true soft - Page 375 - Developer IT

Should tests be in the same Ruby file or in separated Ruby files?

- by Junior Mayhé

While using Selenium and Ruby to do some functional tests, I am worried with the performance. So is it better to add all test methods in the same Ruby file, or I should put each one in separated code files? Below a sample with all tests in the same file: # encoding: utf-8 require "selenium-webdriver" require "test/unit" class Tests < Test::Unit::TestCase def setup @driver = Selenium::WebDriver.for :firefox @base_url = "http://mysite" @driver.manage.timeouts.implicit_wait = 30 @verification_errors = [] @wait = Selenium::WebDriver::Wait.new :timeout => 10 end def teardown @driver.quit assert_equal [], @verification_errors end def element_present?(how, what) @driver.find_element(how, what) true rescue Selenium::WebDriver::Error::NoSuchElementError false end def verify(&blk) yield rescue Test::Unit::AssertionFailedError => ex @verification_errors << ex end def test_1 @driver.get(@base_url + "/") # a huge test here end def test_2 @driver.get(@base_url + "/") # a huge test here end def test_3 @driver.get(@base_url + "/") # a huge test here end def test_4 @driver.get(@base_url + "/") # a huge test here end def test_5 @driver.get(@base_url + "/") # a huge test here end end

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Checking for alternate keys with XNA IsKeyDown

- by jocull

I'm working on picking up XNA and this was a confusing point for me. KeyboardState keyState = Keyboard.GetState(); if (keyState.IsKeyDown(Keys.Left) || keyState.IsKeyDown(Keys.A)) { //Do stuff... } The book I'm using (Learning XNA 4.0, O'Rielly) says that this method accepts a bitwise OR series of keys, which I think should look like this... KeyboardState keyState = Keyboard.GetState(); if (keyState.IsKeyDown(Keys.Left | Keys.A)) { //Do stuff... } But I can't get it work. I also tried using !IsKeyUp(... | ...) as it said that all keys had to be down for it to be true, but had no luck with that either. Ideas? Thanks.

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Applications: The Mathematics of Movement, Part 3

- by TechTwaddle

Previously: Part 1, Part 2 As promised in the previous post, this post will cover two variations of the marble move program. The first one, Infinite Move, keeps the marble moving towards the click point, rebounding it off the screen edges and changing its direction when the user clicks again. The second version, Finite Move, is the same as first except that the marble does not move forever. It moves towards the click point, rebounds off the screen edges and slowly comes to rest. The amount of time that it moves depends on the distance between the click point and marble. Infinite Move This case is simple (actually both cases are simple). In this case all we need is the direction information which is exactly what the unit vector stores. So when the user clicks, you calculate the unit vector towards the click point and then keep updating the marbles position like crazy. And, of course, there is no stop condition. There’s a little more additional code in the bounds checking conditions. Whenever the marble goes off the screen boundaries, we need to reverse its direction. Here is the code for mouse up event and UpdatePosition() method, //stores the unit vector double unitX = 0, unitY = 0; double speed = 6; //speed times the unit vector double incrX = 0, incrY = 0; private void Form1_MouseUp(object sender, MouseEventArgs e) { double x = e.X - marble1.x; double y = e.Y - marble1.y; //calculate distance between click point and current marble position double lenSqrd = x * x + y * y; double len = Math.Sqrt(lenSqrd); //unit vector along the same direction (from marble towards click point) unitX = x / len; unitY = y / len; timer1.Enabled = true; } private void UpdatePosition() { //amount by which to increment marble position incrX = speed * unitX; incrY = speed * unitY; marble1.x += incrX; marble1.y += incrY; //check for bounds if ((int)marble1.x < MinX + marbleWidth / 2) { marble1.x = MinX + marbleWidth / 2; unitX *= -1; } else if ((int)marble1.x > (MaxX - marbleWidth / 2)) { marble1.x = MaxX - marbleWidth / 2; unitX *= -1; } if ((int)marble1.y < MinY + marbleHeight / 2) { marble1.y = MinY + marbleHeight / 2; unitY *= -1; } else if ((int)marble1.y > (MaxY - marbleHeight / 2)) { marble1.y = MaxY - marbleHeight / 2; unitY *= -1; } } So whenever the user clicks we calculate the unit vector along that direction and also the amount by which the marble position needs to be incremented. The speed in this case is fixed at 6. You can experiment with different values. And under bounds checking, whenever the marble position goes out of bounds along the x or y direction we reverse the direction of the unit vector along that direction. Here’s a video of it running; Finite Move The code for finite move is almost exactly same as that of Infinite Move, except for the difference that the speed is not fixed and there is an end condition, so the marble comes to rest after a while. Code follows, //unit vector along the direction of click point double unitX = 0, unitY = 0; //speed of the marble double speed = 0; private void Form1_MouseUp(object sender, MouseEventArgs e) { double x = 0, y = 0; double lengthSqrd = 0, length = 0; x = e.X - marble1.x; y = e.Y - marble1.y; lengthSqrd = x * x + y * y; //length in pixels (between click point and current marble pos) length = Math.Sqrt(lengthSqrd); //unit vector along the same direction as vector(x, y) unitX = x / length; unitY = y / length; speed = length / 12; timer1.Enabled = true; } private void UpdatePosition() { marble1.x += speed * unitX; marble1.y += speed * unitY; //check for bounds if ((int)marble1.x < MinX + marbleWidth / 2) { marble1.x = MinX + marbleWidth / 2; unitX *= -1; } else if ((int)marble1.x > (MaxX - marbleWidth / 2)) { marble1.x = MaxX - marbleWidth / 2; unitX *= -1; } if ((int)marble1.y < MinY + marbleHeight / 2) { marble1.y = MinY + marbleHeight / 2; unitY *= -1; } else if ((int)marble1.y > (MaxY - marbleHeight / 2)) { marble1.y = MaxY - marbleHeight / 2; unitY *= -1; } //reduce speed by 3% in every loop speed = speed * 0.97f; if ((int)speed <= 0) { timer1.Enabled = false; } } So the only difference is that the speed is calculated as a function of length when the mouse up event occurs. Again, this can be experimented with. Bounds checking is same as before. In the update and draw cycle, we reduce the speed by 3% in every cycle. Since speed is calculated as a function of length, speed = length/12, the amount of time it takes speed to reach zero is directly proportional to length. Note that the speed is in ‘pixels per 40ms’ because the timeout value of the timer is 40ms. The readability can be improved by representing speed in ‘pixels per second’. This would require you to add some more calculations to the code, which I leave out as an exercise. Here’s a video of this second version,

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Resources for Virtual Machine programming

- by good_computer

I am a beginner (a little more than that) programmer of C. I am really interested in the field of Virtual Machines. When I read about the Python VM, the PyPy project, the advancements in JVM technology, Google V8, the Erlang VM, I really get excited about these amazing pieces of technology, and really want to get my hands dirty building them or contributing to one of these projects. I need to know.. what are the things (language, concepts, algorithms, math, etc?) I need to know/learn to be able to build a virtual machine any books or other resources that will be helpful career prospects for a virtual machine engineer (but this is least important for me for now) (one more side question: somewhere I'd read something like JVM is on the cutting edge of virtual machine technology -- that it is the most advanced VM so far -- is that true?) Please give me a LONG answer detailing all that you know.

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Great Java EE Concurrency Write-up!

- by reza_rahman

As you are aware JSR-236, Concurrency Utilities for the Java EE platform, is now a candidate for addition into Java EE 7. While it is a critical enabling API it is not necessarily obvious why it is so important. This is especially true with existing features like EJB 3 @Asynchronous, Servlet 3 async and JAX-RS 2 async. On his blog DZone MVB Sander Mak does an excellent job of explaining the motivation and importance of JSR-236. Perhaps even more importantly, he discusses potential issues with the API such alignment with CDI and Java SE Fork/Join. Read the excellent write-up here!

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Access Control Service v2: Registering Web Identities in your Applications [concepts]

- by Your DisplayName here!

ACS v2 support two fundamental types of client identities– I like to call them “enterprise identities” (WS-*) and “web identities” (Google, LiveID, OpenId in general…). I also see two different “mind sets” when it comes to application design using the above identity types: Enterprise identities – often the fact that a client can present a token from a trusted identity provider means he is a legitimate user of the application. Trust relationships and authorization details have been negotiated out of band (often on paper). Web identities – the fact that a user can authenticate with Google et al does not necessarily mean he is a legitimate (or registered) user of an application. Typically additional steps are necessary (like filling out a form, email confirmation etc). Sometimes also a mixture of both approaches exist, for the sake of this post, I will focus on the web identity case. I got a number of questions how to implement the web identity scenario and after some conversations it turns out it is the old authentication vs. authorization problem that gets in the way. Many people use the IsAuthenticated property on IIdentity to make security decisions in their applications (or deny user=”?” in ASP.NET terms). That’s a very natural thing to do, because authentication was done inside the application and we knew exactly when the IsAuthenticated condition is true. Been there, done that. Guilty ;) The fundamental difference between these “old style” apps and federation is, that authentication is not done by the application anymore. It is done by a third party service, and in the case of web identity providers, in services that are not under our control (nor do we have a formal business relationship with these providers). Now the issue is, when you switch to ACS, and someone with a Google account authenticates, indeed IsAuthenticated is true – because that’s what he is! This does not mean, that he is also authorized to use the application. It just proves he was able to authenticate with Google. Now this obviously leads to confusion. How can we solve that? Easy answer: We have to deal with authentication and authorization separately. Job done ;) For many application types I see this general approach: Application uses ACS for authentication (maybe both enterprise and web identities, we focus on web identities but you could easily have a dual approach here) Application offers to authenticate (or sign in) via web identity accounts like LiveID, Google, Facebook etc. Application also maintains a database of its “own” users. Typically you want to store additional information about the user In such an application type it is important to have a unique identifier for your users (think the primary key of your user database). What would that be? Most web identity provider (and all the standard ACS v2 supported ones) emit a NameIdentifier claim. This is a stable ID for the client (scoped to the relying party – more on that later). Furthermore ACS emits a claims identifying the identity provider (like the original issuer concept in WIF). When you combine these two values together, you can be sure to have a unique identifier for the user, e.g.: Facebook-134952459903700\799880347 You can now check on incoming calls, if the user is already registered and if yes, swap the ACS claims with claims coming from your user database. One claims would maybe be a role like “Registered User” which can then be easily used to do authorization checks in the application. The WIF claims authentication manager is a perfect place to do the claims transformation. If the user is not registered, show a register form. Maybe you can use some claims from the identity provider to pre-fill form fields. (see here where I show how to use the Facebook API to fetch additional user properties). After successful registration (which may include other mechanisms like a confirmation email), flip the bit in your database to make the web identity a registered user. This is all very theoretical. In the next post I will show some code and provide a download link for the complete sample. More on NameIdentifier Identity providers “guarantee” that the name identifier for a given user in your application will always be the same. But different applications (in the case of ACS – different ACS namespaces) will see different name identifiers. This is by design to protect the privacy of users because identical name identifiers could be used to create “profiles” of some sort for that user. In technical terms they create the name identifier approximately like this: name identifier = Hash((Provider Internal User ID) + (Relying Party Address)) Why is this important to know? Well – when you change the name of your ACS namespace, the name identifiers will change as well and you will will lose your “connection” to your existing users. Oh an btw – never use any other claims (like email address or name) to form a unique ID – these can often be changed by users.

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#OOW 2012 : IaaS, Private Cloud, Multitenant Database, and X3H2M2

- by Eric Bezille

The title of this post is a summary of the 4 announcements made by Larry Ellison today, during the opening session of Oracle Open World 2012... To know what's behind X3H2M2, you will have to wait a little, as I will go in order, beginning with the IaaS - Infrastructure as a Service - announcement. Oracle IaaS goes Public... and Private... Starting in 2004 with Fusion development, Oracle Cloud was launch last year to provide not only SaaS Application, based on standard development, but also the underlying PaaS, required to build the specifics, and required interconnections between applications, in and outside of the Cloud. Still, to cover the end-to-end Cloud Services spectrum, we had to provide an Infrastructure as a Service, leveraging our Servers, Storage, OS, and Virtualization Technologies, all "Engineered Together". This Cloud Infrastructure, was already available for our customers to build rapidly their own Private Cloud either on SPARC/Solaris or x86/Linux... The second announcement made today bring that proposition a big step further : for cautious customers (like Banks, or sensible industries) who would like to benefits from the Cloud value of "as a Service", but don't want their Data out in the Cloud... We propose to them to operate the same systems, Exadata, Exalogic & SuperCluster, that are providing our Public Cloud Infrastructure, behind their firewall, in a Private Cloud model. Oracle 12c Multitenant Database This is also a major announcement made today, on what's coming with Oracle Database 12c : the ability to consolidate multiple databases with no extra additional cost especially in terms of memory needed on the server node, which is often THE consolidation limiting factor. The principle could be compare to Solaris Zones, where, you will have a Database Container, who is "owning" the memory and Database background processes, and "Pluggable" Database in this Database Container. This particular feature is a strong compelling event to evaluate rapidly Oracle Database 12c once it will be available, as this is major step forward into true Database consolidation with Multitenancy on a shared (optimized) infrastructure. X3H2M2, enabling the new Exadata X3 in-Memory Database Here we are : X3H2M2 stands for X3 (the new version of Exadata announced also today) Heuristic Hierarchical Mass Memory, providing the capability to keep most if not all the Data in the memory cache hierarchy. Of course, this is the major software enhancement of the new X3 Exadata machine, but as this is a software, our current customers would be able to benefit from it on their existing systems by upgrading to the new release. But that' not the only thing that we did with X3, at the same time we have upgraded everything : the CPUs, adding more cores per server node (16 vs. 12, with the arrival of Intel E5 / Sandy Bridge), the memory with 512GB memory as well per node, and the new Flash Fire card, bringing now up to 22 TB of Flash cache. All of this 4TB of RAM + 22TB of Flash being use cleverly not only for read but also for write by the X3H2M2 algorithm... making a very big difference compare to traditional storage flash extension. But what does those extra performances brings to you on an already very efficient system: double your performances compare to the fastest storage array on the market today (including flash) and divide you storage price x10 at the same time... Something to consider closely this days... Especially that we also announced the availability of a new Exadata X3-2 8th rack : a good starting point. As you have seen a major opening for this year again with true innovation. But that was not the only thing that we saw today, as before Larry's talk, Fujitsu did introduce more in deep the up coming new SPARC processor, that they are co-developing with us. And as such Andrew Mendelsohn - Senior Vice President Database Server Technologies came on stage to explain that the next step after I/O optimization for Database with Exadata, was to accelerate the Database at execution level by bringing functions in the SPARC processor silicium. All in all, to process more and more Data... The big theme of the day... and of the Oracle User Groups Conferences that were also happening today and where I had the opportunity to attend some interesting sessions on practical use cases of Big Data one in Finances and Fraud profiling and the other one on practical deployment of Oracle Exalytics for Data Analytics. In conclusion, one picture to try to size Oracle Open World ... and you can understand why, with such a rich content... and this only the first day !

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SSIS 2012 Moving and Resizing

- by andyleonard

Occasionally someone will email or post a comment about how all MVPs are Microsoft shills. I’m sure I enjoy those comments about as much as the Developer Teams at Microsoft. Let me start by saying that’s simply not true. In fact, it is completely off the mark – at least when it comes to the MVPs I know and with whom I interact. If anything, we are Microsoft’s harshest critics. Just last week, I sent someone at Microsoft an email with the following complaint (paraphrased): I do not like chasing down...(read more)

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Markup format or script for data files?

- by Aaron

The game I'm designing will be mainly written in a high level scripting language (leaning towards either Lua or Squirrel) with a C++ core. In addition to scripts I'm also going to need different data files. Many data files will be for static information such as graphical assets and monster types. I'd also want to create and update data files at runtime for user information like option settings and game saves. Can I get away with using plain script files (i.e. .lua or .nut files) for my data files, or is it better to use dedicated markup formats like XML or YAML? If I use script files, loaded separately from my true scripts, then I wouldn't need an extra library to read those files. Scripting languages like Lua also have table syntax that lend themselves towards data definition. On the other hand I'd have to write my own schema check code. These languages also don't seem to support serialization "out of the box" like the markup format libraries do.

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How to Implement Single Sign-On between Websites

- by hmloo

Introduction Single sign-on (SSO) is a way to control access to multiple related but independent systems, a user only needs to log in once and gains access to all other systems. a lot of commercial systems that provide Single sign-on solution and you can also choose some open source solutions like Opensso, CAS etc. both of them use centralized authentication and provide more robust authentication mechanism, but if each system has its own authentication mechanism, how do we provide a seamless transition between them. Here I will show you the case. How it Works The method we’ll use is based on a secret key shared between the sites. Origin site has a method to build up a hashed authentication token with some other parameters and redirect the user to the target site. variables Status Description ssoEncode required hash(ssoSharedSecret + , + ssoTime + , + ssoUserName) ssoTime required timestamp with format YYYYMMDDHHMMSS used to prevent playback attacks ssoUserName required unique username; required when a user is logged in Note : The variables will be sent via POST for security reasons Building a Single Sign-On Solution Origin Site has function to 1. Create the URL for your Request. 2. Generate required authentication parameters 3. Redirect to target site. using System; using System.Web.Security; using System.Text; public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { string postbackUrl = "http://www.targetsite.com/sso.aspx"; string ssoTime = DateTime.Now.ToString("yyyyMMddHHmmss"); string ssoUserName = User.Identity.Name; string ssoSharedSecret = "58ag;ai76"; // get this from config or similar string ssoHash = FormsAuthentication.HashPasswordForStoringInConfigFile(string.Format("{0},{1},{2}", ssoSharedSecret, ssoTime, ssoUserName), "md5"); string value = string.Format("{0}:{1},{2}", ssoHash,ssoTime, ssoUserName); Response.Clear(); StringBuilder sb = new StringBuilder(); sb.Append("<html>"); sb.AppendFormat(@"<body onload='document.forms[""form""].submit()'>"); sb.AppendFormat("<form name='form' action='{0}' method='post'>", postbackUrl); sb.AppendFormat("<input type='hidden' name='t' value='{0}'>", value); sb.Append("</form>"); sb.Append("</body>"); sb.Append("</html>"); Response.Write(sb.ToString()); Response.End(); } } Target Site has function to 1. Get authentication parameters. 2. Validate the parameters with shared secret. 3. If the user is valid, then do authenticate and redirect to target page. 4. If the user is invalid, then show errors and return. using System; using System.Web.Security; using System.Text; public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { if (User.Identity.IsAuthenticated) { Response.Redirect("~/Default.aspx"); } } if (Request.Params.Get("t") != null) { string ticket = Request.Params.Get("t"); char[] delimiters = new char[] { ':', ',' }; string[] ssoVariable = ticket.Split(delimiters, StringSplitOptions.None); string ssoHash = ssoVariable[0]; string ssoTime = ssoVariable[1]; string ssoUserName = ssoVariable[2]; DateTime appTime = DateTime.MinValue; int offsetTime = 60; // get this from config or similar try { appTime = DateTime.ParseExact(ssoTime, "yyyyMMddHHmmss", null); } catch { //show error return; } if (Math.Abs(appTime.Subtract(DateTime.Now).TotalSeconds) > offsetTime) { //show error return; } bool isValid = false; string ssoSharedSecret = "58ag;ai76"; // get this from config or similar string hash = FormsAuthentication.HashPasswordForStoringInConfigFile(string.Format("{0},{1},{2}", ssoSharedSecret, ssoTime, ssoUserName), "md5"); if (string.Compare(ssoHash, hash, true) == 0) { if (Math.Abs(appTime.Subtract(DateTime.Now).TotalSeconds) > offsetTime) { //show error return; } else { isValid = true; } } if (isValid) { //Do authenticate; } else { //show error return; } } else { //show error } } } Summary This is a very simple and basic SSO solution, and its main advantage is its simplicity, only needs to add a single page to do SSO authentication, do not need to modify the existing system infrastructure.

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Alternative way of developing for ASP.NET to WebForms - Any problems with this?

- by John

So I have been developing in ASP.NET WebForms for some time now but often get annoyed with all the overhead (like ViewState and all the JavaScript it generates), and the way WebForms takes over a lot of the HTML generation. Sometimes I just want full control over the markup and produce efficient HTML of my own so I have been experimenting with what I like to call HtmlForms. Essentially this is using ASP.NET WebForms but without the form runat="server" tag. Without this tag, ASP.NET does not seem to add anything to the page at all. From some basic tests it seems that it runs well and you still have the ability to use code-behind pages, and many ASP.NET controls such as repeaters. Of course without the form runat="server" many controls won't work. A post at Enterprise Software Development lists the controls that do require the tag. From that list you will see that all of the form elements like TextBoxes, DropDownLists, RadioButtons, etc cannot be used. Instead you use normal HTML form controls. But how do you access these HTML controls from the code behind? Retrieving values on post back is easy, you just use Request.QueryString or Request.Form. But passing data to the control could be a little messy. Do you use a ASP.NET Literal control in the value field or do you use <%= value % in the markup page? I found it best to add runat="server" to my HTML controls and then you can access the control in your code-behind like this: ((HtmlInputText)txtName).Value = "blah"; Here's a example that shows what you can do with a textbox and drop down list: Default.aspx <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="NoForm.Default" %> <%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="NoForm.Default" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title></title> </head> <body> <form action="" method="post"> <label for="txtName">Name:</label> <input id="txtName" name="txtName" runat="server" /><br /> <label for="ddlState">State:</label> <select id="ddlState" name="ddlState" runat="server"> <option value=""></option> </select><br /> <input type="submit" value="Submit" /> </form> </body> </html> Default.aspx.cs using System; using System.Web.UI.HtmlControls; using System.Web.UI.WebControls; namespace NoForm { public partial class Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { //Default values string name = string.Empty; string state = string.Empty; if (Request.RequestType == "POST") { //If form submitted (post back) name = Request.Form["txtName"]; state = Request.Form["ddlState"]; //Server side form validation would go here //and actions to process form and redirect } ((HtmlInputText)txtName).Value = name; ((HtmlSelect)ddlState).Items.Add(new ListItem("ACT")); ((HtmlSelect)ddlState).Items.Add(new ListItem("NSW")); ((HtmlSelect)ddlState).Items.Add(new ListItem("NT")); ((HtmlSelect)ddlState).Items.Add(new ListItem("QLD")); ((HtmlSelect)ddlState).Items.Add(new ListItem("SA")); ((HtmlSelect)ddlState).Items.Add(new ListItem("TAS")); ((HtmlSelect)ddlState).Items.Add(new ListItem("VIC")); ((HtmlSelect)ddlState).Items.Add(new ListItem("WA")); if (((HtmlSelect)ddlState).Items.FindByValue(state) != null) ((HtmlSelect)ddlState).Value = state; } } } As you can see, you have similar functionality to ASP.NET server controls but more control over the final markup, and less overhead like ViewState and all the JavaScript ASP.NET adds. Interestingly you can also use HttpPostedFile to handle file uploads using your own input type="file" control (and necessary form enctype="multipart/form-data"). So my question is can you see any problems with this method, and any thoughts on it's usefulness? I have further details and tests on my blog.

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Is type safety worth the trade-offs?

- by Prof Plum

I began coding in in Python primarily where there is no type safety, then moved to C# and Java where there is. I found that I could work a bit more quickly and with less headaches in Python, but then again, my C# and Java apps are at much higher level of complexity so I have never given Python a true stress test I suppose. The Java and C# camps make it sound like without the type safety in place, most people would be running into all sorts of horrible bugs left an right and it would be more trouble than its worth. This is not a language comparison, so please do not address issues like compiled vs interpreted. Is type safety worth the hit to speed of development and flexibilty? WHY? to the people who wanted an example of the opinion that dynamic typing is faster: "Use a dynamically typed language during development. It gives you faster feedback, turn-around time, and development speed." - http://blog.jayway.com/2010/04/14/static-typing-is-the-root-of-all-evil/

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Numerical stability in continuous physics simulation

- by Panda Pajama

Pretty much all of the game development I have been involved with runs afoul of simulating a physical world in discrete time steps. This is of course very simple, but hardly elegant (not to mention mathematically inaccurate). It also has severe disadvantages when large values are involved (either very large speeds, or very large time intervals). I'm trying to make a continuous physics simulation, just for learning, which goes like this: time = get_time() while true do new_time = get_time() update_world(new_time - time) render() time = new_time end And update_world() is a continuous physical simulation. Meaning that for example, for an accelerated object, instead of doing object.x = object.x + object.vx * timestep object.vx = object.vx + object.ax * timestep -- timestep is fixed I'm doing something like object.x = object.x + object.vx * deltatime + object.ax * ((deltatime ^ 2) / 2) object.vx = object.vx + object.ax * deltatime However, I'm having a hard time with the numerical stability of my solutions, especially for very large time intervals (think of simulating a physical world for hundreds of thousands of virtual years). Depending on the framerate, I get wildly different solutions. How can I improve the numerical stability of my continuous physical simulations?

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Scrum - how to carry over a partially complete User Story to the next Sprint without skewing the backlog

- by Nick

We're using Scrum and occasionally find that we can't quite finish a User Story in the sprint in which it was planned. In true Scrum style, we ship the software anyway and consider including the User Story in the next sprint during the next Sprint Planning session. Given that the User Story we are carrying over is partially complete, how do we estimate for it correctly in the next Sprint Planning session? We have considered: a) Adjusting the number of Story Points down to reflect just the work which remains to complete the User Story. Unfortunately this will mess up reporting the Product Backlog. b) Close the partially-completed User Story and raise a new one to implement the remainder of that feature, which will have fewer Story Points. This will affect our ability to retrospectively see what we didn't complete in that sprint and seems a bit time consuming. c) Not bother with either a or b and continue to guess during Sprint Planning saying things like "Well that User Story may be X story points, but I know it's 95% finished so I'm sure we can fit it in."

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Simple alternating text in Visual Basic 2008

- by Josh Grate

I have a simple completed program, but i would like to add one more feature to it but I'm not sure how. I have it set up to send a message automatically every 7 seconds when a text field is selected, repeating the message of course. What I would like for it to do is alternate between two separate messages, instead just repeating the one. I would like the new program to post at an interval of 12 seconds. Can you help me? Here is my coding. Public Class Form1 Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick SendKeys.Send(TextBox1.Text) SendKeys.Send("{ENTER}") End Sub Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Timer1.Enabled = True Timer1.Interval = (TextBox2.Text) End Sub Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click Timer1.Enabled = False End Sub Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load Timer1.Enabled = False End Sub End Class

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Movement of body after applying weld joint

- by ved

I have two rectangular bodies. I've applied Weldjoint successfully on these bodies. I want to move that joined body by applying linear impulse. After weld joint, these two bodies becomes single body right? How do I apply force/impulse on the joined body? I am using Box2D with LibGDX. I've tried this: polygon1.applyLinearImpulse(new Vector2(-5, 0), polygon1.getWorldCenter(), true); I thought that if I move polygon1 then polygon2 will also move due to my weld joint but it is not working properly. Why don't they move together after being welded?

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How can I gain access to a player instance in a Minecraft mod?

- by Andrew Graber

I'm creating Minecraft mod with a pickaxe that takes away experience when you break a block. The method for taking away experience from a player is addExperience on EntityPlayer, so I need to get an instance of EntityPlayer for the player using my pickaxe when the pickaxe breaks a block, so that I can remove the appropriate amount of experience. My pickaxe class currently looks like this: public class ExperiencePickaxe extends ItemPickaxe { public ExperiencePickaxe(int ItemID, EnumToolMaterial material){ super(ItemID, material); } public boolean onBlockDestroyed(ItemStack par1ItemStack, World par2World, int par3, int par4, int par5, int par6, EntityLiving par7EntityLiving) { if ((double)Block.blocksList[par3].getBlockHardness(par2World, par4, par5, par6) != 0.0D) { EntityPlayer e = new EntityPlayer(); // create an instance e.addExperience(-1); } return true; } } Obviously, I cannot actually create a new EntityPlayer since it is an abstract class. How can I get access to the player using my pickaxe?

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Switching from abstract class to interface

- by nischayn22

I have an abstract class which has all abstract methods except one which constructs objects of the subclasses. Now my mentor asked me to move this abstract class to an interface. Having an interface is no problem except with the method used to construct subclass objects. Where should this method go now? Also, I read somewhere that interfaces are more efficient than abstract classes. Is this true? Here's an example of my classes abstract class Animal { //many abstract methods getAnimalobject(some parameter) { return //appropriate subclass } } class Dog extends Animal {} class Elephant extends Animal {}

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Switching to WIF SessionMode in ASP.NET

- by Your DisplayName here!

To make it short: to switch to SessionMode (cache to server) in ASP.NET, you need to handle an event and set a property. Sounds easy – but you need to set it in the right place. The most popular blog post about this topic is from Vittorio. He advises to set IsSessionMode in WSFederationAuthenticationModule_SessionSecurityTokenCreated. Now there were some open questions on forum, like this one. So I decided to try it myself – and indeed it didn’t work for me as well. So I digged a little deeper, and after some trial and error I found the right place (in global.asax): void WSFederationAuthenticationModule_SecurityTokenValidated( object sender, SecurityTokenValidatedEventArgs e) { FederatedAuthentication.SessionAuthenticationModule.IsSessionMode = true; } Not sure if anything has changed since Vittorio’s post – but this worked for me. While playing around, I also wrote a little diagnostics tool that allows you to look into the session cookie (for educational purposes). Will post that soon. HTH

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How was collision detection handled in The Legend of Zelda: A Link to the Past?

- by Restart

I would like to know how the collision detection was done in The Legend of Zelda: A Link To The Past. The game is 16x16 tile based, so how did they do the tiles where only a quarter or half of the tile is occupied? Did they use a smaller grid for collision detection like 8x8 tiles, so four of them make one 16x16 tile of the texture grid? But then, they also have true half tiles which are diagonally cut and the corners of the tiles seem to be round or something. If Link walks into tiles corner he can keep on walking and automatically moves around it's corner. How is that done? I hope someone can help me out here.

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What could be a reason for cross-platform server applications developer to make his app work in multiple processes?

- by Kabumbus

So we consider a server app development - heavily loaded with messing with big data streams.An app will be running on one powerful server. a server app shall be developed in form of crossplatform application - so to work on Windows, Mac OS X and Linux. So same code many platforms for standing alone server architecture. We wonder what benefits does distributing applications not only over threads but over processes as wall would bring to programmers and to server end users and why? Some people sad to me that even having 48 cores, 4 process threads would be shared via OS throe all cores... is it true BTW?

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time issue in render libgdx [duplicate]

- by jaysingh

This question is an exact duplicate of: time issue in render libgdx [duplicate] pls. help how to implement this loop in render method next_game_tick and GetTickCount(); always contain same time value. so position never updated @Override public void render() { float deltaTime = Gdx.graphics.getDeltaTime(); Update(deltaTime); Render(deltaTime); } const int TICKS_PER_SECOND = 50; const int SKIP_TICKS = 1000 / TICKS_PER_SECOND; const int MAX_FRAMESKIP = 10; DWORD next_game_tick = GetTickCount(); int loops; bool game_is_running = true; while( game_is_running ) { loops = 0; while( GetTickCount() > next_game_tick && loops < MAX_FRAMESKIP) { update_game(); next_game_tick += SKIP_TICKS; loops++; } display_game(); }

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time issue in render libgdx [duplicate]

- by jaysingh

This question is an exact duplicate of: deWitters Game loop in libgdx(Android) pls. help how to implement this loop in render method next_game_tick and GetTickCount(); always contain same time value so player position not updated. @Override public void render() { float deltaTime = Gdx.graphics.getDeltaTime(); Update(deltaTime); Render(deltaTime); } const int TICKS_PER_SECOND = 50; const int SKIP_TICKS = 1000 / TICKS_PER_SECOND; const int MAX_FRAMESKIP = 10; DWORD next_game_tick = GetTickCount(); int loops; bool game_is_running = true; while( game_is_running ) { loops = 0; while( GetTickCount() > next_game_tick && loops < MAX_FRAMESKIP) { update_game(); next_game_tick += SKIP_TICKS; loops++; } display_game(); }

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2D Particle Explosion

- by TheBroodian

I'm developing a 2D action game, and in said game I've given my primary character an ability he can use to throw a fireball. I'm trying to design an effect so that when said fireball collides (be it with terrain or with an enemy) that the fireball will explode. For the explosion effect I've created a particle that once placed into game space will follow random, yet autonomic behavior based on random variables. Here is my question: When I generate my explosion (essentially 90 of these particles) I get one of two behaviors, 1) They are all generated with the same random variables, and don't resemble an explosion at all, more like a large mass of clumped sprites that all follow the same randomly generated path. 2) If I assign each particle a unique seed to its random number generator, they are a little bit -more- spread out, yet clumping is still visible (they seem to fork out into 3 different directions) Does anybody have any tips for producing particle-based 2D explosions? I'll include the code for my particle and the event I'm generating them in. Fire particle class: public FireParticle(xTile.Dimensions.Location StartLocation, ContentManager content) { worldLocation = StartLocation; fireParticleAnimation = new FireParticleAnimation(content); random = new Random(); int rightorleft = random.Next(0, 3); int upordown = random.Next(1, 3); int xVelocity = random.Next(0, 101); int yVelocity = random.Next(0, 101); Vector2 tempVector2 = new Vector2(0,0); if (rightorleft == 1) { tempVector2 = new Vector2(xVelocity, tempVector2.Y); } else if (rightorleft == 2) { tempVector2 = new Vector2(-xVelocity, tempVector2.Y); } if (upordown == 1) { tempVector2 = new Vector2(tempVector2.X, -yVelocity); } else if (upordown == 2) { tempVector2 = new Vector2(tempVector2.X, yVelocity); } velocity = tempVector2; scale = random.Next(1, 11); upwardForce = -10; dead = false; } public FireParticle(xTile.Dimensions.Location StartLocation, ContentManager content, int seed) { worldLocation = StartLocation; fireParticleAnimation = new FireParticleAnimation(content); random = new Random(seed); int rightorleft = random.Next(0, 3); int upordown = random.Next(1, 3); int xVelocity = random.Next(0, 101); int yVelocity = random.Next(0, 101); Vector2 tempVector2 = new Vector2(0, 0); if (rightorleft == 1) { tempVector2 = new Vector2(xVelocity, tempVector2.Y); } else if (rightorleft == 2) { tempVector2 = new Vector2(-xVelocity, tempVector2.Y); } if (upordown == 1) { tempVector2 = new Vector2(tempVector2.X, -yVelocity); } else if (upordown == 2) { tempVector2 = new Vector2(tempVector2.X, yVelocity); } velocity = tempVector2; scale = random.Next(1, 11); upwardForce = -10; dead = false; } #endregion #region Update and Draw public void Update(GameTime gameTime) { elapsed = (float)gameTime.ElapsedGameTime.TotalSeconds; fireParticleAnimation.Update(gameTime); Vector2 moveAmount = velocity * elapsed; xTile.Dimensions.Location newPosition = new xTile.Dimensions.Location(worldLocation.X + (int)moveAmount.X, worldLocation.Y + (int)moveAmount.Y); worldLocation = newPosition; velocity.Y += upwardForce; if (fireParticleAnimation.finishedPlaying) { dead = true; } } public void Draw(SpriteBatch spriteBatch) { spriteBatch.Draw( fireParticleAnimation.image.Image, new Rectangle((int)drawLocation.X, (int)drawLocation.Y, scale, scale), fireParticleAnimation.image.SizeAndsource, Color.White * fireParticleAnimation.image.Alpha); } Fireball explosion event: public override void Update(GameTime gameTime) { if (enabled) { float elapsed = (float)gameTime.ElapsedGameTime.TotalSeconds; foreach (Heart_of_Fire.World_Objects.Particles.FireParticle particle in explosionParticles.ToList()) { particle.Update(gameTime); if (particle.Dead) { explosionParticles.Remove(particle); } } collisionRectangle = new Microsoft.Xna.Framework.Rectangle((int)wrldPstn.X, (int)wrldPstn.Y, 5, 5); explosionCheck = exploded; if (!exploded) { coreGraphic.Update(gameTime); tailGraphic.Update(gameTime); Vector2 moveAmount = velocity * elapsed; moveAmount = horizontalCollision(moveAmount, layer); moveAmount = verticalCollision(moveAmount, layer); Vector2 newPosition = new Vector2(wrldPstn.X + moveAmount.X, wrldPstn.Y + moveAmount.Y); if (hasCollidedHorizontally || hasCollidedVertically) { exploded = true; } wrldPstn = newPosition; worldLocation = new xTile.Dimensions.Location((int)wrldPstn.X, (int)wrldPstn.Y); } if (explosionCheck != exploded) { for (int i = 0; i < 90; i++) { explosionParticles.Add(new World_Objects.Particles.FireParticle( new Location( collisionRectangle.X + random.Next(0, 6), collisionRectangle.Y + random.Next(0, 6)), contentMgr)); } } if (exploded && explosionParticles.Count() == 0) { //enabled = false; } } }

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