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• Using the Java SE 8 Date Time API with JPA 2.1

  - by reza_rahman

  Most of you are hopefully aware of the new Date Time API included in Java SE 8. If you are not, you should check them out right now using the Java Tutorial Trail dedicated to the topic. It is a significantly leap forward in processing temporal data in Java. For those who already use Joda-Time the changes will look very familiar - very simplistically speaking the Java SE 8 feature is basically Joda-Time standardized. Quite naturally you will likely want to use the new Date Time APIs in your JPA domain model to better represent temporal data. The problem is that JPA 2.1 will not support the new API out of the box. So what are you to do? Fortunately you can make use of fairly simple JPA 2.1 Type Converters to use the Date Time API in your JPA domain classes. Steven Gertiser shows you how to do it in an extremely well written blog entry. Besides explaining the problem and the solution the entry is actually very good for getting a better understanding of JPA 2.1 Type Converters as well. I think such a set of converters may be a good fit for Apache DeltaSpike as a Java EE 7 extension? In case you are wondering about Java SE 8 support in the JPA specification itself, Nick Williams has already entered an excellent, well researched JIRA entry asking for such support in a future version of the JPA specification that's well worth looking at. Another possibility of course is for JPA providers to start supporting the Date Time API natively before anything is formalized in the specification. What do you think?

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• Unable to launch onscreen keyboard (osk.exe) from a 32-bit process on Win7 x64

  - by Steven Robbins

  90% of the time I am unable to launch osk.exe from a 32bit process on Win7 x64. Originally the code was just using: Process.Launch("osk.exe"); Which won't work on x64 because of the directory virtualization. Not a problem I thought, I'll just disable virtualization, launch the app, and enable it again, which I thought was the correct way to do things. I also added some code to bring the keyboard back up if it has been minimized (which works fine) - the code (in a sample WPF app) now looks as follows: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Windows; using System.Windows.Controls; using System.Windows.Data; using System.Windows.Documents; using System.Windows.Input; using System.Windows.Media; using System.Windows.Media.Imaging; using System.Windows.Navigation;using System.Diagnostics; using System.Runtime.InteropServices; namespace KeyboardTest { /// <summary> /// Interaction logic for MainWindow.xaml /// </summary> public partial class MainWindow : Window { [DllImport("kernel32.dll", SetLastError = true)] private static extern bool Wow64DisableWow64FsRedirection(ref IntPtr ptr); [DllImport("kernel32.dll", SetLastError = true)] public static extern bool Wow64RevertWow64FsRedirection(IntPtr ptr); private const UInt32 WM_SYSCOMMAND = 0x112; private const UInt32 SC_RESTORE = 0xf120; [DllImport("user32.dll", CharSet = CharSet.Auto)] static extern IntPtr SendMessage(IntPtr hWnd, UInt32 Msg, IntPtr wParam, IntPtr lParam); private string OnScreenKeyboadApplication = "osk.exe"; public MainWindow() { InitializeComponent(); } private void KeyboardButton_Click(object sender, RoutedEventArgs e) { // Get the name of the On screen keyboard string processName = System.IO.Path.GetFileNameWithoutExtension(OnScreenKeyboadApplication); // Check whether the application is not running var query = from process in Process.GetProcesses() where process.ProcessName == processName select process; var keyboardProcess = query.FirstOrDefault(); // launch it if it doesn't exist if (keyboardProcess == null) { IntPtr ptr = new IntPtr(); ; bool sucessfullyDisabledWow64Redirect = false; // Disable x64 directory virtualization if we're on x64, // otherwise keyboard launch will fail. if (System.Environment.Is64BitOperatingSystem) { sucessfullyDisabledWow64Redirect = Wow64DisableWow64FsRedirection(ref ptr); } // osk.exe is in windows/system folder. So we can directky call it without path using (Process osk = new Process()) { osk.StartInfo.FileName = OnScreenKeyboadApplication; osk.Start(); osk.WaitForInputIdle(2000); } // Re-enable directory virtualisation if it was disabled. if (System.Environment.Is64BitOperatingSystem) if (sucessfullyDisabledWow64Redirect) Wow64RevertWow64FsRedirection(ptr); } else { // Bring keyboard to the front if it's already running var windowHandle = keyboardProcess.MainWindowHandle; SendMessage(windowHandle, WM_SYSCOMMAND, new IntPtr(SC_RESTORE), new IntPtr(0)); } } } } But this code, most of the time, throws the following exception on osk.Start(): The specified procedure could not be found at System.Diagnostics.Process.StartWithShellExecuteEx(ProcessStartInfo startInfo) I've tried putting long Thread.Sleep commands in around the osk.Start line, just to make sure it wasn't a race condition, but the same problem persists. Can anyone spot where I'm doing something wrong, or provide an alternative solution for this? It seems to work fine launching Notepad, it just won't play ball with the onscreen keyboard.

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• How to implement a countdown clock on a product launch web page?

  - by Daniel Earwicker

  I'm asking this on behalf of a certain corporation: http://www.microsoft.com/visualstudio/en-us/watch-it-live Things to bear in mind: It's 8:30 AM at different times depending on where you are in the world. For example, where I am, it is already 10 AM, whereas in Redmond it's still only 2 AM. That's probably the main thing, I guess. Can any SO users recommend ways to improve the existing countdown page so that it works correctly for users in any timezone? (Serious question - clearly this is a pit that is easy to fall into!)

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• 2D Animation Smoothness - Delta time vs. Kinematics

  - by viperld002

  I'm animating a sprite in 2D with key frames of rotation and xy-positions. I've recently had a discussion with someone saying that when the device (happens to be an iPad using cocos2D) hits a performance bump due to whatever else the user may be doing, lag will arise and that the best way to fight it is to not use actual positions, but velocities, accelerations and torques with kinematics. His message is to evaluate the positions and rotations from these speeds at the current point in time. I've never experienced a situation where I've heard of using kinematics to stem lag in 2D animations and am not sure of how effective it could be. Also, it seems to be overkill. The application is not networked so it's all running on a local device. The desired effect is that the animation always plays as closely as it can to the target frame rate. Wouldn't the technique suffer the same problems as just using the time since the last frame or a fixed time step since the kinematics would also require some time value to perform the calculation? What techniques could you suggest to best achieve the desired effect? EDIT 1 Thank you for your responses, they are very illuminating. I want to clarify my question before choosing an answer however, to make sure that this post really serves it's purpose. I have a sprite of a ball, and a text file with 3 arrays worth of information (rotation,translations x, translations y) with each unit of information existing as a key frame to be stepped through (0 to 49 and back to 0 to replay it again). I have this playing by interpolating from the current key frame to the next, every n-units of time. The animation is visibly correct when compared to a video I was given of it, and it is smooth because of the interpolations between the key frames. This is the existing state of the project. There are no physics simulated, only a static animation of a ball moving in a way an artist specifically designed. Should I, instead of rotation in degrees and translations by positions in space, derive velocities, accelerations and torques to express this static animation as a function of time? As in, position now = foo(time now), where foo uses kinematics.

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• Is the expected time shown during file copy the best time or worst time?

  - by chinmoy

  When we copy files in windows, we get an expected time of completion. Is that time the best time or the worst time? Also are you assuming the environmental variables?

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• MySQL: should I use "date" and "time" fields when I already have a timestamp field?

  - by KeyStroke

  Hi, I have a MySQL table where there is a 'date_added' (date) field, 'time_added' (time) field and 'timestamp' (int) field. I found out afterwards that I can convert timestamp to a date or a time anyway, so so does that mean I could get rid of the other date/time fields and keep the timestamp only? Thanks in advance

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• How to change the date/time in Python for all modules?

  - by Felix Schwarz

  When I write with business logic, my code often depends on the current time. For example the algorithm which looks at each unfinished order and checks if an invoice should be sent (which depends on the no of days since the job was ended). In these cases creating an invoice is not triggered by an explicit user action but by a background job. Now this creates a problem for me when it comes to testing: I can test invoice creation itself easily However it is hard to create an order in a test and check that the background job identifies the correct orders at the correct time. So far I found two solutions: In the test setup, calculate the job dates relative to the current date. Downside: The code becomes quite complicated as there are no explicit dates written anymore. Sometimes the business logic is pretty complex for edge cases so it becomes hard to debug due to all these relative dates. I have my own date/time accessor functions which I use throughout my code. In the test I just set a current date and all modules get this date. So I can simulate an order creation in February and check that the invoice is created in April easily. Downside: 3rd party modules do not use this mechanism so it's really hard to integrate+test these. The second approach was way more successful to me after all. Therefore I'm looking for a way to set the time Python's datetime+time modules return. Setting the date is usually enough, I don't need to set the current hour or second (even though this would be nice). Is there such a utility? Is there an (internal) Python API that I can use?

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• How can you set a time limit for a PowerShell script to run for?

  - by calrain

  I want to set a time limit on a PowerShell (v2) script so it forcibly exits after that time limit has expired. I see in PHP they have commands like set_time_limit and max_execution_time where you can limit how long the script and even a function can execute for. With my script, a do/while loop that is looking at the time isn't appropriate as I am calling an external code library that can just hang for a long time. I want to limit a block of code and only allow it to run for x seconds, after which I will terminate that code block and return a response to the user that the script timed out. I have looked at background jobs but they operate in a different thread so won't have kill rights over the parent thread. Has anyone dealt with this or have a solution? Thanks!

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• Series On Embedded Development (Part 2) - Build-Time Optionality

  - by user12612705

  In this entry on embedded development, I'm going to discuss build-time optionality (BTO). BTO is the ability to subset your software at build-time so you only use what is needed. BTO typically pertains more to software providers rather then developers of final products. For example, software providers ship source products, frameworks or platforms which are used by developers to build other products. If you provide a source product, you probably don't have to do anything to support BTO as the developers using your source will only use the source they need to build their product. If you provide a framework, then there are some things you can do to support BTO. Say you provide a Java framework which supports audio and video. If you provide this framework in a single JAR, then developers who only want audio are forced to ship their product with the video portion of your framework even though they aren't using it. In this case, support providing the framework in separate JARs...break the framework into an audio JAR and a video JAR and let the users of your framework decide which JARs to include in their product. Sometimes this is as simple as packaging, but if, for example, the video functionality is dependent on the audio functionality, it may require coding work to cleanly separate the two. BTO can also work at install-time, and this is sometimes overlooked. Let's say your building a phone application which can use Near Field Communications (NFC) if it's available on the phone, but it doesn't require NFC to work. Typically you'd write one app for all phones (saving you time)...both those that have NFC and those that don't, and just use NFC if it's there. However, for better efficiency, you can detect at install-time if the phone supports NFC and not install the NFC portion of your app if the phone doesn't support NFC. This requires that you write the app so it can run without the optional NFC code and that you write your install app so it can detect NFC and do the right thing at install-time. Supporting install-time optionality will save persistent footprint on the phone, something your customers will appreciate, your app "neighbors" will appreciate, and that you'll appreciate when they save static footprint for you. In the next article, I'll talk about runtime optionality.

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• How do I build (get/download) time.h library?

  - by coffeenet

  I am trying to build a project on Linux via Makefile. I keep getting cannot find <sys/time.h> error. I asked around, and I was told that my project doesn't have access to library folders. Therefore, I am trying to solve this problem by using the time library locally inside my project's folder. I am very new to Linux. So, please forgive my question if it sounds naive. I found this, but I don't know what files I need, and how to build the library. http://sourceware.org/git/?p=glibc.git;a=tree;f=time;h=c950c5d4dd90541e8f3c7e1649fcde4aead989bb;hb=master Where can I find the time.h library/package? How do I build the library?

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• Getting current time in milliseconds

  - by user90293423

  How to get the current time in milliseconds? I'm working on a hacking simulation game and when ever someone connects to another computer/NPC, a login screen popups with a button on the side called BruteForce. When BruteForce is clicked, what i want the program to do is, calculate how many seconds cracking the password is going to take based on the player's CPU speed but that's the easy part. The hard part is i want to enter a character in the password's box every X milliseconds based on a TimeToCrack divided by PasswordLength formula. But since i don't know how to find how many milliseconds have elapsed since the second has passed, the program waits until the CurrentTime is higher than the TimeBeforeTheLoopStarted + HowLongItTakesToTypeaCharacter which is always going to be a second. How would you handle my problems? I've commented the game breaking part. std::vector<QString> hardware = user.getHardware(); QString CPU = hardware[0]; unsigned short Speed = 0; if(CPU == "OMG SingleCore 1.8GHZ"){ Speed = 2; } const short passwordLength = password.length(); /* It's equal to 16 */ int Time = passwordLength / Speed; double TypeSpeed = Time / passwordLength; time_t t = time(0); struct tm * now = localtime(&t); unsigned short EndTime = (now->tm_sec + Time) % 60; unsigned short CurrentTime = 0; short i = passwordLength - 1; do{ t = time(0); now = localtime(&t); CurrentTime = now->tm_sec; do{ t = time(0); now = localtime(&t); }while(now->tm_sec < CurrentTime + TypeSpeed); /* Highly flawed */ /* Do this while your integer value is under this double value */ QString tempPass = password; tempPass.chop(i); ui->lineEdit_2->setText(tempPass); i--; }while(CurrentTime != EndTime);

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• Trouble using Upstart to launch Redis as redis user

  - by Chris

  I'm trying to launch redis-server as a user (called redis) via Upstart. My /etc/init/redis-server.conf looks like this: description "redis server" start on runlevel [23] stop on shutdown exec sudo -u redis /usr/local/bin/redis-server /var/lib/redis/redis.conf Looks good, right? I start redis-server using $start redis-server redis-server start/running, process 16808 $redis-cli Could not connect to Redis at 127.0.0.1:6379: Connection refused $ps ax | grep ps 168 16810 tty1 R+ 0:00 ps ax 16811 tty1 S+ 0:00 grep 168 So redis-server definitely isn't running. Let's try executing the Upstart command by hand, shall we? exec sudo -u redis /usr/local/bin/redis-server /var/lib/redis/redis.conf [16852] 19 Jun 10:37:21 # Can't chdir to './': Permission denied Connection to 10.19.2.94 closed. And then I get logged off. I'm at a loss. Any ideas?

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• Mac - Run java program at launch

  - by emd

  I want to launch a java program (server program) at computer start up. I can run it from the command line perfectly. I created /Library/Server/startFS.sh. The file is executable by root and contains: cd /Library/Server/FiloSync /usr/bin/java -jar /Library/Server/FiloSync/filosync-server-latest.jar -p 7000 -s 7001 I can't get my launchd plist included here, the formatting is all off. I can run it fine from the command line: './startFS.sh' but when I put create the plist (via Lingon), nothing happens. Now, when run, it outputs a few lines to the console. Might that be problem?? I have tried prepending 'nohup' and post pending '&', but no combination seems to work. Help please.

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• Launch an arbitrary application with a specific icon

  - by Camilo Martin

  I'm thinking about customizing my Windows 7's application icons, so that they all follow a specific theme (Token-like icons). This would involve using Resource Hacker (or similar) to patch each .exe. Not only this would be tiresome, but also it would require doing it again at each update of each application (nevermind that some could break just because it was tampered with). Instead, is there any way to launch an application with a specific icon? Ideally it would be something from the command-line (so I can make a shortcut), like this: launchwithicon.exe --app C:\myapp.exe --icon C:\myicon.ico Note that while it is possible to do something similar by setting the taskbar to "always combine, hide labels", I do not like this approach and instead am looking for something that works without combining the taskbar icons.

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• How to turn off the unity launch bar in ubuntu 11.10

  - by user22106

  I would like to use the unity option in ubuntu but without the unity sidebar. I've seen how I can select to use just gnome from the login screen but there are some things I like about the unity interface. E.g. From what I've seen I like the integrated application menu with the ubuntu menu up the top that unity option comes with. So I really just want to turn the launch bar off. Any help would be appreciated. Cheers, Ben

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• Can't launch Oneiric x64 instance on Eucalyptus

  - by Bruno Reis

  EDIT: after many hours, I've found out that the problem has nothing to do with Eucalyptus. It looks like the image is buggy. Very, very buggy. More details in the end. I didn't manage to fix it, and I will file a bug. EDIT 2: I managed to fix it, it apparently works. I have a 4-machine cluster running Ubuntu Server Natty (11.04) x64. I've installed "Ubuntu Enterprise Cloud" from the installtion CD (then updated it) on each of these machines. The cloud seems to work fine, I have lots of virtual machines running Natty servers on them. Now I'd like to run Oneiric in a virtual machine, but somehow I can't. I downloaded Oneiric's (x64) image from http://cloud-images.ubuntu.com/oneiric/current/, published it (uec-publish-tarball oneiric-server-cloudimg-amd64.tar.gz oneiric-server-cloudimg-amd64) exactly as I did with Natty, then tried to launch an instance (euca-run-instances -n 1 -k my-key -t m1.small -z my-cloud emi-XXXXXXXX) using Oneiric's image, but the instance is not able to boot. With euca-get-console-output I get the following: [ 0.461269] VFS: Cannot open root device "sda1" or unknown-block(0,0) [ 0.462388] Please append a correct "root=" boot option; here are the available partitions: [ 0.463855] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) [ 0.465331] Pid: 1, comm: swapper Not tainted 3.0.0-13-generic #22-Ubuntu [ 0.466526] Call Trace: [ 0.466989] [<ffffffff815d3ee5>] panic+0x91/0x194 [ 0.467860] [<ffffffff81ad1031>] mount_block_root+0xdc/0x18e [ 0.468891] [<ffffffff81ad126a>] mount_root+0x54/0x59 [ 0.469829] [<ffffffff81ad13dc>] prepare_namespace+0x16d/0x1a7 [ 0.470883] [<ffffffff81ad0d76>] kernel_init+0x140/0x145 [ 0.471837] [<ffffffff815f38e4>] kernel_thread_helper+0x4/0x10 [ 0.472889] [<ffffffff81ad0c36>] ? start_kernel+0x3df/0x3df [ 0.473884] [<ffffffff815f38e0>] ? gs_change+0x13/0x13 The filesystem is labeled "cloudimg-rootfs", inside the image both /etc/fstab and /boot/grub/grub.cfg always refer to the image by the label, everything seems to be correct, yet the kernel says it can't find the root file system. I've spent many hours googling, but nothing came out. I've asked on #ubuntu-server, but nobody knew what to do. I've asked on #eucalyptus but got no answer at all. Any ideas on why this is happening and how to solve it? Thanks EDIT: after many hours, I've found out that the problem has nothing to do with Eucalyptus. It looks like the image is buggy. Very, very buggy. The first problem is that the Kernel in the image is a -generic kernel, while I suppose it should be a -virtual one. I chrooted into the image, removed the -generic packages, replaced it with the -virtual ones. Then I extracted the new kernel (and replaced the original one (-generic) that came with the tarball) because I need it when I publish and launch an image with Eucalyptus. The problem described above was solved. But then, the console started showing this: mount: mount point ext4 does not exist If you check the /etc/fstab file in the image, it says: LABEL=cloudimg-rootfs ext4 defaults 0 1 Damnt, where's my mount point? Note that it is missing /proc as well. Well, when you think it is over, you will notice that your instance will have no network connectivity. Let's check /etc/network/interface: # interfaces(5) file used by ifup(8) and ifdown(8) auto lo iface lo inet loopback Oh my! It is missing eth0... here I stopped. I can't take no more. I give up. Looks like Canonical has just forgotten to properly set up this image. At first, I though: "have I downloaded a server image by mistake?", but no, I double checked. It is really the cloud image, it has even "cloud-init" installed (which is not, by default, on server images). They just forgot to prepare it. I will file a bug (and reference it here once this is done), and hope they fix it soon! EDIT 2: it looks like the network configuration was the last thing missing. I decided to test it with the fixes above, and it booted properly! However, I haven't got the slightest idea if the image is now good to go...

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• Launch elasticsearch dockerfile using my own elasticsearch.yml

  - by Kevin

  I am launching elasticsearch via a dockerfile found here: https://index.docker.io/u/ehazlett/elasticsearch/ It works great. I need to define my own hosts as my environment does not support multicast of any kind. I understand that my options are: 1) supply hosts when elasticsearch is run as a command line parameter 2) modify my elasticsearch.yml file to set the hosts. I know how to build the yml, what I need to know is how to launch elasticsearch via docker using my own yml instead of the one in the container. Is that possible? Thanks.

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• Unable to launch google.com inside Linux Ubuntu

  - by Anuradha

  I have installed Ubuntu Linux VM in my Win XP box. I am able to open http://google.com on Win XP but when I login to, ubuntu linux.. and launch this site: I am getting an error: Server not found. The network settings I have on LinuxUbuntu VM is : Adapter1 : attached to Bridge adapter. I tried NAT as well. But nothing seems to work. I am not in China. I provide google.com as mere example. We have a test website which cannot be launched inside Linux Ubuntu.

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• Launch apps or run commands on Windows via shortcuts

  - by Francisc

  Is it possible to register shortcuts on Windows 7 so that regardless where you are looking (Desktop, a folder etc) the shortcut gets "heard" and the appropriate action is performed. For example, creating a shortcut in the System32 folder which will work if you use Run with the shortcut's name, will not work if you set a key combination when focus is set on the Desktop for example. Is there a native way of registering top-level shortcuts or even an application for enabling this? Example of things I want keyboard shortcuts for: open a specific folder like %path% create a new .js file in the current folder launch an application eventually with its path set to the current location if the app supports this (e.g. command prompt) Thank you.

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• 'Singleton' application - or let the user only launch one instance of a program at the time

  - by Disco

  I'm running a few linux desktops; mainly for kids (yeah, trying to teach them the right OS at early stage) (running Ubuntu 10.10, Gnome) The problem is that they found very funny to make their workstations (actually, old 512 Mb pentium 4) by launching thousands of firefox instances. I'm looking for a way to restrict them to launch 'N' instances of a particular application. Haven't figured yet how. Thought of a monitoring daemon but I think that would be too ressources hungry. Any idea of a script/trick to achieve this ? Note: i might have 1-2 level of users (the kids, and the more grown up kids) so i have also to limit per user; something like user1: 3firefox, user2: 2firefox instances.

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• What causes an MSI package to launch following application install

  - by Damo

  We have an application we have developed, it gets deployed via an MSI I built. The MSI has been used in many locations, on many different builds. On one customers site, on occasion we are seeing some odd occurrences of data from the registry going missing. The 'data' from some select registry keys disappears and we have little idea why. One interesting point is that the MSI installer for our application has been seen in passive mode during OS load / load of our application on stat-up. The MSI loads a progress bar then disappears, following this our application loads up. It has been noted that following this the data disappears from our registry. However I can't say these two events are absolutely linked, it could have been missing before this event. What causes the MSI for an application to launch way after initial installation. How can it be prevented (correctly)

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• Tool to launch a script driven by modem activity

  - by Will M

  Can anyone suggest a software tool (preferably under Windows XP or later) that would launch an application or script in response to a phone call being received on a landline phone line connected to a data modem on the same PC? or, better, in response to a sequence of touch-tones being played over such a phone line. This would allow, for example, using the telephone to manipulate firewall settings so as to create another layer of security in connection with remote internet access to that computer. I seem to recall seeing tools to do this sort of thing in the days before broadband internet access, when there was more attention to various tips and tricks for the dial-up modem, but a few attempts at Google hasn't turned anything up.

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• How to create launch icons on Ubuntu Desktop?

  - by MattSlay

  I installed Ubuntu in a VM using VirtualBox, and after a few hours of Googling all the things I had to install and configure for the rest of the environment, I am finally up and running with a Ruby on Rails IDE and have MySql up and running. After I start up the Ubuntu VM, I have to go to a terminal window and do this to start MySql: /etc/init.d/mysql start So that works fine, but, since I am such a GUI person, I’m wondering how I can create an icon on the Ubuntu Desktop that I can click on to launch this command. Can you tell me how to do that?

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• Catch and identify source of browser launch events

  - by beldaz

  My Windows XP computer is exhibiting strange behaviour, launching multiple browser windows, but not to any URL. Initially this was in Firefox, but when I uninstalled it the same happened in IE. Norton 360 detects no malware, and I wonder if there is some application that is accidentally causing the problem. I'd like to diagnose the problem further. It seems that the default browser is being launched by something, so I'd like to work out the culprit. Is there some method (or handy utility) that can catch requests to XP to launch the default browser, and identify the source?

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• Most efficient way to implement delta time

  - by Starkers

  Here's one way to implement delta time: /// init /// var duration = 5000, currentTime = Date.now(); // and create cube, scene, camera ect ////// function animate() { /// determine delta /// var now = Date.now(), deltat = now - currentTime, currentTime = now, scalar = deltat / duration, angle = (Math.PI * 2) * scalar; ////// /// animate /// cube.rotation.y += angle; ////// /// update /// requestAnimationFrame(render); ////// } Could someone confirm I know how it works? Here what I think is going on: Firstly, we set duration at 5000, which how long the loop will take to complete in an ideal world. With a computer that is slow/busy, let's say the animation loop takes twice as long as it should, so 10000: When this happens, the scalar is set to 2.0: scalar = deltat / duration scalar = 10000 / 5000 scalar = 2.0 We now times all animation by twice as much: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 2.0; angle = (Math.PI * 4) // which is 2 rotations When we do this, the cube rotation will appear to 'jump', but this is good because the animation remains real-time. With a computer that is going too quickly, let's say the animation loop takes half as long as it should, so 2500: When this happens, the scalar is set to 0.5: scalar = deltat / duration scalar = 2500 / 5000 scalar = 0.5 We now times all animation by a half: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 0.5; angle = (Math.PI * 1) // which is half a rotation When we do this, the cube won't jump at all, and the animation remains real time, and doesn't speed up. However, would I be right in thinking this doesn't alter how hard the computer is working? I mean it still goes through the loop as fast as it can, and it still has render the whole scene, just with different smaller angles! So this a bad way to implement delta time, right? Now let's pretend the computer is taking exactly as long as it should, so 5000: When this happens, the scalar is set to 1.0: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 1; angle = (Math.PI * 2) // which is 1 rotation When we do this, everything is timsed by 1, so nothing is changed. We'd get the same result if we weren't using delta time at all! My questions are as follows Mostly importantly, have I got the right end of the stick here? How do we know to set the duration to 5000 ? Or can it be any number? I'm a bit vague about the "computer going too quickly". Is there a way loop less often rather than reduce the animation steps? Seems like a better idea. Using this method, do all of our animations need to be timesed by the scalar? Do we have to hunt down every last one and times it? Is this the best way to implement delta time? I think not, due to the fact the computer can go nuts and all we do is divide each animation step and because we need to hunt down every step and times it by the scalar. Not a very nice DSL, as it were. So what is the best way to implement delta time? Below is one way that I do not really get but may be a better way to implement delta time. Could someone explain please? // Globals INV_MAX_FPS = 1 / 60; frameDelta = 0; clock = new THREE.Clock(); // In the animation loop (the requestAnimationFrame callback)… frameDelta += clock.getDelta(); // API: "Get the seconds passed since the last call to this method." while (frameDelta >= INV_MAX_FPS) { update(INV_MAX_FPS); // calculate physics frameDelta -= INV_MAX_FPS; } How I think this works: Firstly we set INV_MAX_FPS to 0.01666666666 How we will use this number number does not jump out at me. We then intialize a frameDelta which stores how long the last loop took to run. Come the first loop frameDelta is not greater than INV_MAX_FPS so the loop is not run (0 = 0.01666666666). So nothing happens. Now I really don't know what would cause this to happen, but let's pretend that the loop we just went through took 2 seconds to complete: We set frameDelta to 2: frameDelta += clock.getDelta(); frameDelta += 2.00 Now we run an animation thanks to update(0.01666666666). Again what is relevance of 0.01666666666?? And then we take away 0.01666666666 from the frameDelta: frameDelta -= INV_MAX_FPS; frameDelta = frameDelta - INV_MAX_FPS; frameDelta = 2 - 0.01666666666 frameDelta = 1.98333333334 So let's go into the second loop. Let's say it took 2(? Why not 2? Or 12? I am a bit confused): frameDelta += clock.getDelta(); frameDelta = frameDelta + clock.getDelta(); frameDelta = 1.98333333334 + 2 frameDelta = 3.98333333334 This time we enter the while loop because 3.98333333334 = 0.01666666666 We run update We take away 0.01666666666 from frameDelta again: frameDelta -= INV_MAX_FPS; frameDelta = frameDelta - INV_MAX_FPS; frameDelta = 3.98333333334 - 0.01666666666 frameDelta = 3.96666666668 Now let's pretend the loop is super quick and runs in just 0.1 seconds and continues to do this. (Because the computer isn't busy any more). Basically, the update function will be run, and every loop we take away 0.01666666666 from the frameDelta untill the frameDelta is less than 0.01666666666. And then nothing happens until the computer runs slowly again? Could someone shed some light please? Does the update() update the scalar or something like that and we still have to times everything by the scalar like in the first example?

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