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• Algorithm for dynamically calculating a level based on experience points?

  - by George

  One of the struggles I've always had in game development is deciding how to implement experience points attributed to gaining a level. There doesn't seem to be a pattern to gaining a level in many of the games I've played, so I assume they have a static dictionary table which contains experience points vs. the level. e.g. Experience Level 0 1 100 2 175 3 280 4 800 5 ...There isn't a rhyme or reason why 280 points is equal to level 4, it just is. I'm not sure how those levels are decided, but it certainly wouldn't be dynamic. I've also thought about the possibility of exponential levels, as not to have to keep a separate lookup table, e.g. Experience Level 0 1 100 2 200 3 400 4 800 5 1600 6 3200 7 6400 8 ...but that seems like it would grow out of control rather quickly, as towards the upper levels, the enemies in the game would have to provide a whopping amount of experience to level -- and that would be to difficult to control. Leveling would become an impossible task. Does anyone have any pointers, or methods they use to decide how to level a character based on experience? I want to be fair in leveling and I want to stay ahead of the players as not to worry about constantly adding new experience/level lookups.

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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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• Is is common to use the command pattern for property get/sets?

  - by k rey

  Suppose I have a controller class with a bunch of properties. Each time a property is changed, I would like to update the model. Now also suppose that I use the command pattern to perform model updates. Is it common to use command classes within property get and sets of the controller class or is there a better way? Here is an example of what I am currently using: class MyController { private int _myInt; public int MyInt { get { return _myInt; } set { MyCommand cmd = new MyCommand(); cmd.Argument = _myInt; cmd.Execute(); // Command object updates the model } } }

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• Simplifying C++11 optimal parameter passing when a copy is needed

  - by Mr.C64

  It seems to me that in C++11 lots of attention was made to simplify returning values from functions and methods, i.e.: with move semantics it's possible to simply return heavy-to-copy but cheap-to-move values (while in C++98/03 the general guideline was to use output parameters via non-const references or pointers), e.g.: // C++11 style vector<string> MakeAVeryBigStringList(); // C++98/03 style void MakeAVeryBigStringList(vector<string>& result); On the other side, it seems to me that more work should be done on input parameter passing, in particular when a copy of an input parameter is needed, e.g. in constructors and setters. My understanding is that the best technique in this case is to use templates and std::forward<>, e.g. (following the pattern of this answer on C++11 optimal parameter passing): class Person { std::string m_name; public: template <class T, class = typename std::enable_if < std::is_constructible<std::string, T>::value >::type> explicit Person(T&& name) : m_name(std::forward<T>(name)) { } ... }; A similar code could be written for setters. Frankly, this code seems boilerplate and complex, and doesn't scale up well when there are more parameters (e.g. if a surname attribute is added to the above class). Would it be possible to add a new feature to C++11 to simplify code like this (just like lambdas simplify C++98/03 code with functors in several cases)? I was thinking of a syntax with some special character, like @ (since introducing a &&& in addition to && would be too much typing :) e.g.: class Person { std::string m_name; public: /* Simplified syntax to produce boilerplate code like this: template <class T, class = typename std::enable_if < std::is_constructible<std::string, T>::value >::type> */ explicit Person(std::string@ name) : m_name(name) // implicit std::forward as well { } ... }; This would be very convenient also for more complex cases involving more parameters, e.g. Person(std::string@ name, std::string@ surname) : m_name(name), m_surname(surname) { } Would it be possible to add a simplified convenient syntax like this in C++? What would be the downsides of such a syntax?

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• My Last "Catch-Up" Post for 2010 Content

  - by KKline

  I did a lot of writing in 2010. Unfortunately, I didn't do a good job of keeping all of that writing equally distributed throughout all of the channels where I'm active. So here are a few more posts from my blog, put on-line during the months of November and December 2010, that I didn't get posted here on SQLBlog.com: 1. It's Time to Upgrade! So many of my customers and many of you, dear readers, are still on SQL Server 2005. Join Kevin Kline , SQL Server MVP and SQL Server Technology Strategist...(read more)

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• What are examples of games with "minimalist" models/art assets

  - by Ken

  When teaching game development, my student's obsess about building realistic or complex art/models/animation. And spending wayyy to much time trying to get accurate collision detection between two 3D models [despite my best efforts] However I would like them to spend more time thinking about developing the game mechanics, interaction and game play. I'm looking for some games where the visuals are simple but have good game play. Things I am thinking about are Cubes' vs Spheres or Impossible Game. What are more examples of visually simple (preferably 3D) games to help inspire my students?

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• Examples of Liskov Substitution

  - by james lewis

  I'm facilitating a session next week on the Liskov Substitution Principle and I was wondering if anyone had any examples of violations 'from the trenches'? I'm looking for something other than uncle Bob's rectangle - square problem and the persistent set problem he talks about in A-PPP (although that is a great example). So far I'm using the example of a (very simple) List and an IndexedList as the 'correct' use of inheritance. And the addition of a Set to this hierarchy as a violation (as a Set is distinct; strengthening the pre condition of the Add method). I've also taken this great example and it's solution from this question Both those examples are great but I'm looking for something more subtle and harder to spot. So far I've come up with nothing so if you've got a great, subtle example post it up. Also, any metaphors you've come across that helped you understand LSP would be really useful too.

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• What is required for a scope in an injection framework?

  - by johncarl

  Working with libraries like Seam, Guice and Spring I have become accustomed to dealing with variables within a scope. These libraries give you a handful of scopes and allow you to define your own. This is a very handy pattern for dealing with variable lifecycles and dependency injection. I have been trying to identify where scoping is the proper solution, or where another solution is more appropriate (context variable, singleton, etc). I have found that if the scope lifecycle is not well defined it is very difficult and often failure prone to manage injections in this way. I have searched on this topic but have found little discussion on the pattern. Is there some good articles discussing where to use scoping and what are required/suggested prerequisites for scoping? I interested in both reference discussion or your view on what is required or suggested for a proper scope implementation. Keep in mind that I am referring to scoping as a general idea, this includes things like globally scoped singletons, request or session scoped web variable, conversation scopes, and others. Edit: Some simple background on custom scopes: Google Guice custom scope Some definitions relevant to above: “scoping” - A set of requirements that define what objects get injected at what time. A simple example of this is Thread scope, based on a ThreadLocal. This scope would inject a variable based on what thread instantiated the class. Here's an example of this: “context variable” - A repository passed from one object to another holding relevant variables. Much like scoping this is a more brute force way of accessing variables based on the calling code. Example: methodOne(Context context){ methodTwo(context); } methodTwo(Context context){ ... //same context as method one, if called from method one } “globally scoped singleton” - Following the singleton pattern, there is one object per application instance. This applies to scopes because there is a basic lifecycle to this object: there is only one of these objects instantiated. Here's an example of a JSR330 Singleton scoped object: @Singleton public void SingletonExample{ ... } usage: public class One { @Inject SingeltonExample example1; } public class Two { @Inject SingeltonExample example2; } After instantiation: one.example1 == two.example2 //true;

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• Write own messaging system vs. utilize existing ones

  - by A.Rashad

  We are trying to have our own startup, with a middleware application to glue small applications with enterprise legacy systems. for such middle-ware to function properly, we will need some sort of messaging system to make different components talk to each other in a reliable way. the alternatives are: use an existing messaging system, such as 0MQ, jBOSS, WebSphere MQ, etc. build our own messaging system the way we see the problem I am more biased towards the later option for the following reasons: to have more control over our final product to avoid any licensing problems later on to learn about messaging while writing the code to invent something new, that might cost us lots of $$$ if reused an existing system What would you do if in my shoes?

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• Real life example of an agile game development process

  - by Ken

  I'm trying to learn about applying agile methodologies to game development. But seems to be impossible to find real life examples. What I am looking for are things like; Initial user stories Final user stories (complete, covering the entire game requirements) Acceptance criteria Task list Sprint backlogs (before and after each sprint) The agile books seem to have some limited examples, many of which seem contrived. In this era of open source software, there must be an documented example of the process applied to a game that is publicly available. I am asking specifically about games because they are so different from normal applications. Regular applications are built to all users to complete specific tasks in order to get stuff done(book a room, print a report etc). People play games for much less tangible reasons, so I think the process is significantly different. [it doesn't have to be scrum, it could be any process, just needs to be a real life example game and be reasonably complete]

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• Better solution then simple factory method when concrete implementations have different attributes

  - by danip

  abstract class Animal { function eat() {..} function sleep() {..} function isSmart() } class Dog extends Animal { public $blnCanBark; function isSmart() { return $this->blnCanBark; } } class Cat extends Animal { public $blnCanJumpHigh; function isSmart() { return $this->blnCanJumpHigh; } } .. and so on up to 10-20 animals. Now I created a factory using simple factory method and try to create instances like this: class AnimalFactory { public static function create($strName) { switch($strName) { case 'Dog': return new Dog(); case 'Cat': return new Cat(); default: break; } } } The problem is I can't set the specific attributes like blnCanBark, blnCanJumpHigh in an efficient way. I can send all of them as extra params to create but this will not scale to more then a few classes. Also I can't break the inheritance because a lot of the basic functionality is the same. Is there a better pattern to solve this?

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• Where can I hire local programmers with very specific skillsets?

  - by Lostsoul

  I have been browsing the site and haven't found a exact fit to this question so I'll post it but if its already answered(since I'm sure its a common problem, then let me know). I have a business and want to create a totally different product in a different industry than I'm currently in, so I learned how to program and created a working prototype. I have a bit of savings and am getting some cash flow from my current business so I can go out and hire a developer(in the future hopefully it can be permenant but right now I just need a person willing to work on contract and code on weekends or their spare time and I just want to pay in cash instead of equity or future promises). At first I wasn't sure what kind of developer to hire but this question helped me understand I should target specific skills I need as opposed to general programmers. This poses a problem for me since general programmers are everywhere but if I want specific skills I'm unsure how to get them. I thought about a list of approaches but it doesn't feel complete or effective since it seems to be assuming good developers are actively looking. If it helps I want someone local(since this is my first developer hire) and looking for skills like cuda, hadoop, hbase, java and c. Any suggestions? As a FYI, I have been thinking of approaching it as: Go to meet ups for one or more skills I need. Use LinkedIn to find people with the skills I need Search for job postings that contain skills I need and then use linkedIn to reach out to that firms employees since many profiles on linkedin are not very updated or detailed but job postings generally are. Send postings to universities and maybe find a student who loves technology so much they learned these tools on their own. Post on job board. Not sure how successful it will be to post to monster. Use Craigslist, not sure if a highly skilled developer would go here for work. What am I missing? I could be wrong but it seems like good/smart/able developers aren't hunting for work non-stop(especially in this tech job market). Plus most successful people I know have work/life balance so I'm not sure if the best ones really care about code after work. Lastly, most of the skills I need aren't used in big corporations so not sure how aggressively smart developers at small shops look for work. I don’t really know any developers personally, so but should I be using the above plan or if they live balanced lives should I be looking outside of the regular resources(and instead focus on asking around my gym or my accountant or something)? Sorry, I'm making huge assumptions here, I guess because developers are a total mystery to me. I kind of wish Jane Goodall wrote a book on understanding developers social behaviour better :-p

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• Get Info From Database, or Build Inferred Info?

  - by Zaemz

  Does it make more sense to store and retrieve properties or information directly related to an item in a database, or, say in such a case that a product's ID could describe information about it, should the information be gathered from that? Example: Item SKU -- 4HBU12 4 - is the number of motors H - the voltage B - the color, blue U - the model 12 - the length Should I store those individual attributes as well as the SKU, or should I store only the SKU and build the attributes from it?

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• What can make a peaceful game successful?

  - by Miro

  Today, the most successful games are action games like FPS, RPG, MMORPG... I'd like to make peaceful game, but I don't know how to attract people. I can make good graphics, but that's not the main thing that makes people like game more that couple of minutes. The content is important. In game styles mentioned in beginning are main content fight, kill others, make from yourself predator/the most powerful creature/player in the game. But what content can attract people in peaceful game?

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• Is it needed to have your blog title and description in H1 and H2

  - by Saif Bechan

  I have read an article that states that it is not necessary to have your blog title and description on your website at all. Just have the titles of the posts in h1, on the index and the post page. And on the post page have your different sections started with h2. Widget headers start with h3. Title and description are most of the time in the logo image. I have looked at the source of my favorite blog, http://net.tutsplus.com, and I see they do the same. Is this recommended?

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• Help me select a "Simpler" target to create a new language: .NET, LLVM, Go, Own VM

  - by mamcx

  Lets define "Simple". This is my first language. I have no previous experience I will not dedicate +4 years to learn it properly. I'm a professional software [developer], but as an amateur in this area, I want instant gratification. If the idea shows a future, I could rewrite it. I don't want to do everything from scratch. In fact, if there exists a way to get GO (for example), change its syntax, add some sugar, give some extra functions and leave intact everything else, that would be perfect! From the example of coffescript/scala I think is better to build on top of some rich runtime like .NET/GO so I don't need to rewrite everything. HOWEVER, if is better other way, no problem for the first try! I want it in a week. I need it in a week so it will really take a month. Then it truly takes 3 months. But I don't want to put more that 3 months on this. I could reduce the scope of my language, but I hope the tools will help me a lot... I want to build a new language. Similar to python, but typed. I wonder what to build it on top of. I like the idea of building on top of GO. To get their sane (IMHO) OO paradigm (I plan to do the same, using interfaces, not inheritance), get goroutines and some other stuff. In my naive thinking I imagine that spit another language could help me to debug it more easily. However, look like everyone is building on top of something like .NET (don't like Java), LLVM or make it own VM. I read http://createyourproglang.com/ (great!) and the part of the VM look "easy" to me. So, what I need is the proper criteria and question I need to know in advance to have a fair shot at make this.

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• How can I keep directories in sync

  - by Guillaume Boudreau

  I have a directory, dirA, that users can work in: they can create, modify, rename and delete files & sub-directores in dirA. I want to keep another directory, dirB, in sync with dirA. What I'd like, is a discussion on finding a working algorithm that would achieve the above, with the limitations listed below. Requirements: 1. Something asynchronous - I don't want to stop file operations in dirA while I work in dirB. 2. I can't assume that I can just blindly rsync dirA to dirB on regular interval - dirA could contain millions of files & directories, and terrabytes of data. Completely walking the dirA tree could take hours. Those two requirements makes this really difficult. Having it asynchronous means that when I start working on a specific file from dirA, it might have moved a lot since it appeared. And the second limitation means that I really need to watch dirA, and work on atomic file operations that I notice. Current (broken) implementation: 1. Log all file & directory operations in dirA. 2. Using a separate process, read that log, and 'repeat' all the logged operations in dirB. Why is it broken: echo 1 > dirA/file1 # Allow the 'log reader' process to create dirB/file1: log = "write dirA/file1"; action = cp dirA/file1 dirB/file1; result = OK echo 1 > dirA/file2 mv dirA/file1 dirA/file3 mv dirA/file2 dirA/file1 rm dirA/file3 # End result: file1 contains '1' # 'log reader' process starts working on the 4 above file operations: log = "write file2"; action = cp dirA/file2 dirB/file2; result = failed: there is no dirA/file2 log = "rename file1 file3"; action = mv dirB/file1 dirB/file3; result = OK log = "rename file2 file1"; action = mv dirB/file2 dirB/file1; result = failed: there is no dirB/file2 log = "delete file3"; action = rm dirB/file3; result = OK # End result in dirB: no more files! Another broken example: echo 1 > dirA/dir1/file1 mv dirA/dir1 dirA/dir2 # 'log reader' process starts working on the 2 above file operations: log = "write file1"; action = cp dirA/dir1/file1 dirB/dir1/file1; result = failed: there is no dirA/dir1/file1 log = "rename dir1 dir2"; action = mv dirB/dir1 dirB/dir2; result = failed: there is no dirA/dir1 # End result if dirB: nothing!

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• What is meant by, "A user shouldn't decide whether it is an Admin or not. The Privileges or Security system should."

  - by GlenPeterson

  The example used in the question pass bare minimum data to a function touches on the best way to determine whether the user is an administrator or not. One common answer was: user.isAdmin() This prompted a comment which was repeated several times and up-voted many times: A user shouldn't decide whether it is an Admin or not. The Privileges or Security system should. Something being tightly coupled to a class doesn't mean it is a good idea to make it part of that class. I replied, The user isn't deciding anything. The User object/table stores data about each user. Actual users don't get to change everything about themselves. But this was not productive. Clearly there is an underlying difference of perspective which is making communication difficult. Can someone explain to me why user.isAdmin() is bad, and paint a brief sketch of what it looks like done "right"? Really, I fail to see the advantage of separating security from the system that it protects. Any security text will say that security needs to be designed into a system from the beginning and considered at every stage of development, deployment, maintenance, and even end-of-life. It is not something that can be bolted on the side. But 17 up-votes so far on this comment says that I'm missing something important.

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• How to keep balance / Unlock items / achievement rules

  - by Mark Knol

  I'm working on an engine for a game, too learn javascript and just because its fun. I'm a flashdeveloper, I know how to build websites. Now making games is a different challenge, javascript is a challenge, but I'd love to learn how to structure code and what patterns are common. I dont mind if the game ever finish, I'm mostly interested in the programming part of it. I dont have a particular endresult in mind, so I'll see where it takes me. I currently have a system where you can buy items. The items cost a specified amount of gold, silver, diamonds etc. When you have selected and bought the item, it takes time before getting rewarded. When time is over, you are getting rewarded with other properties (gold, energy, diamonds). For example, you can buy an apple for 50gold, It takes a minute, you get rewarded with 75energy. Or if you take a run, it cost 50energy, it takes 5minutes, reward is 25gold and 25silver. These definitions is what i call actions. Currently I already have a system where this already works and I can define as much actions with as much properties as I want. The definitions I have kinda looks like this: {id:101, category:544, onInit:{gold:-75}, onComplete:{energy:75}, time:2000, name:"Apple", locked: false} {id:102, category:544, onInit:{gold:-135}, onComplete:{energy:145}, time:2000, name:"Banana", locked: false} {id:106, category:302, onInit:{energy:-50, power: -25}, onComplete:{gold:100, diamonds:2}, time:10000, name:"Run", locked: false} {id:107, category:302, onInit:{energy:-70, silver: -55}, onComplete:{gold:100}, time:10000, name:"Dance", locked: false} {id:108, category:302, onInit:{energy:-230, power: -355}, onComplete:{gold:70, silver:70}, time:10000, name:"Fitness", locked: false} Now, I would love to add a system where I can lock/unlock the actions using achievement rules. Lets say, if you buy 10 apples, you unlock a new action, like bananas which cost more, and reward more. In the future I maybe want to restrict achievements and actions to levels. I am kinda stuck how to structure this. I have 2 questions: Which patterns are used to define achievements? How/where are they defined? Should it be part of the action, or should it be a separate controller? Is it a good idea to register all completed actions to it? I think I want multiple types of achievement rules, Id love to hear some ideas how to develop it. How do you create/find a good balance, so the user does not get stuck or can cheat by repeat a pattern of actions to get too much rewards. I know there is not a simple answer and i'm lacking of a good game-concept, but I wonder if anyone created such a game and how you dealed and played with it.

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• What can make peaceful game successful?

  - by Miro

  Today, the most successful games are action games like FPS, RPG, MMORPG... I'd like to make peaceful game, but i don't know how to attract people. I can make good graphics, but that's not the main thing that makes people like game more that couple of minutes. The content is important. In game styles mentioned in beginning are main content fight, kill others, make from yourself predator/the most powerful creature/player in the game. But what content can attract people in peaceful game?

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• What is the best website width? [on hold]

  - by Salvis Dišlers

  What is the best website width? I can't decide between 1200px max-width and 1236px....with 300px sidebar as enough or 320px? I personally like wide website, my current website is 1236px; but I hear it's considered very wide for eyesight and all those gadgets keeping in mind... The website is for reading - I mean, mostly articles with around 3000 words on average per page, so no matter - whether they look wide, whether they love to scroll down :) Also - what to decide about Banner size / sidebar? Probably the 300px I can put a 300px banner, but on 320px sidebar I could put 336px banner, if necessary...

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• Information Spilling Across Object Boundaries

  - by Winston Ewert

  Many times my business objects tend to have situations where information needs to cross object boundaries too often. When doing OO, we want information to be in one object and as much as possible all code dealing with that information should be in that object. However, business rules do not follow this principle giving me trouble. As an example suppose that we have an Order which has a number of OrderItems which refers to an InventoryItem which has a price. I invoke Order.GetTotal() which sums the result of OrderItem.GetPrice() which multiples a quantity by InventoryItem.GetPrice(). So far so good. But then we find out that some items are sold with a two for one deal. We can handle this by having OrderItem.GetPrice() do something like InventoryItem.GetPrice( quantity ) and letting InventoryItem deal with this. However, then we find out that the two-for-one deal only lasts for a particular time period. This time period needs to be based on the date of the order. Now we change OrderItem.GetPrice() to be InventoryItem.GetPrice( quatity, order.GetDate() ) But then we need to support different prices depending on how long the customer has been in the system: InventoryItem.GetPrice( quantity, order.GetDate(), order.GetCustomer() ) But then it turns out that the two-for-one deals apply not just to buying multiple of the same inventory item but multiple for any item in a InventoryCategory. At this point we throw up our hands and just give the InventoryItem the order item and allow it to travel over the object reference graph via accessors to get the information its needs: InventoryItem.GetPrice( this ) TL;DR I want to have coupling in objects, but business rules often force me to access information from all over the place in order to make particular decisions. Are there good techniques for dealing with this? Do others find the same problem?

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• Best Creational Pattern for loggers in a multi-threaded system?

  - by Dipan Mehta

  This is a follow up question on my past questions : Concurrency pattern of logger in multithreaded application As suggested by others, I am putting this question separately. As the learning from the last question. In a multi-threaded environment, the logger should be made thread safe and probably asynchronous (where in messages are queued while a background thread does writing releasing the requesting object thread). The logger could be signleton or it can be a per-group logger which is a generalization of the above. Now, the question that arise is how does logger should be assigned to the object? There are two options I can think of: 1. Object requesting for the logger: Should each of the object call some global API such as get_logger()? Such an API returns "the" singleton or the group logger. However, I feel this involves assumption about the Application environment to implement the logger -which I think is some kind of coupling. If the same object needs to be used by other application - this new application also need to implement such a method. 2. Assign logger through some known API The other alternative approach is to create a kind of virtual class which is implemented by application based on App's own structure and assign the object sometime in the constructor. This is more generalized method. Unfortunately, when there are so many objects - and rather a tree of objects passing on the logger objects to each level is quite messy. My question is there a better way to do this? If you need to pick any one of the above, which approach is would you pick and why? Other questions remain open about how to configure them: How do objects' names or ID are assigned so that will be used for printing on the log messages (as the module names) How do these objects find the appropriate properties (such as log levels, and other such parameters) In the first approach, the central API needs to deal with all this varieties. In the second approach - there needs to be additional work. Hence, I want to understand from the real experience of people, as to how to write logger effectively in such an environment.

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• Dependency Injection: Only for single-instance objects?

  - by HappyDeveloper

  What if I want to also decouple my application, from classes like Product or User? (which usually have more than one instance) Take a look at this example: class Controller { public function someAction() { $product_1 = new Product(); $product_2 = new Product(); // do something with the products } } Is it right to say that Controller now depends on Product? I was thinking that we could decouple them too (as we would with single-instance objects like Database) In this example, however ugly, they are decoupled: class Controller { public function someAction(ProductInterface $new_product) { $product_1 = clone $new_product; $product_2 = clone $new_product; // do something with the products } } Has anyone done something like this before? Is it excessive?

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• Does a mobile app need more access than the public API of a site?

  - by Iain

  I have a site with a public API, and some mobile app developers have been brought in to produce an iPhone app for the site. They insist they need to see the database schema, but as I understand it, they should only need access to the documented public API. Am I right? Is there something I've missed? I've told them that if there's a feature missing or data they require I can extend the API so that they can access it. I thought a web service API held to much the same principles as OOP object API's, in that the implementation details should be hidden as much as possible. I'm not a mobile app developer so if there is something I don't quite see then please let me know. Any insight or help will be much appreciated.

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