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• Network latency -- how long does it take for a packet to travel halfway around the world?

  - by kaneuniversal

  If I'm hosting an app in NY, what kind of delay can I expect for a user to get a single packet if they're in Australia, i.e. roughly the maximum distance from NY? I'm looking for the maximum latency I'm likely to encounter on a regular basis -- if Australia's not the right destination point to consider, feel free to substitute another point. Thanks! Michael

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• How to safely immigrate svn repositories and change history?

  - by apache

  Either svnadmin dump or svnadmin export will only has a snapshot of a certain version. How to keep all change logs when immigrating to another server? Will it be OK to just copy the /repositories over there?

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• Google Desktop

  A handy tool that enables desktop searching for files, emails, Web history, and IM chats

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• World's Most Challening MySQL SQL Query (least I think so...)

  - by keruilin

  Whoever answers this question can claim credit for solving the world's most challenging SQL query, according to yours truly. Working with 3 tables: users, badges, awards. Relationships: user has many awards; award belongs to user; badge has many awards; award belongs to badge. So badge_id and user_id are foreign keys in the awards table. The business logic at work here is that every time a user wins a badge, he/she receives it as an award. A user can be awarded the same badge multiple times. Each badge is assigned a designated point value (point_value is a field in the badges table). For example, BadgeA can be worth 500 Points, BadgeB 1000 Points, and so on. As further example, let's say UserX won BadgeA 10 times and BadgeB 5 times. BadgeA being worth 500 Points, and BadgeB being worth 1000 Points, UserX has accumulated a total of 10,000 Points ((10 x 500) + (5 x 1000)). The end game here is to return a list of top 50 users who have accumulated the most badge points. Can you do it?

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• How to read from multiple queues in real-world?

  - by Leon Cullens

  Here's a theoretical question: When I'm building an application using message queueing, I'm going to need multiple queues support different data types for different purposes. Let's assume I have 20 queues (e.g. one to create new users, one to process new orders, one to edit user settings, etc.). I'm going to deploy this to Windows Azure using the 'minimum' of 1 web role and 1 worker role. How does one read from all those 20 queues in a proper way? This is what I had in mind, but I have little or no real-world practical experience with this: Create a class that spawns 20 threads in the worker role 'main' class. Let each of these threads execute a method to poll a different queue, and let all those threads sleep between each poll (of course with a back-off mechanism that increases the sleep time). This leads to have 20 threads (or 21?), and 20 queues that are being actively polled, resulting in a lot of wasted messages (each time you poll an empty queue it's being billed as a message). How do you solve this problem?

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• Farseer tutorial for the absolute beginners

  - by Bil Simser

  This post is inspired (and somewhat a direct copy) of a couple of posts Emanuele Feronato wrote back in 2009 about Box2D (his tutorial was ActionScript 3 based for Box2D, this is C# XNA for the Farseer Physics Engine). Here’s what we’re building: What is Farseer The Farseer Physics Engine is a collision detection system with realistic physics responses to help you easily create simple hobby games or complex simulation systems. Farseer was built as a .NET version of Box2D (based on the Box2D.XNA port of Box2D). While the constructs and syntax has changed over the years, the principles remain the same. This tutorial will walk you through exactly what Emanuele create for Flash but we’ll be doing it using C#, XNA and the Windows Phone platform. The first step is to download the library from its home on CodePlex. If you have NuGet installed, you can install the library itself using the NuGet package that but we’ll also be using some code from the Samples source that can only be obtained by downloading the library. Once you download and unpacked the zip file into a folder and open the solution, this is what you will get: The Samples XNA WP7 project (and content) have all the demos for Farseer. There’s a wealth of info here and great examples to look at to learn. The Farseer Physics XNA WP7 project contains the core libraries that do all the work. DebugView XNA contains an XNA-ready class to let you view debug data and information in the game draw loop (which you can copy into your project or build the source and reference the assembly). The downloaded version has to be compiled as it’s only available in source format so you can do that now if you want (open the solution file and rebuild everything). If you’re using the NuGet package you can just install that. We only need the core library and we’ll be copying in some code from the samples later. Your first Farseer experiment Start Visual Studio and create a new project using the Windows Phone template can call it whatever you want. It’s time to edit Game1.cs 1 public class Game1 : Game 2 { 3 private readonly GraphicsDeviceManager _graphics; 4 private DebugViewXNA _debugView; 5 private Body _floor; 6 private SpriteBatch _spriteBatch; 7 private float _timer; 8 private World _world; 9 10 public Game1() 11 { 12 _graphics = new GraphicsDeviceManager(this) 13 { 14 PreferredBackBufferHeight = 800, 15 PreferredBackBufferWidth = 480, 16 IsFullScreen = true 17 }; 18 19 Content.RootDirectory = "Content"; 20 21 // Frame rate is 30 fps by default for Windows Phone. 22 TargetElapsedTime = TimeSpan.FromTicks(333333); 23 24 // Extend battery life under lock. 25 InactiveSleepTime = TimeSpan.FromSeconds(1); 26 } 27 28 protected override void LoadContent() 29 { 30 // Create a new SpriteBatch, which can be used to draw textures. 31 _spriteBatch = new SpriteBatch(_graphics.GraphicsDevice); 32 33 // Load our font (DebugViewXNA needs it for the DebugPanel) 34 Content.Load<SpriteFont>("font"); 35 36 // Create our World with a gravity of 10 vertical units 37 if (_world == null) 38 { 39 _world = new World(Vector2.UnitY*10); 40 } 41 else 42 { 43 _world.Clear(); 44 } 45 46 if (_debugView == null) 47 { 48 _debugView = new DebugViewXNA(_world); 49 50 // default is shape, controller, joints 51 // we just want shapes to display 52 _debugView.RemoveFlags(DebugViewFlags.Controllers); 53 _debugView.RemoveFlags(DebugViewFlags.Joint); 54 55 _debugView.LoadContent(GraphicsDevice, Content); 56 } 57 58 // Create and position our floor 59 _floor = BodyFactory.CreateRectangle( 60 _world, 61 ConvertUnits.ToSimUnits(480), 62 ConvertUnits.ToSimUnits(50), 63 10f); 64 _floor.Position = ConvertUnits.ToSimUnits(240, 775); 65 _floor.IsStatic = true; 66 _floor.Restitution = 0.2f; 67 _floor.Friction = 0.2f; 68 } 69 70 protected override void Update(GameTime gameTime) 71 { 72 // Allows the game to exit 73 if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed) 74 Exit(); 75 76 // Create a random box every second 77 _timer += (float) gameTime.ElapsedGameTime.TotalSeconds; 78 if (_timer >= 1.0f) 79 { 80 // Reset our timer 81 _timer = 0f; 82 83 // Determine a random size for each box 84 var random = new Random(); 85 var width = random.Next(20, 100); 86 var height = random.Next(20, 100); 87 88 // Create it and store the size in the user data 89 var box = BodyFactory.CreateRectangle( 90 _world, 91 ConvertUnits.ToSimUnits(width), 92 ConvertUnits.ToSimUnits(height), 93 10f, 94 new Point(width, height)); 95 96 box.BodyType = BodyType.Dynamic; 97 box.Restitution = 0.2f; 98 box.Friction = 0.2f; 99 100 // Randomly pick a location along the top to drop it from 101 box.Position = ConvertUnits.ToSimUnits(random.Next(50, 400), 0); 102 } 103 104 // Advance all the elements in the world 105 _world.Step(Math.Min((float) gameTime.ElapsedGameTime.TotalMilliseconds*0.001f, (1f/30f))); 106 107 // Clean up any boxes that have fallen offscreen 108 foreach (var box in from box in _world.BodyList 109 let pos = ConvertUnits.ToDisplayUnits(box.Position) 110 where pos.Y > _graphics.GraphicsDevice.Viewport.Height 111 select box) 112 { 113 _world.RemoveBody(box); 114 } 115 116 base.Update(gameTime); 117 } 118 119 protected override void Draw(GameTime gameTime) 120 { 121 GraphicsDevice.Clear(Color.FromNonPremultiplied(51, 51, 51, 255)); 122 123 _spriteBatch.Begin(); 124 125 var projection = Matrix.CreateOrthographicOffCenter( 126 0f, 127 ConvertUnits.ToSimUnits(_graphics.GraphicsDevice.Viewport.Width), 128 ConvertUnits.ToSimUnits(_graphics.GraphicsDevice.Viewport.Height), 0f, 0f, 129 1f); 130 _debugView.RenderDebugData(ref projection); 131 132 _spriteBatch.End(); 133 134 base.Draw(gameTime); 135 } 136 } 137 Lines 4: Declare the debug view we’ll use for rendering (more on that later). Lines 8: Declare _world variable of type class World. World is the main object to interact with the Farseer engine. It stores all the joints and bodies, and is responsible for stepping through the simulation. Lines 12-17: Create the graphics device we’ll be rendering on. This is an XNA component and we’re just setting it to be the same size as the phone and toggling it to be full screen (no system tray). Lines 34: We create a SpriteFont here by adding it to the project. It’s called “font” because that’s what the DebugView uses but you can name it whatever you want (and if you’re not using DebugView for your production app you might have several fonts). Lines 37-44: We create the physics environment that Farseer uses to contain all the objects by specifying it here. We’re using Vector2.UnitY*10 to represent the gravity to be used in the environment. In other words, 10 units going in a downward motion. Lines 46-56: We create the DebugViewXNA here. This is copied from the […] from the code you downloaded and provides the ability to render all entities onto the screen. In a production release you’ll be doing the rendering yourself of each object but we cheat a bit for the demo and let the DebugView do it for us. The other thing it can provide is to render out a panel of debugging information while the simulation is going on. This is useful in tracking down objects, figuring out how something works, or just keeping track of what’s in the engine. Lines 49-67: Here we create a rigid body (Farseer only supports rigid bodies) to represent the floor that we’ll drop objects onto. We create it by using one of the Farseer factories and specifying the width and height. The ConvertUnits class is copied from the samples code as-is and lets us toggle between display units (pixels) and simulation units (usually metres). We’re creating a floor that’s 480 pixels wide and 50 pixels high (converting them to SimUnits for the engine to understand). We also position it near the bottom of the screen. Values are in metres and when specifying values they refer to the centre of the body object. Lines 77-78: The game Update method fires 30 times a second, too fast to be creating objects this quickly. So we use a variable to track the elapsed seconds since the last update, accumulate that value, then create a new box to drop when 1 second has passed. Lines 89-94: We create a box the same way we created our floor (coming up with a random width and height for the box). Lines 96-101: We set the box to be Dynamic (rather than Static like the floor object) and position it somewhere along the top of the screen. And now you created the world. Gravity does the rest and the boxes fall to the ground. Here’s the result: Farseer Physics Engine Demo using XNA Lines 105: We must update the world at every frame. We do this with the Step method which takes in the time interval. [more] Lines 108-114: Body objects are added to the world but never automatically removed (because Farseer doesn’t know about the display world, it has no idea if an item is on the screen or not). Here we just loop through all the entities and anything that’s dropped off the screen (below the bottom) gets removed from the World. This keeps our entity count down (the simulation never has more than 30 or 40 objects in the world no matter how long you run it for). Too many entities and the app will grind to a halt. Lines 125-130: Farseer knows nothing about the UI so that’s entirely up to you as to how to draw things. Farseer is just tracking the objects and moving them around using the physics engine and it’s rules. You’ll still use XNA to draw items (using the SpriteBatch.Draw method) so you can load up your usual textures and draw items and pirates and dancing zombies all over the screen. Instead in this demo we’re going to cheat a little. In the sample code for Farseer you can download there’s a project called DebugView XNA. This project contains the DebugViewXNA class which just handles iterating through all the bodies in the world and drawing the shapes. So we call the RenderDebugData method here of that class to draw everything correctly. In the case of this demo, we just want to draw Shapes so take a look at the source code for the DebugViewXNA class as to how it extracts all the vertices for the shapes created (in this case simple boxes) and draws them. You’ll learn a *lot* about how Farseer works just by looking at this class. That’s it, that’s all. Simple huh? Hope you enjoy the code and library. Physics is hard and requires some math skills to really grok. The Farseer Physics Engine makes it pretty easy to get up and running and start building games. In future posts we’ll get more in-depth with things you can do with the engine so this is just the beginning. Enjoy!

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• Is the Scala 2.8 collections library a case of "the longest suicide note in history" ?

  - by oxbow_lakes

  First note the inflammatory subject title is a quotation made about the manifesto of a UK political party in the early 1980s. This question is subjective but it is a genuine question, I've made it CW and I'd like some opinions on the matter. Despite whatever my wife and coworkers keep telling me, I don't think I'm an idiot: I have a good degree in mathematics from the University of Oxford and I've been programming commercially for almost 12 years and in Scala for about a year (also commercially). I have just started to look at the Scala collections library re-implementation which is coming in the imminent 2.8 release. Those familiar with the library from 2.7 will notice that the library, from a usage perspective, has changed little. For example... > List("Paris", "London").map(_.length) res0: List[Int] List(5, 6) ...would work in either versions. The library is eminently useable: in fact it's fantastic. However, those previously unfamiliar with Scala and poking around to get a feel for the language now have to make sense of method signatures like: def map[B, That](f: A => B)(implicit bf: CanBuildFrom[Repr, B, That]): That For such simple functionality, this is a daunting signature and one which I find myself struggling to understand. Not that I think Scala was ever likely to be the next Java (or /C/C++/C#) - I don't believe its creators were aiming it at that market - but I think it is/was certainly feasible for Scala to become the next Ruby or Python (i.e. to gain a significant commercial user-base) Is this going to put people off coming to Scala? Is this going to give Scala a bad name in the commercial world as an academic plaything that only dedicated PhD students can understand? Are CTOs and heads of software going to get scared off? Was the library re-design a sensible idea? If you're using Scala commercially, are you worried about this? Are you planning to adopt 2.8 immediately or wait to see what happens? Steve Yegge once attacked Scala (mistakenly in my opinion) for what he saw as its overcomplicated type-system. I worry that someone is going to have a field day spreading fud with this API (similarly to how Josh Bloch scared the JCP out of adding closures to Java). Note - I should be clear that, whilst I believe that Josh Bloch was influential in the rejection of the BGGA closures proposal, I don't ascribe this to anything other than his honestly-held beliefs that the proposal represented a mistake.

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• Is there a path of least resistance that a newcomer to graphics-technology-adoption can take at this point in the .NET graphics world?

  - by Rao

  For the past 5 months or so, I've spent time learning C# using Andrew Troelsen's book and getting familiar with stuff in the .NET 4 stack... bits of ADO.NET, EF4 and a pinch of WCF to taste. I'm really interested in graphics development (not for games though), which is why I chose to go the .NET route when I decided choose from either Java or .NET to learn... since I heard about WPF and saw some sexy screenshots and all. I'm even almost done with the 4 WPF chapters in Troelsen's book. Now, all of a sudden I saw some post on a forum about how "WPF was dead" in the face of something called Silverlight. I searched more and saw all the confusion going on at present... even stuff like "Silverlight is dead too!" wrt HTML5. From what I gather, we are in a delicate period of time that will eventually decide which technology will stabilize, right? Even so, as someone new moving into UI & graphics development via .NET, I wish I could get some guidance from people more experienced people. Maybe I'm reading too much? Maybe I have missed some pieces of information? Maybe a path exists that minimizes tears of blood? In any case, here is a sample vomiting of my thoughts on which I'd appreciate some clarification or assurance or spanking: My present interest lies in desktop development. But on graduating from college, I wish to market myself as a .NET developer. The industry seems to be drooling for web stuff. Can Silverlight do both equally well? (I see on searches that SL works "out of browser"). I have two fair-sized hobby projects planned that will have hawt UIs with lots of drag n drop, sliding animations etc. These are intended to be desktop apps that will use reflection, database stuff using EF4, networking over LAN, reading-writing of files... does this affect which graphics technology can be used? At some laaaater point, if I become interested in doing a bit of 3D stuff in .NET, will that affect which technologies can be used? Or what if I look up to the heavens, stick out my middle finger, and do something crazy like go learn HTML5 even though my knowledge of it can be encapsulated in 2 sentences? Sorry I seem confused so much, I just want to know if there's a path of least resistance that a newcomer to graphics-technology-adoption can take at this point in the graphics world.

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• How do I handle the Maybe result of at in Control.Lens.Indexed without a Monoid instance

  - by Matthias Hörmann

  I recently discovered the lens package on Hackage and have been trying to make use of it now in a small test project that might turn into a MUD/MUSH server one very distant day if I keep working on it. Here is a minimized version of my code illustrating the problem I am facing right now with the at lenses used to access Key/Value containers (Data.Map.Strict in my case) {-# LANGUAGE OverloadedStrings, GeneralizedNewtypeDeriving, TemplateHaskell #-} module World where import Control.Applicative ((<$>),(<*>), pure) import Control.Lens import Data.Map.Strict (Map) import qualified Data.Map.Strict as DM import Data.Maybe import Data.UUID import Data.Text (Text) import qualified Data.Text as T import System.Random (Random, randomIO) newtype RoomId = RoomId UUID deriving (Eq, Ord, Show, Read, Random) newtype PlayerId = PlayerId UUID deriving (Eq, Ord, Show, Read, Random) data Room = Room { _roomId :: RoomId , _roomName :: Text , _roomDescription :: Text , _roomPlayers :: [PlayerId] } deriving (Eq, Ord, Show, Read) makeLenses ''Room data Player = Player { _playerId :: PlayerId , _playerDisplayName :: Text , _playerLocation :: RoomId } deriving (Eq, Ord, Show, Read) makeLenses ''Player data World = World { _worldRooms :: Map RoomId Room , _worldPlayers :: Map PlayerId Player } deriving (Eq, Ord, Show, Read) makeLenses ''World mkWorld :: IO World mkWorld = do r1 <- Room <$> randomIO <*> (pure "The Singularity") <*> (pure "You are standing in the only place in the whole world") <*> (pure []) p1 <- Player <$> randomIO <*> (pure "testplayer1") <*> (pure $ r1^.roomId) let rooms = at (r1^.roomId) ?~ (set roomPlayers [p1^.playerId] r1) $ DM.empty players = at (p1^.playerId) ?~ p1 $ DM.empty in do return $ World rooms players viewPlayerLocation :: World -> PlayerId -> RoomId viewPlayerLocation world playerId= view (worldPlayers.at playerId.traverse.playerLocation) world Since rooms, players and similar objects are referenced all over the code I store them in my World state type as maps of Ids (newtyped UUIDs) to their data objects. To retrieve those with lenses I need to handle the Maybe returned by the at lens (in case the key is not in the map this is Nothing) somehow. In my last line I tried to do this via traverse which does typecheck as long as the final result is an instance of Monoid but this is not generally the case. Right here it is not because playerLocation returns a RoomId which has no Monoid instance. No instance for (Data.Monoid.Monoid RoomId) arising from a use of `traverse' Possible fix: add an instance declaration for (Data.Monoid.Monoid RoomId) In the first argument of `(.)', namely `traverse' In the second argument of `(.)', namely `traverse . playerLocation' In the second argument of `(.)', namely `at playerId . traverse . playerLocation' Since the Monoid is required by traverse only because traverse generalizes to containers of sizes greater than one I was now wondering if there is a better way to handle this that does not require semantically nonsensical Monoid instances on all types possibly contained in one my objects I want to store in the map. Or maybe I misunderstood the issue here completely and I need to use a completely different bit of the rather large lens package?

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• All libGDX input statements are returning TRUE at once

  - by MowDownJoe

  I'm fooling around with Box2D and libGDX and running into a peculiar problem with polling for input. Here's the code for the Screen's render() loop: @Override public void render(float delta) { Gdx.gl20.glClearColor(0, 0, .2f, 1); Gdx.gl20.glClear(GL20.GL_COLOR_BUFFER_BIT); camera.update(); game.batch.setProjectionMatrix(camera.combined); debugRenderer.render(world, camera.combined); if(Gdx.input.isButtonPressed(Keys.LEFT)){ Gdx.app.log("Input", "Left is being pressed."); pushyThingyBody.applyForceToCenter(-10f, 0); } if(Gdx.input.isButtonPressed(Keys.RIGHT)){ Gdx.app.log("Input", "Right is being pressed."); pushyThingyBody.applyForceToCenter(10f, 0); } world.step((1f/45f), 6, 2); } And the constructor is largely just setting up the World, Box2DDebugRenderer, and all the Bodies in the world: public SandBox(PhysicsSandboxGame game) { this.game = game; camera = new OrthographicCamera(800, 480); camera.setToOrtho(false); world = new World(new Vector2(0, -9.8f), true); debugRenderer = new Box2DDebugRenderer(); BodyDef bodyDef = new BodyDef(); bodyDef.type = BodyType.DynamicBody; bodyDef.position.set(100, 300); body = world.createBody(bodyDef); CircleShape circle = new CircleShape(); circle.setRadius(6f); FixtureDef fixtureDef = new FixtureDef(); fixtureDef.shape = circle; fixtureDef.density = .5f; fixtureDef.friction = .4f; fixtureDef.restitution = .6f; fixture = body.createFixture(fixtureDef); circle.dispose(); BodyDef groundBodyDef = new BodyDef(); groundBodyDef.position.set(new Vector2(0, 10)); groundBody = world.createBody(groundBodyDef); PolygonShape groundBox = new PolygonShape(); groundBox.setAsBox(camera.viewportWidth, 10f); groundBody.createFixture(groundBox, 0f); groundBox.dispose(); BodyDef pushyThingyBodyDef = new BodyDef(); pushyThingyBodyDef.type = BodyType.DynamicBody; pushyThingyBodyDef.position.set(new Vector2(400, 30)); pushyThingyBody = world.createBody(pushyThingyBodyDef); PolygonShape pushyThingyShape = new PolygonShape(); pushyThingyShape.setAsBox(40f, 10f); FixtureDef pushyThingyFixtureDef = new FixtureDef(); pushyThingyFixtureDef.shape = pushyThingyShape; pushyThingyFixtureDef.density = .4f; pushyThingyFixtureDef.friction = .1f; pushyThingyFixtureDef.restitution = .5f; pushyFixture = pushyThingyBody.createFixture(pushyThingyFixtureDef); pushyThingyShape.dispose(); } Testing this on the desktop. Basically, whenever I hit the appropriate keys, neither of the if statements in the loop return true. However, when I click in the window, both statements return true, resulting in a 0 net force on the body. Why is this?

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• Collision detection with heightmap based terrain

  - by Truman's world

  I am developing a 2D tank game. The terrain is generated by Midpoint Displacement Algorithm, so the terrain is represented by an array: index ---> height of terrain [0] ---> 5 [1] ---> 8 [2] ---> 4 [3] ---> 6 [4] ---> 8 [5] ---> 9 ... ... The rendered mountain looks like this: * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 0 1 2 3 4 5 ... I want tanks to be able to move smoothly on the terrain (I mean tanks can rotate according to the height when they move), but the surface of the terrain is not flat, it is polygonal. Can anyone give me some help with collision detection in this situation? Thanks in advance.

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• Box2D random crash when adding joints

  - by user46624

  I'm currently working on a project which uses Box2D, when the player uses a certain key it should anchor to the ground. For that I use a weld joint, but when I add the joint the game will sometimes crash, it has a 1/10 change to crash. The error I recieve: Showing the controller Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 11 at org.jbox2d.dynamics.Island.add(Island.java:577) at org.jbox2d.dynamics.World.solve(World.java:1073) at org.jbox2d.dynamics.World.step(World.java:598) The code for adding the joints: WeldJointDef def = new WeldJointDef(); def.initialize(body, anchoredObject.body, body.getWorldCenter()); weldJoint = (WeldJoint) world.createJoint(def); I still get the error if I synchronize it

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• Is there a definitive reference on Pinball playfield design?

  - by World Engineer

  I'm looking at designing tables for Future Pinball but I'm not sure where to start as I've little background in game design per se. I've played scores of pinball tables over the years so I've a fairly good idea of what is "fun" in those terms. However, I'd like to know if there is a definitive "bible" of pinball design as far as layout and scoring/mode design goes. I've looked but there doesn't seem to be anything really coherent that I could find. Is it simply a lost art or am I missing some buried gem?

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• What is the most compatible, widely used production language to export knowledge and skills gained from Haskell?

  - by World Engineer

  I like Haskell, plain and simple. While Haskell is used in production software, it's not especially widely deployed from what I've seen. What is the most similar and still widely used language in regards to production projects so that I might have a snowball's chance of using something similarly awesome in industry? Also is the same language from the first part available on large numbers of platforms? If not, what is the best alternative that has wide platform deployment? I'd like a single language to put on my to-do list rather than a massive swarm or family. Hard evidence would be a plus.

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• Is IronScheme complete enough or stable enough to be worth learning?

  - by World Engineer

  IronScheme is mentioned on Wikipedia as a successor to a failed project called IronLisp, bringing Lisp to CLR and .NET, the way Clojure does for the JVM. Does anyone have experience with this language? It looks fairly complete (99%) but I'm not sure how to judge whether it's worth my time to fiddle with getting it set up or not. By stable or complete, I mean using it for actual projects rather than just fiddling with tools and Project Euler style problems.

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• Projecting a targetting ring using direct3d

  - by JohnB

  I'm trying to draw a "targetting ring" on the ground below a "unit" in a hobby 3d game I'm working on. Basically I want to project a bright red patterned ring onto the ground terrain below the unit. The only approach I can think of is this - Draw the world once as normal Draw the world a second time but in my vertex shader I have the world x,y,z coordinates of the vertex and I can pass in the coordinates of the highlighted unit - so I can calculate what the u,v coordinates in my project texture should be at that point in the world for that vertex. I'd then use the pixel shader to pick pixels from the target ring texture and blend them into the previously drawn world. I believe that should be easy, and should work but it involves me drawing the whole visible world twice as it's hard to determine exactly which polygons the targetting ring might fall onto. It seems a big overhead to draw the whole world twice, once for the normal lit textured ground, and then again just to draw the targetting ring. Is there a better approach that I'm missing?

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• C# Container Class

  - by Jamie

  I'm building a game in c# which allows you to script your own level, although I have come across a bit of a thought. I have a base class called "World" as an object. This was made with a simple: class World { However, when the user is scripting their level, all of the game objects will be contained in the world object. I want them to be able to do something on the lines of: World.ParentObjectName.ParentObjectProperty = "abc"; I know that the System.Windows.Forms.Panel and other classes are like containers and can have objects in them and be accessed in that kind of way... my question is how can I make a class which is like a container in which I can add objects to, and then access them with a World.ObjectName I have tried class World : System.Collections.CollectionBase, but with this method, I have to keep typing World.Item("ObjectName") Can anyone help? Thanks!

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• What's up with LDoms: Part 4 - Virtual Networking Explained

  - by Stefan Hinker

  I'm back from my summer break (and some pressing business that kept me away from this), ready to continue with Oracle VM Server for SPARC ;-) In this article, we'll have a closer look at virtual networking.  Basic connectivity as we've seen it in the first, simple example, is easy enough.  But there are numerous options for the virtual switches and virtual network ports, which we will discuss in more detail now.   In this section, we will concentrate on virtual networking - the capabilities of virtual switches and virtual network ports - only.  Other options involving hardware assignment or redundancy will be covered in separate sections later on. There are two basic components involved in virtual networking for LDoms: Virtual switches and virtual network devices.  The virtual switch should be seen just like a real ethernet switch.  It "runs" in the service domain and moves ethernet packets back and forth.  A virtual network device is plumbed in the guest domain.  It corresponds to a physical network device in the real world.  There, you'd be plugging a cable into the network port, and plug the other end of that cable into a switch.  In the virtual world, you do the same:  You create a virtual network device for your guest and connect it to a virtual switch in a service domain.  The result works just like in the physical world, the network device sends and receives ethernet packets, and the switch does all those things ethernet switches tend to do. If you look at the reference manual of Oracle VM Server for SPARC, there are numerous options for virtual switches and network devices.  Don't be confused, it's rather straight forward, really.  Let's start with the simple case, and work our way to some more sophisticated options later on.  In many cases, you'll want to have several guests that communicate with the outside world on the same ethernet segment.  In the real world, you'd connect each of these systems to the same ethernet switch.  So, let's do the same thing in the virtual world: root@sun # ldm add-vsw net-dev=nxge2 admin-vsw primary root@sun # ldm add-vnet admin-net admin-vsw mars root@sun # ldm add-vnet admin-net admin-vsw venus We've just created a virtual switch called "admin-vsw" and connected it to the physical device nxge2.  In the physical world, we'd have powered up our ethernet switch and installed a cable between it and our big enterprise datacenter switch.  We then created a virtual network interface for each one of the two guest systems "mars" and "venus" and connected both to that virtual switch.  They can now communicate with each other and with any system reachable via nxge2.  If primary were running Solaris 10, communication with the guests would not be possible.  This is different with Solaris 11, please see the Admin Guide for details.  Note that I've given both the vswitch and the vnet devices some sensible names, something I always recommend. Unless told otherwise, the LDoms Manager software will automatically assign MAC addresses to all network elements that need one.  It will also make sure that these MAC addresses are unique and reuse MAC addresses to play nice with all those friendly DHCP servers out there.  However, if we want to do this manually, we can also do that.  (One reason might be firewall rules that work on MAC addresses.)  So let's give mars a manually assigned MAC address: root@sun # ldm set-vnet mac-addr=0:14:4f:f9:c4:13 admin-net mars Within the guest, these virtual network devices have their own device driver.  In Solaris 10, they'd appear as "vnet0".  Solaris 11 would apply it's usual vanity naming scheme.  We can configure these interfaces just like any normal interface, give it an IP-address and configure sophisticated routing rules, just like on bare metal.  In many cases, using Jumbo Frames helps increase throughput performance.  By default, these interfaces will run with the standard ethernet MTU of 1500 bytes.  To change this,  it is usually sufficient to set the desired MTU for the virtual switch.  This will automatically set the same MTU for all vnet devices attached to that switch.  Let's change the MTU size of our admin-vsw from the example above: root@sun # ldm set-vsw mtu=9000 admin-vsw primary Note that that you can set the MTU to any value between 1500 and 16000.  Of course, whatever you set needs to be supported by the physical network, too. Another very common area of network configuration is VLAN tagging. This can be a little confusing - my advise here is to be very clear on what you want, and perhaps draw a little diagram the first few times.  As always, keeping a configuration simple will help avoid errors of all kind.  Nevertheless, VLAN tagging is very usefull to consolidate different networks onto one physical cable.  And as such, this concept needs to be carried over into the virtual world.  Enough of the introduction, here's a little diagram to help in explaining how VLANs work in LDoms: Let's remember that any VLANs not explicitly tagged have the default VLAN ID of 1. In this example, we have a vswitch connected to a physical network that carries untagged traffic (VLAN ID 1) as well as VLANs 11, 22, 33 and 44.  There might also be other VLANs on the wire, but the vswitch will ignore all those packets.  We also have two vnet devices, one for mars and one for venus.  Venus will see traffic from VLANs 33 and 44 only.  For VLAN 44, venus will need to configure a tagged interface "vnet44000".  For VLAN 33, the vswitch will untag all incoming traffic for venus, so that venus will see this as "normal" or untagged ethernet traffic.  This is very useful to simplify guest configuration and also allows venus to perform Jumpstart or AI installations over this network even if the Jumpstart or AI server is connected via VLAN 33.  Mars, on the other hand, has full access to untagged traffic from the outside world, and also to VLANs 11,22 and 33, but not 44.  On the command line, we'd do this like this: root@sun # ldm add-vsw net-dev=nxge2 pvid=1 vid=11,22,33,44 admin-vsw primary root@sun # ldm add-vnet admin-net pvid=1 vid=11,22,33 admin-vsw mars root@sun # ldm add-vnet admin-net pvid=33 vid=44 admin-vsw venus Finally, I'd like to point to a neat little option that will make your live easier in all those cases where configurations tend to change over the live of a guest system.  It's the "id=<somenumber>" option available for both vswitches and vnet devices.  Normally, Solaris in the guest would enumerate network devices sequentially.  However, it has ways of remembering this initial numbering.  This is good in the physical world.  In the virtual world, whenever you unbind (aka power off and disassemble) a guest system, remove and/or add network devices and bind the system again, chances are this numbering will change.  Configuration confusion will follow suit.  To avoid this, nail down the initial numbering by assigning each vnet device it's device-id explicitly: root@sun # ldm add-vnet admin-net id=1 admin-vsw venus Please consult the Admin Guide for details on this, and how to decipher these network ids from Solaris running in the guest. Thanks for reading this far.  Links for further reading are essentially only the Admin Guide and Reference Manual and can be found above.  I hope this is useful and, as always, I welcome any comments.

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• SQL SERVER – Weekly Series – Memory Lane – #003

  - by pinaldave

  Here is the list of curetted articles of SQLAuthority.com across all these years. Instead of just listing all the articles I have selected a few of my most favorite articles and have listed them here with additional notes below it. Let me know which one of the following is your favorite article from memory lane. 2006 This was the first year of my blogging and lots of new things I was learning as I go. I was indeed an infant in blogging a few years ago. However, as time passed by I have learned a lot. This year was year of experiments and new learning. 2007 Working as a full time DBA I often encoutered various errors and I started to learn how to avoid those error and document the same. ERROR Msg 5174 Each file size must be greater than or equal to 512 KB Whenever I see this error I wonder why someone is trying to attempt a database which is extremely small. Anyway, it does not matter what I think I keep on seeing this error often in industries. Anyway the solution of the error is equally interesting – just created larger database. Dilbert Humor This was very first encounter with database humor and I started to love it. It does not matter how many time we read this cartoon it does not get old. Generate Script with Data from Database – Database Publishing Wizard Generating schema script with data is one of the most frequently performed tasks among SQL Server Data Professionals. There are many ways to do the same. In the above article I demonstrated that how we can use the Database Publishing Wizard to accomplish the same. It was new to me at that time but I have not seen much of the adoption of the same still in the industry. Here is one of my videos where I demonstrate how we can generate data with schema. 2008 Delete Backup History – Cleanup Backup History Deleting backup history is important too but should be done carefully. If this is not carried out at regular interval there is good chance that MSDB will be filled up with all the old history. Every organization is different. Some would like to keep the history for 30 days and some for a year but there should be some limit. One should regularly archive the database backup history. South Asia MVP Open Days 2008 This was my very first year Microsoft MVP. I had Indeed big blast at the event and the fun was incredible. After this event I have attended many different MVP events but the fun and learning this particular event presented was amazing and just like me many others are not able to forget the same. Here are other links related to the event: South Asia MVP Open Day 2008 – Goa South Asia MVP Open Day 2008 – Goa – Day 1 South Asia MVP Open Day 2008 – Goa – Day 2 South Asia MVP Open Day 2008 – Goa – Day 3 2009 Enable or Disable Constraint  This is very simple script but I personally keep on forgetting it so I had blogged it. Till today, I keep on referencing this again and again as sometime a very little thing is hard to remember. Policy Based Management – Create, Evaluate and Fix Policies This article will cover the most spectacular feature of SQL 2008 – Policy-based management and how the configuration of SQL Server with policy-based management architecture can make a powerful difference. Policy based management is loaded with several advantages. It can help you implement various policies for reliable configuration of the system. It also provides additional administrative assistance to DBAs and helps them effortlessly manage various tasks of SQL Server across the enterprise. SQLPASS 2009 – My Very First SQPASS Experience Just Brilliant! I never had an experience such a thing in my life. SQL SQL and SQL – all around SQL! I am listing my own reasons here in order of importance to me. Networking with SQL fellows and experts Putting face to the name or avatar Learning and improving my SQL skills Understanding the structure of the largest SQL Server Professional Association Attending my favorite training sessions Since last time I have never missed a single time this event. This event is my favorite event and something keeps me going. Here are additional post related SQLPASS 2009. SQL PASS Summit, Seattle 2009 – Day 1 SQL PASS Summit, Seattle 2009 – Day 2 SQL PASS Summit, Seattle 2009 – Day 3 SQL PASS Summit, Seattle 2009 – Day 4 2010 Get All the Information of Database using sys.databases Even though we believe that we know everything about our database, we do not know a lot of things about our database. This little script enables us to know so many details about databases which we may not be familiar with. Run this on your server today and see how much you know your database. Reducing CXPACKET Wait Stats for High Transactional Database While engaging in a performance tuning consultation for a client, a situation occurred where they were facing a lot of CXPACKET Waits Stats. The client asked me if I could help them reduce this huge number of wait stats. I usually receive this kind of request from other client as well, but the important thing to understand is whether this question has any merits or benefits, or not. I discusses the same in this article – a bit long but insightful for sure. Error related to Database in Use There are so many database management operations in SQL Server which requires exclusive access to the database and it is not always possible to get it. When any database is online in SQL Server it either applications or system thread often accesses them. This means database can’t have exclusive access and the operations which required this access throws an error. There is very easy method to overcome this minor issue – a single line script can give you exclusive access to the database. Difference between DATETIME and DATETIME2 Developers have found the root reason of the problem when dealing with Date Functions – when data time values are converted (implicit or explicit) between different data types, which would lose some precision, so the result cannot match each other as expected. In this blog post I go over very interesting details and difference between DATETIME and DATETIME2 History of SQL Server Database Encryption I recently met Michael Coles and Rodeney Landrum the author of one of the kind book Expert SQL Server 2008 Encryption at SQLPASS in Seattle. During the conversation we ended up how Microsoft is evolving encryption technology. The same discussion lead to talking about history of encryption tools in SQL Server. Michale pointed me to page 18 of his book of encryption. He explicitly gave me permission to re-produce relevant part of history from his book. 2011 Functions FIRST_VALUE and LAST_VALUE with OVER clause and ORDER BY Some time an interesting feature and smart audience make a total difference in places. From last two days, I have been writing on SQL Server 2012 feature FIRST_VALUE and LAST_VALUE. I created a puzzle which was very interesting and got many people attempt to resolve it. It was based on following two articles: Introduction to FIRST_VALUE and LAST_VALUE Introduction to FIRST_VALUE and LAST_VALUE with OVER clause I even provided the hint about how one can solve this problem. The best part was many people solved the problem without using hints! Try your luck!  A Real Story of Book Getting ‘Out of Stock’ to A 25% Discount Story Available This is a great problem and everybody would love to have it. We had it and we loved it. Our book got out of stock in 48 hours of releasing and stocks were empty. We faced many issues and learned many valuable lessons. Some we were able to avoid in the future and some we are still facing it as those problems have no solutions. However, since that day – our books never gone out of stock. This inspiring learning story for us and I am confident that you will love to read it as well. Introduction to LEAD and LAG – Analytic Functions Introduced in SQL Server 2012 SQL Server 2012 introduces new analytical function LEAD() and LAG(). This function accesses data from a subsequent row (for lead) and previous row (for lag) in the same result set without the use of a self-join . It will be very difficult to explain this in words so I will attempt small example to explain you this function. I had a fantastic time writing this blog post and I am very confident when you read it, you will like the same. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Memory Lane, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• Microsoft&rsquo;s new technical computing initiative

  - by Randy Walker

  I made a mental note from earlier in the year.  Microsoft literally buys computers by the truckload.  From what I understand, it’s a typical practice amongst large software vendors.  You plug a few wires in, you test it, and you instantly have mega tera tera flops (don’t hold me to that number).  Microsoft has been trying to plug away at their cloud services (named Azure).  Which, for the layman, means Microsoft runs your software on their computers, and as demand increases you can allocate more computing power on the fly. With this in mind, it doesn’t surprise me that I was recently sent an executive email concerning Microsoft’s new technical computing initiative.  I find it to be a great marketing idea with actual substance behind their real work.  From the programmer academic perspective, in college we dreamed about this type of processing power.  This has decades of computer science theory behind it. A copy of the email received.  (note that I almost deleted this email, thinking it was spam due to it’s length) We don't often think about how complex life really is. Take the relatively simple task of commuting to and from work: it is, in fact, a complicated interplay of variables such as weather, train delays, accidents, traffic patterns, road construction, etc. You can however, take steps to shorten your commute - using a good, predictive understanding of a few of these variables. In fact, you probably are already taking these inputs and instinctively building a predictive model that you act on daily to get to your destination more quickly. Now, when we apply the same method to very complex tasks, this modeling approach becomes much more challenging. Recent world events clearly demonstrated our inability to process vast amounts of information and variables that would have helped to more accurately predict the behavior of global financial markets or the occurrence and impact of a volcano eruption in Iceland. To make sense of issues like these, researchers, engineers and analysts create computer models of the almost infinite number of possible interactions in complex systems. But, they need increasingly more sophisticated computer models to better understand how the world behaves and to make fact-based predictions about the future. And, to do this, it requires a tremendous amount of computing power to process and examine the massive data deluge from cameras, digital sensors and precision instruments of all kinds. This is the key to creating more accurate and realistic models that expose the hidden meaning of data, which gives us the kind of insight we need to solve a myriad of challenges. We have made great strides in our ability to build these kinds of computer models, and yet they are still too difficult, expensive and time consuming to manage. Today, even the most complicated data-rich simulations cannot fully capture all of the intricacies and dependencies of the systems they are trying to model. That is why, across the scientific and engineering world, it is so hard to say with any certainty when or where the next volcano will erupt and what flight patterns it might affect, or to more accurately predict something like a global flu pandemic. So far, we just cannot collect, correlate and compute enough data to create an accurate forecast of the real world. But this is about to change. Innovations in technology are transforming our ability to measure, monitor and model how the world behaves. The implication for scientific research is profound, and it will transform the way we tackle global challenges like health care and climate change. It will also have a huge impact on engineering and business, delivering breakthroughs that could lead to the creation of new products, new businesses and even new industries. Because you are a subscriber to executive e-mails from Microsoft, I want you to be the first to know about a new effort focused specifically on empowering millions of the world's smartest problem solvers. Today, I am happy to introduce Microsoft's Technical Computing initiative. Our goal is to unleash the power of pervasive, accurate, real-time modeling to help people and organizations achieve their objectives and realize their potential. We are bringing together some of the brightest minds in the technical computing community across industry, academia and science at www.modelingtheworld.com to discuss trends, challenges and shared opportunities. New advances provide the foundation for tools and applications that will make technical computing more affordable and accessible where mathematical and computational principles are applied to solve practical problems. One day soon, complicated tasks like building a sophisticated computer model that would typically take a team of advanced software programmers months to build and days to run, will be accomplished in a single afternoon by a scientist, engineer or analyst working at the PC on their desktop. And as technology continues to advance, these models will become more complete and accurate in the way they represent the world. This will speed our ability to test new ideas, improve processes and advance our understanding of systems. Our technical computing initiative reflects the best of Microsoft's heritage. Ever since Bill Gates articulated the then far-fetched vision of "a computer on every desktop" in the early 1980's, Microsoft has been at the forefront of expanding the power and reach of computing to benefit the world. As someone who worked closely with Bill for many years at Microsoft, I am happy to share with you that the passion behind that vision is fully alive at Microsoft and is carried out in the creation of our new Technical Computing group. Enabling more people to make better predictions We have seen the impact of making greater computing power more available firsthand through our investments in high performance computing (HPC) over the past five years. Scientists, engineers and analysts in organizations of all sizes and sectors are finding that using distributed computational power creates societal impact, fuels scientific breakthroughs and delivers competitive advantages. For example, we have seen remarkable results from some of our current customers: Malaria strikes 300,000 to 500,000 people around the world each year. To help in the effort to eradicate malaria worldwide, scientists at Intellectual Ventures use software that simulates how the disease spreads and would respond to prevention and control methods, such as vaccines and the use of bed nets. Technical computing allows researchers to model more detailed parameters for more accurate results and receive those results in less than an hour, rather than waiting a full day. Aerospace engineering firm, a.i. solutions, Inc., needed a more powerful computing platform to keep up with the increasingly complex computational needs of its customers: NASA, the Department of Defense and other government agencies planning space flights. To meet that need, it adopted technical computing. Now, a.i. solutions can produce detailed predictions and analysis of the flight dynamics of a given spacecraft, from optimal launch times and orbit determination to attitude control and navigation, up to eight times faster. This enables them to avoid mistakes in any areas that can cause a space mission to fail and potentially result in the loss of life and millions of dollars. Western & Southern Financial Group faced the challenge of running ever larger and more complex actuarial models as its number of policyholders and products grew and regulatory requirements changed. The company chose an actuarial solution that runs on technical computing technology. The solution is easy for the company's IT staff to manage and adjust to meet business needs. The new solution helps the company reduce modeling time by up to 99 percent - letting the team fine-tune its models for more accurate product pricing and financial projections. Our Technical Computing direction Collaborating closely with partners across industry and academia, we must now extend the reach of technical computing even further to help predictive modelers and data explorers make faster, more accurate predictions. As we build the Technical Computing initiative, we will invest in three core areas: Technical computing to the cloud: Microsoft will play a leading role in bringing technical computing power to scientists, engineers and analysts through the cloud. Existing high- performance computing users will benefit from the ability to augment their on-premises systems with cloud resources that enable 'just-in-time' processing. This platform will help ensure processing resources are available whenever they are needed-reliably, consistently and quickly. Simplify parallel development: Today, computers are shipping with more processing power than ever, including multiple cores, but most modern software only uses a small amount of the available processing power. Parallel programs are extremely difficult to write, test and trouble shoot. However, a consistent model for parallel programming can help more developers unlock the tremendous power in today's modern computers and enable a new generation of technical computing. We are delivering new tools to automate and simplify writing software through parallel processing from the desktop... to the cluster... to the cloud. Develop powerful new technical computing tools and applications: We know scientists, engineers and analysts are pushing common tools (i.e., spreadsheets and databases) to the limits with complex, data-intensive models. They need easy access to more computing power and simplified tools to increase the speed of their work. We are building a platform to do this. Our development efforts will yield new, easy-to-use tools and applications that automate data acquisition, modeling, simulation, visualization, workflow and collaboration. This will allow them to spend more time on their work and less time wrestling with complicated technology. Thinking bigger There is so much left to be discovered and so many questions yet to be answered in the fascinating world around us. We believe the technical computing community will show us that we have not seen anything yet. Imagine just some of the breakthroughs this community could make possible: Better predictions to help improve the understanding of pandemics, contagion and global health trends. Climate change models that predict environmental, economic and human impact, accessible in real-time during key discussions and debates. More accurate prediction of natural disasters and their impact to develop more effective emergency response plans. With an ambitious charter in hand, this new team is ready to build on our progress to-date and execute Microsoft's technical computing vision over the months and years ahead. We will steadily invest in the right technologies, tools and talent, and work to bring together the technical computing community. I invite you to visit www.modelingtheworld.com today. We welcome your ideas and feedback. I look forward to making this journey with you and others who want to answer the world's biggest questions, discover solutions to problems that seem impossible and uncover a host of new opportunities to change the world we live in for the better. Bob

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• Two things I learned this week...

  - by noreply(at)blogger.com (Thomas Kyte)

  I often say "I learn something new about Oracle every day".  It really is true - there is so much to know about it, it is hard to keep up sometimes.Here are the two new things I learned - the first is regarding temporary tablespaces.  In the past - when people have asked "how can I shrink my temporary tablespace" I've said "create a new one that is smaller, alter your database/users to use this new one by default, wait a bit, drop the old one".  Actually I usually said first - "don't, it'll just grow again" but some people really wanted to make it smaller.Now, there is an easier way:http://docs.oracle.com/cd/E11882_01/server.112/e26088/statements_3002.htm#SQLRF53578Using alter tablespace temp shrink space .The second thing is just a little sqlplus quirk that I probably knew at one point but totally forgot.  People run into problems with &'s in sqlplus all of the time as sqlplus tries to substitute in for an &variable.  So, if they try to select '&hello world' from dual - they'll get:ops$tkyte%ORA11GR2> select '&hello world' from dual;Enter value for hello: old   1: select '&hello world' from dualnew   1: select ' world' from dual'WORLD------ worldops$tkyte%ORA11GR2> One solution is to "set define off" to disable the substitution (or set define to some other character).  Another oft quoted solution is to use chr(38) - select chr(38)||'hello world' from dual.  I never liked that one personally.  Today - I was shown another wayhttps://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:4549764300346084350#4573022300346189787 ops$tkyte%ORA11GR2> select '&' || 'hello world' from dual;'&'||'HELLOW------------&hello worldops$tkyte%ORA11GR2>just concatenate '&' to the string, sqlplus doesn't touch that one!  I like that better than chr(38) (but a little less than set define off....)

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• Software design of a browser-based strategic MMO game

  - by Mehran

  I wonder if there are any known tested software designs for Travian-like browser-based strategic MMO games? I mean how would they implement the server of such games or what is stored in database and what is stored in RAM? Is the state of the world stored in one piece or is it distributed among a number of storage? Does anyone know a resource to study the problems and solutions of creating such games? [UPDATE] Suggested in comments, I'm going to give an example how would I design such a project. Even though I'm not sure if I'm proposing the right one. Having stored the world state in a MongoDB, I would implement an event collection in which all the changes to the world will register. Changes that are meant to happen in the future will come with an action date set to the future and those that are to be carried out immediately will be set to now. Having this datastore as the central point of the system, players will issue their actions as events inserted in datastore. At the other end of the system, I'll have a constant-running software taking out events out of the datastore which are due to be carried out and not done yet. Executing an event means apply some update on the world's state and thus the datastore. As scalable as this design sounds, I'm not sure if it will be worth implementing. For one, it is pointless to cache the datastore as most of updates happen once without any follow ups. For instance if you have the growth of resources in your game, you'll be updating the whole world state periodically in which case, having incorporated a cache, you are keeping the whole world in RAM (which most likely is impossible). So can someone come up with a better design?

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• Relative encapsulation design

  - by taher1992

  Let's say I am doing a 2D application with the following design: There is the Level object that manages the world, and there are world objects which are entities inside the Level object. A world object has a location and velocity, as well as size and a texture. However, a world object only exposes get properties. The set properties are private (or protected) and are only available to inherited classes. But of course, Level is responsible for these world objects, and must somehow be able to manipulate at least some of its private setters. But as of now, Level has no access, meaning world objects must change its private setters to public (violating encapsulation). How to tackle this problem? Should I just make everything public? Currently what I'm doing is having a inner class inside game object that does the set work. So when Level needs to update an objects location it goes something like this: void ChangeObject(GameObject targetObject, int newX, int newY){ // targetObject.SetX and targetObject.SetY cannot be set directly var setter = new GameObject.Setter(targetObject); setter.SetX(newX); setter.SetY(newY); } This code feels like overkill, but it doesn't feel right to have everything public so that anything can change an objects location for example.

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• HLSL How to flip geometry horizontally

  - by cubrman

  I want to flip my asymmetric 3d model horizontally in the vertex shader alongside an arbitrary plane parallel to the YZ plane. This should switch everything for the model from the left hand side to the right hand side (like flipping it in Photoshop). Doing it in pixel shader would be a huge computational cost (extra RT, more fullscreen samples...), so it must be done in the vertex shader. Once more: this is NOT reflection, i need to flip THE WHOLE MODEL. I thought I could simply do the following: Turn off culling. Run the following code in the vertex shader: input.Position = mul(input.Position, World); // World[3][0] holds x value of the model's pivot in the World. if (input.Position.x <= World[3][0]) input.Position.x += World[3][0] - input.Position.x; else input.Position.x -= input.Position.x - World[3][0]; ... The model is never drawn. Where am I wrong? I presume that messes up the index buffer. Can something be done about it? P.S. it's INSANELY HARD to format code here. Thanks to Panda I found my problem. SOLUTION: // Do thins before anything else in the vertex shader. Position.x *= -1; // To invert alongside the object's YZ plane.

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• EXC_BAD_ACCESS error when box2d joint is destroyed

  - by colilo

  When I destroy the weldJoint in the update method (see below) I get an EXC_BAD_ACCESS error pointing to the line world->DestroyJoint(weldJoint); in the update method below: -(void) update: (ccTime) dt { int32 velocityIterations = 8; int32 positionIterations = 1; // Instruct the world to perform a single step of simulation. It is // generally best to keep the time step and iterations fixed. world->Step(dt, velocityIterations, positionIterations); // using the iterator pos over the set std::set<BodyPair *>::iterator pos; for(pos = bodiesForJoints.begin(); pos != bodiesForJoints.end(); ++pos) { b2WeldJointDef weldJointDef; BodyPair *bodyPair = *pos; b2Body *bodyA = bodyPair->bodyA; b2Body *bodyB = bodyPair->bodyB; weldJointDef.Initialize(bodyA, bodyB, bodyA->GetWorldCenter()); weldJointDef.collideConnected = false; weldJoint = (b2WeldJoint*) world->CreateJoint(&weldJointDef); // Free the structure we allocated earlier. free(bodyPair); // Remove the entry from the set. bodiesForJoints.erase(pos); } for(b2Body *b = world->GetBodyList(); b; b=b->GetNext()) { if (b->GetUserData() != NULL) { CCSprite *mainSprite = (CCSprite*)b->GetUserData(); if (mainSprite.tag == 1) { mainSprite.position = CGPointMake( b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO); CGPoint mainSpritePosition = mainSprite.position; if (mainSprite.isMoved) { world->DestroyJoint(weldJoint); } } } } } In the HelloWorldLayer.h I set the weldJoint with the assign property. Am I destroying the joint in the wrong way? I would really appreciate any help. Thanks

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