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  • DDD and filtering

    - by tikhop
    I am developing an app in ddd maner. So I have a complex domain model. Suppose I have a Fare object and Airline. Each Airline should contain several or much more Fares. My UI should represent Model (only small part of complex model) as a list of Airline, when the user select the Airline, I must show the list of Fares. User can filtering the Fares (by travel time, cost, etc.). What is the appropriate place for filtering Fares and Airlines? I am assuming that I should do it in ViewModel. Like: My domain model has wrapped with Service Layer - UI works with ViewModel - ViewModel obtain data from Service Layer filtering it and create DTO objects for UI. Or I'm wrong?

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  • Writing Large Portions Of Code Then Debugging?

    - by The Floating Brain
    Lately I have been writing a game engine, and I have been writing a lot of "foundation stuff" (standard interfaces, modules, a message system ect.), but I have noticed a pattern, a lot of the stuff is interdependent and I can not debug until everything is done, hence I do not debug for about 3 to 5 hours at a time. I am wondering if this is an acceptable practice for this part of the project, and if not, if anyone can give me some advice? -----Update-----: I downloaded some code metrics tools, and my programs cyclomatic complexity is 1.52 which as I understand it is good, and should correlate to high cohesion, if I am wrong please correct me/

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  • Interesting sessions/tips from RMOUG

    - by jean-pierre.dijcks
    One of the sessions I was at at last week's RMOUG was a session on Temp Tablespace Groups. I had a look because I had no experience with this and it seemed to help with parallel processing and the allocation/usage of temp. You can read the excellent write-up at Kellyn Pedersen's blog - who did the session and all the work - here. So for all of those who may be seeing lot's of waits like enq: TS - Contention when you are doing hash joins and sorts, do have a look at the above blog post. I also had the chance to listen in at Stewart Bryson's session on Restartability (he had 3 R-s) where he gave very useful tips about how to deal with your data warehouse loads. Questions like archive log mode - should I or should I not were well covered. Flashback archives, also nice to hear about. Very nice talk, very interesting. Unfortunately he hasn't blogged about it yes, so no pointers to that one. Got to see a couple of other interesting sessions, and as conferences go got to meet some interesting Oracle folks from the region. As usual RMOUG was useful and fun. Off to the drawing boards to design next year's session!

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  • Exposing warnings\errors from data objects (that are also list returned)

    - by Oren Schwartz
    I'm exposing Data objects via service oriented assembly (which on future usages might become a WCF service). The data object is tree designed, as well as formed from allot of properties.Moreover, some services return one objects, others retrieve a list of them (thus disables throwing exceptions). I now want to expose data flow warnings and wondering what's the best way to do it having to things to consider: (1) seperation (2) ease of access. On the one hand, i want the UI team to be able to access a fields warnings (or errors) without having them mapping the field names to an external source but on the other hand, i don't want the warnings "hanged" on the object itself (as i don't see it a correct design). I tought of creating a new type of wrapper for each field, that'll expose events and they'll have to register the one's they care about (but totally not sure) I'll be happy to hear your thoughts. Could you please direct me to a respectful design pattern ? what dp will do best here ? Thank you very much!

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  • How to refactor and improve this XNA mouse input code?

    - by Andrew Price
    Currently I have something like this: public bool IsLeftMouseButtonDown() { return currentMouseState.LeftButton == ButtonState.Pressed && previousMouseSate.LeftButton == ButtonState.Pressed; } public bool IsLeftMouseButtonPressed() { return currentMouseState.LeftButton == ButtonState.Pressed && previousMouseSate.LeftButton == ButtonState.Released; } public bool IsLeftMouseButtonUp() { return currentMouseState.LeftButton == ButtonState.Released && previousMouseSate.LeftButton == ButtonState.Released; } public bool IsLeftMouseButtonReleased() { return currentMouseState.LeftButton == ButtonState.Released && previousMouseSate.LeftButton == ButtonState.Pressed; } This is fine. In fact, I kind of like it. However, I'd hate to have to repeat this same code five times (for right, middle, X1, X2). Is there any way to pass in the button I want to the function so I could have something like this? public bool IsMouseButtonDown(MouseButton button) { return currentMouseState.IsPressed(button) && previousMouseState.IsPressed(button); } public bool IsMouseButtonPressed(MouseButton button) { return currentMouseState.IsPressed(button) && !previousMouseState.IsPressed(button); } public bool IsMouseButtonUp(MouseButton button) { return !currentMouseState.IsPressed(button) && previousMouseState.IsPressed(button); } public bool IsMouseButtonReleased(MouseButton button) { return !currentMouseState.IsPressed(button) && previousMouseState.IsPressed(button); } I suppose I could create some custom enumeration and switch through it in each function, but I'd like to first see if there is a built-in solution or a better way.. Thanks!

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  • A way to return multiple return values from a method: put method inside class representing return value. Is it a good design?

    - by john smith optional
    I need to return 2 values from a method. My approach is as follows: create an inner class with 2 fields that will be used to keep those 2 values put the method inside that class instantiate the class and call the method. The only thing that will be changed in the method is that in the end it will assign those 2 values to the fields of the instance. Then I can address those values by referencing to the fields of that object. Is it a good design and why?

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  • What's the best algorithm for... [closed]

    - by Paska
    Hi programmers! Today come out a little problem. I have an array of coordinates (latitude and longitude) maded in this way: [0] = "45.01234,9.12345" [1] = "46.11111,9.12345" [2] = "47.22222,9.98765" [...] etc In a loop, convert these coordinates in meters (UTM northing / UTM easting) and after that i convert these coords in pixel (X / Y) on screen (the output device is an iphone) to draw a route line on a custom map. [0] = "512335.00000,502333.666666" [...] etc The returning pixel are passed to a method that draw a line on screen (simulating a route calculation). [0] = "20,30" [1] = "21,31" [2] = "25,40" [...] etc As coordinate (lat/lon) are too many, i need to truncate lat/lon array eliminating the values that doesn't fill in the map bound (the visible part of map on screen). Map bounds are 2 couple of coords lat/lon, upper left and lower right. Now, what is the best way to loop on this array (NOT SORTED) and check if a value is or not in bound and after remove the value that is outside? To return a clean array that contains only the coords visible on screen? Note: the coords array is a very big array. 4000/5000 couple of items. This is a method that should be looped every drag or zoom. Anyone have an idea to optimize search and controls in this array? many thanks, A

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  • Design pattern for logging changes in parent/child objects saved to database

    - by andrew
    I’ve got a 2 database tables in parent/child relationship as one-many. I’ve got three classes representing the data in these two tables: Parent Class { Public int ID {get; set;} .. other properties } Child Class { Public int ID {get;set;} Public int ParentID {get; set;} .. other properties } TogetherClass { Public Parent Parent; Public List<Child> ChildList; } Lastly I’ve got a client and server application – I’m in control of both ends so can make changes to both programs as I need to. Client makes a request for ParentID and receives a Together Class for the matching parent, and all of the child records. The client app may make changes to the children – add new children, remove or modify existing ones. Client app then sends the Together Class back to the server app. Server app needs to update the parent and child records in the database. In addition I would like to be able to log the changes – I’m doing this by having 2 separate tables one for Parent, one for child; each containing the same columns as the original plus date time modified, by whom and a list of the changes. I’m unsure as to the best approach to detect the changes in records – new records, records to be deleted, records with no fields changed, records with some fields changed. I figure I need to read the parent & children records and compare those to the ones in the Together Class. Strategy A: If Together class’s child record has an ID of say 0, that indicates a new record; insert. Any deleted child records are no longer in the Together Class; see if any of the comparison child records are not found in the Together class and delete if not found (Compare using ID). Check each child record for changes and if changed log. Strategy B: Make a new Updated TogetherClass UpdatedClass { Public Parent Parent {get; set} Public List<Child> ListNewChild {get;set;} Public List<Child> DeletedChild {get;set;} Public List<Child> ExistingChild {get;set;} // used for no changes and modified rows } And then process as per the list. The reason why I’m asking for ideas is that both of these solutions don’t seem optimal to me and I suspect this problem has been solved already – some kind of design pattern ? I am aware of one potential problem in this general approach – that where Client App A requests a record; App B requests same record; A then saves changes; B then saves changes which may overwrite changes A made. This is a separate locking issue which I’ll raise a separate question for if I’ve got trouble implementing. The actual implementation is c#, SQL Server and WCF between client and server - sharing a library containing the class implementations. Apologies if this is a duplicate post – I tried searching various terms without finding a match though.

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  • Google Programmers

    - by seth
    As a soon-to-be software engineer, I have studied some languages during my time in college. I can name C, C++, Java, Scheme, Ruby, PHP, for example. However, one of the main principles in my college (recognized by many as the best in my country) is to teach us how to learn for ourselves and how to search the web when we have a doubt. This leads to a proactive attitude, when I need something, I go get it and this has worked so far for me. Recently, I started wondering though, how much development would I be able to do without internet access. The answer bugged me quite a bit. I know the concept of the languages, mostly I know what to do, but I was amazed by how "slow" things were without having the google to help in the development. The problem was mostly related to specific syntax but it was not without some effort that i solved some of the SPOJ problems in C++. Is this normal? Should I be worried and try to change something in my programming behaviour? UPDATE: I'll give a concrete example. Reading and writing to a file in java. I have done this about a dozen times in my life, yet every time I need to do it, I end up googling "read file java" and refreshing my memory. I completely understand the code, i fully understand what it does. But I am sure, that without google, it would take me a few tries to read and write correctly (if I had to sit in front of the screen with a blank page and write this without consulting any source whatsoever).

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  • beginner - best way to do a 'Confirm' page? [closed]

    - by W_P
    I am a beginning web app developer, wondering about the best way to implement a "Confirm Page" upon form submission. I have heard that it's best for the script that a form POSTs to to be implemented by handling the POST data and then redirecting to another page, so the user isn't directly viewing the page that was POSTed to. My question is about the best way to implement a "Confirm before data save" page. Do I Have my form POST to a script, which marshals the data, puts in a GET, and redirects to the confirm page, which unmarshals and displays the data in another form, where the user can then either confirm (which causes another POST to a script that actually saves the data) or deny (which causes the user to be redirected back to the original form, with their input added)? Have my form POST directly to the confirm page, which is displayed to the user and then, like #1, gives the user the option to confirm or deny? Have my form GET the confirm page, which then does the expected behavior? I feel like there is a common-sense answer to this question that I am just not getting.

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  • How should I make progress further as a programmer?

    - by mushfiq
    Hello, I have just left my college after doing graduation in computer engineering,during my college life I tried to do some freelancing in local market.I succeeded in the last year and earned some small amounts based on joomla,wordpress and visual basic based job.I had some small projects on php,mysql also. After finishing my undergrad life,I sat for an written test for post of python programmer and luckily I got the job and is working there(Its a small software firm do most of the task in python).Day by day I have gained some experience with core python. Meanwhile an USA based web service firm called me for the interview and after finishing three steps(oral+mini coding project+final oral)they selected me(i was wondered!).And I am going to join their with in few days.There I have to work in python(based on Django framework,I know only basic of this framework). My problem is when I started to work with python simultaneously I worked in Odesk as a wordpress,joomla,drupal,php developer. Now a days I am feeling that I am getting "Jack of all trades master of none". My current situation is i am familiar with several popular web technologies but not an expert.I want to make myself skilled. How should I organize myself to be a skilled web programmer?

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  • Changing the Game: Why Oracle is in the IT Operations Management Business

    - by DanKoloski
    v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri","sans-serif"; mso-bidi-font-family:"Times New Roman";} Next week, in Orlando, is the annual Gartner IT Operations Management Summit. Oracle is a premier sponsor of this annual event, which brings together IT executives for several days of high level talks about the state of operational management of enterprise IT. This year, Sushil Kumar, VP Product Strategy and Business Development for Oracle’s Systems & Applications Management, will be presenting on the transformation in IT Operations required to support enterprise cloud computing. IT Operations transformation is an important subject, because year after year, we hear essentially the same refrain – large enterprises spend an average of two-thirds (67%!) of their IT resources (budget, energy, time, people, etc.) on running the business, with far too little left over to spend on growing and transforming the business (which is what the business actually needs and wants). In the thirtieth year of the distributed computing revolution (give or take, depending on how you count it), it’s amazing that we have still not moved the needle on the single biggest component of enterprise IT resource utilization. Oracle is in the IT Operations Management business because when management is engineered together with the technology under management, the resulting efficiency gains can be truly staggering. To put it simply – what if you could turn that 67% of IT resources spent on running the business into 50%? Or 40%? Imagine what you could do with those resources. It’s now not just possible, but happening. This seems like a simple idea, but it is a radical change from “business as usual” in enterprise IT Operations. For the last thirty years, management has been a bolted-on afterthought – we pick and deploy our technology, then figure out how to manage it. This pervasive dysfunction is a broken cycle that guarantees high ongoing operating costs and low agility. If we want to break the cycle, we need to take a more tightly-coupled approach. As a complete applications-to-disk platform provider, Oracle is engineering management together with technology across our stack and hooking that on-premise management up live to My Oracle Support. Let’s examine the results with just one piece of the Oracle stack – the Oracle Database. Oracle began this journey with the Oracle Database 9i many years ago with the introduction of low-impact instrumentation in the database kernel (“tell me what’s wrong”) and through Database 10g, 11g and 11gR2 has successively added integrated advisory (“tell me how to fix what’s wrong”) and lifecycle management and automated self-tuning (“fix it for me, and do it on an ongoing basis for all my assets”). When enterprises take advantage of this tight-coupling, the results are game-changing. Consider the following (for a full list of public references, visit this link): British Telecom improved database provisioning time 1000% (from weeks to minutes) which allows them to provide a new DBaaS service to their internal customers with no additional resources Cerner Corporation Saved $9.5 million in CapEx and OpEx AND launched a brand-new cloud business at the same time Vodafone Group plc improved response times 50% and reduced maintenance planning times 50-60% while serving 391 million registered mobile customers Or the recent Database Manageability and Productivity Cost Comparisons: Oracle Database 11g Release 2 vs. SAP Sybase ASE 15.7, Microsoft SQL Server 2008 R2 and IBM DB2 9.7 as conducted by independent analyst firm ORC. In later entries, we’ll discuss similar results across other portions of the Oracle stack and how these efficiency gains are required to achieve the agility benefits of Enterprise Cloud. Stay Connected: Twitter |  Face book |  You Tube |  Linked in |  Newsletter

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  • Why not AJAX'ify entire websites?

    - by Anonymous -
    Is there any solid reasoning as to why sites shouldn't be developed with ajax functionality that loads major parts of each part (assuming there are elements like the header, navigation etc that remain the same)? Surely it would be less resource-intensive since the server wouldn't have to serve content that appears on every page, benefiting both the host and end-user. Answer the question taking into consideration: The sites javascript behaviour degrades gracefully in every instance For my question I'm talking about new sites where this behaviour could be implemented rather from the off, so it doesn't technically cost any money - we're not returning to a finished product to implement it.

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  • Is committing/checking code everyday a good practice?

    - by ArtB
    I've been reading Martin Fowler's note on Continuous Integration and he lists as a must "Everyone Commits To the Mainline Every Day". I do not like to commit code unless the section I'm working on is complete and that in practice I commit my code every three days: one day to investigate/reproduce the task and make some preliminary changes, a second day to complete the changes, and a third day to write the tests and clean it up^ for submission. I would not feel comfortable submitting the code sooner. Now, I pull changes from the repository and integrate them locally usually twice a day, but I do not commit that often unless I can carve out a smaller piece of work. Question: is committing everyday such a good practice that I should change my workflow to accomodate it, or it is not that advisable? ^ The order is more arbitrary and depends on the task, my point was to illustrate the time span and activities, not the exact sequence.

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  • Why should I use List<T> over IEnumerable<T>?

    - by Rowan Freeman
    In my ASP.net MVC4 web application I use IEnumerables, trying to follow the mantra to program to the interface, not the implementation. Return IEnumerable(Of Student) vs Return New List(Of Student) People are telling me to use List and not IEnumerable, because lists force the query to be executed and IEumerable does not. Is this really best practice? Is there any alternative? I feel strange using concrete objects where an interface could be used. Is my strange feeling justified?

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  • Is reference to bug/issue in commit message considered good practice?

    - by Christian P
    I'm working on a project where we have the source control set up to automatically write notes in the bug tracker. We simply write the bug issue ID in the commit message and the commit message is added as a note to the bug tracker. I can see only a few downsides for this practice. If sometime in the future the source code gets separated from the bug tracking software (or the reported bugs/issues are somehow lost). Or when someone is looking in the history of commits but doesn't have access to our bug tracker. My question is if having a bug/issue reference in the commit message is considered good practice? Are there some other downsides?

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  • Is it better to build HTML Code string on the server or on the client side?

    - by Ionut
    The result of the following process should be a html form. This form's structure varies from one to user. For example there might be a different number of rows or there may be the need for rowspan and colspan. When the user chooses to see this table an ajax call is made to the server where the structure of the table is decided from the database. Then I have to create the html code for the table structure which will be inserted in the DOM via JavaScript. The following problem comes to my mind: Where should I build the HTML code which will be inserted in the DOM? On the server side or should I send some parameters in the ajax call method and process the structure there? Therefore the main question involves good practice when it comes to decide between Server side processing or client side processing. Thank you!

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  • MVP Pattern Philsophical Question - Security Checking in UI

    - by Brian
    Hello, I have a philosophical question about the MVP pattern: I have a component that checks whether a user has access to a certain privilege. This privilege turns on or off certain UI features. For instance, suppose you have a UI grid, and for each row that gets bound, I do a security check to see if certain features in the grid should be enabled or disabled. There are two ways to do this: have the UI/view call the component's method, determine if it has access, and enable/disable or show/hide. The other is have the view fire an event to the presenter, have the presenter do the check and return the access back down to the view through the model or through the event arg. As per the MVP pattern, which component should security checks fit into, the presenter or the view? Since the view is using it to determine its accessibility, it seems more fitting in the view, but it is doing database checks and all inside this business component, and there is business logic there, so I can see the reverse argument too. Thoughts? Thanks.

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  • How do we keep dependent data structures up to date?

    - by Geo
    Suppose you have a parse tree, an abstract syntax tree, and a control flow graph, each one logically derived from the one before. In principle it is easy to construct each graph given the parse tree, but how can we manage the complexity of updating the graphs when the parse tree is modified? We know exactly how the tree has been modified, but how can the change be propagated to the other trees in a way that doesn't become difficult to manage? Naturally the dependent graph can be updated by simply reconstructing it from scratch every time the first graph changes, but then there would be no way of knowing the details of the changes in the dependent graph. I currently have four ways to attempt to solve this problem, but each one has difficulties. Nodes of the dependent tree each observe the relevant nodes of the original tree, updating themselves and the observer lists of original tree nodes as necessary. The conceptual complexity of this can become daunting. Each node of the original tree has a list of the dependent tree nodes that specifically depend upon it, and when the node changes it sets a flag on the dependent nodes to mark them as dirty, including the parents of the dependent nodes all the way down to the root. After each change we run an algorithm that is much like the algorithm for constructing the dependent graph from scratch, but it skips over any clean node and reconstructs each dirty node, keeping track of whether the reconstructed node is actually different from the dirty node. This can also get tricky. We can represent the logical connection between the original graph and the dependent graph as a data structure, like a list of constraints, perhaps designed using a declarative language. When the original graph changes we need only scan the list to discover which constraints are violated and how the dependent tree needs to change to correct the violation, all encoded as data. We can reconstruct the dependent graph from scratch as though there were no existing dependent graph, and then compare the existing graph and the new graph to discover how it has changed. I'm sure this is the easiest way because I know there are algorithms available for detecting differences, but they are all quite computationally expensive and in principle it seems unnecessary so I'm deliberately avoiding this option. What is the right way to deal with these sorts of problems? Surely there must be a design pattern that makes this whole thing almost easy. It would be nice to have a good solution for every problem of this general description. Does this class of problem have a name?

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  • Would you use UML if it kept stakeholders from requesting changes frequently?

    - by Huperniketes
    As much as programmers hate to document their code/system and draw UML (especially, Sequencing, Activity and State machine diagrams) or other diagramming notation, would you agree to do it if it kept managers from requesting a "minor change" every couple of weeks? IOW, would you put together visual models to document the system if it helped you demonstrate to managers what the effect of changes are and why it takes so long to implement them? (Edited to help programmers understand what type of answer I'm looking for.) 2nd edit: Restating my question again, "Would you be willing to use some diagramming notation, against your better nature as a programmer, if it helped you manage change requests?" This question isn't asking if there might be something wrong with the process. It's a given that there's something wrong with the process. Would you be willing to do more work to improve it?

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  • Is Linq having a mind-numbing effect on .NET programmers?

    - by Aaronaught
    A lot of us started seeing this phenomenon with jQuery about a year ago when people started asking how to do absolutely insane things like retrieve the query string with jQuery. The difference between the library (jQuery) and the language (JavaScript) is apparently lost on many programmers, and results in a lot of inappropriate, convoluted code being written where it is not necessary. Maybe it's just my imagination, but I swear I'm starting to see an uptick in the number of questions where people are asking to do similarly insane things with Linq, like find ranges in a sorted array. I can't get over how thoroughly inappropriate the Linq extensions are for solving that problem, but more importantly the fact that the author just assumed that the ideal solution would involve Linq without actually thinking about it (as far as I can tell). It seems that we are repeating history, breeding a new generation of .NET programmers who can't tell the difference between the language (C#/VB.NET) and the library (Linq). What is responsible for this phenomenon? Is it just hype? Magpie tendencies? Has Linq picked up a reputation as a form of magic, where instead of actually writing code you just have to utter the right incantation? I'm hardly satisfied with those explanations but I can't really think of anything else. More importantly, is it really a problem, and if so, what's the best way to help enlighten these people?

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  • Publish/Subscribe/Request for exchange of big, complex, and confidential data?

    - by Morten
    I am working on a project where a website needs to exchange complex and confidential (and thus encrypted) data with other systems. The data includes personal information, technical drawings, public documents etc. We would prefer to avoid the Request-Reply pattern to the dependent systems (and there are a LOT of them), as that would create an awful lot of empty traffic. On the other hand, I am not sure that a pure Publisher/Subscriber pattern would be apropriate -- mainly because of the complex and bulky nature of the data to be exchanged. For that reason we have discussed the possibility of a "publish/subscribe/request" solution. The Publish/Subscribe part would be to publish a message to the dependent systems, that something is ready for pickup. The actual content is then picked up by old-school Request-Reply action. How does this sound to you?? Regards, Morten

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  • How to expose game data in the game without a singelton?

    - by zardon
    I'm quite new to cocos2d and games programming, and am currently I am writing a game that is currently in Prototype stage. Everything is going okay, but I've realized a potentially big problem and I am not sure how to solve it. I am using a singelton to store a bunch of arrays for everything, a global list of planets, a global list of troops, a global list of products, etc. And only now I'm realizing that all of this will be in memory and this is the wrong way to do it. I am not storing files or anything on the disk just yet, with exception to a save/load state, which is a capture of everything. My game makes use of a map which allows you to select a planet, then it will give you a breakdown of that planets troops and resources, Lets use this scenario: My game has 20 planets. On which you can have 20 troops. Straight away that's an array of 400! This does not add the NPC, which is another 10. So, 20x10 = 200 So, now we have 600 all in arrays inside a Singelton. This is obviously very bad, and very wrong. Especially as the game scales in the amount of data. But I need to expose pretty much everything, especially on the map page, and I am not sure how else to do it. I've been told that I can use a controller for the map page which has the information I need for each planet, and other controllers for other items I require global display for. I've also thought about storing each planet's data in a save file, using initWithCoder however there could be a boatload of files on the user's device? I really don't want to use a database, mainly because I would need to translate NSObjects and non-NSObjects like CGRects and CGPoints and Colors into/from SQL. I am open to other ideas on how to store and read game data to prevent using a singelton to store everything, everywhere. Thanks for your time.

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  • Are there any examples of a temporal field/object updater?

    - by Bryan Agee
    The system in question has numerous examples of temporal objects and fields--ones which are a certain variable at a certain point in time. An example of this would be someone's rate of pay--there are different answers depending on when you ask and what the constraints might be; eg, can there ever be more than one of a certain temporal object concurrently, etc. Ideally, there would be an object that handles those constraints when a new state/stateful object is introduced; when a new value is set, it would prevent creating negative ranges and overlaps. Martin Fowler has written some great material on this (such as this description of Temporal Objects) , but what I've found of it tends to be entirely theoretic, with no concrete implementations. PHP is the target language, but examples in any language would be most helpful.

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  • Trying to detect collision between two polygons using Separating Axis Theorem

    - by Holly
    The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(vertices[0]); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(vertices[i]); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if( other.x <= y || other.y >= x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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