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  • Increasing efficiency of N-Body gravity simulation

    - by Postman
    I'm making a space exploration type game, it will have many planets and other objects that will all have realistic gravity. I currently have a system in place that works, but if the number of planets goes above 70, the FPS decreases an practically exponential rates. I'm making it in C# and XNA. My guess is that I should be able to do gravity calculations between 100 objects without this kind of strain, so clearly my method is not as efficient as it should be. I have two files, Gravity.cs and EntityEngine.cs. Gravity manages JUST the gravity calculations, EntityEngine creates an instance of Gravity and runs it, along with other entity related methods. EntityEngine.cs public void Update() { foreach (KeyValuePair<string, Entity> e in Entities) { e.Value.Update(); } gravity.Update(); } (Only relevant piece of code from EntityEngine, self explanatory. When an instance of Gravity is made in entityEngine, it passes itself (this) into it, so that gravity can have access to entityEngine.Entities (a dictionary of all planet objects)) Gravity.cs namespace ExplorationEngine { public class Gravity { private EntityEngine entityEngine; private Vector2 Force; private Vector2 VecForce; private float distance; private float mult; public Gravity(EntityEngine e) { entityEngine = e; } public void Update() { //First loop foreach (KeyValuePair<string, Entity> e in entityEngine.Entities) { //Reset the force vector Force = new Vector2(); //Second loop foreach (KeyValuePair<string, Entity> e2 in entityEngine.Entities) { //Make sure the second value is not the current value from the first loop if (e2.Value != e.Value ) { //Find the distance between the two objects. Because Fg = G * ((M1 * M2) / r^2), using Vector2.Distance() and then squaring it //is pointless and inefficient because distance uses a sqrt, squaring the result simple cancels that sqrt. distance = Vector2.DistanceSquared(e2.Value.Position, e.Value.Position); //This makes sure that two planets do not attract eachother if they are touching, completely unnecessary when I add collision, //For now it just makes it so that the planets are not glitchy, performance is not significantly improved by removing this IF if (Math.Sqrt(distance) > (e.Value.Texture.Width / 2 + e2.Value.Texture.Width / 2)) { //Calculate the magnitude of Fg (I'm using my own gravitational constant (G) for the sake of time (I know it's 1 at the moment, but I've been changing it) mult = 1.0f * ((e.Value.Mass * e2.Value.Mass) / distance); //Calculate the direction of the force, simply subtracting the positions and normalizing works, this fixes diagonal vectors //from having a larger value, and basically makes VecForce a direction. VecForce = e2.Value.Position - e.Value.Position; VecForce.Normalize(); //Add the vector for each planet in the second loop to a force var. Force = Vector2.Add(Force, VecForce * mult); //I have tried Force += VecForce * mult, and have not noticed much of an increase in speed. } } } //Add that force to the first loop's planet's position (later on I'll instead add to acceleration, to account for inertia) e.Value.Position += Force; } } } } I have used various tips (about gravity optimizing, not threading) from THIS question (that I made yesterday). I've made this gravity method (Gravity.Update) as efficient as I know how to make it. This O(N^2) algorithm still seems to be eating up all of my CPU power though. Here is a LINK (google drive, go to File download, keep .Exe with the content folder, you will need XNA Framework 4.0 Redist. if you don't already have it) to the current version of my game. Left click makes a planet, right click removes the last planet. Mouse moves the camera, scroll wheel zooms in and out. Watch the FPS and Planet Count to see what I mean about performance issues past 70 planets. (ALL 70 planets must be moving, I've had 100 stationary planets and only 5 or so moving ones while still having 300 fps, the issue arises when 70+ are moving around) After 70 planets are made, performance tanks exponentially. With < 70 planets, I get 330 fps (I have it capped at 300). At 90 planets, the FPS is about 2, more than that and it sticks around at 0 FPS. Strangely enough, when all planets are stationary, the FPS climbs back up to around 300, but as soon as something moves, it goes right back down to what it was, I have no systems in place to make this happen, it just does. I considered multithreading, but that previous question I asked taught me a thing or two, and I see now that that's not a viable option. I've also thought maybe I could do the calculations on my GPU instead, though I don't think it should be necessary. I also do not know how to do this, it is not a simple concept and I want to avoid it unless someone knows a really noob friendly simple way to do it that will work for an n-body gravity calculation. (I have an NVidia gtx 660) Lastly I've considered using a quadtree type system. (Barnes Hut simulation) I've been told (in the previous question) that this is a good method that is commonly used, and it seems logical and straightforward, however the implementation is way over my head and I haven't found a good tutorial for C# yet that explains it in a way I can understand, or uses code I can eventually figure out. So my question is this: How can I make my gravity method more efficient, allowing me to use more than 100 objects (I can render 1000 planets with constant 300+ FPS without gravity calculations), and if I can't do much to improve performance (including some kind of quadtree system), could I use my GPU to do the calculations?

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  • Assembly as a First Programming Language?

    - by Anto
    How good of an idea do you think it would be to teach people Assembly (some variant) as a first programming language? It would take a lot more effort than learning for instance Java or Python, but one would have good understanding of the machine more or less from "programming day one" (compared to many higher level languages, at least). What do you think? Is it a realistic idea, at least to those who are ready to make the extra effort? Advantages and disadvantages? Note: I'm no teacher, just curious

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  • Feed Reader Fix

    - by Geertjan
    In the FeedReader sample (available in the New Projects window), there's this piece of code: private static Feed getFeed(Node node) { InstanceCookie ck = node.getLookup().lookup(InstanceCookie.class); if (ck == null) { throw new IllegalStateException("Bogus file in feeds folder: " + node.getLookup().lookup(FileObject.class)); } try { return (Feed) ck.instanceCreate(); } catch (ClassNotFoundException ex) { Exceptions.printStackTrace(ex); } catch (IOException ex) { Exceptions.printStackTrace(ex); } return null; } Since 7.1, for some reason, the above doesn't work. What does work, and is simpler, is this, instead of the above: private static Feed getFeed(Node node) { Feed f = FileUtil.getConfigObject("RssFeeds/sample.instance", Feed.class); if (f == null) { throw new IllegalStateException("Bogus file in feeds folder: " + node.getLookup().lookup(FileObject.class)); } return f; } So, the code needs to be fixed in the sample.

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  • What is the traditional way to maintain extensibility in a database-driven application like this?

    - by Jsess
    I'm working on a simple application for a game in Java that allows a user to record whether they have collected a given item and how much experience it contains. This will work for multiple item types (weapons, armor) and each will have its own tab with a list of all items that qualify under it. Making changes as new types are added is not such a big deal (if a clothing slot is added, for instance), but new items are added to the game all the time in biweekly patches, and I'm not sure what the traditional/customary way to make sure the application is user-extensible without requiring me to would be. Whether that would be adding a configuration menu that allows users to add news items (new rows to the local SQLite database) or a text file with something similar, but I'm certain there's a well-accepted way to do this that I'm not aware of. I'm new to databases and ignorant of the solution, so what's the professional/futureproof way to do this?

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  • UDK : UTWeap_RocketLauncher gift CreateInventory: Any idea why this does not work properly?

    - by John Sloan
    I am giving the player an instanced class of UTWeap_RocketLauncher in an instance of UTGame. PlayerPawn.CreateInventory(class'FobikRocketLauncher',false); // Does not work PlayerPawn.CreateInventory(class'FobikLinkGun',false); // Works Even if I give the original class (eg. UTWeap_RocketLauncher) it does not actually show up. However if I do a "GiveWeapons" cheat, I get it just fine. It also works if I had code it into the map. - But UTWeap_LinkGun works fine either way. Any ideas? It shows the default ammo amount, and the icon on the HUD.

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  • What does private cloud Daas or DBaaS really mean ?

    - by llaszews
    Just had meeting with Fortune 1000 company regarding their private DBaaS or DaaS offering. Interesting to see what DBaaS really means to them: 1. Automated Database provisioning - Being able to 'one button' provision databases and database objects. This includings creating the database instance, creating database objects, network configuration and security provisioning. It is estimated that just being able to provision a new DB table in automated fashion will reduce time required to create a new DB table from 60 hours down to 8 hours. 2. Virtualization and blades - DBaaS infrastructure is all based upon VMs and blades. 3. Consolidation of database vendors - Moving from over ten database vendors down to three.

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  • Class design for calling "the same method" on different classes from one place

    - by betatester07
    Let me introduce my situation: I have Java EE application and in one package, I want to have classes which will act primarily as cache for some data from database, for example: class that will hold all articles for our website class that will hold all categories etc. Every class should have some update() method, which will update data for that class from database and also some other methods for data manipulation specific for that data type. Now, I would like to call update() method for all class instances (there will be exactly one class instance for every class) from one place. What is the best design?

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  • Best language or tool for automating tedious manual tasks [closed]

    - by Jon Hopkins
    We all have tasks that come up from time to time that we think we'd be better off scripting or automating than doing manually. Obviously some tools or languages are better for this than others - no-one (in their right mind) is doing a one off job of cross referencing a bunch of text lists their PM has just given them in assembler for instance. What one tool or language would you recommend for the sort of general quick and dirty jobs you get asked to do where time (rather than elegance) is of the essence? Background: I'm a former programmer, now development manager PM, looking to learn a new language for fun. If I'm going to learn something for fun I'd like it to be useful and this sort of use case is the most likely to come up.

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  • Microsoft Office 2013 Takes New Approach

    You can check out an article from Computerworld for a good look at the questions and answers about the new software. For instance, you've probably noticed that I'm not giving the full name. That's because Microsoft seems to be using several names. If you go the traditional route and pay the one-time upfront fee for the shrink-wrapped edition, it's Office 2013. There's also a tablet version called Office Home and Student 2013 RT - but that won't include the iPad, or at least not at first. The consumer preview, which I'll be linking to in a minute, is dubbed Office 365 Home Premium. There ...

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  • Should package structure closely resemble class hierarchy?

    - by Panzercrisis
    Pretty simple question. Should package structure closely resemble class hierarchy? If so, how closely? Why or why not? For instance, let's say you've got class A and class B, plus class AFactory and class BFactory. You put class A and class B in the package com.something.elements, and you put AFactory and BFactory in com.something.elements.factories. AFactory and BFactory would be further down the hierarchy package-wise, but they'd be further up class-wise. Is this sort of thing a good idea or a bad idea?

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  • FTP won't open a connection to client

    - by Ben
    I am running Windows server 2008 on Ubuntu server 12.04.1 via devstack and I am trying to download a file from an ftp server using the windows command line ftp client. When I run the ftp get command I get the following error message: 500 I won't open a connection to 10.0.0.2 (only to XX.XX.XX.XX) 425 No data connection 10.0.0.2 is the internal IP address of the instance, whereas XX.XX.XX.XX is the external address. Is there anyway to make the ftp client use the external address for the data connection, or alternatively have the client establish the connection? Thanks

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  • Cocos2d Box2d contact listener call different method in collided object

    - by roma86
    I have the building object, wen it hit with other, i want to call some method inside it. Building.mm -(void)printTest { NSLog(@"printTest method work correctly"); } in my ContactListener i trying to call it so: ContactListener.mm #import "ContactListener.h" #import "Building.h" void ContactListener::BeginContact(b2Contact* contact) { b2Body* bodyA = contact->GetFixtureA()->GetBody(); b2Body* bodyB = contact->GetFixtureB()->GetBody(); Building *buildA = (Building *)bodyA->GetUserData(); Building *buildB = (Building *)bodyB->GetUserData(); if (buildB.tag == 1) { NSLog(@"tag == 1"); } if (buildA.tag == 2) { NSLog(@"tag == 2"); [buildA printTest]; } } NSLog(@"tag == 2"); work correctly, but [buildA printTest]; get error Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[CCSprite printTest]: unrecognized selector sent to instance 0x18595f0' Obviously I'm referring to the wrong object. How i can get different method and property in contacted objects from contactlistener class? Thanks.

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  • In a 2D tile-based game, how should NPCs and tiles reference each other?

    - by lezebulon
    I'm making a tile engine for 2D games (seen from the top). Basically the world is composed of a grid of tiles. Now I want to put for instance NPCs that can move on the map. What do you think is best: 1) each tile has a pointer to the NPC that is on its tile, or a NULL pointer 2) having a list of NPCs, and they have the coordinates of the tile they are on. 3) something else? 1) is faster for collision detection but it would use much more memory space and it is slower to find all NPCs in a map. 2) is the opposite. thanks

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  • New Development Snapshot

    More bug fixing and rounding out IKVM.Reflection. Changes: Fixed resolution of generic type instance names with "fake" type as type argument. Fixed bug in Finalize/finalize special casing for .NET types that caused exception when reflecting on them. Fixed Finalize/finalize special casing for .NET types to also work for java.lang.Throwable derived types. Removed fake core class library types from ikvmstub and added a -bootstrap...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • clone() only partially doable; how to react?

    - by hllnll
    Suppose we have a class-hierarchy whose base class B requires a clone() method to be defined in its derivations. Whilst this works perfectly for most of them there is this one derivation X that holds an optional reference to a resource/object that can only be referenced from one instance of X. Whilst the rest of X can be cloned without problems this reference would have to be set to null/nil/nullptr. What is the correct way to handle this situation? X::clone() could throw an UncloneableException. Though this would be correct, it is not satisfying. Set the reference to null/nil/nullptr and leave no notice of it. The user of X has to know about Xs "particularities". Require derivations of B to define B::nearestClone(): the user of B has to be aware that the return value might not be a 1:1 clone. Something else?

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  • ASP.NET Combo Box and List Box Performance Improvements - v2010 vol 1

    Check out this great new performance feature of our ASP.NET combo box and list box controls for the DXperience v2010.1 release. You can now manually populate lists with items based on the currently applied filter criteria. This means that you can significantly decrease web server workload by loading only a subset of all items when working with large datasets. For instance, when using a large data source, you can only request a few records to be visible on the screen. The rest of the items can...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • css - use universal '*' selector vs. html or body selector?

    - by Michael Durrant
    Applying styles to the body tag will be applied to the whole page, so body { font-family: Verdana } will be applied to the whole page. This could also be done with * {font-family: Verdana} which would apply to all elements and so would seem to have the same effect. I understand the principle that in the first instance the style is being applied to one tag, body for the whole page whereas in the second example the font is being applied against each individual html elements. What I am asking is what is the practical difference in doing that, what are the implications and what is a reason, situation or best practice that leads to using one over another. One side-effect is certainly speed (+1 Rob). I am most interested in the actual reason to choose one over the other in terms of functionality.

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  • Phantom activity on MySQL

    - by LoveMeSomeCode
    This is probably just my total lack of MySQL expertise, but is it typical to see lots of phantom activity on a MySQL instance via phpMyAdmin? I have a shared hosting plan through Lithium, and when I log in through the phpMyAdmin console and click on the 'Status' tab, it's showing crazy high numbers for queries. Within an hour of activating my account I had 1 million queries. At first I thought this was them setting things up, but the number is climbing constantly, averaging 170/second. I've got a support ticket in with Lithium, but I thought I'd ask here if this were a MySQL/shared host thing, because I had the same thing happen with a shared hosting plan through Joyent.

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  • What's a good open source cloud computing software? [closed]

    - by boy
    In particular, the "cloud" computing that I'm referring to is: I'm going to get some Linux servers. Then I have pretty big computing tasks to do every day. So my goal is to be able to run some shell command to request an "instance" (ie, if a server has 4 CPU, then the computing software will configure that server to have 4 instances, assuming all my tasks are single thread). Ideally, then I can run the following command: ./addjobs somebatchfile where somebatch file contains one command per line ./removejobs all ./listalljobs (ie, everything is done in shell. And the "computing software" can return me the hostname that's available in some environment variable, etc) And that's all I needed. I run into OpenStack.. but it seems too complicated for this purpose (ie, it does all the Imagine sharing stuff, etc).. All I want, is something SIMPLE that manages the Linux boxes for me and I'm just going to run shell commands on them... Is there such open source software? Thanks,

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  • Using 'new' in a projection?

    - by davenewza
    I wish to project a collection from one type (Something) to another type (SomethingElse). Yes, this is a very open-eneded question, but which of the two options below do you prefer? Creating a new instance using new: var result = query.Select(something => new SomethingElse(something)); Using a factory: var result = query.Select(something => SomethingElse.FromSomething(something)); When I think of a projection, I generally think of it as a conversion. Using new gives me this idea that I'm creating new objects during a conversion, which doesn't feel right. Semantically, SomethingElse.FromSomething() most definitely fits better. Although, the second option does require addition code to setup a factory, which could become unnecessarily compulsive.

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  • HTML5 - check if font has loaded

    - by espais
    At present I load my font for my game in with @font-face For instance: @font-face { font-family: 'Orbitron'; src: url('res/orbitron-medium.ttf'); } and then reference it throughout my JS implementation as such: ctx.font = "12pt Orbitron"; where ctx is my 2d context from the canvas. However, I notice a certain lag time while the font is downloaded to the user. Is there a way I can use a default font until it is loaded in? Edit - I'll expand the question, because I hadn't taken the first comment into account. What would the proper method of handling this be in the case that a user has disabled custom fonts?

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  • Should I Learn C/C++ Even If I Just Want To Do Web Programming?

    - by Daniel
    My goal is to be able to create online apps and dynamic, database driven websites. For instance, if in the future I get the idea for the next Digg or Facebook, I want to be able to code it myself. To arrive there I think I have basically two paths: Path 1 Start at a basic level, learning C, then C++ for OOP, then algorithms and data structures, with the goal of getting a solid grasp of computer programming. Only then move to PHP/MySQL/HTTP and start working on practical programming projects. Path 2 Start directly with PHP/MySQL/HTTP and getting my hands dirty with practical projects right away. What would you guys recommend?

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  • New Oracle Cloud support in OEPE

    - by gstachni
    Oracle Enterprise Pack for Eclipse 12c (12.1.1.1.1) includes updated support for development with the Java Cloud Service. Users can now do iterative development against their Java Cloud Service instance in addition to testing against local and remote WebLogic Server installations. Some details of the cloud tools are below: Templates and wizards to create projects and server configurations for Oracle Java Cloud Service Develop applications to run and deploy to the cloud, including Oracle ADF. Check cloud server runtime and deployment logs in new log analyzers Test applications before deployment with integrated whitelist scans. Whitelist tools support as-you-type validation, project build validation, and on demand scans to highlight coding violations. Errors are reported in application source, the Problems view, and a new Whitelist violations view. Access the Oracle Public Cloud administrative consoles directly from within Eclipse.

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  • XNA GameTime TotalGameTime slower than real time

    - by robasaurus
    I have set-up an empty test project consisting of a System.Diagnostics.Stopwatch and this in the draw method: spriteBatch.DrawString(font, gameTime.TotalGameTime.TotalSeconds.ToString(), new Vector2(100, 100), Color.White); spriteBatch.DrawString(font, stopwatch.Elapsed.TotalSeconds.ToString(), new Vector2(100, 200), Color.White); The GameTime.TotalGameTime displayed is slower than the stop watch (by about 5 seconds per minute) even though GameTime.IsRunningSlowly is always false, why is this? The reason this is an issue is because I have a server which uses stopwatch and it is faster than my client game. For instance my client notifies the server it has dropped a mine which explodes in one minute. Because the stopwatch is faster the server state explodes the mine before the client and they are out of sync. I don't want to have to notify the client when the server explodes it as this would use unnecessary bandwidth.

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  • How do you explain commented-out code to a non-programmer? [closed]

    - by whirlwin
    What is the quickest and most comprehensible way to explain to a non-programmer what commented-out code is? When I mentioned it in a conversation to non-programmers, they seemed lost. Such people could for instance be graphical designers, when working on the same team to make an application. Typically I would need to mention what I will be/currently am working with during an update meeting. At first I thought about substituting commented-out with unused code. While it is true to some degree, it is also very ambiguous. If you are wondering, I am working with legacy code with commented-out code. This leads to my question: "how do you explain commented-out code to a non-programmer?"

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