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  • Passing Derived Class Instances as void* to Generic Callbacks in C++

    - by Matthew Iselin
    This is a bit of an involved problem, so I'll do the best I can to explain what's going on. If I miss something, please tell me so I can clarify. We have a callback system where on one side a module or application provides a "Service" and clients can perform actions with this Service (A very rudimentary IPC, basically). For future reference let's say we have some definitions like so: typedef int (*callback)(void*); // This is NOT in our code, but makes explaining easier. installCallback(string serviceName, callback cb); // Really handled by a proper management system sendMessage(string serviceName, void* arg); // arg = value to pass to callback This works fine for basic types such as structs or builtins. We have an MI structure a bit like this: Device <- Disk <- MyDiskProvider class Disk : public virtual Device class MyDiskProvider : public Disk The provider may be anything from a hardware driver to a bit of glue that handles disk images. The point is that classes inherit Disk. We have a "service" which is to be notified of all new Disks in the system, and this is where things unravel: void diskHandler(void *p) { Disk *pDisk = reinterpret_cast<Disk*>(p); // Uh oh! // Remainder is not important } SomeDiskProvider::initialise() { // Probe hardware, whatever... // Tell the disk system we're here! sendMessage("disk-handler", reinterpret_cast<void*>(this)); // Uh oh! } The problem is, SomeDiskProvider inherits Disk, but the callback handler can't receive that type (as the callback function pointer must be generic). Could RTTI and templates help here? Any suggestions would be greatly appreciated.

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  • how to model a follower stream in appengine?

    - by molicule
    I am trying to design tables to buildout a follower relationship. Say I have a stream of 140char records that have user, hashtag and other text. Users follow other users, and can also follow hashtags. I am outlining the way I've designed this below, but there are two limitaions in my design. I was wondering if others had smarter ways to accomplish the same goal. The issues with this are The list of followers is copied in for each record If a new follower is added or one removed, 'all' the records have to be updated. The code class HashtagFollowers(db.Model): """ This table contains the followers for each hashtag """ hashtag = db.StringProperty() followers = db.StringListProperty() class UserFollowers(db.Model): """ This table contains the followers for each user """ username = db.StringProperty() followers = db.StringListProperty() class stream(db.Model): """ This table contains the data stream """ username = db.StringProperty() hashtag = db.StringProperty() text = db.TextProperty() def save(self): """ On each save all the followers for each hashtag and user are added into a another table with this record as the parent """ super(stream, self).save() hfs = HashtagFollowers.all().filter("hashtag =", self.hashtag).fetch(10) for hf in hfs: sh = streamHashtags(parent=self, followers=hf.followers) sh.save() ufs = UserFollowers.all().filter("username =", self.username).fetch(10) for uf in ufs: uh = streamUsers(parent=self, followers=uf.followers) uh.save() class streamHashtags(db.Model): """ The stream record is the parent of this record """ followers = db.StringListProperty() class streamUsers(db.Model): """ The stream record is the parent of this record """ followers = db.StringListProperty() Now, to get the stream of followed hastags indexes = db.GqlQuery("""SELECT __key__ from streamHashtags where followers = 'myusername'""") keys = [k,parent() for k in indexes[offset:numresults]] return db.get(keys) Is there a smarter way to do this?

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  • Adding a website link to the Member Directory in DotNetNuke 6.2

    - by Chris Hammond
    In case you missed it, DotNetNuke 6.2 was released today, check out Will Morgenweck’s blog post for more details on the release . With some of the new features DotNetNuke 6.2 makes it easier to start to customize the listing of members on your site, and also the Profile display for users on the website. I started implementing DotNetNuke 6.2 on one of my racing websites last night (yeah, so I upgraded before the release happened, a benefit of working for the corp ). In doing so I configured the profile...(read more)

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  • MCP 70-536 Acquired

    - by dave
    Yeah...   Today I passed the 70-536 exam, so my way to 70-562 (ASP.NET 3.5) is open. Points: 815 Points needed for pass:700 Strarting to read new book :)

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  • JavaScript Sucks.

    - by Matt Watson
    JavaScript Sucks. Yes, I said it. Microsoft's announcement of TypeScript got me thinking today. Is this a step in the right direction? It sounds like it fixes a lot of problems with JavaScript development. But is it really just duct tape and super glue for a programming model that needs to be replaced?I have had a love hate relationship with JavaScript, like most developers who would prefer avoiding client side code. I started doing web development over 10 years ago and I have done some pretty cool stuff with JavaScript. It has came a long ways and is the universal standard these days for client side scripting in the web browser. Over the years the browsers have become much faster at processing JavaScript. Now people are even trying to use it on the server side via node.js. OK, so why do I think JavaScript sucks?Well first off, as an enterprise web application developer, I don't like any scripting or dynamic languages. I like code that compiles for lots of obvious reasons. It is messy to code with and lacks all kinds of modern programming features. We spend a lot of time trying to hack it to do things it was never really designed for.Ever try to use different jQuery based plugins that require conflicting jQuery versions? Yeah, that sucks.How about trying to figure out how to make 20 javascript include files load quicker as one request? Yeah that sucks too.Performance? Let me just point to the old Facebook mobile app made with JS & HTML5. It sucked. Enough said.How about unit testing JavaScript? I've never tried it, but it sure sounds like fun.My biggest problem with JavaScript is code security. If I make some awesome product, there is no way to protect my code. How can we expect game makers to write apps in 100% JavaScript and HTML5 if they can't protect their intellectual property?There are compiling tools like Closure, unit test frameworks, minify, coffee script, TypeScript and a bunch of other tools. But to me, they all try to make up for the weaknesses and problems with JavaScript. JavaScript is a mess and we spend a lot of time trying to work around all of it's problems. It is possible to program in Silverlight, Java or Flash and run that in the browser instead of JavaScript, but they all have their own problems and lack universal mobile support. I believe Microsoft's new TypeScript is a step forward for JavaScript, but I think we need to start planning to go a whole different direction. We need a new universal client side programming model, because JavaScript sucks.

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  • Would you expect this error ?

    - by GrumpyOldDBA
    Now I know why, but what I'm thinking is that if I create an error should I get valid data returned? To explain, I was browsing through the dmvs for queries which might benefit from tuning and I identified a query with two clustered index scans ( table scans ). I don't know all the schema off by heart and I was looking for a select by a LoginID column. I assumed this would be numeric and promptly entered an integer value to examine the query plan, yeah I should have looked at the table definition...(read more)

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  • Windows Server 2003 network boogey men every DBA should know

    - by merrillaldrich
    Recently I was again visited by my old friends TCP Chimney and SynAttackProtect . (Yeah, sometimes I feel like I mostly blog about 5-year old problems, but many of us as DBA's have to work on older versions or older systems, and so repeat older problems :-). This has been written about before, but as I BinGoogled around I noticed you are more likely to find the documents if you search for the cause, and not the symptoms. Most people who face a problem, of course, know the symptoms but not the cause....(read more)

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  • Windows Server 2003 network boogey men every DBA should know

    - by merrillaldrich
    Recently I was again visited by my old friends TCP Chimney and SynAttackProtect . (Yeah, sometimes I feel like I mostly blog about 5-year old problems, but many of us as DBA's have to work on older versions or older systems, and so repeat older problems :-). This has been written about before, but as I BinGoogled around I noticed you are more likely to find the documents if you search for the cause, and not the symptoms. Most people who face a problem, of course, know the symptoms but not the cause....(read more)

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  • There is Hardly a Scratch on It! [Humorous Image]

    - by Asian Angel
    That hard drive has lots of life left in it… View the Entire Set of Photos of this Hard Drive (29 Image Set) I finally removed this failed SCSI drive 2 years after the server reported it had failed. Yeah that report seems about right. [via Fail Desk] HTG Explains: How Windows 8′s Secure Boot Feature Works & What It Means for Linux Hack Your Kindle for Easy Font Customization HTG Explains: What Is RSS and How Can I Benefit From Using It?

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  • Showrooming: What's the big deal?

    - by David Dorf
    There's been lots of chatter recently on how retailers will combat showrooming this holiday season.  Best Buy and Target, for example, plan to price-match certain online sites.  But from my perspective, the whole showrooming concept is overblown.  Yes, mobile phones make is easier to comparison-shop, but consumers have been doing that all along.  Retailers have to work hard to merchandise their stores with the right products at the right price with the right promotions.  Its Retail 101. Yeah ok, many websites don't have to charge tax so they have an advantage, but they also have to cover shipping costs. Brick-and-mortar stores have the opportunity to provide expertise, fit, and instant gratification all of which are pretty big advantages. I see lots of studies that claim a large percentage of shoppers are showrooming.  Now I don't do much shopping, but when I do I rarely see anyone scanning UPC codes in the aisles.  If you dig into those studies, the question is usually something like, "have you used your mobile phone to price compare while shopping in the last year."  Well yeah, I did it once -- out of the 20 shopping trips.  And by the way, the in-store price was close enough to just buy the item.  Based on casual observation and informal surveys of friends, showrooming is not the modus-operandi for today's busy shoppers. I never see people showrooming in grocery stores, and most people don't bother for fashion.  For big purchases like appliances and furniture, I bet most people do their research online before entering the store.  The cases where I've done it was to see if a promotion was in fact a good deal.  Or even to make sure the in-store price is the same as the online price for the same brand. So, if you think you're a victim of showrooming, I suggest you look at the bigger picture.  Are you providing an engaging store experience?  Are you allowing customers to shop the way they want to shop, using various touchpoints?  Are you monitoring the competition to ensure prices are competitive?  Are your promotions attracting the right customers? Hubert Jolly, CEO of Best Buy, recently commented that showrooming might just get more people into his stores. "Once customers are in our stores, they're ours to lose."

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  • How do you transition from a desktop developer to a web based role?

    - by Fanatic23
    Background: Developer with loads of experience in desktop computing. C++, Java etc Wants to dabble in: Living social. Yeah, you guessed it right -- website development. Perhaps will need to learn PHP or Javascript, SOAP, XML etc. Positives: Knows nothing about ASP or jQuery -- clean slate really. What's that 1 piece of advice that you'd give here? Could be anything: choice of technology, frameworks, potential pitfall and portability issues etc.

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  • Steam overlay doesn't work

    - by TheDarktonik
    Steam overlay doesn't work for me in wine. Yeah, I guess, it's known bug, but some persons say I need to compile wine with right gcc. Some of them just download the latest deb-packaged wine and the overlay works flawlessly for them. I tried to compile wine myself, but it didn't work. Now I have the latest wine installed (ver 1.5.6 from PPA) but this overlay still doesn't work. (My English is not really good:))

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  • PHP or C++? I just want to choose a language and focus on it!

    - by user19177
    I love C++, but I feel I don't know if I should focus on web, so PHP, or C++. It's just an hard choice because right now I want to focus on one language and don't want to switch it a few months later. With C++ I'd program in SDL, while with PHP I don't know yet. I am not a very advanced programmer but I know basics of programming and can get going very well if determined. The problem is I just don't know.. I'm like OK! I'll go for C++! Then a minute later, wait what if I went with C#? Why this that.. ! I've read milion threads about C vs VB C# Python Ruby etc, all of them which I could find! It got me nowhere. The problem is probably I need to know something from some experts I guess.. I'm sure I'm not the only one who feels/felt like I do right now yeah? Uhm... I guess I might help you with some details so your answer may be easier to write! ( And also, if you want to say something else which is not related to PHP or C++, you can do that, I've just got to the conclusion that C++ and PHP are the ones that are worth it but yeah. C# I've discarded due to some stuff I read which says in future the projects I'd start now could just be useless and stuff like that.. ) Ok well : I'm 18 years old, and I program as hobby right now, but I do hope to go to a programming college in future. ( That would be in 2 years ). Hmm, I like programming games, and I'm mostly bothered by the fact "this language could be useless to what I need to do" ( I don't know how to explain this feeling! ) I don't know which other details I could add... I hope you guys can help me choose my path, this is really stressing me I'm wasting my time not doing anything right now because I don't know which language to use..! Thanks!

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  • How can a pygame image be colored?

    - by Juicy
    I'm writing a 2d particle system for a game in Pygame[1]. For the particles, I have an image surface loaded from a file -- basically a white primitive drawn over a transparent background. I'd like the particle engine to emit variously colored particles, but I'm not sure how to tell Pygame to color the surface. I've looked through what passes for documentation, but I'm having trouble finding anything. [1] Yeah, I don't really like Pygame, but my course insists I write this project in Python.

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  • I am one step closer to installing ubuntu, back is grayed out and I was stupid enough to not make a backup

    - by user283544
    Ok, so yeah, i've been stupid enough not to make a backup and 1 step closer to installing ubuntu. What I need is that is windows totally safe and not gonna be touched I made a new partition from windows, and in ubuntu installer I chose "Something else" Then I chose that partition as an ext4 and mount "/" Device for bootloader is my hard disk, /dev/sda/, that's what keeps me a little aware. So I need a quick answer is my windows 7 gonna be touched?

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  • pfSense 2.1 OpenVPN client not using tunnelled interface

    - by Brian M. Hunt
    I'm having some trouble getting OpenVPN working on my pfSense box. The issue is quite strange to me. When I have the OpenVPN turned on, only my router is able to connect to the Internet. From the router I can use ping, links, etc., and connections work exactly as expected - through the VPN, with the IP address assigned by my VPN provider (Proxy.sh, incidentally). However, none of the clients on the local network can connect to the Internet. I get timeouts when using ping or a web browser. I can ping my router, and the IP address of the gateway. When I switch the default gateway from the VPN to my ISP's gateway, all works exactly as expected. Here the routing table (netstat -r) when in VPN mode, and a key for it: IPv4 Destination Gateway Flags Refs Use Mtu Netif Expire 0.0.0.0/1 10.XX.X.53 UGS 0 122 1500 ovpnc1 = default 10.XX.X.53 UGS 0 235 1500 ovpnc1 8.8.8.8 10.XX.X.53 UGHS 0 82 1500 ovpnc1 10.XX.X.1/32 10.11.0.53 UGS 0 0 1500 ovpnc1 10.XX.X.53 link#12 UH 0 0 1500 ovpnc1 10.XX.X.54 link#12 UHS 0 0 16384 lo0 ZZ.XX.XXX.0/20 link#1 U 0 83 1500 re0 ZZ.XX.XXX.XXX link#1 UHS 0 0 16384 lo0 127.0.0.1 link#9 UH 0 12 16384 lo0 128.0.0.0/1 10.11.0.53 UGS 0 123 1500 ovpnc1 192.168.1.0/24 link#11 U 0 1434 1500 ue0 192.168.1.1 link#11 UHS 0 0 16384 lo0 YYY.YYY.YYY.YYY/32 ZZ.XX.XXX.1 UGS 0 249 1500 re0 IP addresses 10.XX.X.53/54 - My DHCP-assigned IP address/pair from the VPN provider ZZ.XX.XXX.XXX - My external IP assigned by my ISP YYY.YYY.YYY.YYY - The external IP assigned by the VPN provider Interfaces ovpnc1 - My VPN client interface re0 - My LAN interface ue0 - My WAN interface This looks essentially what I would expect it to be. The default route is through the VPN provider. The VPN address is routed through the ISP-assigned IP address. I am not sure what would be wrong here. So figuring this was a firewall issue, I basically tried enabling all in/out traffic. This did not seem to remedy the problem. Also figuring it could possibly be some client networking issue, I restarted the clients on the LAN. This did not help. I also ran route flush and reset the routes manually. So I am a bit stumped, and would be very grateful for any thoughts on what the problem might be.

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  • Productive Writing Software

    - by Nick Retallack
    What do you guys use to write a personal journal, notes, and reference information that you want to group and search through later? I'm not one of those crazy people who likes to share their journal with the world. Some things I like to keep to myself. It's quite nice to have a reference. Preferences for cross-platform stuff (windows, mac, linux) Some Background For Windows, there's a program called Yeah Write, which really changed my expectations about how easy it should be to start writing something. You don't open or close files -- just click an empty slot and start writing, or click a filled slot to work on another file. And you can organize things into categories by creating tabs. Now that I carry a Macbook, I've just been using TextEdit. I like it because I can't lose my work when my computer crashes: it auto-saves everything and restores it when I launch TextEdit again. But I make a mess, leave thirty open files, and save everything to one directory with no tags for easy grouping. Saving files and selecting the directory they should be in is too clunky to do in the middle of a meeting. And organizing files into folders in the Finder is a pain, since there's no tree view like on Windows. Sure, I'm lazy, but I miss Yeah Write. I'm not going to get a windows laptop just to use it though. Since the laptop I take my notes on is a mac, I'm gonna be biased toward mac solutions.

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  • initrd problem and Kernel panics after openSUSE 11.2 upgrade.

    - by unixbhaskar
    Once I have done the upgrade form openSUSE11.1 to openSUSE11.2 by doing this: zypper dup Now I tried to boot the system and it failed sync with VFS and kernel panic, so clearly a initrd problem . if I'm not mistaken. Now a bit of explanation about the problem: while upgrading it shows me the error updating initramfs( I forgot the exact error or might be warning).Oh yeah it shows some grub warning too. I have had been doing that from a chroot environment.. with all the required file mounted in proper place in the chroot environment. Now .after bit googling and painfully looking the susegeek.com forum and opensuse.org forum I have decided to recreate the initrd ...but the fellow called "mkinitrd" is real real crap as I hev been pointed out by few forum members. I tried to make an initrd image by myself, failed to do so .as it shows error that device not found( if I boot into suse live cd and mount the partition ) then I tried from the chrooted env and it says "there is no space left on the device" A bit bemused :( yeah most of you pointed it right may lack of knowledge of mine. Kindly suggest me and show me steps to do it correctly and get opensuse11.2 up and running. TIA

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  • "Mail" command hangs and maillogs shows error

    - by harmony
    i tried linux command on my CentOS 5.x: mail -s "mysubject" [email protected] minutes takes, it dont finish, i do Ctrl+C, it says "(Interrupt -- one more to kill letter)" i tried command: mail No mail for root /var/log/maillog is empty /var/log/kloxo/maillog is full of messages: Oct 25 17:28:17 vps qmail: 1382736497.255902 delivery 1246425: deferral: Uh-oh:_.qmail_has_prog_delivery_but_has_x_bit_set._(#4.7.0)/ Oct 25 17:28:17 vps qmail: 1382736497.255915 status: local 1/10 remote 0/60 i checked all my .qmail files and none has execution permissions. Any idea please how to debug?

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  • Pluralsight Meet the Author Podcast on HTML5 Canvas Programming

    - by dwahlin
      In the latest installment of Pluralsight’s Meet the Author podcast series, Fritz Onion and I talk about my new course, HTML5 Canvas Fundamentals.  In the interview I describe different canvas technologies covered throughout the course and a sample application at the end of the course that covers how to build a custom business chart from start to finish. Meet the Author:  Dan Wahlin on HTML5 Canvas Fundamentals   Transcript [Fritz] Hi. This is Fritz Onion. I’m here today with Dan Wahlin to talk about his new course HTML5 Canvas Fundamentals. Dan founded the Wahlin Group, which you can find at thewahlingroup.com, which specializes in ASP.NET, jQuery, Silverlight, and SharePoint consulting. He’s a Microsoft Regional Director and has been awarded Microsoft’s MVP for ASP.NET, Connected Systems, and Silverlight. Dan is on the INETA Bureau’s — Speaker’s Bureau, speaks at conferences and user groups around the world, and has written several books on .NET. Thanks for talking to me today, Dan. [Dan] Always good to talk with you, Fritz. [Fritz] So this new course of yours, HTML5 Canvas Fundamentals, I have to say that most of the really snazzy demos I’ve seen with HTML5 have involved Canvas, so I thought it would be a good starting point to chat with you about why we decided to create a course dedicated just to Canvas. If you want to kind of give us that perspective. [Dan] Sure. So, you know, there’s quite a bit of material out there on HTML5 in general, and as people that have done a lot with HTML5 are probably aware, a lot of HTML5 is actually JavaScript centric. You know, a lot of people when they first learn it, think it’s tags, but most of it’s actually JavaScript, and it just so happens that the HTML5 Canvas is one of those things. And so it’s not just, you know, a tag you add and it just magically draws all these things. You mentioned there’s a lot of cool things you can do from games to there’s some really cool multimedia applications out there where they integrate video and audio and all kinds of things into the Canvas, to more business scenarios such as charting and things along those lines. So the reason we made a course specifically on it is, a lot of the material out there touches on it but the Canvas is actually a pretty deep topic. You can do some pretty advanced stuff or easy stuff depending on what your application requirements are, and the API itself, you know, there’s over 30 functions just in the Canvas API and then a whole set of properties that actually go with that as well. So it’s a pretty big topic, and that’s why we created a course specifically tailored towards just the Canvas. [Fritz] Right. And let’s — let me just review the outline briefly here for everyone. So you start off with an introduction to getting started with Canvas, drawing with the HTML5 Canvas, then you talk about manipulating pixels, and you finish up with building a custom data chart. So I really like your example flow here. I think it will appeal to even business developers, right. Even if you’re not into HTML5 for the games or the media capabilities, there’s still something here for everyone I think working with the Canvas. Which leads me to another question, which is, where do you see the Canvas fitting in to kind of your day-to-day developer, people that are working business applications and maybe vanilla websites that aren’t doing kind of cutting edge stuff with interactivity with users? Is there a still a place for the Canvas in those scenarios? [Dan] Yeah, definitely. I think a lot of us — and I include myself here — over the last few years, the focus has generally been, especially if you’re, let’s say, a PHP or ASP.NET or Java type of developer, we’re kind of accustomed to working on the server side, and, you know, we kind of relied on Flash or Silverlight or these other plug-ins for the client side stuff when it was kind of fancy, like charts and graphs and things along those lines. With the what I call massive shift of applications, you know, mainly because of mobile, to more of client side, one of the big benefits I think from a maybe corporate standard way of thinking of things, since we do a lot of work with different corporations, is that, number one, rather than having to have the plug-in, which of course isn’t going to work on iPad and some of these other devices out there that are pretty popular, you can now use a built-in technology that all the modern browsers support, and that includes things like Safari on the iPad and iPhone and the Android tablets and things like that with their browsers, and actually render some really sophisticated charts. Whether you do it by scratch or from scratch or, you know, get a third party type of library involved, it’s just JavaScript. So it downloads fast so it’s good from a performance perspective; and when it comes to what you can render, it’s extremely robust. You can do everything from, you know, your basic circles to polygons or polylines to really advanced gradients as well and even provide some interactivity and animations, and that’s some of the stuff I touch upon in the class. In fact, you mentioned the last part of the outline there is building a custom data chart and that’s kind of gears towards more of the, what I’d call enterprise or corporate type developer. [Fritz] Yeah, that makes sense. And it’s, you know, a lot of the demos I’ve seen with HTML5 focus on more the interactivity and kind of game side of things, but the Canvas is such a diverse element within HTML5 that I can see it being applicable pretty much anywhere. So why don’t we talk a little bit about some of the specifics of what you cover? You talk about drawing and then manipulating pixels. You want to kind of give us the different ways of working with the Canvas and what some of those APIs provide for you? [Dan] Sure. So going all the way back to the start of the outline, we actually started off by showing different demonstrations of the Canvas in action, and we show some fun stuff — multimedia apps and games and things like that — and then also some more business scenarios; and then once you see that, hopefully it kinds of piques your interest and you go, oh, wow, this is actually pretty phenomenal what you can do. So then we start you off with, so how to you actually draw things. Now, there are some libraries out there that will draw things like graphs, but if you want to customize those or just build something you have from scratch, you need to know the basics, such as, you know, how do you draw circles and lines and arcs and Bezier curves and all those fancy types of shapes that a given chart may have on it or that a game may have in it for that matter. So we start off by covering what I call the core API functions; how do you, for instance, fill a rectangle or convert that to a square by setting the height and the width; how do you draw arcs or different types of curves and there’s different types supported such as I mentioned Bezier curves or quadratic curves; and then we also talk about how do you integrate text into it. You might have some images already that are just regular bitmap type images that you want to integrate, you can do that with a Canvas. And you can even sync video into the Canvas, which actually opens up some pretty interesting possibilities for both business and I think just general multimedia apps. Once you kind of get those core functions down for the basic shapes that you need to be able to draw on any type of Canvas, then we go a little deeper into what are the pixels that are there to manipulate. And that’s one of the important things to understand about the HTML5 Canvas, scalable vector graphics is another thing you can use now in the modern browsers; it’s vector based. Canvas is pixel based. And so we talk about how to do gradients, how can you do transforms, you know, how do you scale things or rotate things, which is extremely useful for charts ’cause you might have text that, you know, flips up on its side for a y-axis or something like that. And you can even do direct pixel manipulation. So it’s really, really powerful. If you want to get down to the RGBA level, you can do that, and I show how to do that in the course, and then kind of wrap that section up with some animation fundamentals. [Fritz] Great. Yeah, that’s really powerful stuff for programmatically rendering data to clients and responding to user inputs. Look forward to seeing what everyone’s going to come up with building this stuff. So great. That’s — that’s HTML5 Canvas Fundamentals with Dan Wahlin. Thanks very much, Dan. [Dan] Thanks again. I appreciate it.

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  • SQL Spatial: Getting “nearest” calculations working properly

    - by Rob Farley
    If you’ve ever done spatial work with SQL Server, I hope you’ve come across the ‘nearest’ problem. You have five thousand stores around the world, and you want to identify the one that’s closest to a particular place. Maybe you want the store closest to the LobsterPot office in Adelaide, at -34.925806, 138.605073. Or our new US office, at 42.524929, -87.858244. Or maybe both! You know how to do this. You don’t want to use an aggregate MIN or MAX, because you want the whole row, telling you which store it is. You want to use TOP, and if you want to find the closest store for multiple locations, you use APPLY. Let’s do this (but I’m going to use addresses in AdventureWorks2012, as I don’t have a list of stores). Oh, and before I do, let’s make sure we have a spatial index in place. I’m going to use the default options. CREATE SPATIAL INDEX spin_Address ON Person.Address(SpatialLocation); And my actual query: WITH MyLocations AS (SELECT * FROM (VALUES ('LobsterPot Adelaide', geography::Point(-34.925806, 138.605073, 4326)),                        ('LobsterPot USA', geography::Point(42.524929, -87.858244, 4326))                ) t (Name, Geo)) SELECT l.Name, a.AddressLine1, a.City, s.Name AS [State], c.Name AS Country FROM MyLocations AS l CROSS APPLY (     SELECT TOP (1) *     FROM Person.Address AS ad     ORDER BY l.Geo.STDistance(ad.SpatialLocation)     ) AS a JOIN Person.StateProvince AS s     ON s.StateProvinceID = a.StateProvinceID JOIN Person.CountryRegion AS c     ON c.CountryRegionCode = s.CountryRegionCode ; Great! This is definitely working. I know both those City locations, even if the AddressLine1s don’t quite ring a bell. I’m sure I’ll be able to find them next time I’m in the area. But of course what I’m concerned about from a querying perspective is what’s happened behind the scenes – the execution plan. This isn’t pretty. It’s not using my index. It’s sucking every row out of the Address table TWICE (which sucks), and then it’s sorting them by the distance to find the smallest one. It’s not pretty, and it takes a while. Mind you, I do like the fact that it saw an indexed view it could use for the State and Country details – that’s pretty neat. But yeah – users of my nifty website aren’t going to like how long that query takes. The frustrating thing is that I know that I can use the index to find locations that are within a particular distance of my locations quite easily, and Microsoft recommends this for solving the ‘nearest’ problem, as described at http://msdn.microsoft.com/en-au/library/ff929109.aspx. Now, in the first example on this page, it says that the query there will use the spatial index. But when I run it on my machine, it does nothing of the sort. I’m not particularly impressed. But what we see here is that parallelism has kicked in. In my scenario, it’s split the data up into 4 threads, but it’s still slow, and not using my index. It’s disappointing. But I can persuade it with hints! If I tell it to FORCESEEK, or use my index, or even turn off the parallelism with MAXDOP 1, then I get the index being used, and it’s a thing of beauty! Part of the plan is here: It’s massive, and it’s ugly, and it uses a TVF… but it’s quick. The way it works is to hook into the GeodeticTessellation function, which is essentially finds where the point is, and works out through the spatial index cells that surround it. This then provides a framework to be able to see into the spatial index for the items we want. You can read more about it at http://msdn.microsoft.com/en-us/library/bb895265.aspx#tessellation – including a bunch of pretty diagrams. One of those times when we have a much more complex-looking plan, but just because of the good that’s going on. This tessellation stuff was introduced in SQL Server 2012. But my query isn’t using it. When I try to use the FORCESEEK hint on the Person.Address table, I get the friendly error: Msg 8622, Level 16, State 1, Line 1 Query processor could not produce a query plan because of the hints defined in this query. Resubmit the query without specifying any hints and without using SET FORCEPLAN. And I’m almost tempted to just give up and move back to the old method of checking increasingly large circles around my location. After all, I can even leverage multiple OUTER APPLY clauses just like I did in my recent Lookup post. WITH MyLocations AS (SELECT * FROM (VALUES ('LobsterPot Adelaide', geography::Point(-34.925806, 138.605073, 4326)),                        ('LobsterPot USA', geography::Point(42.524929, -87.858244, 4326))                ) t (Name, Geo)) SELECT     l.Name,     COALESCE(a1.AddressLine1,a2.AddressLine1,a3.AddressLine1),     COALESCE(a1.City,a2.City,a3.City),     s.Name AS [State],     c.Name AS Country FROM MyLocations AS l OUTER APPLY (     SELECT TOP (1) *     FROM Person.Address AS ad     WHERE l.Geo.STDistance(ad.SpatialLocation) < 1000     ORDER BY l.Geo.STDistance(ad.SpatialLocation)     ) AS a1 OUTER APPLY (     SELECT TOP (1) *     FROM Person.Address AS ad     WHERE l.Geo.STDistance(ad.SpatialLocation) < 5000     AND a1.AddressID IS NULL     ORDER BY l.Geo.STDistance(ad.SpatialLocation)     ) AS a2 OUTER APPLY (     SELECT TOP (1) *     FROM Person.Address AS ad     WHERE l.Geo.STDistance(ad.SpatialLocation) < 20000     AND a2.AddressID IS NULL     ORDER BY l.Geo.STDistance(ad.SpatialLocation)     ) AS a3 JOIN Person.StateProvince AS s     ON s.StateProvinceID = COALESCE(a1.StateProvinceID,a2.StateProvinceID,a3.StateProvinceID) JOIN Person.CountryRegion AS c     ON c.CountryRegionCode = s.CountryRegionCode ; But this isn’t friendly-looking at all, and I’d use the method recommended by Isaac Kunen, who uses a table of numbers for the expanding circles. It feels old-school though, when I’m dealing with SQL 2012 (and later) versions. So why isn’t my query doing what it’s supposed to? Remember the query... WITH MyLocations AS (SELECT * FROM (VALUES ('LobsterPot Adelaide', geography::Point(-34.925806, 138.605073, 4326)),                        ('LobsterPot USA', geography::Point(42.524929, -87.858244, 4326))                ) t (Name, Geo)) SELECT l.Name, a.AddressLine1, a.City, s.Name AS [State], c.Name AS Country FROM MyLocations AS l CROSS APPLY (     SELECT TOP (1) *     FROM Person.Address AS ad     ORDER BY l.Geo.STDistance(ad.SpatialLocation)     ) AS a JOIN Person.StateProvince AS s     ON s.StateProvinceID = a.StateProvinceID JOIN Person.CountryRegion AS c     ON c.CountryRegionCode = s.CountryRegionCode ; Well, I just wasn’t reading http://msdn.microsoft.com/en-us/library/ff929109.aspx properly. The following requirements must be met for a Nearest Neighbor query to use a spatial index: A spatial index must be present on one of the spatial columns and the STDistance() method must use that column in the WHERE and ORDER BY clauses. The TOP clause cannot contain a PERCENT statement. The WHERE clause must contain a STDistance() method. If there are multiple predicates in the WHERE clause then the predicate containing STDistance() method must be connected by an AND conjunction to the other predicates. The STDistance() method cannot be in an optional part of the WHERE clause. The first expression in the ORDER BY clause must use the STDistance() method. Sort order for the first STDistance() expression in the ORDER BY clause must be ASC. All the rows for which STDistance returns NULL must be filtered out. Let’s start from the top. 1. Needs a spatial index on one of the columns that’s in the STDistance call. Yup, got the index. 2. No ‘PERCENT’. Yeah, I don’t have that. 3. The WHERE clause needs to use STDistance(). Ok, but I’m not filtering, so that should be fine. 4. Yeah, I don’t have multiple predicates. 5. The first expression in the ORDER BY is my distance, that’s fine. 6. Sort order is ASC, because otherwise we’d be starting with the ones that are furthest away, and that’s tricky. 7. All the rows for which STDistance returns NULL must be filtered out. But I don’t have any NULL values, so that shouldn’t affect me either. ...but something’s wrong. I do actually need to satisfy #3. And I do need to make sure #7 is being handled properly, because there are some situations (eg, differing SRIDs) where STDistance can return NULL. It says so at http://msdn.microsoft.com/en-us/library/bb933808.aspx – “STDistance() always returns null if the spatial reference IDs (SRIDs) of the geography instances do not match.” So if I simply make sure that I’m filtering out the rows that return NULL… …then it’s blindingly fast, I get the right results, and I’ve got the complex-but-brilliant plan that I wanted. It just wasn’t overly intuitive, despite being documented. @rob_farley

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  • How I understood monads, part 1/2: sleepless and self-loathing in Seattle

    - by Bertrand Le Roy
    For some time now, I had been noticing some interest for monads, mostly in the form of unintelligible (to me) blog posts and comments saying “oh, yeah, that’s a monad” about random stuff as if it were absolutely obvious and if I didn’t know what they were talking about, I was probably an uneducated idiot, ignorant about the simplest and most fundamental concepts of functional programming. Fair enough, I am pretty much exactly that. Being the kind of guy who can spend eight years in college just to understand a few interesting concepts about the universe, I had to check it out and try to understand monads so that I too can say “oh, yeah, that’s a monad”. Man, was I hit hard in the face with the limitations of my own abstract thinking abilities. All the articles I could find about the subject seemed to be vaguely understandable at first but very quickly overloaded the very few concept slots I have available in my brain. They also seemed to be consistently using arcane notation that I was entirely unfamiliar with. It finally all clicked together one Friday afternoon during the team’s beer symposium when Louis was patient enough to break it down for me in a language I could understand (C#). I don’t know if being intoxicated helped. Feel free to read this with or without a drink in hand. So here it is in a nutshell: a monad allows you to manipulate stuff in interesting ways. Oh, OK, you might say. Yeah. Exactly. Let’s start with a trivial case: public static class Trivial { public static TResult Execute<T, TResult>( this T argument, Func<T, TResult> operation) { return operation(argument); } } This is not a monad. I removed most concepts here to start with something very simple. There is only one concept here: the idea of executing an operation on an object. This is of course trivial and it would actually be simpler to just apply that operation directly on the object. But please bear with me, this is our first baby step. Here’s how you use that thing: "some string" .Execute(s => s + " processed by trivial proto-monad.") .Execute(s => s + " And it's chainable!"); What we’re doing here is analogous to having an assembly chain in a factory: you can feed it raw material (the string here) and a number of machines that each implement a step in the manufacturing process and you can start building stuff. The Trivial class here represents the empty assembly chain, the conveyor belt if you will, but it doesn’t care what kind of raw material gets in, what gets out or what each machine is doing. It is pure process. A real monad will need a couple of additional concepts. Let’s say the conveyor belt needs the material to be processed to be contained in standardized boxes, just so that it can safely and efficiently be transported from machine to machine or so that tracking information can be attached to it. Each machine knows how to treat raw material or partly processed material, but it doesn’t know how to treat the boxes so the conveyor belt will have to extract the material from the box before feeding it into each machine, and it will have to box it back afterwards. This conveyor belt with boxes is essentially what a monad is. It has one method to box stuff, one to extract stuff from its box and one to feed stuff into a machine. So let’s reformulate the previous example but this time with the boxes, which will do nothing for the moment except containing stuff. public class Identity<T> { public Identity(T value) { Value = value; } public T Value { get; private set;} public static Identity<T> Unit(T value) { return new Identity<T>(value); } public static Identity<U> Bind<U>( Identity<T> argument, Func<T, Identity<U>> operation) { return operation(argument.Value); } } Now this is a true to the definition Monad, including the weird naming of the methods. It is the simplest monad, called the identity monad and of course it does nothing useful. Here’s how you use it: Identity<string>.Bind( Identity<string>.Unit("some string"), s => Identity<string>.Unit( s + " was processed by identity monad.")).Value That of course is seriously ugly. Note that the operation is responsible for re-boxing its result. That is a part of strict monads that I don’t quite get and I’ll take the liberty to lift that strange constraint in the next examples. To make this more readable and easier to use, let’s build a few extension methods: public static class IdentityExtensions { public static Identity<T> ToIdentity<T>(this T value) { return new Identity<T>(value); } public static Identity<U> Bind<T, U>( this Identity<T> argument, Func<T, U> operation) { return operation(argument.Value).ToIdentity(); } } With those, we can rewrite our code as follows: "some string".ToIdentity() .Bind(s => s + " was processed by monad extensions.") .Bind(s => s + " And it's chainable...") .Value; This is considerably simpler but still retains the qualities of a monad. But it is still pointless. Let’s look at a more useful example, the state monad, which is basically a monad where the boxes have a label. It’s useful to perform operations on arbitrary objects that have been enriched with an attached state object. public class Stateful<TValue, TState> { public Stateful(TValue value, TState state) { Value = value; State = state; } public TValue Value { get; private set; } public TState State { get; set; } } public static class StateExtensions { public static Stateful<TValue, TState> ToStateful<TValue, TState>( this TValue value, TState state) { return new Stateful<TValue, TState>(value, state); } public static Stateful<TResult, TState> Execute<TValue, TState, TResult>( this Stateful<TValue, TState> argument, Func<TValue, TResult> operation) { return operation(argument.Value) .ToStateful(argument.State); } } You can get a stateful version of any object by calling the ToStateful extension method, passing the state object in. You can then execute ordinary operations on the values while retaining the state: var statefulInt = 3.ToStateful("This is the state"); var processedStatefulInt = statefulInt .Execute(i => ++i) .Execute(i => i * 10) .Execute(i => i + 2); Console.WriteLine("Value: {0}; state: {1}", processedStatefulInt.Value, processedStatefulInt.State); This monad differs from the identity by enriching the boxes. There is another way to give value to the monad, which is to enrich the processing. An example of that is the writer monad, which can be typically used to log the operations that are being performed by the monad. Of course, the richest monads enrich both the boxes and the processing. That’s all for today. I hope with this you won’t have to go through the same process that I did to understand monads and that you haven’t gone into concept overload like I did. Next time, we’ll examine some examples that you already know but we will shine the monadic light, hopefully illuminating them in a whole new way. Realizing that this pattern is actually in many places but mostly unnoticed is what will enable the truly casual “oh, yes, that’s a monad” comments. Here’s the code for this article: http://weblogs.asp.net/blogs/bleroy/Samples/Monads.zip The Wikipedia article on monads: http://en.wikipedia.org/wiki/Monads_in_functional_programming This article was invaluable for me in understanding how to express the canonical monads in C# (interesting Linq stuff in there): http://blogs.msdn.com/b/wesdyer/archive/2008/01/11/the-marvels-of-monads.aspx

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