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• Reducing moire when downsampling halftone comic images.

  - by drawnonward

  How can I reduce moire effects when downsampling halftone comic book images during live zoom on an iPhone or iPad? I am writing a comic book viewer. It would be nice to provide higher resolution images and allow the user to zoom in while reading the comic book. However, my client is averse to moire effects and will not allow this feature if there are noticeable moire artifacts while zooming, which of course there are. Modifying the images to be less susceptible to moire would only work if the modifications were not perceptible. Blur was specifically prohibited, as is anything that removes the beloved halftone dots. The images are black and white halftone and line art. The originals are 600 dpi but what we ship with the application will be half that at best, so probably 2500 pixels or less tall. So what are my options? If I write a custom downsampling algorithm would it be fast enough for real time on these devices? Are there other tricks I can do? Would it work to just avoid the size ratios that have the most visual moire effects? As you zoom in an out, there are definitely peaks where the moire effects are worst. Is there a way to calculate what those points are and just zoom to a nearby scale that is not as bad? Any suggestions are welcome. I have very little experience with image and signal processing, but am enjoying the opportunity to learn. I know nothing of wavelets and acutance and other jargon, so please be verbose.

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• Copy constructor using private attributes

  - by Pedro Magueija

  Hello all, My first question here so be gentle. I would like arguments for the following code: public class Example { private String name; private int age; ... // copy constructor here public Example(Example e) { this.name = e.name; // accessing a private attribute of an instance this.age = e.age; } ... } I believe this breaks the modularity of the instance passed to the copy construct. This is what I believe to be correct: public class Example { private String name; private int age; ... // copy constructor here public Example(Example e) { this.setName(e.getName()); this.setAge(e.getAge()); } ... } A friend has exposed a valid point of view, saying that in the copy construct we should create the object as fast as possible. And adding getter/setter methods would result in unnecessary overhead. I stand on a crossroad. Can you shed some light?

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• Getting a key in the ActionScript Dictionary

  - by Rudy

  Hello, I am using a Dictionary in ActionScript as a queue, sort of, still reading most of the time as an associative container, but I need one time to make a loop to run through the whole dictionary, such as for (var key:String in queue) . Inside this for loop I perform some actions on an element and then call delete on that key. My issue is that I would like to wait for an Event before fetching the next element in this queue. Basically my for loop runs too fast. I would like to fetch the next key all the time, but I know there is no built in method. A solution I thought is to add a break to the loop, as the for.. in will automatically fetch the next key, but it would be a loop which always executes one time, simply to fetch the next key. This sounds a bit counter intuitive. I hope my problem makes sense and I really look for some better ideas than what I currently have. Thanks for your help! Rudy

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• How to Avoid PHP Object Nesting/Creation Limit?

  - by Will Shaver

  I've got a handmade ORM in PHP that seems to be bumping up against an object limit and causing php to crash. Here's a simple script that will cause crashes: <? class Bob { protected $parent; public function Bob($parent) { $this->parent = $parent; } public function __toString() { if($this->parent) return (string) "x " . $this->parent; return "top"; } } $bobs = array(); for($i = 1; $i < 40000; $i++) { $bobs[] = new Bob($bobs[$1 -1]); } ?> Even running this from the command line will cause issues. Some boxes take more than 40,000 objects. I've tried it on Linux/Appache (fail) but my app runs on IIS/FastCGI. On FastCGI this causes the famous "The FastCGI process exited unexpectedly" error. Obviously 20k objects is a bit high, but it crashes with far fewer objects if they have data and nested complexity. Fast CGI isn't the issue - I've tried running it from the command line. I've tried setting the memory to something really high - 6,000MB and to something really low - 24MB. If I set it low enough I'll get the "allocated memory size xxx bytes exhausted" error. I'm thinking that it has to do with the number of functions that are called - some kind of nesting prevention. I didn't think that my ORM's nesting was that complicated but perhaps it is. I've got some pretty clear cases where if I load just ONE more object it dies, but loads in under 3 seconds if it works.

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• Can you recommend a full-text search engine?

  - by Jen

  Can you recommend a full-text search engine? (Preferably open source) I have a database of many (though relatively short) HTML documents. I want users to be able to search this database by entering one or more search words in my C++ desktop application. Hence, I’m looking for a fast full-text search solution to integrate with my app. Ideally, it should: Skip common words, such as the, of, and, etc. Support stemming, i.e. search for run also finds documents containing runner, running and ran. Be able to update its index in the background as new documents are added to the database. Be able to provide search word suggestions (like Google Suggest) Have a well-documented API To illustrate, assume the database has just two documents: Document 1: This is a test of text search. Document 2: Testing is fun. The following words should be in the index: fun, search, test, testing, text. If the user types t in the search box, I want the application to be able to suggest test, testing and text (Ideally, the application should be able to query the search engine for the 10 most common search words starting with t). A search for testing should return both documents. Other points: I don't need multi-user support I don't need support for complex queries The database resides on the user's computer, so the indexing should be performed locally. Can you suggest a C or C++ based solution? (I’ve briefly reviewed CLucene and Xapian, but I’m not sure if either will address my needs, especially querying the search word indexes for the suggest feature).

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• Netty options for real-time distribution of small messages to a large number of clients?

  - by user439407

  I am designing a (near) real-time Netty server to distribute a large number of very small messages to a large number of clients across the internet. In internal, go as fast as you can testing, I found that I could do 10k clients no sweat, but now that we are trying to go across the internet, where the latency, bandwidth etc varies pretty wildly we are running into the dreaded outOfMemory issues, even with 2 gigs of RAM. I have tried various workarounds(setting the socket stack sizes smaller, setting high and low water marks, cancelling things that are too old), and they help a little, but they seem to only help a little bit. What would some good ways to optimize Netty for sending large #s of small messages without significant delays? Also, the bulk of the message only consists of one kind of message that I don't particularly care if it doesn't arrive. I would use UDP but because we don't control the client, thats not really a possibility. Is it possible to set a separate timeout solely for this kind of message without affecting the other messages? Any insight you could offer would be greatly appreciated.

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• Passing options in autospec with Cucumber in Ruby on Rails Development

  - by TK

  I always run autospec to run features and RSpec at the same time, but running all the features is often time-consuming on my local computer. I would run every feature before committing code. I would like to pass the argument in autospec command. autospec doesn't obviously doesn't accept the arguments directly. Here's the output of autospec -h: autotest [options] options: -h -help You're looking at it. -v Be verbose. Prints files that autotest doesn't know how to map to tests. -q Be more quiet. -f Fast start. Doesn't initially run tests at start. I do have a cucumber.yml in config directory. I also have rerun.txt in the Rails root directory. cucumber -h gives me a lot of information about arguments. How can I run autospec against features that are tagged as @wip? I think I can make use of config/cucumber.yml. There are profile definitions. I can run cucumber -p wip to run only @wip-tagged features, but I'd like to do this with autospec. I would appreciate any tips for working with many spec and feature files.

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• What's the best practice to setup testing for ASP.Net MVC? What to use/process/etc?

  - by melaos

  hi there, i'm trying to learn how to properly setup testing for an ASP.Net MVC. and from what i've been reading here and there thus far, the definition of legacy code kind of piques my interests, where it mentions that legacy codes are any codes without unit tests. so i did my project in a hurry not having the time to properly setup unit tests for the app and i'm still learning how to properly do TDD and unit testing at the same time. then i came upon selenium IDE/RC and was using it to test on the browser end. it was during that time too that i came upon the concept of integration testing, so from my understanding it seems that unit testing should be done to define the test and basic assumptions of each function, and if the function is dependent on something else, that something else needs to be mocked so that the tests is always singular and can be run fast. Questions: so am i right to say that the project should have started with unit test with proper mocks using something like rhino mocks. then anything else which requires 3rd party dll, database data access etc to be done via integration testing using selenium? because i have a function which calls a third party dll, i'm not sure whether to write a unit test in nunit to just instantiate the object and pass it some dummy data which breaks the mocking part to test it or just cover that part in my selenium integration testing when i submit my forms and call the dll. and for user acceptance tests, is it safe to say we can just use selenium again? Am i missing something or is there a better way/framework? i'm trying to put in more tests for regression testing, and to ensure that nothing breaks when we put in new features. i also like the idea of TDD because it helps to better define the function, sort of like a meta documentation. thanks!! hope this question isn't too subjective because i need it for my case.

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• How do I track down sporadic ASP.NET performance problems in a production environment?

  - by Steve Wortham

  I've had sporadic performance problems with my website for awhile now. 90% of the time the site is very fast. But occasionally it is just really, really slow. I mean like 5-10 seconds load time kind of slow. I thought I had narrowed it down to the server I was on so I migrated everything to a new dedicated server from a completely different web hosting company. But the problems continue. I guess what I'm looking for is a good tool that'll help me track down the problem, because it's clearly not the hardware. I'd like to be able to log certain events in my ASP.NET code and have that same logger also track server performance/resources at the time. If I can then look back at the logs then I can see what exactly my website was doing at the time of extreme slowness. Is there a .NET logging system that'll allow me to make calls into it with code while simultaneously tracking performance? What would you recommend?

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• how do I insert an hidden token in my form to prevent double posts? (PHP)

  - by jpjp

  I want to prevent users from accidentally posting a comment twice. I use the PRG (post redirect get) method, so that I insert the data on another page then redirect the user back to the page which shows the comment. This allows users to refresh as many times as they want. However this doesn't work when the user goes back and clicks submit again or when they click submit 100 times really fast. I don't want 100 of the same comments. I looked at related questions on SO and found that a token is best. But I am having trouble using it. //makerandomtoken(20) returns a random 20 length char. <form method="post" ... > <input type="text" id="comments" name="comments" class="commentbox" /><br/> <input type="hidden" name="_token" value="<?php echo $token=makerandomtoken(20); ?>" /> <input type="submit" value="submit" name="submit" /> </form> if (isset($_POST['submit']) && !empty($comments)) { $comments= mysqli_real_escape_string($dbc,trim($_POST['comments'])); //how do I make the if-statment to check if the token has been already set once? if ( ____________){ //don't insert comment because already clicked submit } else{ //insert the comment into the database } } So I have the token as a hidden value, but how do I use that to prevent multiple clicking of submit.

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• How can I protect my .NET assemblies from decompilation?

  - by Holli

  One if the first things I learned when I started with C# was the most important one. You can decompile any .NET assembly with Reflector or other tools. Many developers are not aware of this fact and most of them are shocked when I show them their source code. Protection against decompilation is still a difficult task. I am still looking for a fast, easy and secure way to do it. I don't want to obfuscate my code so my method names will be a,b,c or so. Reflector or other tools should be unable to recognize my application as .NET assembly at all. I know about some tools already but they are very expensive. Is there any other way to protect my applications? EDIT: The reason for my question is not to prevent piracy. I only want to stop competitors from reading my code. I know they will and they already did. They even told me so. Maybe I am a bit paranoid but business rivals reading my code doesn't make me feel good.

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• Managing large binary files with git

  - by pi

  Hi there. I am looking for opinions of how to handle large binary files on which my source code (web application) is dependent. We are currently discussing several alternatives: Copy the binary files by hand. Pro: Not sure. Contra: I am strongly against this, as it increases the likelihood of errors when setting up a new site/migrating the old one. Builds up another hurdle to take. Manage them all with git. Pro: Removes the possibility to 'forget' to copy a important file Contra: Bloats the repository and decreases flexibility to manage the code-base and checkouts/clones/etc will take quite a while. Separate repositories. Pro: Checking out/cloning the source code is fast as ever, and the images are properly archived in their own repository. Contra: Removes the simpleness of having the one and only git repository on the project. Surely introduces some other things I haven't thought about. What are your experiences/thoughts regarding this? Also: Does anybody have experience with multiple git repositories and managing them in one project? Update: The files are images for a program which generates PDFs with those files in it. The files will not change very often(as in years) but are very relevant to a program. The program will not work without the files. Update2: I found a really nice screencast on using git-submodule at GitCasts.

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• Using java.util.regex in Android apps - are there issues with this?

  - by johnrock

  In an Android app I have a utility class that I use to parse strings for 2 regEx's. I compile the 2 patterns in a static initializer so they only get compiled once, then activities can use the parsing methods statically. This works fine except that the first time the class is accessed and loaded, and the static initializer compiles the pattern, the UI hangs for close to a MINUTE while it compiles the pattern! After the first time, it flies on all subsequent calls to parseString(). My regEx that I am using is rather large - 847 characters, but in a normal java webapp this is lightning fast. I am testing this so far only in the emulator with a 1.5 AVD. Could this just be an emulator issue or is there some other reason that this pattern is taking so long to compile? private static final String exp1 = "(insertratherlong---847character--regexhere)"; private static Pattern regex1 = null; private static final String newLineAndTagsExp = "[<>\\s]"; private static Pattern regexNewLineAndTags = null; static { regex1 = Pattern.compile(exp1, Pattern.CASE_INSENSITIVE); regexNewLineAndTags = Pattern.compile(newLineAndTagsExp); } public static String parseString(CharSequence inputStr) { String replacementStr = "replaceMentText"; String resultString = "none"; try { Matcher regexMatcher = regex1.matcher(inputStr); try { resultString = regexMatcher.replaceAll(replacementStr); } catch (IllegalArgumentException ex) { } catch (IndexOutOfBoundsException ex) { } } catch (PatternSyntaxException ex) { } return resultString; }

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• Nested namespaces, correct static library design issues

  - by PeterK

  Hello all, I'm currently in the process of developing a fairly large static library which will be used by some tools when it's finished. Now since this project is somewhat larger than anything i've been involved in so far, I realized its time to think of a good structure for the project. Using namespaces is one of those logical steps. My current approach is to divide the library into parts (which are not standalone, but their purpose calls for such a separation). I have a 'core' part which now just holds some very common typedefs and constants (used by many different parts of the library). Other parts are for example some 'utils' (hash etc.), file i/o and so on. Each of these parts has its own namespace. I have nearly finished the 'utils' part and realized that my approach probably is not the best. The problem (if we want to call it so) is that in the 'utils' namespace i need something from the 'core' namespace which results in including the core header files and many using directives. So i began to think that this probably is not a good thing and should be changed somehow. My first idea is to use nested namespaces as to have something like core::utils. Since this will require some heavy refactoring i want to ask here first. What do you think? How would you handle this? Or more generally: How to correctly design a static library in terms of namespaces and code organization? If there are some guidelines or articles about it, please mentoin them too. Thanks. Note: i'm quite sure that there are more good approaches than just one. Feel free to post your ideas, suggestions etc. Since i'm designing this library i want it to be really good. The goal is to make it as clean and FAST as possible. The only problem is that i will have to integrate a LOT of existing code and refactor it, which will really be a painful process (sigh) - thats why good structure is so important)

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• Transitioning from FlexBuilder 3 to FlashBuilder 4 ... there and back again.

  - by Robusto

  It's growing pains time again. Some of our stuff requires FlashBuilder 4 and some still requires FlexBuilder 3. Both are installed OK, and no projects use both IDEs. The trouble is, when I go back to work on a FlexBuilder 3 project it takes freakin' forever to build and I get weird errors like these: This doesn't seem to cause any identifiable problems except to throw up a modal dialog at various points in the build process, forcing user interaction. But I do notice that memory fills up fast in FB3 and generally FB3 starts behaving strangely and ultimately quits once it gets up over 700MB. This is only a temporary bridge situation until we get all projects into FB4, but "temporary" could mean weeks if not months. Does anyone have any advice for how to get through this bridge period? Is there anything I can do to make these two IDEs work and play well together? Failing that, does anyone know what "java.lang.String" is the "reason" for the problem? Does Eclipse have a resource bundle somewhere that is getting corrupted when i go back and forth between the two?

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• ArrayAccess multidimensional (un)set?

  - by anomareh

  I have a class implementing ArrayAccess and I'm trying to get it to work with a multidimensional array. exists and get work. set and unset are giving me a problem though. class ArrayTest implements ArrayAccess { private $_arr = array( 'test' => array( 'bar' => 1, 'baz' => 2 ) ); public function offsetExists($name) { return isset($this->_arr[$name]); } public function offsetSet($name, $value) { $this->_arr[$name] = $value; } public function offsetGet($name) { return $this->_arr[$name]; } public function offsetUnset($name) { unset($this->_arr[$name]); } } $arrTest = new ArrayTest(); isset($arrTest['test']['bar']); // Returns TRUE echo $arrTest['test']['baz']; // Echo's 2 unset($arrTest['test']['bar']; // Error $arrTest['test']['bar'] = 5; // Error I know $_arr could just be made public so you could access it directly, but for my implementation it's not desired and is private. The last 2 lines throw an error: Notice: Indirect modification of overloaded element. I know ArrayAccess just generally doesn't work with multidimensional arrays, but is there anyway around this or any somewhat clean implementation that will allow the desired functionality? The best idea I could come up with is using a character as a separator and testing for it in set and unset and acting accordingly. Though this gets really ugly really fast if you're dealing with a variable depth. Does anyone know why exists and get work so as to maybe copy over the functionality? Thanks for any help anyone can offer.

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• Method for defining simultaneous has-many and has-one associations between two models in CakePHP?

  - by Hobonium

  One thing with which I have long had problems, within the CakePHP framework, is defining simultaneous hasOne and hasMany relationships between two models. For example: BlogEntry hasMany Comment BlogEntry hasOne MostRecentComment (where MostRecentComment is the Comment with the most recent created field) Defining these relationships in the BlogEntry model properties is problematic. CakePHP's ORM implements a has-one relationship as an INNER JOIN, so as soon as there is more than one Comment, BlogEntry::find('all') calls return multiple results per BlogEntry. I've worked around these situations in the past in a few ways: Using a model callback (or, sometimes, even in the controller or view!), I've simulated a MostRecentComment with: $this->data['MostRecentComment'] = $this->data['Comment'][0]; This gets ugly fast if, say, I need to order the Comments any way other than by Comment.created. It also doesn't Cake's in-built pagination features to sort by MostRecentComment fields (e.g. sort BlogEntry results reverse-chronologically by MostRecentComment.created. Maintaining an additional foreign key, BlogEntry.most_recent_comment_id. This is annoying to maintain, and breaks Cake's ORM: the implication is BlogEntry belongsTo MostRecentComment. It works, but just looks...wrong. These solutions left much to be desired, so I sat down with this problem the other day, and worked on a better solution. I've posted my eventual solution below, but I'd be thrilled (and maybe just a little mortified) to discover there is some mind-blowingly simple solution that has escaped me this whole time. Or any other solution that meets my criteria: it must be able to sort by MostRecentComment fields at the Model::find level (ie. not just a massage of the results); it shouldn't require additional fields in the comments or blog_entries tables; it should respect the 'spirit' of the CakePHP ORM. (I'm also not sure the title of this question is as concise/informative as it could be.)

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• Laggy interface with NSSearchField hooked up to an NSArrayController via bindings

  - by Simone Manganelli

  So I've got an NSSearchField hooked up directly to an NSArrayController via bindings, attached to the filterPredicate, so that without any code, the user can just type in the NSSearchField and filter the list of objects in the NSArrayController presented to him in the interface (an NSCollectionView, to be specific). The NSSearchField is hooked up to provide live searching, so that the NSCollectionView is filtered instantly as the user types, not after waiting for a short period for the user to stop typing. However, the problem is that this makes the interface really laggy. Typing is delayed significantly, by 0.5-1 seconds, and it seems like the NSCollectionView is trying to animate each and every rearrangement of items for each portion of the search string that the user enters. What I'd like is for the searching to be live, but the typing in the search field to be fluid, and the results to filter as fast as possible. Is there a way to do this via bindings, or will I need to put in some custom code that triggers the filterPredicate on a separate thread? (Note that I've got a custom sorting algorithm set up on the NSArrayController, and removing it seems to help a bit with the laggyness, but not completely.)

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• IO operation taking long time for files in remote server

  - by user841311

  I have files of size 150 MB each in a remote server in a different domain in the network. I am accessing them thorugh UNC path. I want to read the file content and perform a basic string search. When I try reading the files line by line, the operation just don't finish and takes long time, more than 30 minutes. However when I copy those files to my local machine, the same code reads and performs the string search in less than 5 seconds. I don't have .NET framework installed in the server so I have to do this from my machine. I want to perform all this through C# code in .NET framework 3.5 so I don't want to explictly ftp all the files to my machine before performing this operation. Sample Code DirectoryInfo dir = new DirectoryInfo(@strFilePath); FileInfo[] fiArray = dir.getFiles("*.txt"); foreach (FileInfo fi in fiArray) { //reading file content from server takes long time but fast in local machine //perform string search } Let me know if my requirement is not clear. Thanks in advance!

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• Python: slow read & write for millions of small files

  - by Jami

  I am building directory tree which has tons of subdirectories and files. The total directory count is somewhere along 256^32 subdirectories with 256 files in each end which are only a few bytes long. I did this so I would have fast access to these files (since i'm not searching and i'm just directly accessing then via a known file path) I have a python script that builds this filesystem and reads & writes those files. The problem is that when I reach more than 1Gb of total filesize, the read and write methods become extremely slow. Here's the function I have that reads the contents of a file (the file contains an integer string), adds a certain number to it, then writes it back to the original file. def addInFile(path, scoreToAdd): num = scoreToAdd try: shutil.copyfile(path, '/tmp/tmp.txt') fp = open('/tmp/tmp.txt', 'r') num += int(fp.readlines()[0]) fp.close() except: pass fp = open('/tmp/tmp.txt', 'w') fp.write(str(num)) fp.close() shutil.copyfile('/tmp/tmp.txt', path) I previously tried performing linux console commands but it was slower. I copy the file to a temporary file first then access/modify it then copy it back because i found this was faster than directly accessing the file. I think the cause of the slowdown is because there're tons of files. performing this function 1000 times sometimes reach 1 minute now, but before (when there were only a few files, 1000 calls was performed for only less than 1 second) How do you suggest I fix this?

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• I can't figure out why this fps counter is inaccurate.

  - by rmetzger

  I'm trying to track frames per second in my game. I don't want the fps to show as an average. I want to see how the frame rate is affected when I push keys and add models etc. So I am using a variable to store the current time and previous time, and when they differ by 1 second, then I update the fps. My problem is that it is showing around 33fps but when I move the mouse around really fast, the fps jumps up to 49fps. Other times, if I change a simple line of code elsewhere not related to the frame counter, or close the project and open it later, the fps will be around 60. Vsync is on so I can't tell if the mouse is still effecting the fps. Here is my code which is in an update function that happens every frame: FrameCount++; currentTime = timeGetTime (); static unsigned long prevTime = currentTime; TimeDelta = (currentTime - prevTime) / 1000; if (TimeDelta > 1.0f) { fps = FrameCount / TimeDelta; prevTime = currentTime; FrameCount = 0; TimeDelta = 0; } Here are the variable declarations: int FrameCount; double fps, currentTime, prevTime, TimeDelta, TimeElapsed; Please let me know what is wrong here and how to fix it, or if you have a better way to count fps. Thanks!!!!!! I am using DirectX 9 btw but I doubt that is relevant, and I am using PeekMessage. Should I be using an if else statement instead? Here is my message processing loop: MSG msg; ZeroMemory (&msg, sizeof (MSG)); while (msg.message != WM_QUIT) { if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) { TranslateMessage (&msg); DispatchMessage (&msg); } Update (); RenderFrame (); }

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• I need some pointers on how to implement inertia

  - by gargantaun

  Ok, so I've created a little plugin that takes a bunch of elements and creates a sort of never ending list. I'll try to explain... I have a div, and it's got about 20 elements tags in it. When the user scrolls up, the top element moves out of view and is moved to the bottom of the list. And vice-versa so that when the user scrolls down, the bottom element is moved to the top of the list. This is specifically for Mobile Safari (iPad, iPhone) web content and you can see the work in progress here... http://appliedworks.co.uk/files/times/SVGTests/drumView/drum.html You'll need an iPad or iPhone top see the scrolling in action. You can see the plugin code here... http://appliedworks.co.uk/files/times/SVGTests/drumView/drumView-0.1b.js What I would like to do is implement inertia so the scrolling slows to a halt in response to how fast or slow the user is scrolling when their finger leaves the screen. Just like the inertia commonly found in the iPhone / iPad UI. The problem is, every time an element moves to the top or the bottom of the list, the scollTop value for the parent div is adjusted to make it look like all the elements are staying in the same place. Which means the scrollTop value is never more than the top elements total height. So there's no value I can think of that I can keep on manipulating to give the illusion of inertia. I'm stumped. Does anyone have any suggestions?

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• Optimizing a shared buffer in a producer/consumer multithreaded environment

  - by Etan

  I have some project where I have a single producer thread which writes events into a buffer, and an additional single consumer thread which takes events from the buffer. My goal is to optimize this thing for a single machine to achieve maximum throughput. Currently, I am using some simple lock-free ring buffer (lock-free is possible since I have only one consumer and one producer thread and therefore the pointers are only updated by a single thread). #define BUF_SIZE 32768 struct buf_t { volatile int writepos; volatile void * buffer[BUF_SIZE]; volatile int readpos;) }; void produce (buf_t *b, void * e) { int next = (b->writepos+1) % BUF_SIZE; while (b->readpos == next); // queue is full. wait b->buffer[b->writepos] = e; b->writepos = next; } void * consume (buf_t *b) { while (b->readpos == b->writepos); // nothing to consume. wait int next = (b->readpos+1) % BUF_SIZE; void * res = b->buffer[b->readpos]; b->readpos = next; return res; } buf_t *alloc () { buf_t *b = (buf_t *)malloc(sizeof(buf_t)); b->writepos = 0; b->readpos = 0; return b; } However, this implementation is not yet fast enough and should be optimized further. I've tried with different BUF_SIZE values and got some speed-up. Additionaly, I've moved writepos before the buffer and readpos after the buffer to ensure that both variables are on different cache lines which resulted also in some speed. What I need is a speedup of about 400 %. Do you have any ideas how I could achieve this using things like padding etc?

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• Need guidelines for optimizing WebGL performance by minimizing shader changes

  - by brainjam

  I'm trying to get an idea of the practicality of WebGL for rendering large architectural interior scenes, consisting of 100K's of triangles. These triangles are distributed over many objects, and there are many materials in the scene. On the other hand, there are no moving parts. And the materials tend to be fairly simple, mostly based on texture maps. There is a lot of texture map sharing .. for example all the chairs in scene will share a common map. There is also some multitexturing - up to three textures overlaid in a material. I've been doing a little experimentation and reading, and gather that frequently switching materials during a rendering pass will slow things down. For example, a scene with 200K triangles will have significant performance differences, depending on whether there are 10 or 1000 objects, assuming that each time an object is displayed a new material is set up. So it seems that if performance is important the scene should be sorted by materials so as to minimize material switching. What I'm looking for is guidelines on how to think of the overhead of various state changes, and where do I get the biggest bang for the buck. For example, what are the relative performance costs of, say, gl.useProgram(), gl.uniformMatrix4fv(), gl.drawElements() should I try to write ubershaders to minimize shader switching? should I try to aggregate geometry to minimize the number of gl.drawElements() calls I realize that mileage may vary depending on browser, OS, and graphics hardware. And I'm also not looking for heroic measures. Just some guidelines from people who have already had some experience in making scenes fast. I'll add that while I've had some experience with fixed-pipeline OpenGL programming in the past, I'm rather new to the WebGL/OpenGL ES 2.0 way of doing things.

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• How to find if a branch is a locally tracked branch or user created local branch?

  - by Senthil A Kumar

  I have a remote tracking branch tracked locally in my local repository using 'git branch -b branch-name origin/branch-name'. My remote branch is test2/test2 (origin/branch-name) which is being tracked locally as test2. The origin is also named test2. I haven't checked-out my local tracking branch test2. When i do a 'git pull origin remote-branch:local-tracked-branch' i get this error [test2]$ git pull test2 test2:test2 From /gitvobs/git_bare/test2 ! [rejected] test2 - test2 (non fast forward) Whereas when i checkout my local tracking branch test2 and do pull 'git pull origin local-tracked-branch' i don't get the error and i do a pull using 'git pull test2 test2' From /gitvobs/git_bare/test2 * branch test2 - FETCH_HEAD Auto-merging a.txt Automatic merge failed; fix conflicts and then commit the result. i know that adding a + (git pull test2 +test2:test2) would help but it overwrites local changes. So how do i know which of my local branches are created by me locally using 'git branch new-branch-name' or tracked locally from remote branches using git branch -b branch-name origin/branch-name'?

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