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• Strange behavior of RigidBody with gravity and impulse applied

  - by Heisenbug

  I'm doing some experiments trying to figure out how physics works in Unity. I created a cube mesh with a BoxCollider and a RigidBody. The cuve is laying on a mesh plane with a BoxCollider. I'm trying to update the object position applying a force on its RigidBody. Inside script FixedUpdate function I'm doing the following: public void FixedUpdate() { if (leftButtonPressed()) this.rigidbody.AddForce( this.transform.forward * this.forceStrength, ForceMode.Impulse); } Despite the object is aligned with the world axis and the force is applied along Z axis, it performs a quite big rotation movement around its y axis. Since I didn't modify the center of mass and the BoxCollider position and dimension, all values should be fine. Removing gravity and letting the object flying without touching the plane, the problem doesn't show. So I suppose it's related to the friction between objects, but I can't understand exactly which is the problem. Why this? What's my mistake? How can I fix this, or what's the right way to do such a moving an object on a plane through a force impulse?

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• How to keep track of previous scenes and return to them in libgdx

  - by MxyL

  I have three scenes: SceneTitle, SceneMenu, SceneLoad. (The difference between the title scene and the menu scene is that the title scene is what you see when you first turn on the game, and the menu scene is what you can access during the game. During the game, meaning, after you've hit "play!" in the title scene.) I provide the ability to save progress and consequently load a particular game. An issue that I've run into is being able to easily keep track of the previous scene. For example, if you enter the load scene and then decide to change your mind, the game needs to go back to where you were before; this isn't something that can be hardcoded. Now, an easy solution off the top of my head is to simply maintain a scene stack, which basically keeps track of history for me. A simple transaction would be as follows I'm currently in the menu scene, so the top of the stack is SceneMenu I go to the load scene, so the game pushes SceneLoad onto the stack. When I return from the load scene, the game pops SceneLoad off the stack and initializes the scene that's currently at the top, which is SceneMenu I'm coding in Java, so I can't simply pass around Classes as if they were objects, so I've decided implemented as enum for eac scene and put that on the stack and then have my scene managing class go through a list of if conditions to return the appropriate instance of the class. How can I implement my scene stack without having to do too much work maintaining it?

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• Remove enemy when bullet hits enemy

  - by jordi12100

  For my education I have to make a basic game in HTML5 canvas. The game is a shooter game. When you can move left - right and space is shoot. When I shoot the bullets will move up. The enemy moves down. When the bullet hits the enemy the enemy has to dissapear and it will gain +1 score. But the enemy will dissapear after it comes up the screen. Demo: http://jordikroon.nl/test.html space = shoot + enemy shows up This is my code: for (i=0;i<enemyX.length;i++) { if(enemyX[i] > canvas.height) { enemyY.splice(i,1); enemyX.splice(i,1); } else { enemyY[i] += 5; moveEnemy(enemyX[i],enemyY[i]); } } for (i=0;i<bulletX.length;i++) { if(bulletY[i] < 0) { bulletY.splice(i,1); bulletX.splice(i,1); } else { bulletY[i] -= 5; moveBullet(bulletX[i],bulletY[i]); for (ib=0;ib<enemyX.length;ib++) { if(bulletX[i] + 50 < enemyX[ib] || enemyX[ib] + 50 < bulletX[i] || bulletY[i] + 50 < enemyY[ib] || enemyY[ib] + 50 < bulletY[i]) { ++score; enemyY.splice(i,1); enemyX.splice(i,1); } } } } Objects: function moveBullet(posX,posY) { //console.log(posY); ctx.arc(posX, (posY-150), 10, 0 , 2 * Math.PI, false); } function moveEnemy(posX,posY) { ctx.rect(posX, posY, 50, 50); ctx.fillStyle = '#ffffff'; ctx.fill(); }

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• Limiting the speed of the mouse cursor

  - by idlewire

  I am working on a simple game where you can drag objects around with the mouse cursor. As I drag the object around quickly, I notice there is some juddering, which seems to be due to the fact that I can move the mouse cursor faster than the game's update/draw. So, although I maintain the offset from where the player initially clicked on the object, the mouse's relative position to the object shifts around slightly before settling as I move the object very quickly. The only way I have found to get smooth, exact 1:1 movement is if I turn both IsFixedTimeStep and SynchronizeWithVerticalRetrace to false. However, I'd rather not have to do that. I have also tried making a custom mouse cursor, hiding the real mouse, taking the real mouse delta and clamping it to a maximum speed. Here is the problem: In windowed mode, the "real" mouse cursor moves off the window while the custom mouse cursor (since it's movement is being scaled) is still somewhere inside the game window. This becomes bizarre and is obviously not desired, as clicking at this point means clicking on things outside the game window. Is there any way to accomplish this in windowed mode? In fullscreen mode, the "real" mouse cursor is bounded to the edges of the screen. So I get to a point where there is no more mouse delta, yet my custom cursor is still somewhere in the middle of the screen and hence can't move further in that direction. If I wanted to clamp it to the edge of the screen when the real cursor is at the edge, then I would get an abrupt jump to the edge of the screen, which isn't desired either Any help would be appreciated. I'd like to be able to limit the speed of the mouse, but also would appreciate help with the first issue (the non-smooth relative offset between mouse cursor movement and object movement).

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• Functional programming compared to OOP with classes

  - by luckysmack

  I have been interested in some of the concepts of functional programming lately. I have used OOP for some time now. I can see how I would build a fairly complex app in OOP. Each object would know how to do things that object does. Or anything it's parents class does as well. So I can simply tell Person().speak() to make the person talk. But how do I do similar things in functional programming? I see how functions are first class items. But that function only does one specific thing. Would I simply have a say() method floating around and call it with an equivalent of Person() argument so I know what kind of thing is saying something? So I can see the simple things, just how would I do the comparable of OOP and objects in functional programming, so I can modularize and organize my code base? For reference, my primary experience with OOP is Python, PHP, and some C#. The languages that I am looking at that have functional features are Scala and Haskell. Though I am leaning towards Scala. Basic Example (Python): Animal(object): def say(self, what): print(what) Dog(Animal): def say(self, what): super().say('dog barks: {0}'.format(what)) Cat(Animal): def say(self, what): super().say('cat meows: {0}'.format(what)) dog = Dog() cat = Cat() dog.say('ruff') cat.say('purr')

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

  - by Kaleb Pederson

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

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• XPath & XML EDI B2B

  - by PearlFactory

  GoodToGo :) Best XML Editor is Altova XMLSpy 2011 http://www.torrenthound.com/hash/bfdbf55baa4ca6f8e93464c9a42cbd66450bb950/torrent-info/Altova-XMLSpy-Enterprise-Edition-SP1-2011-v13-0-1-0-h33t-com-Full For whatever reason Piratebay has trojans and other nasties..Search in torrent.eu for Altova XMLSpy Enterprise Edition SP1 2011 v13.0.1.0 Also if you like the product purchase it in a Commercial Enviroment Any well structured/complex XML can be parsed @ the speed of light using XPATH querys and not the C# objects XPathNodeIterator and others etc ....Never do loops  or Genirics or whatever highlevel language technology. Use the power of XPATH i.e Will use a Simple (Do while) as an example. We could have many different techs all achieveing the same result Instead of   xmlNI2 = xmlNav.Select("/p:BookShop")         if (xmlNI2.Count != 0)            {                                 while ((xmlNI2.MoveNext()))              string aNode =xmlNI2.SelectSingleNode('Book', nsmgr); if (aNode =="The Book I am after")       Console.WriteLine("Found My Book);   This lengthy cumbersome task can be achieved with a simple XPATH query Console.WriteLine((xmlNavg.SelectSingleNode("/p:BookShop/Book[.='The Book I am aFter ']", nsmgr)).Value.ToString()); Use the power of the parser and eliminate the middleman C#/MSIL/JIT etc etc Get Started Fast and use the parser as Outlined 1) Open XML and goto Grid Mode 2) Select XPATH tab on the bottom viewer/window as shown  From here you get intellisense and can quickly learn how to navigate/find the data using XPATH A key component to Navigation with XPATH is to use the "../ " command . This basically says from where I am now go up 1 level . With Xpath all commands are cumalative. i.e you can search for a book title @ the 2nd level of the XML and from there traverse 15 layers to paragraphs or words on a page with expression validation occuring throughout this process etc  (So in essence you may have arrived @ a node within the XML and have met 15 conditions along the way ) Given 1-2 days with XmlSpy and XPATH you unlock a technology that is super fast and simple to use. XML is a core component to what lays under the hood of so many techs. So it is no wonder that you want to be able to goto  the atomic level to achieve the result you want Justin P.S For a long time I saw XML as slow and a bit boring but now converted

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• Turning a problem into a data

  - by Fogmeister

  OK, I have an app that I'm creating but I'm just really not sure about how to approach the problem. The idea is fairly simple. I'm just not sure how to wrap it in a data model (or even if I should). TBH I feel like I'm making it more complicated than it needs to be. How it works. The app will have circles along the top in a row that need to be connected to circles along the bottom in a row. 10 circles at the top. 10 at the bottom. One connection per pair of dots. Anyway, I can get the dots to connect I'm just not sure how to wrap it in a data model so that I can analyse what has been connected and see if it is right or not. The circles will be questions and answers. I can make an array of question objects with a question and answer properties. I can then display these as the dot pairs. I'm just not sure how to record which questions have been connected to which answers. It is valid for a user to connect a wrong answer as they all get checked at the end. I was thinking of using SpriteKit but this isn't a restriction. I could use UIKit or something else. TBH, this question is fairly language free as I'm just after a way of modelling it.

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• Building a template engine - starting point

  - by Anirudh

  We're building a Django-based project with a template component. This component will be separate from the project as such and can be Django/Python, Node, Java or whatever works. The template has to be rendered into HTML. The templates will contain references to objects with properties that are defined in the DB, say, a Bus. For eg, it could be something like [object type="vehicle" weight="heavy"] and it would have to pull a random object from the DB fulfilling the criteria : type="vehicle" weight="heavy" (bus/truck/jet) and then substitute that tag with an image, say, of a Bus. Also it would have to be able to handle some processing. Eg: What is [X type="integer" lte="10"] + [Y type="integer" lte="10"] [option X+Y correct_ans="true"] [option X-Y correct_ans="false"] [option X+y+1 correct_ans="false"] The engine would be expected to fill in a random integer value <= 10 for X and Y and show radioboxes for each of the options. Would also have to store the fact that the first option is the correct answer. Does it to make sense to write something from the scratch? Or is it better to use an existing templating system (like Django's own templating system) as a starting point? Any suggestions on how I can approach this?

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• How to remove a box2d body when collision happens?

  - by Ayham

  I’m still new to java and android programming and I am having so much trouble Removing an object when collision happens. I looked around the web and found that I should never handle removing BOX2D bodies during collision detection (a contact listener) and I should add my objects to an arraylist and set a variable in the User Data section of the body to delete or not and handle the removing action in an update handler. So I did this: First I define two ArrayLists one for the faces and one for the bodies: ArrayList<Sprite> myFaces = new ArrayList<Sprite>(); ArrayList<Body> myBodies = new ArrayList<Body>(); Then when I create a face and connect that face to its body I add them to their ArrayLists like this: face = new AnimatedSprite(pX, pY, pWidth, pHeight, this.mBoxFaceTextureRegion); Body BoxBody = PhysicsFactory.createBoxBody(mPhysicsWorld, face, BodyType.DynamicBody, objectFixtureDef); mPhysicsWorld.registerPhysicsConnector(new PhysicsConnector(face, BoxBody, true, true)); myFaces.add(face); myBodies.add(BoxBody); now I add a contact listener and an update handler in the onloadscene like this: this.mPhysicsWorld.setContactListener(new ContactListener() { private AnimatedSprite face2; @Override public void beginContact(final Contact pContact) { } @Override public void endContact(final Contact pContact) { } @Override public void preSolve(Contact contact,Manifold oldManifold) { } @Override public void postSolve(Contact contact,ContactImpulse impulse) { } }); scene.registerUpdateHandler(new IUpdateHandler() { @Override public void reset() { } @Override public void onUpdate(final float pSecondsElapsed) { } }); My plan is to detect which two bodies collided in the contact listener by checking a variable from the user data section of the body, get their numbers in the array list and finally use the update handler to remove these bodies. The questions are: Am I using the arraylist correctly? How to add a variable to the User Data (the code please). I tried removing a body in this update handler but it still throws me NullPointerException , so what is the right way to add an update handler and where should I add it. Any other advices to do this would be great. Thanks in advance.

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• Object oriented wrapper around a dll

  - by Tom Davies

  So, I'm writing a C# managed wrapper around a native dll. The dll contains several hundred functions. In most cases, the first argument to each function is an opaque handle to a type internal to the dll. So, an obvious starting point for defining some classes in the wrapper would be to define classes corresponding to each of these opaque types, with each instance holding and managing the opaque handle (passed to its constructor) Things are a little awkward when dealing with callbacks from the dll. Naturally, the callback handlers in my wrapper have to be static, but the callbacks arguments invariable contain an opaque handle. In order to get from the static callback back to an object instance, I've created a static dictionary in each class, associating handles with class instances. In the constructor of each class, an entry is put into the dictionary, and this entry is then removed in the Destructors. When I receive a callback, I can then consult the dictionary to retrieve the class instance corresponding to the opaque reference. Are there any obvious flaws to this? Something that seems to be a problem is that the existence static dictionary means that the garbage collector will not act on my class instances that are otherwise unreachable. As they are never garbage collected, they never get removed from the dictionary, so the dictionary grows. It seems I might have to manually dispose of my objects, which is something absolutely would like to avoid. Can anyone suggest a good design that allows me to avoid having to do this?

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• Copy-and-Pasted Test Code: How Bad is This?

  - by joshin4colours

  My current job is mostly writing GUI test code for various applications that we work on. However, I find that I tend to copy and paste a lot of code within tests. The reason for this is that the areas I'm testing tend to be similar enough to need repetition but not quite similar enough to encapsulate code into methods or objects. I find that when I try to use classes or methods more extensively, tests become more cumbersome to maintain and sometimes outright difficult to write in the first place. Instead, I usually copy a big chunk of test code from one section and paste it to another, and make any minor changes I need. I don't use more structured ways of coding, such as using more OO-principles or functions. Do other coders feel this way when writing test code? Obviously I want to follow DRY and YAGNI principles, but I find that test code (automated test code for GUI testing anyway) can make these principles tough to follow. Or do I just need more coding practice and a better overall system of doing things? EDIT: The tool I'm using is SilkTest, which is in a proprietary language called 4Test. As well, these tests are mostly for Windows desktop applications, but I also have tested web apps using this setup as well.

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• DataContractSerializer truncated string when used with MemoryStream,but works with StringWriter

  - by Michael Freidgeim

  We've used the following DataContractSerializeToXml method for a long time, but recently noticed, that it doesn't return full XML for a long object, but  truncated it and returns XML string with the length of  multiple-of-1024 , but the reminder is not included. internal static string DataContractSerializeToXml<T>(T obj) { string strXml = ""; Type type= obj.GetType();//typeof(T) DataContractSerializer serializer = new DataContractSerializer(type); System.IO.MemoryStream aMemStr = new System.IO.MemoryStream(); System.Xml.XmlTextWriter writer = new System.Xml.XmlTextWriter(aMemStr, null); serializer.WriteObject(writer, obj); strXml = System.Text.Encoding.UTF8.GetString(aMemStr.ToArray()); return strXml; }   I tried to debug and searched Google for similar problems, but didn't find explanation of the error. The most closed http://forums.codeguru.com/showthread.php?309479-MemoryStream-allocates-size-multiple-of-1024-( talking about incorrect length, but not about truncated string.fortunately replacing MemoryStream to StringWriter according to http://billrob.com/archive/2010/02/09/datacontractserializer-converting-objects-to-xml-string.aspxfixed the issue.   1: var serializer = new DataContractSerializer(tempData.GetType());   2: using (var backing = new System.IO.StringWriter())   3: using (var writer = new System.Xml.XmlTextWriter(backing))   4: {   5:     serializer.WriteObject(writer, tempData);   6:     data.XmlData = backing.ToString();   7: }v

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• How bad it's have two methods with the same name but differents signatures in two classes?

  - by Super User

  I have a design problem relationated with the public interface, the names of methods and the understanding of my API and my code. I have two classes like this: class A: ... function collision(self): .... ... class B: .... function _collision(self, another_object, l, r, t, b): .... The first class have one public method named collision and the second have one private method called _collision. The two methods differs in arguments type and number. In the API _m method is private. For the example let's say that the _collision method checks if the object is colliding with another_ object with certain conditions l, r, t, b (for example, collide the left side, the right side, etc) and returns true or false according to the case. The collision method, on the other hand, resolves all the collisions of the object with other objects. The two methods have the same name because I think is better avoid overload the design with different names for methods who do almost the same think, but in distinct contexts and classes. This is clear enough to the reader or I should change the method's name?

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• I've been told that Exceptions should only be used in exceptional cases. How do I know if my case is exceptional?

  - by tieTYT

  My specific case here is that the user can pass in a string into the application, the application parses it and assigns it to structured objects. Sometimes the user may type in something invalid. For example, their input may describe a person but they may say their age is "apple". Correct behavior in that case is roll back the transaction and to tell the user an error occurred and they'll have to try again. There may be a requirement to report on every error we can find in the input, not just the first. In this case, I argued we should throw an exception. He disagreed, saying, "Exceptions should be exceptional: It's expected that the user may input invalid data, so this isn't an exceptional case" I didn't really know how to argue that point, because by definition of the word, he seems to be right. But, it's my understanding that this is why Exceptions were invented in the first place. It used to be you had to inspect the result to see if an error occurred. If you failed to check, bad things could happen without you noticing. Without exceptions every level of the stack needs to check the result of the methods they call and if a programmer forgets to check in one of these levels, the code could accidentally proceed and save invalid data (for example). Seems more error prone that way. Anyway, feel free to correct anything I've said here. My main question is if someone says Exceptions should be exceptional, how do I know if my case is exceptional?

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• How can I pass an external instance to the constructor of an object that's being created using the default XNA XML content loader?

  - by Michael

  I'm trying to understand how to use the XNA XML content importer to instantiate non-trivial objects that are more than a collection of basic properties (e.g., a class that inherits from DrawableGameObject or GameObject and requires other things to be passed into its constructor). Is it possible to pass existing external instances (e.g., an instance of the current Game) to the constructor of an object that's being created using the default XNA XML content loader? For example, imagine that I have the following class, inheriting from DrawableGameComponent: public class Character : DrawableGameComponent { public string Name { get; set; } public Character(Game game) : base(game) { } public override void Update(GameTime gameTime) { } public override void Draw(GameTime gameTime) { } } If I had a simple class that did not need other parameters in its constructor (i.e., the Game instance), then I could simply use this XML: <XnaContent> <Asset Type="MyNamespace.Character"> <Name>John Doe</Name> </Asset> </XnaContent> ...and then create an instance of Character using this code: var character = Content.Load<Character>("MyXmlAssetName"); But that won't work because I need to pass the need to pass the Game into the constructor. What's the best way to handle this situation? Is there a way to pass in things like the current Game using the default XNA XML content loader? Do I need to write my own XML loader? (If so, how?) Is there a better object-oriented design that I should be using for my classes? Note: Although I used Game in this example, I'm really just asking how to pass any type of existing instance to my constructors. (For example, I'm using the Farseer Physics Engine, and some of my classes also need a reference to the Farseer World object too.) Thanks in advance.

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• Learning OpenGL GLSL - VAO buffer problems?

  - by Bleary

  I've just started digging through OpenGL and GLSL, and now stumbled on something I can't get my head around this one!? I've stepped back to loading a simple cube and using a simple shader on it, but the result is triangles drawn incorrectly and/or missing. The code I had working perfectly on meshes, but was attempting to move to using VAOs so none of the code for storing the vertices and indices has changed. http://i.stack.imgur.com/RxxZ5.jpg http://i.stack.imgur.com/zSU50.jpg What I have for creating the VAO and buffers is this //Create the Vertex array object glGenVertexArrays(1, &vaoID); // Finally create our vertex buffer objects glGenBuffers(VBO_COUNT, mVBONames); glBindVertexArray(vaoID); // Save vertex attributes into GPU glBindBuffer(GL_ARRAY_BUFFER, mVBONames[VERTEX_VBO]); // Copy data into the buffer object glBufferData(GL_ARRAY_BUFFER, lPolygonVertexCount*VERTEX_STRIDE*sizeof(GLfloat), lVertices, GL_STATIC_DRAW); glEnableVertexAttribArray(pos); glVertexAttribPointer(pos, 3, GL_FLOAT, GL_FALSE, VERTEX_STRIDE*sizeof(GLfloat),0); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mVBONames[INDEX_VBO]); glBufferData(GL_ELEMENT_ARRAY_BUFFER, lPolygonCount*sizeof(unsigned int), lIndices, GL_STATIC_DRAW); glBindVertexArray(0); And the code for drawing the mesh. glBindVertexArray(vaoID); glUseProgram(shader->programID); GLsizei lOffset = mSubMeshes[pMaterialIndex]->IndexOffset*sizeof(unsigned int); const GLsizei lElementCount = mSubMeshes[pMaterialIndex]->TriangleCount*TRIAGNLE_VERTEX_COUNT; glDrawElements(GL_TRIANGLES, lElementCount, GL_UNSIGNED_SHORT, reinterpret_cast<const GLvoid*>(lOffset)); // All the points are indeed in the correct place!? //glPointSize(10.0f); //glDrawElements(GL_POINTS, lElementCount, GL_UNSIGNED_SHORT, 0); glUseProgram(0); glBindVertexArray(0); Eyes have become bleary looking at this today so any thoughts or a fresh set of eyes would be greatly appreciated.

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• Problem graphics with ATI Radeon x1270 (RS690M) on Ubuntu 12.04

  - by Giuseppe Della Corte

  I'm Italian and so I apologize for my English! I'm a beginner to Ubuntu and I tried it on my desktop PC and it's fantastic, fast and fun! I decided to try it on my netbook Packard Bell DOT M/A and this is the configuration: AMD Athlon L110 1.2GHz 2GB of RAM ATI Radeon x1270 (RS690M) 150GB Hard Disk I installed Ubuntu 12.04 with Wubi (dualboot Windows 7 + Ubuntu 12.04), because the netbook does not have a DVD player! During the installation everything is OK, after it was installed I see mistakes in the graphical display! I see objects that are seen in different colors and moving (buttons, mouse pointer, text bar ... etc ...) At one point came not to see anything, such as this screenshot: The drivers are open, that is already installed in Ubuntu. Windows 7 video card runs fine, can run well Aero (transparent window effects), I can watch movies in HD and play some games with the Catalyst drivers from AMD. Now I ask a favor, you can help me solve this problem? Is there a fix for this driver or drivers different on the Internet? Thanks for your attention, good bye!

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• How should I load level data in java?

  - by Matthew G.

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

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• What should a domain object's validation cover?

  - by MarcoR88

  I'm trying to figure out how to do validation of domain objects that need external resources, such as data mappers/dao Firstly here's my code class User { const INVALID_ID = 1; const INVALID_NAME = 2; const INVALID_EMAIL = 4; int getID(); void setID(Int i); string getName(); void setName(String s); string getEmail(); void setEmail(String s); int getErrorsForInsert(); // returns a bitmask for INVALID_* constants int getErrorsForUpdate(); } My worries are about the uniqueness of the email, checking it would require the storage layer. Reading others' code seems that two solutions are equally accepted: both perform the unique validation in data mapper but some set an error state to the DO user.addError(User.INVALID_EMAIL) while others prefer to throw a totally different type of exception that covers only persistence, like: UserStorageException { const INVALID_EMAIL = 1; const INVALID_CITY = 2; } What are the pros and cons of these solutions?

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• What is the best approach to solve a factory method problem which has to be an instance?

  - by Iago

  I have to add new funcionality in a web service legacy project and I'm thinking what is the best approach for a concrete situation. The web service is simple: It receives a XML file, unmarshalling, generates response's objects, marshalling and finally it sends the response as a XML file. For every XML files received, the web service always responds with the same XML structure. What I have to do is to generate a different XML file according to the XML received. So I have a controller class which has all marshalling/unmarshalling operations, but this controller class has to be an instance. Depending on XML received I need some marshalling methods or others. Trying to make few changes on legacy source, what is the best approach? My first approach was to do a factory method pattern with the controller class, but this class has to be an instance. I want to keep, as far as it goes, this structure: classController.doMarshalling(); I think this one is a bit smelly: if(XMLReceived.isTypeOne()) classController.doMarshallingOne(); else if(XMLReceived.isTypeTwo()) classController.doMarshallingTwo(); else if(XMLReceived.isTypeThree()) classController.doMarshallingThree(); else if ... I hope my question is well understood

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• When module calling gets ugly

  - by Pete

  Has this ever happened to you? You've got a suite of well designed, single-responsibility modules, covered by unit tests. In any higher-level function you code, you are (95% of the code) simply taking output from one module and passing it as input to the next. Then, you notice this higher-level function has turned into a 100+ line script with multiple responsibilities. Here is the problem. It is difficult (impossible) to test that script. At least, it seems so. Do you agree? In my current project, all of the bugs came from this script. Further detail: each script represents a unique solution, or algorithm, formed by using different modules in different ways. Question: how can you remedy this situation? Knee-jerk answer: break the script up into single-responsibility modules. Comment on knee-jerk answer: it already is! Best answer I can come up with so far: create higher-level connector objects which "wire" modules together in particular ways (take output from one module, feed it as input to another module). Thus if our script was: FooInput fooIn = new FooInput(1, 2); FooOutput fooOutput = fooModule(fooIn); Double runtimevalue = getsomething(fooOutput.whatever); BarInput barIn = new BarInput( runtimevalue, fooOutput.someOtherValue); BarOutput barOut = barModule(BarIn); It would become with a connector: FooBarConnectionAlgo fooBarConnector = new fooBarConnector(fooModule, barModule); FooInput fooIn = new FooInput(1, 2); BarOutput barOut = fooBarConnector(fooIn); So the advantage is, besides hiding some code and making things clearer, we can test FooBarConnectionAlgo. I'm sure this situation comes up a lot. What do you do?

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• Deferred rendering order?

  - by Nick Wiggill

  There are some effects for which I must do multi-pass rendering. I've got the basics set up (FBO rendering etc.), but I'm trying to get my head around the most suitable setup. Here's what I'm thinking... The framebuffer objects: FBO 1 has a color attachment and a depth attachment. FBO 2 has a color attachment. The render passes: Render g-buffer: normals and depth (used by outline & DoF blur shaders); output to FBO no. 1. Render solid geometry, bold outlines (as in toon shader), and fog; output to FBO no. 2. (can all render via a single fragment shader -- I think.) (optional) DoF blur the scene; output to the default frame buffer OR ELSE render FBO2 directly to default frame buffer. (optional) Mesh wireframes; composite over what's already in the default framebuffer. Does this order seem viable? Any obvious mistakes?

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

  - by Rami

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

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• Android From Local DB (DAO) to Server sync (JSON) - Design issue

  - by Taiko

  I sync data between my local DB and a Server. I'm looking for the cleanest way to modelise all of this. I have a com.something.db package That contains a Data Helper and couple of DAO classes that represents objects stored in the db (I didn't write that part) com.something.db --public DataHelper --public Employee @DatabaseField e.g. "name" will be an actual column name in the DB -name @DatabaseField -salary etc... (all in all 50 fields) I have a com.something.sync package That contains all the implementation detail on how to send data to the server. It boils down to a ConnectionManager that is fed by different classes that implements a 'Request' interface com.something.sync --public interface ConnectionManager --package ConnectionManagerImpl --public interface Request --package LoginRequest --package GetEmployeesRequest My issue is, at some point in the sync process, I have to JSONise and de-JSONise my data (E.g. the Employee class). But I really don't feel like having the same Employee class be responsible for both his JSONisation and his actual representation inside the local database. It really doesn't feel right, because I carefully decoupled the rest, I am only stuck on this JSON thing. What should I do ? Should I write 3 Employee classes ? EmployeeDB @DatabaseField e.g. "name" will be an actual column name in the DB -name @DatabaseField -salary -etc... 50 fields EmployeeInterface -getName -getSalary -etc... 50 fields EmployeeJSON -JSON_KEY_NAME = "name" The JSON key happens to be the same as the table name, but it isn't requirement -name -JSON_KEY_SALARY = "salary" -salary -etc... 50 fields It feels like a lot of duplicates. Is there a common pattern I can use there ?

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