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  • Logic in Entity Components Systems

    - by aaron
    I'm making a game that uses an Entity/Component architecture basically a port of Artemis's framework to c++,the problem arises when I try to make a PlayerControllerComponent, my original idea was this. class PlayerControllerComponent: Component { public: virtual void update() = 0; }; class FpsPlayerControllerComponent: PlayerControllerComponent { public: void update() { //handle input } }; and have a system that updates PlayerControllerComponents, but I found out that the artemis framework does not look at sub-classes the way I thought it would. So all in all my question here is should I make the framework aware of subclasses or should I add a new Component like object that is used for logic.

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  • Why do we use Pythagoras in game physics?

    - by Starkers
    I've recently learned that we use Pythagoras a lot in our physics calculations and I'm afraid I don't really get the point. Here's an example from a book to make sure an object doesn't travel faster than a MAXIMUM_VELOCITY constant in the horizontal plane: MAXIMUM_VELOCITY = <any number>; SQUARED_MAXIMUM_VELOCITY = MAXIMUM_VELOCITY * MAXIMUM_VELOCITY; function animate(){ var squared_horizontal_velocity = (x_velocity * x_velocity) + (z_velocity * z_velocity); if( squared_horizontal_velocity <= SQUARED_MAXIMUM_VELOCITY ){ scalar = squared_horizontal_velocity / SQUARED_MAXIMUM_VELOCITY; x_velocity = x_velocity / scalar; z_velocity = x_velocity / scalar; } } Let's try this with some numbers: An object is attempting to move 5 units in x and 5 units in z. It should only be able to move 5 units horizontally in total! MAXIMUM_VELOCITY = 5; SQUARED_MAXIMUM_VELOCITY = 5 * 5; SQUARED_MAXIMUM_VELOCITY = 25; function animate(){ var x_velocity = 5; var z_velocity = 5; var squared_horizontal_velocity = (x_velocity * x_velocity) + (z_velocity * z_velocity); var squared_horizontal_velocity = 5 * 5 + 5 * 5; var squared_horizontal_velocity = 25 + 25; var squared_horizontal_velocity = 50; // if( squared_horizontal_velocity <= SQUARED_MAXIMUM_VELOCITY ){ if( 50 <= 25 ){ scalar = squared_horizontal_velocity / SQUARED_MAXIMUM_VELOCITY; scalar = 50 / 25; scalar = 2.0; x_velocity = x_velocity / scalar; x_velocity = 5 / 2.0; x_velocity = 2.5; z_velocity = z_velocity / scalar; z_velocity = 5 / 2.0; z_velocity = 2.5; // new_horizontal_velocity = x_velocity + z_velocity // new_horizontal_velocity = 2.5 + 2.5 // new_horizontal_velocity = 5 } } Now this works well, but we can do the same thing without Pythagoras: MAXIMUM_VELOCITY = 5; function animate(){ var x_velocity = 5; var z_velocity = 5; var horizontal_velocity = x_velocity + z_velocity; var horizontal_velocity = 5 + 5; var horizontal_velocity = 10; // if( horizontal_velocity >= MAXIMUM_VELOCITY ){ if( 10 >= 5 ){ scalar = horizontal_velocity / MAXIMUM_VELOCITY; scalar = 10 / 5; scalar = 2.0; x_velocity = x_velocity / scalar; x_velocity = 5 / 2.0; x_velocity = 2.5; z_velocity = z_velocity / scalar; z_velocity = 5 / 2.0; z_velocity = 2.5; // new_horizontal_velocity = x_velocity + z_velocity // new_horizontal_velocity = 2.5 + 2.5 // new_horizontal_velocity = 5 } } Benefits of doing it without Pythagoras: Less lines Within those lines, it's easier to read what's going on ...and it takes less time to compute, as there are less multiplications Seems to me like computers and humans get a better deal without Pythagoras! However, I'm sure I'm wrong as I've seen Pythagoras' theorem in a number of reputable places, so I'd like someone to explain me the benefit of using Pythagoras to a maths newbie. Does this have anything to do with unit vectors? To me a unit vector is when we normalize a vector and turn it into a fraction. We do this by dividing the vector by a larger constant. I'm not sure what constant it is. The total size of the graph? Anyway, because it's a fraction, I take it, a unit vector is basically a graph that can fit inside a 3D grid with the x-axis running from -1 to 1, z-axis running from -1 to 1, and the y-axis running from -1 to 1. That's literally everything I know about unit vectors... not much :P And I fail to see their usefulness. Also, we're not really creating a unit vector in the above examples. Should I be determining the scalar like this: // a mathematical work-around of my own invention. There may be a cleverer way to do this! I've also made up my own terms such as 'divisive_scalar' so don't bother googling var divisive_scalar = (squared_horizontal_velocity / SQUARED_MAXIMUM_VELOCITY); var divisive_scalar = ( 50 / 25 ); var divisive_scalar = 2; var multiplicative_scalar = (divisive_scalar / (2*divisive_scalar)); var multiplicative_scalar = (2 / (2*2)); var multiplicative_scalar = (2 / 4); var multiplicative_scalar = 0.5; x_velocity = x_velocity * multiplicative_scalar x_velocity = 5 * 0.5 x_velocity = 2.5 Again, I can't see why this is better, but it's more "unit-vector-y" because the multiplicative_scalar is a unit_vector? As you can see, I use words such as "unit-vector-y" so I'm really not a maths whiz! Also aware that unit vectors might have nothing to do with Pythagoras so ignore all of this if I'm barking up the wrong tree. I'm a very visual person (3D modeller and concept artist by trade!) and I find diagrams and graphs really, really helpful so as many as humanely possible please!

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  • Obtain rectangle indicating 2D world space camera can see

    - by Gareth
    I have a 2D tile based game in XNA, with a moveable camera that can scroll around and zoom. I'm trying to obtain a rectangle which indicates the area, in world space, that my camera is looking at, so I can render anything this rectangle intersects with (currently, everything is rendered). So, I'm drawing the world like this: _SpriteBatch.Begin( SpriteSortMode.FrontToBack, null, SamplerState.PointClamp, // Don't smooth null, null, null, _Camera.GetTransformation()); The GetTransformation() method on my Camera object does this: public Matrix GetTransformation() { _transform = Matrix.CreateTranslation(new Vector3(-_pos.X, -_pos.Y, 0)) * Matrix.CreateRotationZ(Rotation) * Matrix.CreateScale(new Vector3(Zoom, Zoom, 1)) * Matrix.CreateTranslation(new Vector3(_viewportWidth * 0.5f, _viewportHeight * 0.5f, 0)); return _transform; } The camera properties in the method above should be self explanatory. How can I get a rectangle indicating what the camera is looking at in world space?

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  • Rotate 3D Model from a custom position

    - by Nipuna Silva
    I have a 3D Model like above in which i want to rotate it from a given location(pointed in red) but I can only rotate it from the middle. How can I rotate it from a custom point. Edit: I successfully able to rotate the model from the below position by getting the radius of the model and applying it to the world matrix Vector3 point = new Vector3(-radius, 0, 0); world = Matrix.CreateTranslation(-radius, 0, 0); But now I cannot change the position of the object and it always centered in middle of the screen. I think that's because i applied the above code. How can I place it anywhere I want?

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  • Correct order of tasks in each frame for a Physics simulation

    - by Johny
    I'm playing a bit around with 2D physics. I created now some physic blocks which should collide with each other. This works fine "mostly" but sometimes one of the blocks does not react to a collision and i think that's because of my order of tasks done in each frame. At the moment it looks something like this: function GameFrame(){ foreach physicObject do AddVelocityToPosition(); DoCollisionStuff(); // Only for this object not to forget! AddGravitationToVelocity(); end RedrawScene(); } Is this the correct order of tasks in each frame?

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  • The how of a collision engine

    - by JXPheonix
    This is a very, very broad question - what is the general algorithm of how a collision engine works? No code in specific, but rather, just a general idea of how a collision engine does what it does, constantly refreshing the points of an object and comparing it to other objects? (see, I have the general gist of it here.) A collision engine is basically an engine used in games (generally) so that your player (call him Bob), whenever bob moves into a wall, Bob stops, Bob does not walk through the wall. They also generally handle the gravity in a game and environmental things like that.

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  • What are the basic skills a beginner JavaScript programmer should have?

    - by Sanford
    In NYC, we are working on creating a collaborative community programming environment and trying to segment out software engineers into differing buckets. At present, we are trying to define: Beginners Intermediates Advanced Experts (and/or Masters) Similar to an apprenticeship, you would need to demonstrate specific skills to achieve different levels. Right now, we have identified beginner programming skills as: Object - method, attributes, inheritance Variable - math, string, array, boolean - all are objects Basic arithmetic functions - precedence of functions String manipulation Looping - flow control Conditionals - boolean algebra This is a first attempt, and it is a challenge since we know the natural tension between programming and software engineering. How would you create such a skills-based ranking for JavaScript in this manner? For example, what would be the beginner JavaScript skills that you would need to have to advance to the intermediate training? And so on.

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  • Multiple Vertex Buffers per Mesh

    - by Daniel
    I've run into the situation where the size of my mesh with all its vertices and indices, is larger than the (optimal) vertex buffer object upper limit (~8MB). I was wondering if I can sub-divide the mesh across multiple vertex buffers, and somehow retain validity of the indices. Ie a triangle with a indice at the first vertex, and an indice at the last (ie in seperate VBOs). All the while maintaining this within Vertex Array Objects. My thoughts are, save myself the hassle, and for meshes (messes :P) such as this, just use the necessary size ( 8MB); which is what I do at the moment. But ideally my buffer manager (wip) at the moment is using optimal sizes; I may just have to make a special case then... Any ideas? If necessary, a simple C++ code example is appreciated. Note: I have also cross-posted this on stackoverflow, as I was not sure as to which it would be more suitable (its partly a design question).

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  • Oracle Speakers at QCon New York, June 18-20, 2012

    - by Bob Rhubart
    If you're attending the QCon Conference in NYC, June 18-20, 2012, you'll find several presenters from Oracle among the impressive roster of speakers. Among those sharing their expertise at the New York event: Arun Gupta: Java EE & GlassFish Guy, Oracle Presentation: Java EE 7 and HTML5: Developing for the Cloud Brian Oliver: Global Solutions Architect, Oracle Presentation: The Live Object Pattern Cameron Purdy: Vice President of Development, Oracle Presentation: How the 10 key lessons from Java and C++ history inform the Cloud Charlie Hunt: JVM Performance Lead Engineer, Oracle Presentation: Extreme Performance with Java Registration for the event is still open. According to the website, registering before June 1 will save you $300. If you snooze, you lose.

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  • Useful Extension Method for ICloneable

    - by DesigningCode
    In the past, I’ve had to put a type specific clone in each cloneable class, but with extension methods you can write a generic T specific clone class Program { static void Main(string[] args) { var b = new Blah() {X = 1, Y = 2}; var bb = b.Clone(); Console.WriteLine(string.Format("{0} {1}", bb.X, bb.Y)); } } public class Blah : ICloneable { public int X; public int Y; object ICloneable.Clone() { return MemberwiseClone(); } } public static class CloneExtension { public static T Clone<T>(this T o) where T : ICloneable { return (T)o.Clone(); } }

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  • SharePoint 2010 Diagnostic Studio Remote Diag

    - by juanlarios
    I have had some time this week to try out some tools that I have been meaning to try out. This week I am trying out the SP 2010 Diagnostic Studio. I installed it successfully and tried it on my development evironment. I was able to build a report and a snapshot of the environment. I decided to turn my attention to my Employer's intranet environment. This would allow me to analyze it and measure it against benchmarks. I didn't want to install the Diagnostic studio on the Production Envorinment, lucky for me, the Diagnostic studio can be run remotely, well...kind of. Issue My development environment is a stand alone, full installation of SharePoint 2010 Server. It has Office 2010, SQL 2008 Enterprise, a DC...well you get the point, it's jammed packed! But more importantly it's a stand alone, self contained VM environment. Well Microsoft has instructions as to how to connect remotely with Diagnostic Studio here. The deciving part of this is that the SP2010DS prompts you for credentails. So I thought I was getting the right account to run the reports. I tried all the Power Shell commands in the link above but I still ended up getting the following errors: 06/28/2011 12:50:18    Connecting to remote server failed with the following error message : The WinRM client cannot process the request...If the SPN exists, but CredSSP cannot use Kerberos to validate the identity of the target computer and you still want to allow the delegation of the user credentials to the target computer, use gpedit.msc and look at the following policy: Computer Configuration -> Administrative Templates -> System -> Credentials Delegation -> Allow Fresh Credentials with NTLM-only Server Authentication.  Verify that it is enabled and configured with an SPN appropriate for the target computer. For example, for a target computer name "myserver.domain.com", the SPN can be one of the following: WSMAN/myserver.domain.com or WSMAN/*.domain.com. Try the request again after these changes. For more information, see the about_Remote_Troubleshooting Help topic. 06/28/2011 12:54:47    Access to the path '\\<targetserver>\C$\Users\<account logging in>\AppData\Local\Temp' is denied. You might also get an error message like this: The WinRM client cannot process the request. A computer policy does not allow the delegation of the user credentials to the target computer. Explanation After looking at the event logs on the target environment, I noticed that there were a several Security Exceptions. After looking at the specifics around who was denied access, I was able to see the account that was being denied access, it was the client machine administrator account. Well of course that was never going to work!!! After some quick Googling, the last error message above will lead you to edit the Local Group Policy on the client server. And although there are instructions from microsoft around doing this, it really will not work in this scenario. Notice the Description and how it only applices to authentication mentioned? Resolution I can tell you what I did, but I wish there was a better way but I simply don't know if it's duable any other way. Because my development environment had it's own DC, I didn't really want to mess with Kerberos authentication. I would also not be smart to connect that server to the domain, considering it has it's own DC. I ended up installing SharePoint 2010 Diagnostic Studio on another Windows 7 Dev environment I have, and connected the machien to the domain. I ran all the necesary remote credentials commands mentioned here. Those commands add the group policy for you! Once I did this I was able to authenticate properly and I was able to get the reports. Conclusion   You can run SharePoint 2010 Diagnostic Studio Remotely but it will require some specific scenarions. A couple of things I should mention is that as far as I understand, SP2010 DS, will install agents on your target environment to run tests and retrieve the data. I was a Farm Administrator, and also a Server Admin on SharePoint Server. I am not 100% sure if you need all those permissions but I that's just what I have to my internal intranet.   I deally I would like to have a machine that I can have SharePoint 2010 DIagnostic Studio installed and I can run that against client environments. It appears that I will not be able to do that, unless I enable Kerberos on my Windows 7 Machine now. If you have it installed in the same way I would like to have it, please let me know, I'll keep trying to get what I'm after. Hope this helps someone out there doing the same.

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  • jqGrid - dynamically load different drop down values for different rows depending on another column value

    - by Renso
    Goal: As we all know the jqGrid examples in the demo and the Wiki always refer to static values for drop down boxes. This of course is a personal preference but in dynamic design these values should be populated from the database/xml file, etc, ideally JSON formatted. Can you do this in jqGrid, yes, but with some custom coding which we will briefly show below (refer to some of my other blog entries for a more detailed discussion on this topic). What you CANNOT do in jqGrid, referrign here up and to version 3.8.x, is to load different drop down values for different rows in the jqGrid. Well, not without some trickery, which is what this discussion is about. Issue: Of course the issue is that jqGrid has been designed for high performance and thus I have no issue with them loading a  reference to a single drop down values list for every column. This way if you have 500 rows or one, each row only refers to a single list for that particuolar column. Nice! SO how easy would it be to simply traverse the grid once loaded on gridComplete or loadComplete and simply load the select tag's options from scratch, via ajax, from memory variable, hard coded etc? Impossible! Since their is no embedded SELECT tag within each cell containing the drop down values (remeber it only has a reference to that list in memory), all you will see when you inspect the cell prior to clicking on it, or even before and on beforeEditCell, is an empty <TD></TD>. When trying to load that list via a click event on that cell will temporarily load the list but jqGrid's last internal callback event will remove it and replace it with the old one, and you are back to square one. Solution: Yes, after spending a few hours on this found a solution to the problem that does not require any updates to jqGrid source code, thank GOD! Before we get into the coding details, the solution here can of course be customized to suite your specific needs, this one loads the entire drop down list that would be needed across all rows once into global variable. I then parse this object that contains all the properties I need to filter the rows depending on which ones I want the user to see based off of another cell value in that row. This only happens when clicking the cell, so no performance penalty. You may of course to load it via ajax when the user clicks the cell, but I found it more effecient to load the entire list as part of jqGrid's normal editoptions: { multiple: false, value: listingStatus } colModel options which again keeps only a reference to the sinlge list, no duplciation. Lets get into the meat and potatoes of it.         var acctId = $('#Id').val();         var data = $.ajax({ url: $('#ajaxGetAllMaterialsTrackingLookupDataUrl').val(), data: { accountId: acctId }, dataType: 'json', async: false, success: function(data, result) { if (!result) alert('Failure to retrieve the Alert related lookup data.'); } }).responseText;         var lookupData = eval('(' + data + ')');         var listingCategory = lookupData.ListingCategory;         var listingStatus = lookupData.ListingStatus;         var catList = '{';         $(lookupData.ListingCategory).each(function() {             catList += this.Id + ':"' + this.Name + '",';         });         catList += '}';         var lastsel;         var ignoreAlert = true;         $(item)         .jqGrid({             url: listURL,             postData: '',             datatype: "local",             colNames: ['Id', 'Name', 'Commission<br />Rep', 'Business<br />Group', 'Order<br />Date', 'Edit', 'TBD', 'Month', 'Year', 'Week', 'Product', 'Product<br />Type', 'Online/<br />Magazine', 'Materials', 'Special<br />Placement', 'Logo', 'Image', 'Text', 'Contact<br />Info', 'Everthing<br />In', 'Category', 'Status'],             colModel: [                 { name: 'Id', index: 'Id', hidden: true, hidedlg: true },                 { name: 'AccountName', index: 'AccountName', align: "left", resizable: true, search: true, width: 100 },                 { name: 'OnlineName', index: 'OnlineName', align: 'left', sortable: false, width: 80 },                 { name: 'ListingCategoryName', index: 'ListingCategoryName', width: 85, editable: true, hidden: false, edittype: "select", editoptions: { multiple: false, value: eval('(' + catList + ')') }, editrules: { required: false }, formatoptions: { disabled: false} }             ],             jsonReader: {                 root: "List",                 page: "CurrentPage",                 total: "TotalPages",                 records: "TotalRecords",                 userdata: "Errors",                 repeatitems: false,                 id: "0"             },             rowNum: $rows,             rowList: [10, 20, 50, 200, 500, 1000, 2000],             imgpath: jQueryImageRoot,             pager: $(item + 'Pager'),             shrinkToFit: true,             width: 1455,             recordtext: 'Traffic lines',             sortname: 'OrderDate',             viewrecords: true,             sortorder: "asc",             altRows: true,             cellEdit: true,             cellsubmit: "remote",             cellurl: editURL + '?rows=' + $rows + '&page=1',             loadComplete: function() {               },             gridComplete: function() {             },             loadError: function(xhr, st, err) {             },             afterEditCell: function(rowid, cellname, value, iRow, iCol) {                 var select = $(item).find('td.edit-cell select');                 $(item).find('td.edit-cell select option').each(function() {                     var option = $(this);                     var optionId = $(this).val();                     $(lookupData.ListingCategory).each(function() {                         if (this.Id == optionId) {                                                       if (this.OnlineName != $(item).getCell(rowid, 'OnlineName')) {                                 option.remove();                                 return false;                             }                         }                     });                 });             },             search: true,             searchdata: {},             caption: "List of all Traffic lines",             editurl: editURL + '?rows=' + $rows + '&page=1',             hiddengrid: hideGrid   Here is the JSON data returned via the ajax call during the jqGrid function call above (NOTE it must be { async: false}: {"ListingCategory":[{"Id":29,"Name":"Document Imaging & Management","OnlineName":"RF Globalnet"} ,{"Id":1,"Name":"Ancillary Department Hardware","OnlineName":"Healthcare Technology Online"} ,{"Id":2,"Name":"Asset Tracking","OnlineName":"Healthcare Technology Online"} ,{"Id":3,"Name":"Asset Tracking","OnlineName":"Healthcare Technology Online"} ,{"Id":4,"Name":"Asset Tracking","OnlineName":"Healthcare Technology Online"} ,{"Id":5,"Name":"Document Imaging & Management","OnlineName":"Healthcare Technology Online"} ,{"Id":6,"Name":"Document Imaging & Management","OnlineName":"Healthcare Technology Online"} ,{"Id":7,"Name":"EMR/EHR Software","OnlineName":"Healthcare Technology Online"}]} I only need the Id and Name for the drop down list, but the third column in the JSON object is important, it is the only that I match up with the OnlineName in the jqGrid column, and then in the loop during afterEditCell simply remove the ones I don't want the user to see. That's it!

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  • EclipseLink 2.4 Released: RESTful Persistence, Tenant Isolation, NoSQL, and JSON

    - by arungupta
    EclipseLink 2.4 is released as part of Eclipse Juno release train. In addition to providing the Reference Implementation for JPA 2.0, the key features in the release are: RESTful Persistence - Expose Java Persistence units over REST using either JSON or XML Tenant Isolation - Manage entities for multiple tenants in the same application NoSQL - NoSQL support for MongoDB and Oracle NoSQL JSON - Marshaling and unmarshaling of JSON object Here is the complete list of bugs fixed in this release. The landing page provide the complete list of documentation and examples. Read Doug Clarke's blog for a color commentary as well. This release is already integrated in the latest GlassFish 4.0 promoted build. Try the functionality and give us feedback at GlassFish Forum or EclipseLink Forum.

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  • Is it bad practice to pass instances through several layers?

    - by Puckl
    In my program design, I often come to the point where I have to pass object instances through several classes. For example, if I have a controller that loads an audio file, and then passes it to a player, and the player passes it to the playerRunnable, which passes it again somewhere else etc. It looks kind of bad, but I don´t know how to avoid it. Or is it OK to do this? EDIT: Maybe the player example is not the best because I could load the file later, but in other cases that does not work.

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  • Saving an interface instance into a Bundle

    - by user22241
    All I've have an interface that allows me to switch between different scenes in my Android game. When the home key is pressed, I am saving all of my states (score, sprite positions etc) into a Bundle. When re-launching, I am restoring all my states and all is OK - however, I can't figure out how to save my 'Scene', thus when I return, it always starts at the default screen which is the 'Main Menu'. How would I go about saving my 'Scene' (into a Bundle)? Code import android.view.MotionEvent; public interface Scene{ void render(); void updateLogic(); boolean onTouchEvent(MotionEvent event); } I assume the interface is the relevant piece of code which is why I've posted that snippet. I set my scene like so: ('options' is an object of my Options class which extends MainMenu (Another custom class) which, in turn implements the interface 'Scene') SceneManager.getInstance().setCurrentScene(options); //Current scene is optionscreen

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  • Subterranean IL: The ThreadLocal type

    - by Simon Cooper
    I came across ThreadLocal<T> while I was researching ConcurrentBag. To look at it, it doesn't really make much sense. What's all those extra Cn classes doing in there? Why is there a GenericHolder<T,U,V,W> class? What's going on? However, digging deeper, it's a rather ingenious solution to a tricky problem. Thread statics Declaring that a variable is thread static, that is, values assigned and read from the field is specific to the thread doing the reading, is quite easy in .NET: [ThreadStatic] private static string s_ThreadStaticField; ThreadStaticAttribute is not a pseudo-custom attribute; it is compiled as a normal attribute, but the CLR has in-built magic, activated by that attribute, to redirect accesses to the field based on the executing thread's identity. TheadStaticAttribute provides a simple solution when you want to use a single field as thread-static. What if you want to create an arbitary number of thread static variables at runtime? Thread-static fields can only be declared, and are fixed, at compile time. Prior to .NET 4, you only had one solution - thread local data slots. This is a lesser-known function of Thread that has existed since .NET 1.1: LocalDataStoreSlot threadSlot = Thread.AllocateNamedDataSlot("slot1"); string value = "foo"; Thread.SetData(threadSlot, value); string gettedValue = (string)Thread.GetData(threadSlot); Each instance of LocalStoreDataSlot mediates access to a single slot, and each slot acts like a separate thread-static field. As you can see, using thread data slots is quite cumbersome. You need to keep track of LocalDataStoreSlot objects, it's not obvious how instances of LocalDataStoreSlot correspond to individual thread-static variables, and it's not type safe. It's also relatively slow and complicated; the internal implementation consists of a whole series of classes hanging off a single thread-static field in Thread itself, using various arrays, lists, and locks for synchronization. ThreadLocal<T> is far simpler and easier to use. ThreadLocal ThreadLocal provides an abstraction around thread-static fields that allows it to be used just like any other class; it can be used as a replacement for a thread-static field, it can be used in a List<ThreadLocal<T>>, you can create as many as you need at runtime. So what does it do? It can't just have an instance-specific thread-static field, because thread-static fields have to be declared as static, and so shared between all instances of the declaring type. There's something else going on here. The values stored in instances of ThreadLocal<T> are stored in instantiations of the GenericHolder<T,U,V,W> class, which contains a single ThreadStatic field (s_value) to store the actual value. This class is then instantiated with various combinations of the Cn types for generic arguments. In .NET, each separate instantiation of a generic type has its own static state. For example, GenericHolder<int,C0,C1,C2> has a completely separate s_value field to GenericHolder<int,C1,C14,C1>. This feature is (ab)used by ThreadLocal to emulate instance thread-static fields. Every time an instance of ThreadLocal is constructed, it is assigned a unique number from the static s_currentTypeId field using Interlocked.Increment, in the FindNextTypeIndex method. The hexadecimal representation of that number then defines the specific Cn types that instantiates the GenericHolder class. That instantiation is therefore 'owned' by that instance of ThreadLocal. This gives each instance of ThreadLocal its own ThreadStatic field through a specific unique instantiation of the GenericHolder class. Although GenericHolder has four type variables, the first one is always instantiated to the type stored in the ThreadLocal<T>. This gives three free type variables, each of which can be instantiated to one of 16 types (C0 to C15). This puts an upper limit of 4096 (163) on the number of ThreadLocal<T> instances that can be created for each value of T. That is, there can be a maximum of 4096 instances of ThreadLocal<string>, and separately a maximum of 4096 instances of ThreadLocal<object>, etc. However, there is an upper limit of 16384 enforced on the total number of ThreadLocal instances in the AppDomain. This is to stop too much memory being used by thousands of instantiations of GenericHolder<T,U,V,W>, as once a type is loaded into an AppDomain it cannot be unloaded, and will continue to sit there taking up memory until the AppDomain is unloaded. The total number of ThreadLocal instances created is tracked by the ThreadLocalGlobalCounter class. So what happens when either limit is reached? Firstly, to try and stop this limit being reached, it recycles GenericHolder type indexes of ThreadLocal instances that get disposed using the s_availableIndices concurrent stack. This allows GenericHolder instantiations of disposed ThreadLocal instances to be re-used. But if there aren't any available instantiations, then ThreadLocal falls back on a standard thread local slot using TLSHolder. This makes it very important to dispose of your ThreadLocal instances if you'll be using lots of them, so the type instantiations can be recycled. The previous way of creating arbitary thread-static variables, thread data slots, was slow, clunky, and hard to use. In comparison, ThreadLocal can be used just like any other type, and each instance appears from the outside to be a non-static thread-static variable. It does this by using the CLR type system to assign each instance of ThreadLocal its own instantiated type containing a thread-static field, and so delegating a lot of the bookkeeping that thread data slots had to do to the CLR type system itself! That's a very clever use of the CLR type system.

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  • How to write functionally in a web framework

    - by Kevin Burke
    I love Rich Hickey, Clojure and Haskell and I get it when he talks about functions and the unreliability of side-effecting code. However I work in an environment where nearly all the functions I write have to read from the database, write to the database, make HTTP requests, decrement a user's balance, modify a frontend HTML component based on a click action, return different results based on the URI or the POST body. We also use PHP for the frontend, which is littered with functions like parse_str(), which modifies an object in place. All of these are side-effecting to one degree or another. Given these constraints and the side-effecting nature of the logic I'm coding, what can I do to make my code more reliable and function-able?

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  • How do you navigate and refactor code written in a dynamic language?

    - by Philippe Beaudoin
    I love that writing Python, Ruby or Javascript requires so little boilerplate. I love simple functional constructs. I love the clean and simple syntax. However, there are three things I'm really bad at when developing a large software in a dynamic language: Navigating the code Identifying the interfaces of the objects I'm using Refactoring efficiently I have been trying simple editors (i.e. Vim) as well as IDE (Eclipse + PyDev) but in both cases I feel like I have to commit a lot more to memory and/or to constantly "grep" and read through the code to identify the interfaces. As for refactoring, for example changing method names, it becomes hugely dependent on the quality of my unit tests. And if I try to isolate my unit tests by "cutting them off" the rest of the application, then there is no guarantee that my stub's interface stays up to date with the object I'm stubbing. I'm sure there are workarounds for these problems. How do you work efficiently in Python, Ruby or Javascript?

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  • How do you handle increasingly long compile times when working with templates?

    - by Ghita
    I use Visual Studio 2012 and he have cases where we added templates parameters to a class "just" in order to introduce a "seam point" so that in unit-test we can replace those parts with mock objects. How do you usually introduce seam points in C++: using interfaces and/or mixing based on some criteria with implicit interfaces by using templates parameters also ? One reason to ask this is also because when compiling sometimes a single C++ file (that includes templates files, that could also include other templates) results in an object file being generated that takes in the order of around 5-10 seconds on a developer machine. VS compiler is also not particularly fast on compiling templates as far as I understand, and because of the templates inclusion model (you practically include the definition of the template in every file that uses it indirectly and possibly re-instantiate that template every time you modify something that has nothing to do with that template) you could have problems with compile times (when doing incremental compiling). What are your ways of handling incremental(and not only) compile time when working with templates (besides a better/faster compiler :-)).

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  • Inspecting the model in a Rails application

    - by Matt Sherman
    I am learning some Ruby on Rails, and am a newbie. Most of my background is in ASP.net MVC on the back end. As I play with a basic scaffold project, I wonder about this case: you jump into an established Rails project and want to get to know the model. Based on what I have seen so far (again, simple scaffold), the properties for a given class are not immediately revealed. I don't see property accessors on the model classes. I do understand that this is because of the dynamic nature of Ruby and such things are not necessary or even perhaps desirable. Convention over code, I get that. (Am familiar with dynamic concepts, mostly via JS.) But if I am somewhere off in a view, and want to quickly know whether the (eg) Person object has a MiddleName property, how would I find that out? I don't have to go into the migrations, do I?

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

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

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  • Logitech m510 mouse not working on 12.04 64bit

    - by Alonso
    When I run lsusb, this shows up: Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 008 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub Bus 006 Device 004: ID 046d:c52b Logitech, Inc. Unifying Receiver I have followed and done all of the stuff in: http://askubuntu.com/questions/154963/ubuntu-cannot-detect-my-logitech-wireless-m510-mouse Yet my mouse still fails to work. When trying to install HIDpoint, this appears after entering Y: libpng does not exist libtiff does not exist Gathering System information and generating a log Launching HIDPoint Installer ./hidpointsetup: error while loading shared libraries: libpng.so.3: cannot open shared object file: No such file or directory What can I do to fix this?

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  • How do GameEngines stop Pixel Seams appearing in adjacent mesh boundaries due to FP imprecision?

    - by ufomorace
    Graphics cards are mathematically imprecise. So when some meshes are joined by their borders, the graphics card often makes mistakes and decides that some pixels at the seam represent neither object, and unwanted pixels appear. It's a natural behaviour on all graphics cards. How are such worries avoided in Pro Games? Batching? Shaders? Different tangent vectors? Merging? Overlaping seams? Dark backgrounds? Extra vertices at borders? Z precision? Camera distance tweaks? Screencap of a fix that ended up not working:

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  • concurrency::index<N> from amp.h

    - by Daniel Moth
    Overview C++ AMP introduces a new template class index<N>, where N can be any value greater than zero, that represents a unique point in N-dimensional space, e.g. if N=2 then an index<2> object represents a point in 2-dimensional space. This class is essentially a coordinate vector of N integers representing a position in space relative to the origin of that space. It is ordered from most-significant to least-significant (so, if the 2-dimensional space is rows and columns, the first component represents the rows). The underlying type is a signed 32-bit integer, and component values can be negative. The rank field returns N. Creating an index The default parameterless constructor returns an index with each dimension set to zero, e.g. index<3> idx; //represents point (0,0,0) An index can also be created from another index through the copy constructor or assignment, e.g. index<3> idx2(idx); //or index<3> idx2 = idx; To create an index representing something other than 0, you call its constructor as per the following 4-dimensional example: int temp[4] = {2,4,-2,0}; index<4> idx(temp); Note that there are convenience constructors (that don’t require an array argument) for creating index objects of rank 1, 2, and 3, since those are the most common dimensions used, e.g. index<1> idx(3); index<2> idx(3, 6); index<3> idx(3, 6, 12); Accessing the component values You can access each component using the familiar subscript operator, e.g. One-dimensional example: index<1> idx(4); int i = idx[0]; // i=4 Two-dimensional example: index<2> idx(4,5); int i = idx[0]; // i=4 int j = idx[1]; // j=5 Three-dimensional example: index<3> idx(4,5,6); int i = idx[0]; // i=4 int j = idx[1]; // j=5 int k = idx[2]; // k=6 Basic operations Once you have your multi-dimensional point represented in the index, you can now treat it as a single entity, including performing common operations between it and an integer (through operator overloading): -- (pre- and post- decrement), ++ (pre- and post- increment), %=, *=, /=, +=, -=,%, *, /, +, -. There are also operator overloads for operations between index objects, i.e. ==, !=, +=, -=, +, –. Here is an example (where no assertions are broken): index<2> idx_a; index<2> idx_b(0, 0); index<2> idx_c(6, 9); _ASSERT(idx_a.rank == 2); _ASSERT(idx_a == idx_b); _ASSERT(idx_a != idx_c); idx_a += 5; idx_a[1] += 3; idx_a++; _ASSERT(idx_a != idx_b); _ASSERT(idx_a == idx_c); idx_b = idx_b + 10; idx_b -= index<2>(4, 1); _ASSERT(idx_a == idx_b); Usage You'll most commonly use index<N> objects to index into data types that we'll cover in future posts (namely array and array_view). Also when we look at the new parallel_for_each function we'll see that an index<N> object is the single parameter to the lambda, representing the (multi-dimensional) thread index… In the next post we'll go beyond being able to represent an N-dimensional point in space, and we'll see how to define the N-dimensional space itself through the extent<N> class. Comments about this post by Daniel Moth welcome at the original blog.

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  • How do I show a minimap in a 3D world?

    - by Bubblewrap
    Got a really typical use-case here. I have large map made up of hexagons and at any given time only a small section of the map is visible. To provide an overview of the complete map, I want to show a small 2D representation of the map in a corner of the screen. What is the recommended approach for this in libgdx? Keep in mind the minimap must be updated when the currently visible section changes and when the map is updated. I've found SpriteBatch(info here), but the warning label on it made me think twice: A SpriteBatch is a pretty heavy object so you should only ever have one in your program. I'm not sure I'm supposed to use the one SpriteBatch that I can have on the minimap, and I'm also not sure how to interpret "heavy" in this context. Another thing to possibly keep in mind is that the minimap will probably be part of a larger UI, is there any way to integrate these two?

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