it extend from some Abstract superclass..? Should I an interface? What level of abstraction am I going to use in my class that contains methods for sending requests and parsing data?" I end up stalling for a long time because I want to code for extensibility and reusability. But I feel it almost impossible to get past thinking about how to implement perfectly. And then, if I try to just say "screw it, just get it done!", I hit a brick wall pretty quickly because my code isn't organized, I mixed levels of abstractions, etc. What are some techniques/methods you have for launching into a new project while also setting up a logical/modular structure that will scale well?

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• AABB > AABB collision response?

  - by Levi

  I'm really confused about how to fix this in 3d? I want it so that I can slide along cubes but without getting caught if there's 2 adjacent cubes. I've gotten it so that I can do x collision, with sliding, and y, and z, but I can't do them together, probably because I don't know how to resolve it correctly. e.g. [] [] []^ []O [] O is the player, ^ is the direction the player is moving, with the methods which I was trying I would get stuck between the cubes because the z axis was responding and kicking me out :/. I don't know how to resolve this in all 3 direction, like how would I go about telling which direction I have to resolve in. My previous methods involved me checking 4 points in a axis aligned square around the player, I was checking if these points where inside the cubes and if they where fixing my position, but I couldn't get it working correctly. Help is appreciated. edit: pretend all the blocks are touching.

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• What defines good developer culture? [closed]

  - by Sven

  We are a team of 6 people developing applications for mobile devices (Android & iOS). In our company, which consists of many teams responsible for "classic" software development, business intelligence, virtualization, hardware, etc., we are kind of a small startup because we were the first to use agile methods like Scrum and we are open to new technologies and methods. Also our team is pretty young with me being the oldest with 30 years. We would like to further raise productivity and motivation and thus are currently collecting points which make up a good developer/hacker culture and which may be improved in our team/company. This can be points that we can either improve ourselves or have to pass on to management. I would like to know what in your opinion defines good, modern developer culture? What does developer culture consists of? For example is it clearly defined career opportunities geeky office benefits like trips to extraordinary conferences like WWDC or Google I/O ...

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• Lan, vpn on Amazon EC2, how to?

  The problem is as follows: I have 2 windows2003 server instances running on the cloud. 1) How can I create a local area network from these 2 instances? 2) Assuming that I want to create a VPN network from these 2 instances, how do I do that? (I'm not very good in networking, therefor the above problem description might be incomplete or not very clear.) A detailed answer or clarification would be praised and appreciated! What I tried: 1) Setting up OpenVPN, but I got lost in the process. 2) Creating a VPN from windows2003 server in the following manner: on instance a): set up a dhcp server; set up an "accept income vpn" connection; with the followin tcp ip settings: obtain an ip from the dhcp server; on instance b): created a new vpn connection, tried to connect to intance A, using the instance A static IP but error 806 was thrown, something relate to a GRE protocol.

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• Auto update for application hosted on multiple servers on cloud

  - by mots_g

  I'm working on an application which will run on multiple Amazon EC2 instances. I wish to incorporate auto update feature for my application. The updater should update all the Ec2 instances. Also, there is a central server which governs the creation/termination of EC2 instances as per load. The central server creates a EC2 new instance from a pre-configured custom AMI (custom image which has our application pre-installed). Also, once there is an update, the pre-configured AMI needs to be updated too else it would create new instances which are not updated. Should the central server notify all the ec2 instances for an update and then the instances update themselves?Or should the application on Ec2 instance have a check for periodically updating themselves? Also how should the Amazon custom AMI be updated? Should a new instance be created from it, updated and then a new AMI be re-created and then new images be created from this AMI? What is the best way to incorporate an auto update feature for this architecture? The central server is written in Java and the application running on the cloud is written in C++. Is there a good framework available that can be used for this architecture? Please let me know on what I could be missing in the design and how it would help me to have a nice, extensible and fail safe auto update architecture. Thanks

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• Amazon EC2 migration from one region to the other

  - by Gnanam

  I'm using the following Amazon EC2 resources in the US East (Virginia) region: 1 Running Instance 1 Elastic IP 2 EBS Volumes 100 EBS Snapshots 1 Key Pair 2 Security Groups 5 My Own AMIs (customized based on my application stack) My instance is based on Linux distribution (CentOS) and my AMIs are S3-backed. Both EBS volumes are mounted on this running instance. We're planning to migrate our deployment to US-West region. Because Amazon EC2 resources are not shared across regions, my questions are: What are all the factors that I need to consider in advance? What are all the recommended & different ways of migrating each EC2 resources from one region to the other? Are there any hidden risks involved during and/or after the migration? Experts ideas/suggestions/recommendations on this are highly appreciated.

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• Need advise on choosing aws EC2

  - by Mayank

  I'm planning to host a website where in the first phase I would target 30,000 users. It is in php and runs on Apache server. I'm assuming 8,000 users can be online in worst case scenario and 1000 of them will be uploading photographs. A photograph will be resized to around 1MB at client side and one HTTP request is uploading only one photograph. My plan: 2 Small EC2 instances to run Apache httpd 2 Small EC2 instances to DB (Postgresql). I to write data and other its read replica. EBS volumes for DBs Last, Amazon S3 for uploaded photographs. My question here Is Small EC2 instance more than what I require. I mean should I go for micro Is 8000 simultaneous user a right no. (to decide what EC2 instance to choose) for a new website Or should I go for Small instance so to make it capable of spikes

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• Immutable Method in Java

  - by Chris Okyen

  In Java, there is the final keyword in lieu of the const keyword in C and C++. In the latter languages there are mutable and immutable methods such as stated in the answer by Johannes Schaub - litb to the question How many and which are the uses of “const” in C++? Use const to tell others methods won't change the logical state of this object. struct SmartPtr { int getCopies() const { return mCopiesMade; } }ptr1; ... int var = ptr.getCopies(); // returns mCopiesMade and is specified that to not modify objects state. How is this performed in Java?

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• Does anyone actually use the /// comment blocks?

  - by Rachel

  Someone once said we should prefix all our methods with the /// <summary> comment blocks (C#) and I am wondering if that is true or not. I started to use them and found they annoyed me quite a bit, so stopped using them except for libraries and static methods. They're bulky and I'm always forgetting to update them. Do you recommend using them? Why? EDIT: I normally use // comments all the time, it's just the /// <summary> blocks I was wondering about

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• C# String.format extension method

  - by Paul Roe

  With the addtion of Extension methods to C# we've seen a lot of them crop up in our group. One debate revolves around extension methods like this one: public static class StringExt { /// <summary> /// Shortcut for string.Format. /// </summary> /// <param name="str"></param> /// <param name="args"></param> /// <returns></returns> public static string Format(this string str, params object[] args) { if (str == null) return null; return string.Format(str, args); } } Does this extension method break any programming best practices that you can name? Would you use it anyway, if not why? If I renamed the function to "F" but left the xml comments would that be epic fail or just a wonderful savings of keystrokes?

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• Direct3d - Code structure

  - by marcg11

  I'm learning directx in a master's degree and they taught us to have a GraphicsLayer class which is the one connecting with the direct3d library. That way this class is completly independent from the other classes (my game classes), meaning changing the renderer to OpenGL wouldn't require much effort but only changing the graphicLayer. This classe has it's LoadAssets, Paint methods, but I have a question, they told us to load all the assets inside this class. This means all these methods will be in the loadAssets method: D3DXCreateTextureFromFileEx(g_pD3DDevice,"tiles.png",0,0,1,0,D3DFMT_UNKNOWN,D3DPOOL_DEFAULT,D3DX_FILTER_NONE,D3DX_FILTER_NONE,NULL,NULL,NULL,&texTiles); // And more resources to load //... texTiles as you see is a LPDIRECT3DTEXTURE9 instance which is declared in the graphicLayer.h. So my question is, how do you manage all the resources? Do I have to declare in the .h all my game textures even if I'm not using them? How would you load only those resources there are in a scene and draw them in a code-strucured way?

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• Increase the size of a memory mapped file

  - by sandun dhammika

  I am maintaning a memory mapped file to store my tree like datastructure. When I'm updating the datastructure ,I got this problem. The file is limited on it's size and can't be too long or too small. I have a methods like void mapfile_insert_record(RECORD* /* record*/); void mapfile_modify_record(RECORD* /* record*/); Both operations could lead to exceed the space which is free on memory file. How do I overcome this? What strategy I should use. calculate whether it requires to exceed the file as a pre-condition on both methods. Dynamically exceed it , for a example manage a timer and constantly polling file for it's free avaliable size and then automatically extend it. Any ideas or patterns to overcome this problem?

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• Receive emails on Amazon EC2 Server

  - by Kartik

  I just got started with an EC2 instance and got my mail sending limit removed, allowing me to send emails from my instance. But due to lack of experience, I have no clue on how to enable receiving emails send to me on that server. The instance has an elastic IP and I have a domain name with an A record pointing to that IP. I cant seem to find better documentation on what steps need to be taken so if someone sends an email to [email protected] it either actually receives it or simply forwards it to my personal email. I know that it involves using postfix but cant find a guide to properly configure it after the installation. Thanks

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• Techniques for getting off the ground in any language

  - by AndyBursh

  When I start learning a new language, I have a couple of simple implementations that I like to complete to familiarise myself with the language. Currently, I write: Fibonacci and/or factorial to get the hang of writing and calling methods, and basic recursion Djikstras shortest path (with a node type) to get to grips with making classes (or whatever the language equivalent is) with methods and properties, and also using them in slightly more complex code. I was wondering: does anybody else have any techniques or tools they like to use when getting off the ground in a new language? I'm always looking for new things to add to my "start-up routine".

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• Immutable Method Java

  - by Chris Okyen

  In Java, there is the final keyword in lieu of the const keyword in c and c++. In the latter languages their is mutable and immutable methods such as stated in one answer by Johannes Schaub - litb the question how-many-and-which-are-the-uses-of-const-in-ce Use const to tell others methods won't change the logical state of this object. struct SmartPtr { int getCopies() const { return mCopiesMade; } }ptr1; ... int var = ptr.getCopies(); // returns mCopiesMade and is specified that to not modify objects state. How is this performed in Java?

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• Jazz up your web forms using jQuery animation effects

  - by bipinjoshi

  In this part I cover how to add jazz to your web forms using jQuery effects. jQuery provides a set of methods that allow you to create animations in your web pages. Collectively these methods are called as Effects. The effects they render include fading in and out, sliding in and out, changing opacity of elements, hiding and showing elements and so on. You can, of course, define custom animations. In this part we will use these effects to develop a tooltip, master-detail listing and progress indicator.http://www.bipinjoshi.net/articles/9b1f4a81-ae07-4859-8ff2-067e5887adbd.aspx   

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• Why is testing MVC Views frowned upon?

  - by Peter Bernier

  I'm currently setting the groundwork for an ASP.Net MVC application and I'm looking into what sort of unit-tests I should be prepared to write. I've seen in multiple places people essentially saying 'don't bother testing your views, there's no logic and it's trivial and will be covered by an integration test'. I don't understand how this has become the accepted wisdom. Integration tests serve an entirely different purpose than unit tests. If I break something, I don't want to know a half-hour later when my integration tests break, I want to know immediately. Sample Scenario : Lets say we're dealing with a standard CRUD app with a Customer entity. The customer has a name and an address. At each level of testing, I want to verify that the Customer retrieval logic gets both the name and the address properly. To unit-test the repository, I write an integration test to hit the database. To unit-test the business rules, I mock out the repository, feed the business rules appropriate data, and verify my expected results are returned. What I'd like to do : To unit-test the UI, I mock out the business rules, setup my expected customer instance, render the view, and verify that the view contains the appropriate values for the instance I specified. What I'm stuck doing : To unit-test the repository, I write an integration test, setup an appropriate login, create the required data in the database, open a browser, navigate to the customer, and verify the resulting page contains the appropriate values for the instance I specified. I realize that there is overlap between the two scenarios discussed above, but the key difference it time and effort required to setup and execute the tests. If I (or another dev) removes the address field from the view, I don't want to wait for the integration test to discover this. I want is discovered and flagged in a unit-test that gets multiple times daily. I get the feeling that I'm just not grasping some key concept. Can someone explain why wanting immediate test feedback on the validity of an MVC view is a bad thing? (or if not bad, then not the expected way to get said feedback)

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• Basis of definitions

  - by Yttrill

  Let us suppose we have a set of functions which characterise something: in the OO world methods characterising a type. In mathematics these are propositions and we have two kinds: axioms and lemmas. Axioms are assumptions, lemmas are easily derived from them. In C++ axioms are pure virtual functions. Here's the problem: there's more than one way to axiomatise a system. Given a set of propositions or methods, a subset of the propositions which is necessary and sufficient to derive all the others is called a basis. So too, for methods or functions, we have a desired set which must be defined, and typically every one has one or more definitions in terms of the others, and we require the programmer to provide instance definitions which are sufficient to allow all the others to be defined, and, if there is an overspecification, then it is consistent. Let me give an example (in Felix, Haskell code would be similar): class Eq[t] { virtual fun ==(x:t,y:t):bool => eq(x,y); virtual fun eq(x:t, y:t)=> x == y; virtual fun != (x:t,y:t):bool => not (x == y); axiom reflex(x:t): x == x; axiom sym(x:t, y:t): (x == y) == (y == x); axiom trans(x:t, y:t, z:t): implies(x == y and y == z, x == z); } Here it is clear: the programmer must define either == or eq or both. If both are defined, the definitions must be equivalent. Failing to define one doesn't cause a compiler error, it causes an infinite loop at run time. Defining both inequivalently doesn't cause an error either, it is just inconsistent. Note the axioms specified constrain the semantics of any definition. Given a definition of == either directly or via a definition of eq, then != is defined automatically, although the programmer might replace the default with something more efficient, clearly such an overspecification has to be consistent. Please note, == could also be defined in terms of !=, but we didn't do that. A characterisation of a partial or total order is more complex. It is much more demanding since there is a combinatorial explosion of possible bases. There is an reason to desire overspecification: performance. There also another reason: choice and convenience. So here, there are several questions: one is how to check semantics are obeyed and I am not looking for an answer here (way too hard!). The other question is: How can we specify, and check, that an instance provides at least a basis? And a much harder question: how can we provide several default definitions which depend on the basis chosen?

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• Checking is sides of cubes are solid

  - by Christian Frantz

  In relation to this question: http://gamedev.stackexchange.com/a/28524/31664 And a question I asked earlier: Creating a DrawableGameComponent And also because my internet is too slow to get on chat. I'm wondering how to check if the sides of a cube are solid. I've created 12 methods, each one creating indices and vertices for sides of a cube. Now when I use these methods, the cube creates how it should. All 6 sides show up and its like I didnt change a thing. How can use if statements to check if the side of a cube is solid? The pseudocode from the question above shows this: if(!isSolidAt(x+1,y,z)) verticesToDraw += AddXPlusFace(x,y,z) But in my case is would be: if(!sideIsSolid) SetUpFrontFaceIndices(); My method simply takes these index and vertex values and adds them to a list indicesToDraw and verticesToDraw, as shown in the answer above

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• UML Diagrams of Multi-Threaded Applications

  - by PersonalNexus

  For single-threaded applications I like to use class diagrams to get an overview of the architecture of that application. This type of diagram, however, hasn’t been very helpful when trying to understand heavily multi-threaded/concurrent applications, for instance because different instances of a class "live" on different threads (meaning accessing an instance is save only from the one thread it lives on). Consequently, associations between classes don’t necessarily mean that I can call methods on those objects, but instead I have to make that call on the target object's thread. Most literature I have dug up on the topic such as Designing Concurrent, Distributed, and Real-Time Applications with UML by Hassan Gomaa had some nice ideas, such as drawing thread boundaries into object diagrams, but overall seemed a bit too academic and wordy to be really useful. I don’t want to use these diagrams as a high-level view of the problem domain, but rather as a detailed description of my classes/objects, their interactions and the limitations due to thread-boundaries I mentioned above. I would therefore like to know: What types of diagrams have you found to be most helpful in understanding multi-threaded applications? Are there any extensions to classic UML that take into account the peculiarities of multi-threaded applications, e.g. through annotations illustrating that some objects might live in a certain thread while others have no thread-affinity; some fields of an object may be read from any thread, but written to only from one; some methods are synchronous and return a result while others are asynchronous that get requests queued up and return results for instance via a callback on a different thread.

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• SceneManagers as systems in entity system or as a core class used by a system?

  - by Hatoru Hansou

  It seems entity systems are really popular here. Links posted by other users convinced me of the power of such system and I decided to try it. (Well, that and my original code getting messy) In my project, I originally had a SceneManager class that maintained needed logic and structures to organize the scene (QuadTree, 2D game). Before rendering I call selectRect() and pass the x,y of the camera and the width and height of the screen and then obtain a minimized list containing only visible entities ordered from back to front. Now with Systems, originally in my first attempt my Render system required to get added all entities it should handle. This may sound like the correct approach but I realized this was not efficient. Trying to optimize It I reused the SceneManager class internally in the Renderer system, but then I realized I needed methods such as selectRect() in others systems too (AI principally) and make the SceneManager accessible globally again. Currently I converted SceneManager to a system, and ended up with the following interface (only relevant methods): /// Base system interface class System { public: virtual void tick (double delta_time) = 0; // (methods to add and remove entities) }; typedef std::vector<Entity*> EntitiesVector; /// Specialized system interface to allow query the scene class SceneManager: public System { public: virtual EntitiesVector& cull () = 0; /// Sets the entity to be used as the camera and replaces previous ones. virtual void setCamera (Entity* entity) = 0; }; class SceneRenderer // Not a system { vitual void render (EntitiesVector& entities) = 0; }; Also I could not guess how to convert renderers to systems. My game separates logic updates from screen updates, my main class have a tick() method and a render() method that may not be called the same times. In my first attempt renderers were systems but they was saved in a separated manager, updated only in render() and not in tick() like all other systems. I realized that was silly and simply created a SceneRenderer interface and give up about converting them to systems, but that may be for another question. Then... something does not feel right, isn't it? If I understood correctly a system should not depend on another or even count with another system exposing an specific interface. Each system should care only about its entities, or nodes (as optimization, so they have direct references to relevant components without having to constantly call the component() or getComponent() method of the entity).

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