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• How do I get C# to garbage collect aggressively?

  - by mmr

  I have an application that is used in image processing, and I find myself typically allocating arrays in the 4000x4000 ushort size, as well as the occasional float and the like. Currently, the .NET framework tends to crash in this app apparently randomly, almost always with an out of memory error. 32mb is not a huge declaration, but if .NET is fragmenting memory, then it's very possible that such large continuous allocations aren't behaving as expected. Is there a way to tell the garbage collector to be more aggressive, or to defrag memory (if that's the problem)? I realize that there's the GC.Collect and GC.WaitForPendingFinalizers calls, and I've sprinkled them pretty liberally through my code, but I'm still getting the errors. It may be because I'm calling dll routines that use native code a lot, but I'm not sure. I've gone over that C++ code, and make sure that any memory I declare I delete, but still I get these C# crashes, so I'm pretty sure it's not there. I wonder if the C++ calls could be interfering with the GC, making it leave behind memory because it once interacted with a native call-- is that possible? If so, can I turn that functionality off?

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• Webkit browsers rendering CSS different than Mozilla Firefox...Why??

  - by JAG2007

  I'm styling a form that was already marked up (made some markup changes), and I normally work in Firefox to style so I can use firebug and the web developer toolbar. On this project, I noticed that my styles are displaying quite differently for one particular area (several elements) in webkit based browsers Chrome and Safari, than in Firefox (we won't even get into Internet Explorer, although it is siding with the Firefox display). I can't figure out though why the styles are displaying so differently. Normally there is some rule that I'm neglecting that Firefox just takes for granted, and the others need it specified. But here I'm not getting why it's displaying this way. In particular I'm referring to the bottom area of the form where users can enter their contact info, then submit the form. I'll attach screen shots for reference as to the discrepancy. Here's the URL so feel free to check it out on your own. Although be advised that this is a production page (already released) so if you try out the form, you WILL BE added to CURE's contact database. http://www.helpcurenow.org/survey2010 Here's the screen shots: Firefox (the way I intend it to look) Chrome, and then Safari - strange change to submit button As a bonus, if anybody wants to help me with figuring out why on earth IE7 wants to not show the background behind the questions only, and how to fix that I would be much obliged! Thanks very much.

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• Strange behaviour of CheckBox and TwoWay bound property

  - by walkor

  Hello, everyone. I fell in the following situation: I have a main UserControl with a DataGrid (which contains List). I need to show different panels depending on properties of the selected row(object). So i've created 2 controls and included them into this main control. Main control has 2 public properties - public List<ComplexObject> SourceList { get; set; } and public ComplexObject CurrentObject { get; set; } Pseudo-code: <UserControl x:Name="Main"> <DataGrid ItemsSource="{Binding SourceList}" SelectedItem="{Binding CurrentObject, Mode=TwoWay}"/> <Controls:RightPanelFirst Visibility="condition2"/> <Controls:RightPanelSecond Visibility="condition2"/> </UserControl> RightPanelFirst and RightPanelSecond have the following xaml: <UserControl> <... content here...> <CheckBox IsChecked="{Binding CurrentObject.ComplexProperty.SimpleProperty1, Mode=TwoWay}"> <CheckBox IsChecked="{Binding CurrentObject.ComplexProperty.SimpleProperty2, Mode=TwoWay}" x:Name="cbSecond"> <TextBox IsEnabled="{Binding IsChecked, ElementName=cbSecond}"/> </UserControl> So, my actual steps: Check both checkboxes (object values are set to true) Make other actions in code behind which modify CurrentObject. Then i want UI to reflect the changes, so I call NotifyPropertyChanged("CurrentObject"); SimpleProperty1 remains the same, but SimpleProperty2 resets to false I have no idea why this happens, can anyone help me please? Silverlight drives me mad.

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• Some questions about special operators i've never seen in C++ code.

  - by toto

  I have downloaded the Phoenix SDK June 2008 (Tools for compilers) and when I'm reading the code of the Hello sample, I really feel lost. public ref class Hello { //-------------------------------------------------------------------------- // // Description: // // Class Variables. // // Remarks: // // A normal compiler would have more flexible means for holding // on to all this information, but in our case it's simplest (if // somewhat inelegant) if we just keep references to all the // structures we'll need to access as classstatic variables. // //-------------------------------------------------------------------------- static Phx::ModuleUnit ^ module; static Phx::Targets::Runtimes::Runtime ^ runtime; static Phx::Targets::Architectures::Architecture ^ architecture; static Phx::Lifetime ^ lifetime; static Phx::Types::Table ^ typeTable; static Phx::Symbols::Table ^ symbolTable; static Phx::Phases::PhaseConfiguration ^ phaseConfiguration; 2 Questions : What's that ref keyword? What is that sign ^ ? What is it doing protected: virtual void Execute ( Phx::Unit ^ unit ) override; }; override is a C++ keyword too? It's colored as such in my Visual Studio. I really want to play with this framework, but this advanced C++ is really an obstacle right now. Thank you.

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• final transient fields and serialization

  - by doublep

  Is it possible to have final transient fields that are set to any non-default value after serialization in Java? My usecase is a cache variable — that's why it is transient. I also have a habit of making Map fields that won't be changed (i.e. contents of the map is changed, but object itself remains the same) final. However, these attributes seem to be contradictory — while compiler allows such a combination, I cannot have the field set to anything but null after unserialization. I tried the following, without success: simple field initialization (shown in the example): this is what I normally do, but the initialization doesn't seem to happen after unserialization; initialization in constructor (I believe this is semantically the same as above though); assigning the field in readObject() — cannot be done since the field is final. In the example cache is public only for testing. import java.io.*; import java.util.*; public class test { public static void main (String[] args) throws Exception { X x = new X (); System.out.println (x + " " + x.cache); ByteArrayOutputStream buffer = new ByteArrayOutputStream (); new ObjectOutputStream (buffer).writeObject (x); x = (X) new ObjectInputStream (new ByteArrayInputStream (buffer.toByteArray ())).readObject (); System.out.println (x + " " + x.cache); } public static class X implements Serializable { public final transient Map <Object, Object> cache = new HashMap <Object, Object> (); } } Output: test$X@1a46e30 {} test$X@190d11 null

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• My python program always brings down my internet connection after several hours running, how do I debug and fix this problem?

  - by Shane

  I'm writing a python script checking/monitoring several server/websites status(response time and similar stuff), it's a GUI program and I use separate thread to check different server/website, and the basic structure of each thread is using an infinite while loop to request that site every random time period(15 to 30 seconds), once there's changes in website/server each thread will start a new thread to do a thorough check(requesting more pages and similar stuff). The problem is, my internet connection always got blocked/jammed/messed up after several hours running of this script, the situation is, from my script side I got urlopen error timed out each time it's requesting a page, and from my FireFox browser side I cannot open any site. But the weird thing is, the moment I close my script my Internet connection got back on immediately which means now I can surf any site through my browser, so it must be the script causing all the problem. I've checked the program carefully and even use del to delete any connection once it's used, still get the same problem. I only use urllib2, urllib, mechanize to do network requests. Anybody knows why such thing happens? How do I debug this problem? Is there a tool or something to check my network status once such situation occurs? It's really bugging me for a while... By the way I'm behind a VPN, does it have something to do with this problem? Although I don't think so because my network always get back on once the script closed, and the VPN connection never drops(as it appears) during the whole process.

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• Binding Data into a Resource

  - by Jordan

  How do you bind data from the view model into an object in the resources of the user control? Here is a very abstract example: <UserControl ... xmlns:local="clr-namespace:My.Local.Namespace" Name="userControl"> <UserControl.Resources> <local:GroupingProvider x:Key="groupingProvider" GroupValue="{Binding ???}" /> </UserControl.Resources> <Grid> <local:GroupingConsumer Name="groupingConsumer1" Provider={StaticResource groupingProvider"} /> <local:GroupingConsumer Name="groupingConsumer2" Provider={StaticResource groupingProvider"} /> </Grid> </UserControl> How do I bind GroupValue to a property in the view model behind this view. I've tried the following: <local:GroupingProvider x:Key="groupingProvider" GroupValue="{Binding ElementName=userControl, Path=DataContext.Property}"/> But this doesn't work. Edit: GroupProvider extends DependencyObject and GroupValue is the name of a DependencyProperty. I'm getting an debugging message telling me that the property to which I am binding doesn't exist.

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• Anyone NOT using a Web Framework? Why?

  - by tom

  I'm well aware of the many reasons to use a web framework. I'm just wondering whether anyone out there is using absolutely no web framework whatsoever to develop their web projects. I would really love to know the reason(s) why you're not using a web framework. For the sake of this discussion, your programming language of choice does not matter. Some possibilities for discussion: You don't hide behind an ORM. You don't rely on any sort of templating system. You think MVC is a really nice TLA but lacks an essential vowel or two. No need for any additional javascript framework tomfoolery. You just write as much code as possible in your native programming language(s). Summary of reasons thus far: Language learning opportunities. Specific performance reasons (write-intensive transaction processing). Seeking more nuanced control over your data and applications (less abstraction). You're building your own framework! Prove to yourself that you can succeed (or fail) just like the big framework-building gurus. Integration issues with unpopular/legacy technologies (exotic databases or protocols come to mind). Big company, lots of code, no talent nor buy-in present to move to a web framework. Some frameworks really lock you in and cannot perpetually grow along with your needs. These few black sheep don't make it easy to jump outside of the framework, write some custom code, and easily jump back in. When you finally escape the asylum, you'll never look back.

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• Would an immutable keyword in Java be a good idea?

  - by berry120

  Generally speaking, the more I use immutable objects in Java the more I'm thinking they're a great idea. They've got lots of advantages from automatically being thread-safe to not needing to worry about cloning or copy constructors. This has got me thinking, would an "immutable" keyword go amiss? Obviously there's the disadvantages with adding another reserved word to the language, and I doubt it will actually happen primarily for the above reason - but ignoring that I can't really see many disadvantages. At present great care has to be taken to make sure objects are immutable, and even then a dodgy javadoc comment claiming a component object is immutable when it's in fact not can wreck the whole thing. There's also the argument that even basic objects like string aren't truly immutable because they're easily vunerable to reflection attacks. If we had an immutable keyword the compiler could surely recursively check and give an iron clad guarantee that all instances of a class were immutable, something that can't presently be done. Especially with concurrency becoming more and more used, I personally think it'd be good to add a keyword to this effect. But are there any disadvantages or implementation details I'm missing that makes this a bad idea?

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• ISO C90 forbids mixed declarations and code sscanf

  - by Need4Sleep

  I'm getting a strange error attempting to compile my unit test code,. For some reason the compiler treats my sscanf call as a mixed declaration? I don't quite understand, here is the entire error: cc1: warnings being treated as errors /home/brlcad/brlcad/src/libbn/tests/bn_complex.c: In function 'main': /home/brlcad/brlcad/src/libbn/tests/bn_complex.c:53: error: ISO C90 forbids mixed declarations and code make[2]: *** [src/libbn/tests/CMakeFiles/tester_bn_complex.dir/bn_complex.c.o] Error 1 make[1]: *** [src/libbn/tests/CMakeFiles/tester_bn_complex.dir/all] Error 2 make: *** [all] Error 2 int main(int argc, char *argv[]) { double expRe1, expIm2, expSqRe1, expSqIm2; double actRe1, actIm2, actSqRe1, actSqIm2; actRe1 = actIm2 = actSqRe1 = actSqIm2 = expRe1 = expIm2 = expSqRe1 = expSqIm2 = 0.0; bn_complex_t com1,com2; //a struct that holds two doubles if(argc < 5) bu_exit(1, "ERROR: Invalid parameters[%s]\n", argv[0]); sscanf(argv[1], "%lf,%lf", &com1.re, &com1.im); /* Error is HERE */ sscanf(argv[2], "%lf,%lf", &com2.re, &com2.im); sscanf(argv[3], "%lf,%lf", &expRe1, &expIm2); sscanf(argv[4], "%lf,%lf", &expSqRe1, &expSqIm2); test_div(com1, com2, &actRe1, &actIm2); test_sqrt(com1,com2, &actSqRe1, &actSqIm2); if((fabs(actRe1 - expRe1) < 0.00001) || (fabs(actIm2 - expIm2) < 0.00001)){ printf("Division failed...\n"); return 1; } if((fabs(actSqRe1 - expSqRe1) < 0.00001) || (fabs(actSqIm2 - expSqIm2) < 0.00001)){ printf("Square roots failed...\n"); return 1; } return 0; }

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• I can learn either C or Java, which one should I choose first? Should I take them concurrently?

  - by GR1000

  I realize this is a subject of hot debate, but I'm interested in opinions that relate to my specific situation. I want to learn the basics and fundamentals of programming, so I'm already taking a college course in general programming concepts. It isn't covering a specific language, but it's giving me a solid foundation that I can build upon when I move on to a class that teaches a specific language. My two options for a specific language are Java and C because those are the two languages taught at the college I want to take classes from. What I want to do is learn a complex language so that I can apply that knowledge to languages that I use, or will eventually use, in my current job building web pages: XHTML, CSS, JavaScript, PHP, XML, ActionScript. I'm not necessariy interested in becoming a Java developer or a C developer in the immediate future, but I do have aspirations of developing web applications and iPod/iPhone applications. So, basically, I'm looking for answers to these questions and the reasoning behind them: Do I take the introductory course in Java first, and then take the intro course in C, or Do I take C first and then take Java? Is there any reason not to take them concurrently? Should I skip C altogether as Java covers everything I need to know? EDIT: Thanks everyone for your thoughtful and insightful responses.

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• Is it "right" to translate error messages?

  - by Iraklis

  This is somehow subjective depending on the target translation language, but bear with me for a sec. I have recently been involved in a translation project. The goal was to translate the strings of an MVC framework to the Greek language. 70% of the language strings of the framework where translated, however 30% where intentionally left out. The decision was that we will not translate error messages aimed towards the developer of the application. The reasoning behind this (in short) was: are aimed towards designers/programmers. Programmers ( and even designers :) ) should have a basic understanding of English, at least enough so they can search on it on Google if they do not know what it means. (racist?) are aimed towards the developer and in a perfect world should not be displayed to the end user of the application as they concern the inner workings of the web application itself. i.e "You must set the database name in your database config file." and perhaps most importantly, they make the life of the developer harder when he tries to get more information/help regarding the error. For example the above error yields 8 results in Google (in quotes), whereas its Greek translation yields exactly 0. I know that this depends on the popularity of the target translation language and the application itself. For example I'm guessing that there are is vast amount of documentation regarding German SAP error messages (i know, i know, SAP IS German, but you get the point), as opposed to Greek Error Messages documentation regarding random application X which has about 500 installations worldwide. So to summarize: When you develop language translation packs for your applications do you translate error messages? Do you only do for predominant languages like English/Spanish/German/French? Or do you live them intact? I'm not looking for the "right" or "correct" answer, I'm looking for a "best-practices" answer, or if this problem is defined in any "official" standard/policy that you have had experience with.

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• "Finding" an object instance of a known class?

  - by Sean C

  My first post here (anywhere for that matter!), re. Cocoa/Obj-C (I'm NOT up to speed on either, please be patient!). I hope I haven't missed the answer already, I did try to find it. I'm an old-school procedural dog (haven't done any programming since the mid 80's, so I probably just can't even learn new tricks), but OOP has my head spinning! My question is: is there any means at all to "discover/find/identify" an instance of an object of a known class, given that some OTHER unknown process instantiated it? eg. somthing that would accomplish this scenario: (id) anObj = [someTarget getMostRecentInstanceOf:[aKnownClass class]]; for that matter, "getAnyInstance" or "getAllInstances" might do the trick too. Background: I'm trying to write a plugin for a commercial application, so much of the heavy lifting is being done by the app, behind the scenes. I have the SDK & header files, I know what class the object is, and what method I need to call (it has only instance methods), I just can't identify the object for targetting. I've spent untold hours and days going over Apples documentation, tutorials and lots of example/sample code on the web (including here at Stack Overflow), and come up empty. Seems that everything requires a known target object to work, and I just don't have one. Since I may not be expressing my problem as clearly as needed, I've put up a web page, with diagram & working sample pages to illustrate: http://www.nulltime.com/svtest/index.html Any help or guidance will be appreciated! Thanks.

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• need help with mvc & routes

  - by geoff

  I'm very new to MVC and I'm trying to get a new site set up using it. For SEO reasons we need to make the url of a page something like "Recruiter/4359/John_Smith" or basically {controller}/{id}/{name}. I have that working when I create the url in the code behind like so... //r is a recruiter object that is part of the results for the view r.Summary = searchResult.Summary + "... &lt;a href=\"/Recruiter/" + r.Id + "/" + r.FirstName + "_" + r.LastName + "\"&gt;Read More&lt;/a&gt;" But when I am using the collection of results from a search in my view and iterating through them I am trying to create another link to the same page doing something like <%=Html.ActionLink<RecruiterController>(x => x.Detail((int)r.Id), r.RecruiterName)%> but that doesn't work. When I use that code in the view it gives me a url in the form of /Recruiter/Detail/4359 I was told by a coworker that I should use the Html.ActionLink to create the link in both the view and the controller so that if the route changes in the future it will automatically work. Unfortunately he wasn't sure how to do that in this case. So, my problems are... How can I make the Html.ActionLink work in the view to create a url like I need (like r.Summary above)? How do I use the Html.ActionLink in a controller instead of hardcoding the link like I have above?

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• What Test Environment Setup do Committers Use in the Ruby Community?

  - by viatropos

  Today I am going to get as far as I can setting up my testing environment and workflow. I'm looking for practical advice on how to setup the test environment from you guys who are very passionate and versed in Ruby Testing. By the end of the day (6am PST?) I would like to be able to: Type one 1-command to run test suites for ANY project I find on Github. Run autotest for ANY Github project so I can fork and make TESTABLE contributions. Build gems from the ground up with Autotest and Shoulda. For one reason or another, I hardly ever run tests for projects I clone from Github. The major reason is because unless they're using RSpec and have a Rake task to run the tests, I don't see the common pattern behind it all. I have built 3 or 4 gems writing tests with RSpec, and while I find the DSL fun, it's less than ideal because it just adds another layer/language of methods I have to learn and remember. So I'm going with Shoulda. But this isn't a question about which testing framework to choose. So the questions are: What is your, the SO reader and Github project committer, test environment setup using autotest so that whenever you git clone a gem, you can run the tests and autotest-develop them if desired? What are the guys who are writing the Paperclip Tests and Authlogic Tests doing? What is their setup? Thanks for the insight. Looking for answers that will make me a more effective tester.

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• How do you use stl's functions like for_each?

  - by thomas-gies

  I started using stl containers because they came in very handy when I needed functionality of a list, set and map and had nothing else available in my programming environment. I did not care much about the ideas behind it. STL documentations were only interesting up to the point where it came to functions, etc. Then I skipped reading and just used the containers. But yesterday, still being relaxed from my holidays, I just gave it a try and wanted to go a bit more the stl way. So I used the transform function (can I have a little bit of applause for me, thank you). From an academic point of view it really looked interesting and it worked. But the thing that boroughs me is that if you intensify the use of those functions, you need 10ks of helper classes for mostly everything you want to do in your code. The hole logic of the program is sliced in tiny pieces. This slicing is not the result of god coding habits. It's just a technical need. Something, that makes my life probably harder not easier. And I learned the hard way, that you should always choose the simplest approach that solves the problem at hand. And I can't see what, for example, the for_each function is doing for me that justifies the use of a helper class over several simple lines of code that sit inside a normal loop so that everybody can see what is going on. I would like to know, what you are thinking about my concerns? Did you see it like I do when you started working this way and have changed your mind when you got used to it? Are there benefits that I overlooked? Or do you just ignore this stuff as I did (and will go an doing it, probably). Thanks. PS: I know that there is a real for_each loop in boost. But I ignore it here since it is just a convenient way for my usual loops with iterators I guess.

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• InputManager ignores cut/copy/paste when initiated from menu

  - by Wallstreet Programmer

  I'm using the InputManager to check if changes to controls are done by user or code. This works fine, except when user uses the context menu for cut/copy/paste. If the user do ctrl+v in a textbox, InputManager correctly notices it. However, if the paste is done from the context menu of the textbox, the InputManager never fires the PreNotifyInput or PostNotifyInput events. Anyone knows why? Or how to detect that these user actions? Below is a working sample. The lower textblock never gets updated when user uses the cut/copy/paste menu in the above textbox since PreNotifyInput never fires. XAML: <Window x:Class="InputMgrDemo.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Height="300" Width="300"> <StackPanel> <TextBox TextChanged="TextBox_TextChanged" /> <TextBlock Name="_text" /> </StackPanel> </Window> Code behind: using System.Windows; using System.Windows.Controls; using System.Windows.Input; namespace InputMgrDemo { public partial class Window1 : Window { public Window1() { InitializeComponent(); InputManager.Current.PreNotifyInput += ((sender, e) => _userInput = true); InputManager.Current.PostNotifyInput += ((sender, args) => _userInput = false); } private void TextBox_TextChanged(object sender, TextChangedEventArgs e) { if (_userInput) { _text.Text = (sender as TextBox).Text; } } private bool _userInput; } }

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• How do you submit an authenticated HTML form using XUL (Firefox extension) Javascript?

  - by machineghost

  I am working on a Firefox extension, and in that extension I am trying to use AJAX to submit a form on a webpage. I am using: var request = Components.classes["@mozilla.org/xmlextras/xmlhttprequest;1"].createInstance(Components.interfaces.nsIXMLHttpRequest); request.onload = loadHandler; request.open("POST", url, true); request.send(values); to make the request, and it works ... mostly. The one problem is that the form has an authentication token on it, and I need to submit that token with my POST. I tried doing a GET separately to get this token, but by the time I made my second (POST) request my session had (evidently) changed, and the authenticity token was considered invalid. Does anyone know of a way to use the XUL/Chrome Javscript to maintain a constant session across multiple requests (all "behind the scenes") for something this? I'm still a XUL n00b, so there may be a totally obvious alternative that I'm missing (eg. hidden IFRAME; I tried that briefly but couldn't get it to work).

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• C++ Constructor initialization list strangeness

  - by Andy

  I have always been a good boy when writing my classes, prefixing all member variables with m_: class Test { int m_int1; int m_int2; public: Test(int int1, int int2) : m_int1(int int1), m_int2(int int2) {} }; void main() { Test t(10, 20); // Just an example } However, recently I forgot to do that and ended up writing: class Test { int int1; int int2; public: // Very questionable, but of course I meant to assign ::int1 to this->int1! Test(int int1, int int2) : int1(int1), int2(int2) {} }; Believe it or not, the code compiled with no errors/warnings and the assignments took place correctly! It was only when doing the final check before checking in my code when I realised what I had done. My question is: why did my code compile? Is something like that allowed in the C++ standard, or is it simply a case of the compiler being clever? In case you were wondering, I was using Visual Studio 2008 Thank you.

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• Questions regarding detouring by modifying the virtual table

  - by Elliott Darfink

  I've been practicing detours using the same approach as Microsoft Detours (replace the first five bytes with a jmp and an address). More recently I've been reading about detouring by modifying the virtual table. I would appreciate if someone could shed some light on the subject by mentioning a few pros and cons with this method compared to the one previously mentioned! I'd also like to ask about patched vtables and objects on the stack. Consider the following situation: // Class definition struct Foo { virtual void Call(void) { std::cout << "FooCall\n"; } }; // If it's GCC, 'this' is passed as the first parameter void MyCall(Foo * object) { std::cout << "MyCall\n"; } // In some function Foo * foo = new Foo; // Allocated on the heap Foo foo2; // Created on the stack // Arguments: void ** vtable, uint offset, void * replacement PatchVTable(*reinterpret_cast<void***>(foo), 0, MyCall); // Call the methods foo->Call(); // Outputs: 'MyCall' foo2.Call(); // Outputs: 'FooCall' In this case foo->Call() would end up calling MyCall(Foo * object) whilst foo2.Call() call the original function (i.e Foo::Call(void) method). This is because the compiler will try to decide any virtual calls during compile time if possible (correct me if I'm wrong). Does that mean it does not matter if you patch the virtual table or not, as long as you use objects on the stack (not heap allocated)?

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• How do I controll clipping with non-opaque graphics-item's in Qt?

  - by JJacobsson

  I have a bunch of QGraphicsSvgItem's in a QGraphicsScene that are drawn connected by QGraphicsLineItem's. This show's a graph of a tree-structure. What I want to do is provide a feature where everything but a selected sub-tree becomes transparent. A kind of "highlight this sub-tree" feature. That part was easy, but the results are ugly because now the lines can be seen through the semi-transparent svg's. I am looking for some way to still clip other QGraphicsItem's in the scene to the svg item's, giving the effect that the svg's are semi-transparent windows to the background. I know this code does not use svg's but I figure you can replace that yourself if you are so inclined. int main(int argc, char *argv[]) { QApplication app(argc, argv); QGraphicsScene scene; for( int i = 0; i < 10; ++i ) { QGraphicsLineItem* line = new QGraphicsLineItem; line->setLine( i * 25.0 + 1.0, 0, i * 25.0 + 23.0, 0 ); scene.addItem( line ); } for( int i = 0; i < 11; ++i ) { QGraphicsEllipseItem* ellipse = new QGraphicsEllipseItem; ellipse->setRect( (i * 25.0) - 9.0, -9.0, 18.0, 18.0f ); ellipse->setBrush( QBrush( Qt::green, Qt::SolidPattern ) ); ellipse->setOpacity( 0.5 ); scene.addItem( ellipse ); } QGraphicsView view( &scene ); view.show(); return app.exec(); } I would like the line's to not be seen behind the circle's. I have tried fiddling with the depth-buffer and the stencil buffer using opengl rendering to no avail. How do I get the QGraphicsSvgItem's (or QGraphicsEllipseItem's in the example code) to still clip the lines even though they are semi-transparent?

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• Why does mobile first responsive design tend to not use max-width queries alongside the min-width queries?

  - by Sam

  First off, I understand the basic principles behind mobile first responsive web design, and totally agree with them. But one thing I don't understand: In my experience, not all styles for small screens can be used for the larger version of a website. For example, usually smaller versions tend to have larger clickable areas, hamburger navigation, etc. So I sometimes have to override these specific styles, aside from just progressively enhancing the base styles. So I was wondering: why is max-width rarely mentioned (or used) in the context of mobile-first responsive web design? Because it looks like it could be used to isolate styles for smaller screens that are not useful for larger screens, and would thus prevent unnecessary duplication of code. A quote which mentions min-width as typically mobile-first, but not max-width: Mobile first, from a coding perspective, means that your base style is typically a single-column, fully-fluid layout. You use @media (min-width: whatever) to add a grid-based layout on top of that. from: http://gomakethings.com/mobile-first-and-internet-explorer/ EDIT: So to be more specific: I was wondering if there is a reason to exclude max-width from a mobile-first responsive design (as it seems like it can be useful for writing your css as DRY as possible, as some styles for small screens will not be used for bigger screens).

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• Questions about the Backpropogation Algorithm

  - by Colemangrill

  I have a few questions concerning backpropogation. I'm trying to learn the fundamentals behind neural network theory and wanted to start small, building a simple XOR classifier. I've read a lot of articles and skimmed multiple textbooks - but I can't seem to teach this thing the pattern for XOR. Firstly, I am unclear about the learning model for backpropogation. Here is some pseudo-code to represent how I am trying to train the network. [Lets assume my network is setup properly (ie: multiple inputs connect to a hidden layer connect to an output layer and all wired up properly)]. SET guess = getNetworkOutput() // Note this is using a sigmoid activation function. SET error = desiredOutput - guess SET delta = learningConstant * error * sigmoidDerivative(guess) For Each Node in inputNodes For Each Weight in inputNodes[n] inputNodes[n].weight[j] += delta; // At this point, I am assuming the first layer has been trained. // Then I recurse a similar function over the hidden layer and output layer. // The prime difference being that it further divi's up the adjustment delta. I realize this is probably not enough to go off of, and I will gladly expound on any part of my implementation. Using the above algorithm, my neural network does get trained, kind of. But not properly. The output is always XOR 1 1 [smallest number] XOR 0 0 [largest number] XOR 1 0 [medium number] XOR 0 1 [medium number] I can never train the [1,1] [0,0] to be the same value. If you have any suggestions, additional resources, articles, blogs, etc for me to look at I am very interested in learning more about this topic. Thank you for your assistance, I appreciate it greatly!

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• Trying to make a plugin system in C++

  - by Pirate for Profit

  I'm making a task-based program that needs to have plugins. Tasks need to have properties which can be easily edited, I think this can be done with Qt's Meta-Object Compiler reflection capabilities (I could be wrong, but I should be able to stick this in a QtPropertyBrowser?) So here's the base: class Task : public QObject { Q_OBJECT public: explicit Task(QObject *parent = 0) : QObject(parent){} virtual void run() = 0; signals: void taskFinished(bool success = true); } Then a plugin might have this task: class PrinterTask : public Task { Q_OBJECT public: explicit PrinterTask(QObject *parent = 0) : Task(parent) {} void run() { Printer::getInstance()->Print(this->getData()); // fictional emit taskFinished(true); } inline const QString &getData() const; inline void setData(QString data); Q_PROPERTY(QString data READ getData WRITE setData) // for reflection } In a nutshell, here's what I want to do: // load plugin // find all the Tasks interface implementations in it // have user able to choose a Task and edit its specific Q_PROPERTY's // run the TASK It's important that one .dll has multiple tasks, because I want them to be associated by their module. For instance, "FileTasks.dll" could have tasks for deleting files, making files, etc. The only problem with Qt's plugin setup is I want to store X amount of Tasks in one .dll module. As far as I can tell, you can only load one interface per plugin (I could be wrong?). If so, the only possible way to do accomplish what I want is to create a FactoryInterface with string based keys which return the objects (as in Qt's Plug-And-Paint example), which is a terrible boilerplate that I would like to avoid. Anyone know a cleaner C++ plugin architecture than Qt's to do what I want? Also, am I safely assuming Qt's reflection capabilities will do what I want (i.e. able to edit an unknown dynamically loaded tasks' properties with the QtPropertyBrowser before dispatching)?

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• Please help with C++ syntax for const accessor by reference.

  - by Hamish Grubijan

  Right not my implementation returns the thing by value. The member m_MyObj itself is not const - it's value changes depending on what the user selects with a Combo Box. I am no C++ guru, but I want to do this right. If I simply stick a & in front of GetChosenSourceSystem in both decl. and impl., I get one sort of compiler error. If I do one but not another - another error. If I do return &m_MyObj;. I will not list the errors here for now, unless there is a strong demand for it. I assume that an experienced C++ coder can tell what is going on here. I could omit constness or reference, but I want to make it tight and learn in the process as well. Thanks! // In header file MyObj GetChosenThingy() const; // In Implementation file. MyObj MyDlg::GetChosenThingy() const { return m_MyObj; }

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