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• Should I cache the data or hit the database?

  - by JD01

  I have not worked with any caching mechanisms and was wondering what my options are in the .net world for the following scenario. We basically have a a REST Service where the user passes an ID of a Category (think folder) and this category may have lots of sub categories and each of the sub categories could have 1000 of media containers (think file reference objects) which contain information about a file that may be on a NAS or SAN server (files are videos in this case). The relationship between these categories is stored in a database together with some permission rules and meta data about the sub categories. So from a UI perspective we have a lazy loaded tree control which is driven by the user by clicking on each sub folder (think of Windows explorer). Once they come to a URL of the video file, they then can watch the video. The number of users could grow into the 1000s and the sub categories and videos could be in the 10000s as the system grows. The question is should we carry on the way it is currently working where each request hits the database or should we think about caching the data? We are on using IIS 6/7 and Asp.net.

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• No sound through DisplayPort

  - by Chris Koknat

  I'm trying to connect my Elitebook 8440p laptop to my Samsung HDTV. The laptop does not have a HDMI connection, but it does have DisplayPort. I bought a DisplayPort-to-HDMI adapter here http://www.amazon.com/gp/product/B002CSRFD8/ref=oss_product, and connected it with a 3' HDMI cable. The video shows up fine, but there is no audio. DisplayPort, HDMI, and the adapter all support audio. I contacted HP tech support, who told me to update my sound drivers. I installed the driver and rebooted. Supposedly, I should see a "HD Audio" tab. No luck, even after installing the driver again and rebooting. HP closed the case. I'm using XP Pro.

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• Proper updating of GeoClipMaps

  - by thr

  I have been working on an implementation of gpu-based geo clip maps, but there is a section of the GPU Gems 2 article that i just can't seem to understand, specifically this paragraph and more precisely the bolded part: The choice of grid size n = 2k-1 has the further advantage that the finer level is never exactly centered with respect to its parent next-coarser level. In other words, it is always offset by 1 grid unit either left or right, as well as either top or bottom (see Figure 2-4), depending on the position of the viewpoint. In fact, it is necessary to allow a finer level to shift while its next-coarser level stays fixed, and therefore the finer level must sometimes be off-center with respect to the next-coarser level. An alternative choice of grid size, such as n = 2k-3, would provide the possibility for exact centering Let's take an example image from the article: My "understanding" of the way the clip maps were update was that you floor the position of the viewpoint to an int, and such get the center vertex point if this is not the same as the previous center point, you update the entire map. Now, this obviously is not the case - but what I am failing to understand is this: If you look at the image above, if the viewpoint was to move one unit to the right, then the inner ring (the one just around the view point + white center square) would end up getting a 1 unit space on both the left and right side of itself. But there is nothing in the paper that deals with this, what i mean is that it would end up looking like this (excuse my crummy cut-and-paste editing of the above image): This is obviously not a valid state of the. So, would the solution be that a clip ring (layer) can only move in increments of the ring/layer it's contained within? Wouldn't this end up being very restrictive? I feel like I am missing some crucial understanding of parts of the algorithm, but I have been over both this paper and the original paper from 2004 and I just can't see what I am not getting.

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• Why might powerpoint not let me adjust the height of a table row?

  - by YGA

  Powerpoint is fighting me every time I try to adjust the height of a table row, and I'm wondering if folks have ideas why that might be the case. See the attached picture; the Argentina row is of height 0.41", while the Nicaragua row is 0.61". Whenever I change to change the Nicaragua row (either by manually moving the row line, or by typing in a new height into the box) powerpoint immediately resets it. The difference? The Argentina row I typed in directly, while the Nicaragua row I pasted in from Excel. Thoughts what might be the difference?

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• GPG Invalid Signature

  - by user46421

  I am having problems with the following (in an attempt to remove hyperlinks, I have removed one of the "/" from the addresses): W: GPG error: http://archive.ubuntu.com oneiric Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <[email protected]> W: GPG error: http://ppa.launchpad.net oneiric Release: The following signatures were invalid: BADSIG B725097B3ACC3965 Launchpad lffl W: GPG error: http://ppa.launchpad.net oneiric Release: The following signatures were invalid: BADSIG 4874D3686E80C6B7 Launchpad PPA for Banshee Team W: GPG error: http://archive.getdeb.net jaunty-getdeb Release: The following signatures were invalid: BADSIG A8A515F046D7E7CF GetDeb Archive Automatic Signing Key <[email protected]> W: GPG error: http://badgerports.org lucid Release: The following signatures were invalid: BADSIG C90F9CB90E1FAD0C Jo Shields <[email protected]> W: GPG error: http://ppa.launchpad.net oneiric Release: The following signatures were invalid: BADSIG 976B5901365C5CA1 Launchpad PPA for transmissionbt W: Failed to fetch http://ppa.launchpad.net/dlecan/openjdk/ubuntu/dists/oneiric/main/source/Sources 404 Not Found W: Failed to fetch http://ppa.launchpad.net/dlecan/openjdk/ubuntu/dists/oneiric/main/binary-i386/Packages 404 Not Found W: Failed to fetch http://ppa.launchpad.net/sevenmachines/flash/ubuntu/dists/oneiric/main/binary-i386/Packages 404 Not Found W: Failed to fetch http://ppa.launchpad.net/sun-java-community-team/sun-java6/ubuntu/dists/oneiric/main/source/Sources 404 Not Found W: Failed to fetch http://ppa.launchpad.net/sun-java-community-team/sun-java6/ubuntu/dists/oneiric/main/binary-i386/Packages 404 Not Found I have tried the following solutions which were in a closed case titled "The following signatures were invalid": First of all try sudo apt-get clean sudo apt-get update && sudo apt-get upgrade Some ISPs cache the packages and errors like these are reported then. If the above commands don't work, try sudo apt-get update -o Acquire::http::No-Cache=True and again sudo apt-get update && sudo apt-get upgrade If it still doesn't work, sudo apt-get update -o Acquire::BrokenProxy=true sudo apt-get update && sudo apt-get upgrade

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• Windows 7 ReadyBoost - What File System To Use With Flash Card/Drive?

  - by Boris_yo

  NTFS, exFAT or FAT32? I know that FAT32 has a limit of 4GB transfer per file, but is it faster and better than NTFS or exFAT? Since Windows 7 by itself uses NTFS, it remains logical to format flash card/drive with NTFS file system, however will NTFS or even exFAT be fine for flash card/drive? P.S. In case i decide to use SD flash card, what should i do if it is already plugged in and i decide to use another SD flash card in order to transfer photos? What will happen if i take out suddenly ReadyBoost SD flash card?

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• Nginx + PHP FASTCGI FAILS - how to debug ?

  - by Niro

  I have a server on AMAZON EC2 running Nginx +PHP with PHP FASTCGI via port 9000. The server runs fine for a few minutes and after a while (several thousands of hits in this case) FastCGI Dies and Nginx returns 502 Error. Nginx log shows 2010/01/12 16:49:24 [error] 1093#0: *9965 connect() failed (111: Connection refused) while connecting to upstream, client: 79.180.27.241, server: localhost, request: "GET /data.php?data=7781 HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "site1.mysite.com", referrer: "http://www.othersite.com/subc.asp?t=10" How can I debug what is causing FastCGI to die?

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• Is there a constraint-based scheduling/calendar application?

  - by wonsungi

  Is there a constraint-based scheduling/calendar application? This application would be used to coordinate multiple people's schedules. Two basic use cases: Multiple people need to schedule a time to meet together. Everyone is busy at different days/times. Each person enters blocks of days/times they cannot meet, and the application suggests the best times to meet given a desired time range. Multiple people need to use some common resources for a specific length of time (over some time span like a week), but the exact date/time does not matter. These people enter the resources and time needed, and the application suggests the best way to share these resources. This use case still accounts for people's blocks of busy time. I imagine this program would be graphical, but other interfaces would be acceptable. Also preferable if web-based/works on both PC's and Mac's, but PC-only/Mac-only solutions are acceptable.

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• Email forwarding for hundreds of domains [closed]

  - by Jim Westergren

  I run a free website builder. More than one thousand so far have mapped their own domain name to their site. I provide either email forward or installation of Google Apps as a solution for email. Email forward are today setup manually at my VPS provider which is a pain. I need administer email forwarding via an API so it is done automatically. If I choose to run my own mail server. What is the recommended setup in my use case?

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• Puppet causes endless restarts of CUPS (how does one prevent this)

  - by Purfideas

  Hi! It makes sense, and is in fact suggested on this site, to have a critical file change trigger a service restart with puppet meta-parameters (such as notify or subscribe). For example: ## file definition for printers.conf file { "/etc/cups/printers.conf": [snip], source => "puppet:///module/etc/cups/printers.conf" } ## service definition for sshd service { 'cups': ensure => running, subscribe => File['/etc/cups/printers.conf'] } But in the case of CUPS, this triggers and endless loop of restarts; the logic works like this: Change puppetmaster's version of /etc/cups/printers.conf puppetmaster pushes new version to client, triggering cups restart cupsd restart insists on putting its own time stamp at the top of printers.conf, 'Written by cupsd...' This change will be seen as out of date, so after runinterval, we return to (1). Is there a way to suppress cupsd's need to time stamp the file? Or is there a puppet trick that could help here? Thanks!

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• Static IP Address on Ubuntu 12.04 Virtual Machine

  - by chrisnankervis

  I've setup a VM running Ubuntu 12.04 specifically for local web development and am having some problems ensuring it has a static IP address. A static IP address is important as I'm using the IP address in my hosts file to assign a .local suffix to addresses used both in browser and to connect to the correct database on the VM. Currently, every time I connect to a new network or my VM is assigned a new IP address I need to reconfigure my whole environment which is becoming quite a pain. It also probably doesn't help that the default-lease-time on the Ubuntu VM is set to 1800 by default. At the moment I'm using VMWare Fusion and the Network Adapter is enabled and set to "Autodetect" under Bridged Networking. I've tried to set a static IP address within the dhcpd.conf using the code below: host ubuntu { hardware ethernet 00:50:56:35:0f:f1; fixed-address: 192.168.100.100; } The fixed-address that I've used is also outside the range specified in the subnet block (which in this case is 192.168.100.128 to 192.168.100.254). I've tried adding and removing the network adapter and restarting my Mac after each time to no avail. Below is an ifconfig of the VM that might be of some help: eth0 Link encap:Ethernet HWaddr 00:50:56:35:0f:f1 inet addr:192.168.0.25 Bcast:192.168.0.255 Mask:255.255.255.0 inet6 addr: fe80::250:56ff:fe35:ff1/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1624 errors:0 dropped:0 overruns:0 frame:0 TX packets:416 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:147348 (147.3 KB) TX bytes:41756 (41.7 KB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) Are there any specific issues with 12.04 that I'm missing? Otherwise has anyone else got any ideas? Thanks in advance.

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• Best solution for getting referral information in PHP

  - by absentx

  I am currently redoing some link structuring on a website. In the past we have used specific php files on the last step to direct the user to the proper place. Example: www.mysite.com/action/go-to-blue.php or www.mysite.com/action/short/go-to-red.php www.mysite.com/action/tall/go-to-red.php We are now restructuring to eliminate the /short/ or /tall/ directory. What this means is now "go-to-blue.php" will be doing some extra processing to make sure it sends the visitor to the proper place. The static method of the past was quite effective, because, well, if they left from that page we knew we had it right. Now since we are 301 redirecting action/short/go-to-red.php to just action/go-to-red.php it is quite important on "go-to-red.php" that we realize a user may have been redirected from /short/ or /tall/. So right now I am using HTTP_REFERRER and of course in my testing that works fine, but after a lot of reading it is clear that this is not a solid solution, so I was starting to brainstorm on other ways to check and make sure we get the proper referral information. If we could check HTTP_REFERRER plus some other test, I would feel confident we have a pretty good system in place to send the visitor to the right place. Some questions/comments: Could I use a session variable or a cookie to accomplish this goal? If so, would that be maintained through the 301 redirect? I don't see why it wouldn't be.. Passing the url in the url is not an option in this case.

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• Tools for game script / storyboard

  - by Pietro Polsinelli

  I am searching for a tool that will help in writing a game script. By "script" I mean the text core of a storyboard - without the drawing drafts, which may or may not be there (yet). What I'm thinking of will let write a piece of text of the script, define a simplified workflow from that step, and then define the text of next steps, and so on. Searching online, I found Inform http://inform7.com/ ("A Design System for Interactive Fiction Based on Natural Language") which in theory is exactly what I am searching for, but trying to use it it has this model of a space (a dungeon, a library) where you are picking up objects and exploring them. In my case I am designing more a Sims like game, the flow is entirely different. Considering non specific software, mind mapping tools miss the linearity of the process. What I am writing is a directed graph - simply a work-flow, but the way I want to design it is more text based than work-flow based. SO what I'm doing now is using a text editor, which I'll transform directly in code. Any suggestions?

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• Design for object with optional and modifiable attributtes?

  - by Ikuzen

  I've been using the Builder pattern to create objects with a large number of attributes, where most of them are optional. But up until now, I've defined them as final, as recommended by Joshua Block and other authors, and haven't needed to change their values. I am wondering what should I do though if I need a class with a substantial number of optional but non-final (mutable) attributes? My Builder pattern code looks like this: public class Example { //All possible parameters (optional or not) private final int param1; private final int param2; //Builder class public static class Builder { private final int param1; //Required parameters private int param2 = 0; //Optional parameters - initialized to default //Builder constructor public Builder (int param1) { this.param1 = param1; } //Setter-like methods for optional parameters public Builder param2(int value) { param2 = value; return this; } //build() method public Example build() { return new Example(this); } } //Private constructor private Example(Builder builder) { param1 = builder.param1; param2 = builder.param2; } } Can I just remove the final keyword from the declaration to be able to access the attributes externally (through normal setters, for example)? Or is there a creational pattern that allows optional but non-final attributes that would be better suited in this case?

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• NTFS Error - file system structure is corrupt and unusable

  - by SomeGuy

  My Windows 7 (64) keeps completely locking up, and I have to hold the power button to shit it down. Event logs are showing EventID 55. I realize that this can be a warning sign of an impending disk failure, but my data on this machine is safely backed up and I don't feel like taking the time to replace the drive right now. When I have seen this problem before, I have been able to delete the offending folder with a Linux Live CD. (When CHKDSK /F didn't work). In this case, the folder is from VSS. I assume this is from Crashplan, my online backup provider. What are the ramifications of deleting this folder from Linux? Is it safe to do? "The file system structure on the disk is corrupt and unusable. Please run the chkdsk utility on the volume \Device\HarddiskVolumeShadowCopy26."

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• Learning Programming during the job?

  - by Hossein

  Introduction: I have read and heard advice, about learning programming by accepting programming projects. I need real assistance to understand this, because: Problem: Although, it would seem to me that one would gain much more technical knowledge by doing, real world projects, if one doesn't know much about a technology, it would add much more risk to the actual delivery of the final product! Even the smallest of real world projects could be too much for a newbie. There is a contradiction here: You need to know the job to do it! and It's recommended to do the job, in order to learn it! Question: Any personal experiences in this case would be very pleasant to know while describing: How new was the subject to you? didn't have a clue at all? Or, did you have experience with similar technologies? Was it a solo project or were you in a team? If team, then did others help you with learning it? Did it work as expected? Did you deliver on time? Do you recommend this approach to others as well?

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• Looking for a small, light scene graph style abstraction lib for shader based OpenGL

  - by Pris

  I'm looking for a 'lean and mean' c/c++ scene graph library for OpenGL that doesn't use any deprecated functionality. It should be cross platform (strictly speaking I just dev on Linux so no love lost if it doesn't work on Windows), and it should be possible to deploy to mobile targets (ie OpenGLES2, and no crazy mandatory dependencies that wouldn't port well to modern mobile frameworks like iOS, Android, etc), with a license that's compatible with closed source software (LGPL or more liberal). Specific nice-to-haves would be: Cameras and Viewers (trackball, fly-by, etc) Object transform hierarchies (if B is a child of A, and you move A, B has the same transform applied to it) Simple animation Scene optimization (frustum culling, use VBOs, minimize state changes, etc) Text I've played around with OpenSceneGraph a lot and it's pretty amazing for fixed function pipeline stuff, but I've had a few of problems using it with the programmable pipeline and after going through their mailing list, it seems several people have had similar issues (going back years). Kitware's VES looks neat (http://www.vtk.org/Wiki/VES), but VES + VTK is pretty heavy. VTK is also typically for analyzing scientific data and I've read that it's not that appropriate for a general use case (not that great at rendering a lot of objects on scene,etc) I'm currently looking at VisualizationLibrary (http://www.visualizationlibrary.org/documentation/pag_gallery.html) which looks like it offers some of the functionality I'd like, but it doesn't explicitly support mobile targets. Other solutions like Ogre, Horde3D, Irrlicht, etc tend to be full on game engines and that's not really what I'm looking for. I'd like some suggestions for other libraries that I may have missed... please note I'm not willing to roll my own solution from scratch.

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• SQL 2008 R2 3rd Party Peer-to-Peer Replication, Global Site Distribution

  - by gombala

  We are looking at hosting 3 globally distributed SQL Server installations at different data centers. The intent is that Site A will serve web traffic and data for a specific region, same with Site B and C. In the case that Site A data center goes down, looses connectivity, etc. the users of Site A users will fail over to Site B or C (depending which is up). Also, if a user from Site A travels to Site C they should be able to access their data as it was on Site A. My questions is what SQL replication technology (SQL Replication or 3rd party) can support this scenario? We are using SQL 2008 R2 Enterprise at each site, each site runs on top of VMWare with a Netapp filer. Would something like distributed caching help in this scenario as well? We have looked at and tested Peer-to-Peer replication but have encountered issues with conflicts during our testing. I imagine there are other global data centers that have encountered and solved this issue.

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• Office arangement - comfort vs. teamwork?

  - by finrod

  Our team works in an open-space office. Luckily the cubicles are quite big (L shaped tables for everyone!), there is quite a lot of space so we are not sandwiched. Without going into further detail, there are comfortable spots (window), normal spots and stupid spots (near the corridor). Until recently, the development team of twelve engineers was seated so that all types of spots were occupied and we were all close together. In the old arrangement, verbal communication was very easy - half of the team was withing talking distance. The other half was like ten steps away. Often times I could ask, discuss, solve problems without leaving the cube. Most of the communication is work related, no bullshit or mental masturbation that would unnecessarily distract others. Now we have moved to another part of the building and have larger space to occupy. At this point, everyone could pick their spot. Naturally all stupid spots are left empty (for the poor newcomers to occupy bwehaha). In the new arrangement, the development team is stretched across the floor and some of the key engineers are seated 'far' from each other - definitely not within talking distance. I have yet to experience how this works out but am getting concerned that team work and communication may have been traded for personal comfort. Finally the questions... What do you think is better office arrangement? Such that allows for free verbal communication but trading for some developer's comfort, or such that potentially hinders verbal communication but makes developer's more comfortable in their spot? Or maybe it does not matter at all and we will evolve to be efficient in any arrangement? What is your personal experience? Note - yes I read books and posts how workplace is important in our job. However in this case - we are all still in open space and the difference between the different spots are not really groundbreaking. So I'm thinking the little comfort that few developers gain is not worth the loss of easy communication.

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• How to test the tests?

  - by Ryszard Szopa

  We test our code to make it more correct (actually, less likely to be incorrect). However, the tests are also code -- they can also contain errors. And if your tests are buggy, they hardly make your code better. I can think of three possible types of errors in tests: Logical errors, when the programmer misunderstood the task at hand, and the tests do what he thought they should do, which is wrong; Errors in the underlying testing framework (eg. a leaky mocking abstraction); Bugs in the tests: the test is doing slightly different than what the programmer thinks it is. Type (1) errors seem to be impossible to prevent (unless the programmer just... gets smarter). However, (2) and (3) may be tractable. How do you deal with these types of errors? Do you have any special strategies to avoid them? For example, do you write some special "empty" tests, that only check the test author's presuppositions? Also, how do you approach debugging a broken test case?

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• Remove unwanted Mount option from Places Menu

  - by Jack

  On Ubuntu 10.10, I added a CIFS network share into /etc/fstab using /media/pub as my mount point. The share becomes visible on the Desktop and under Places (drive icon), which is what I want. But the problem is, Ubuntu 10.10 (unlike 10.04) creates another entry under Places with same name "pub", except this appears to be a mount shortcut rather than another link to the share. When I move my mouse over it says "Mount pub" and if I click on it, it will mount the share and again each time (if already mounted) - it does not display contents of share. In either case, an error pops up soon after "Unable to mount pub - Timeout waiting for mount to appear". The share itself is accessible, but I can't unmount via GUI, system reports its mounted multiple times and I have to unmount via terminal. (sudo umount -a) As I'm mounting the share at boot time, I don't need this manual option under Places. Is there an easy way to stop Ubuntu from listing it under Places? I have tried making the mount point under /mnt, this fixes the problem, except creates another as it removes the drive icon from Desktop and Places. I could create a bookmark, but just wondered if there's an easy fix to this unwanted entry under Places. Thanks

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• What hardware makes a good MongoDB Server ? Where to get it ?

  - by João Pinto Jerónimo

  Suppose you're on dell.com right now and you're buying a server to run your MongoDB database for your small startup. You will have to handle literally tens of thousands of writes and reads per minute (but small objects). Would you go for 2 processors ? Invest more on RAM ? I've heard (correct me if I'm wrong) MongoDB handles the most it can on the RAM and then flushes everything to the disk, in that case I should invest on a CPU with a large L2 cache, probably 40GB of RAM and a solid state drive.. right ? Would I be better off with a high end (~$11,309, 2 expensive processors, 96GB of RAM) server or 2x(~$6,419, 2 expensive processors, 12GB of RAM) servers ? Is Dell ok or do you have better sugestions ? (I'm outside the US, on Portugal)

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• Create MSDB Folders Through Code

  You can create package folders through SSMS, but you may also wish to do this as part of a deployment process or installation. In this case you will want programmatic method for managing folders, so how can this be done? The short answer is, go and look at the table msdb.dbo. sysdtspackagefolders90. This where folder information is stored, using a simple parent and child hierarchy format. To add new folder directly we just insert into the table - INSERT INTO dbo.sysdtspackagefolders90 ( folderid ,parentfolderid ,foldername) VALUES ( NEWID() -- New GUID for our new folder ,<<Parent Folder GUID>> -- Lookup the parent folder GUID if a child or another folder, or use the root GUID 00000000-0000-0000-0000-000000000000 ,<<Folder Name>>) -- New folder name There are also some stored procedures - sp_dts_addfolder sp_dts_deletefolder sp_dts_getfolder sp_dts_listfolders sp_dts_renamefolder To add a new folder to the root we could call the sp_dts_addfolder to stored procedure - EXEC msdb.dbo.sp_dts_addfolder @parentfolderid = '00000000-0000-0000-0000-000000000000' -- Root GUID ,@name = 'New Folder Name The stored procedures wrap very simple SQL statements, but provide a level of security, as they check the role membership of the user, and do not require permissions to perform direct table modifications.

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• How to make VirtualBox headless answer on rdp port?

  - by stiv

  I'd like to run windows xp on RDP: $ VBoxManage modifyvm winxp32 --vrdeport 3389 $ VBoxHeadless -s winxp32 -v on Oracle VM VirtualBox Headless Interface 4.1.18_Debian (C) 2008-2012 Oracle Corporation All rights reserved. (waiting) in another window: $ telnet localhost 3389 Trying 127.0.0.1... telnet: Unable to connect to remote host: Connection refused Yes, I've read about extension: $ sudo VBoxManage extpack install Oracle_VM_VirtualBox_Extension_Pack-4.1.20-80170.vbox-extpack 0%... Progress state: NS_ERROR_FAILURE VBoxManage: error: Failed to install "Oracle_VM_VirtualBox_Extension_Pack-4.1.20- 80170.vbox-extpack": Extension pack 'Oracle VM VirtualBox Extension Pack' is already installed. In case of a reinstallation, please uninstall it first Looked through all manuals and all help requests. No success. What's wrong? Any ideas?

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• Farseer tutorial for the absolute beginners

  - by Bil Simser

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

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