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• Quaddratic Bezier Curve: Calculate Tangent

  - by stefan.at.wpf

  Hello, I have have a quadratic bezier curve and I want to calculate the slope of the tangent in a given point. For example, let it be the middlepoint of the quadratic bezier curve, therefore t=0.5 (please see the link below for a picture of this). I've calculated the first derivation of the formula for the quadratic bezier curve, however I get 400 as value for the slope, though it should be 0. Maybe I'm using the first derivation in a wrong way? I know I could also calculate the tangents using trigonometric functions, however I'd like to do it using the first derivation, shouldn't this be possible? Thanks for any hint! For clarification / please note: I'm interested in a general way to get the slope in a arbitrary given point on a quadratic bezier curve, not only to get the tangent in the start- and end point. A picture of my problem including the text above: http://cid-0432ee4cfe9c26a0.skydrive.live.com/self.aspx/%c3%96ffentlich/Quadratic%20Bezier%20Curve.pdf Thank you very much for any hint!

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• Test Case Design and Responsibility

  - by Sakamoto Kazuma

  So it seems like a lot of people are playing the blame game around where I work, and it brings up an interesting question. Knowns: Requirements team writes requirements for product. Developers create their own unit tests out of requirements. Testing team creates their general tests out of requirements and past customer issues. Product released if and only if X% of testcases from Testing team passes Customer response team gets bugs from the field, and lets the testing team know about these issues. Question: If the customer ends up filing a lot of defects, who is to blame? Is it the Testing team for not covering those? Or is it the requirements team for not writing better requirements? And how does one improve upon the system?

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• MongoMapper and bson_ext problem

  - by Fossmo

  I can't get MongoMapper to work with my Rails app. I get this error message: **Notice: C extension not loaded. This is required for optimum MongoDB Ruby driver performance. You can install the extension as follows: gem install bson_ext If you continue to receive this message after installing, make sure that the bson_ext gem is in your load path and that the bson_ext and mongo gems are of the same version. I have installed DevKit and installed the gem: gem install bson_ext --no-rdoc --no-ri (result: bson_ext-1.0.1 installed) I'm running on Windows 7. The Rails version is 2.3.7. I used the RubyInstaller when installing. Can anyone point me in the right direction?

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• PyPy -- How can it possible beat CPython?

  - by Vulcan Eager

  From the Google Open Source Blog: PyPy is a reimplementation of Python in Python, using advanced techniques to try to attain better performance than CPython. Many years of hard work have finally paid off. Our speed results often beat CPython, ranging from being slightly slower, to speedups of up to 2x on real application code, to speedups of up to 10x on small benchmarks. How is this possible? Which Python implementation was used to implement PyPy? CPython? And what are the chances of a PyPyPy or PyPyPyPy beating their score? (On a related note... why would anyone try something like this?)

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• How to implement a Digg-like algorithm?

  - by Niklas

  Hi, How to implement a website with a recommendation system similar to stackoverflow/digg/reddit? I.e., users submit content and the website needs to calculate some sort of "hotness" according to how popular the item is. The flow is as follows: Users submit content Other users view and vote on the content (assume 90% of the users only views content and 10% actively votes up or down on content) New content is continuously submitted How do I implement an algorithm that calculates the "hotness" of a submitted item, preferably in real-time? Are there any best-practices or design patterns? I would assume that the algorithm takes the following into consideration: When an item was submitted When each vote was cast When the item was viewed E.g. an item that gets a constant trickle of votes would stay somewhat "hot" constantly while an item that receives a burst of votes when it is first submitted will jump to the top of the "hotness"-list but then fall down as the votes stop coming in. (I am using a MySQL+PHP but I am interested in general design patterns).

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• grammar parser lexer antlr letteral

  - by BB

  What's the difference between this grammar: ... if_statement : 'if' condition 'then' statement 'else' statement 'end_if'; ... and this: ... if_statement : IF condition THEN statement ELSE statement END_IF; ... IF : 'if'; THEN: 'then'; ELSE: 'else'; END_IF: 'end_if'; .... ? If there is any difference, as this impacts on performance ... Thanks

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• What are your thoughts on Raven DB?

  - by Ronnie Overby

  What are your thoughts on Raven DB? I see this below my title: The question you're asking appears subjective and is likely to be closed. Please don't do that. I think the question is legit because: Raven DB is brand-spanking-new. RDBMS's are probably the de facto for data persistence for .net developers, which Raven DB is not. Given these points, I would like to know your general opinions. Admittedly, the question is sort of broad. That is intentional, because I am trying to learn as much about it as possible, however here are some of my initial concerns and questions: What about using Raven DB for data storage in a shared web hosting environment, since Raven DB is interacted with through HTTP? Are there any areas that Raven DB is particularly well or not well suited for? How does it rank among alternatives, from a .net developer's perspective?

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• Data structure for Settlers of Catan map?

  - by templatetypedef

  Hello all- A while back someone asked me if I knew of a nice way to encode the information for the game Settlers of Catan. This would require storing a hexagonal grid in a way where each hex can have data associated with it. More importantly, though, I would need some way of efficiently looking up vertices and edges on the sides of these hexagons, since that's where all the action is. My question is this: is there a good, simple data structure for storing a hexagonal grid while allowing for fast lookup of hexagons, edges between hexagons, and vertices at the intersections of hexagons? I know that general structures like a winged-edge or quad-edge could do this, but that seems like massive overkill. Thanks!

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• SQL Server, temporary tables with truncate vs table variable with delete

  - by Richard

  I have a stored procedure inside which I create a temporary table that typically contains between 1 and 10 rows. This table is truncated and filled many times during the stored procedure. It is truncated as this is faster than delete. Do I get any performance increase by replacing this temporary table with a table variable when I suffer a penalty for using delete (truncate does not work on table variables) Whilst table variables are mainly in memory and are generally faster than temp tables do I loose any benefit by having to delete rather than truncate?

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• "Authorize" attribute and 403 error page

  - by zerkms

  [Authorize] property is nice and handy MS invention, and I hope it can solve the issues I have now To be more specific: When current client isn't authenticated - [Authorize] redirects from secured action to logon page and after logon was successfull - brings user back, this is good. But when current cilent already authenticated but not authorized to run specific action - all I need is to just display my general 403 page. Is it possible without moving authorization logic within controller's body? UPD: The behavior I need in should be semantically equals to this sketch: public ActionResult DoWork() { if (!NotAuthorized()) { return RedirectToAction("403"); } return View(); } so - there should no any redirect and url should be stay the same, but contents of the page should be replaced with 403-page

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• Quick question regarding CSS sprites and memory usage

  - by Andy E

  Well, it's more to do with images and memory in general. If I use the same image multiple times on a page, will each image be consolidated in memory? Or will each image use a seperate amount of memory? I'm concerned about this because I'm building a skinning system for a Windows Desktop Gadget, and I'm looking at spriting the images in the default skin so that I can keep the file system looking clean. At the same time I want to try and keep the memory footprint to a minimum. If I end up with a single file containing 100 images and re-use that image 100 times across the gadget I don't want to have performance issues. Cheers.

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• External XMPP component - Anyone know a Tutorial or Open Source Example please?

  - by gav

  Hi All, I want to run an XMPP server (Openfire) and register an external component to handle the messages it will recieve (using the Whack library). The external component will run my game logic and I will be using XMPP to send player moves to the server and status updates in the other direction. The bonus with XMPP is that we get built in chat for free. The trouble is, although Ignite look fairly established, I can't find a tutorial on how to write, register and debug an External XMPP component written with Whack, there are very few in general for that matter. I am not invested in either the server implementation or the External Component library, java is just my language of choice. If I was to move to Erlang or Scala or something it would have to be a very simple in that language. A single tutorial or example would go a long way here, I just need an basic External XMPP component pretty please! Kind regards, Gavin

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• Can I do video communication with silverlight 4.0?

  - by tom greene

  With silverlight 4.0, it is possible to show a live video of the user on the screen: Here is the code VideoBrush videoBrush = new VideoBrush(); CaptureSource captureSource = new CaptureSource { VideoCaptureDevice = CaptureDeviceConfiguration.GetAvailableVideoCaptureDevices().First() }; bool b = CaptureDeviceConfiguration.RequestDeviceAccess(); videoBrush.SetSource(captureSource); captureSource.Start(); myrect.Fill = videoBrush; However, I am looking at a way to show the video to someone else - seeing oneself on screen is not that interesting. Is it possible? Do I need my own server? Can I use clowd services to do the communication? Are there performance issues?

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• Java Prepared Statement arguments!

  - by Epitaph

  I am planning to replace repeatedly executed Statement objects with PreparedStatement objects to improve performance. I am using arguments like the MySQL function now(), and string variables. Most of the PreparedStatement queries I have seen contained constant values (like 10, and strings like "New York") as arguments used for the "?" in the queries. How would I go about using functions like now(), and variables as arguments? Is it necessary to use the "?"s in the queries instead of actual values? I am quite confounded.

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• Turning an NSImage* into a CGImageRef?

  - by Brian Postow

  Is there an easy way to do this that works in 10.5? In 10.6 I can use nsImage CGImageForProposedRect: NULL context: NULL hints: NULL If I'm not using 1b black and white images (Like Group 4 TIFF), I can use bitmaps, but cgbitmaps seem to not like that setup... Is there a general way of doing this? I need to do this because I have an IKImageView that seems to only want to add CGImages, but all I've got are NSImages. Currently, I'm using a private setImage:(NSImage*) method that I'd REALLY REALLY rather not be using...

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• Vsync in Flex/Flash/AS3?

  - by oshyshko

  I work on a 2D shooter game with lots of moving objects on the screen (bullets etc). I use BitmapData.copyPixels(...) to render entire screen to a buffer:BitmapData. Then I "copyPixels" from "buffer" to screen:BitmapData. The framerate is 60. private var bitmap:Bitmap = new Bitmap(); private var buffer:Bitmap = new Bitmap(); private function start():void { addChild(bitmap); } private function onEnterFrame():void { // render into "buffer" // copy "buffer" -> "bitmap" } The problem is that the sprites are tearing apart: some part of a sprite got shifted horizontally. It looks like a PC game with VSYNC turned off. Did anyone solve this problem? UPDATE: the question is not about performance, but about getting rid of screen tearing. [!] UPDATE: I've created another question and here you may try both implementations: using Flash way or BitmapData+copyPixels()

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• Style: Dot notation vs. message notation in Objective-C 2.0

  - by groundhog

  In Objective-C 2.0 we got the "dot" notation for properties. I've seen various back and forths about the merits of dot notation vs. message notation. To keep the responses untainted I'm not going to respond either way in the question. What is your thought about dot notation vs. message notation for property accessing? Please try to keep it focused on Objective-C - my one bias I'll put forth is that Objective-C is Objective-C, so your preference that it be like Java or JavaScript aren't valid. Valid commentary is to do with technical issues (operation ordering, cast precedence, performance, etc), clarity (structure vs. object nature, both pro and con!), succinctness, etc. Note, I'm of the school of rigorous quality and readability in code having worked on huge projects where code convention and quality is paramount (the write once read a thousand times paradigm).

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• spring.net application scope repository object on loadbalanced application

  - by Bert Vandamme

  Hi, We have an application running on a loadbalanced environment, let say webserver A and B. The loadbalancing is on the HTTP level, so the loadbalancer directs each user request to one of both webservers. The scope of the repositories in the application is managed by the spring.net container, and the application relies on data that can be cached by the repository (performance reasons). In this case we can never be sure that the cached data in the repositories on both webservers is the same. Is there mechanism in spring.net that can manage this kind problem? Or is there another common approach for this kind of thing? Any ideas? Thx, Bert

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• Loading fixtures in django unit tests

  - by loder

  I'm trying to start writing unit tests for django and I'm having some questions about fixtures: I made a fixture of my whole project db (not certain application) and I want to load it for each test, because it looks like loading only the fixture for certain app won't be enough. I'd like to have the fixture stored in /proj_folder/fixtures/proj_fixture.json. I've set the FIXTURE_DIRS = ('/fixtures/',) in my settings.py. Then in my testcase I'm trying fixtures = ['proj_fixture.json'] but my fixtures don't load. How can this be solved? How to add the place for searching fixtures? In general, is it ok to load the fixture for the whole test_db for each test in each app (if it's quite small)? Thanks!

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• Tutorials for .NET database app using SQLite

  - by ChrisC

  I have some MS Access experience, and had a class on console c++ apps, now I am trying to develop my first program. It's a little C# db app. I have the db tables and columns planned and keyed into VS, but that's where I'm stuck. I'm needing C#/VS tutorials that will guide me on configuring relationships, datatyping, etc, on the db so I can get it ready for testing of the schema. The only tutorials I've been able to find either talk about general db basics (ie, not helping me with VS/C#), or about C# communications with an existing SQL db. Thank you. (In case it matters, I'm using the open source System.Data.SQLite (sqlite.phxsoftware.com) for the db. I chose it over SQL Server CE after seeing a comparison between the two. Also I wanted a server-less version of SQL because this little app will be on other people's computers and I want to to do as little support as possible.)

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• Handler invocation speed: Objective-C vs virtual functions

  - by Kerido

  I heard that calling a handler (delegate, etc.) in Objective-C can be even faster than calling a virtual function in C++. Is it really correct? If so, how can that be? AFAIK, virtual functions are not that slow to call. At least, this is my understanding of what happens when a virtual function is called: Compute the index of the function pointer location in vtbl. Obtain the pointer to vtbl. Dereference the pointer and obtain the beginning of the array of function pointers. Offset (in pointer scale) the beginning of the array with the index value obtained on step 1. Issue a call instruction. Unfortunately, I don't know Objective-C so it's hard for me to compare performance. But at least, the mechanism of a virtual function call doesn't look that slow, right? How can something other than static function call be faster?

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• PageMethods security

  - by TenaciousImpy

  Hi, I'm trying to 'AJAX-ify' my site in order to improve the UI experience. In terms of performance, I'm also trying to get rid of the UpdatePanel. I've come across a great article over at Encosia showing a way of posting using PageMethods. My question is, how secure are page methods in a production environment? Being public, can anyone create a JSON script to POST directly to the server, or are there cross-domain checks taking place? My PageMethods would also write the data into the database (after filtering). I'm using Forms Authentication in my pages and, on page load, it redirects unauthenticated users to the login page. Would the Page Methods on this page also need to check authentication if the user POSTs directly to the method, or is that authentication inherited for the entire page? (Essentially, does the entire page cycle occur even if a user has managed to post only to the PageMethod)? Thanks

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• Best practices for combining Lucene.NET and a relational database?

  - by FlySwat

  I'm working on a project where I will have a LOT of data, and it will be searchable by several forms that are very efficiently expressed as SQL Queries, but it also needs to be searched via natural language processing. My plan is to build an index using Lucene for this form of search. My question is that if I do this, and perform a search, Lucene will then return the ID's of matching documents in the index, I then have to lookup these entities from the relational database. This could be done in two ways (That I can think of so far): N amount of queries (Horrible) Pass all the ID's to a stored procedure at once (Perhaps as a comma delimited parameter). This has the downside of being limited to the max parameter size, and the slow performance of a UDF to split the string into a temporary table. I'm almost tempted to mirror everything into lucenes index, so that I can periodicly generate the index from the backing store, but only need to access it for the frontend. Advice?

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• Storing and comparing biometric information

  - by Chathuranga Chandrasekara

  I am not sure whether this is the best place to post this. But this is strongly related with programming so decided to put this here. In general we use biometrics in computer applications say for authentication. Lets get 2 examples finger prints and facial recognition. In those cases how we keep the information for comparison. As an example we can't keep a image and process it every time. So what are the methodologies we use to store/determine the similarity in such cases? Are there any special algorithms that designed for that purposes.? (Ex : To return a approximately equal value for a finger print of a certain person every time)

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• Which programming languages have helped you to understand programming better?

  - by Xaisoft

  Which programming languages not only make you more proficient in the particular language your are learning, but also have a direct impact on the way you think and understand programming in general; therefore, making you a better programmer in other languages. Basically, which languages have the biggest impact on understanding the how and why of different programming concepts? What about Scheme? I have heard good things about that. I thought about taking the simplest of problems and implementing them in various languages. Has anyone done this?

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