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• Why doesn't it seem to be any development in the field of 3D VR gear, especially with regard to gaming?

  - by neuviemeporte

  I remember that way back around 1995, there was this big craze with VR in the media, a whole bunch of (mostly mediocre) games labeled as "virtual-reality-interactive-movie (...)" were published. If I recall correctly, the first 3D VR helmet was called VFX-1 and was sold bundled with Descent and some dedicated joystick. I never owned one, and I read just one review which was mostly enthusiastic, but pointed to some weak points, like the eyes getting tired after an hour or so of playing. Then the whole thing basically flickered down and died. I suppose the main reason it wasn't successful was that the hardware of the day was not powerful enough, the VR gear's design wasn't perfected to make it comfortable and natural to use, and the companies that made it failed to market it successfully. What I can't understand is why isn't there any development in the field today. There is some vr-ish hardware mostly targeted at the consoles (Kinect, Wii remote, TrackIR), but all projects of creating some 3d head-mounted display system seem to be in early infancy, appear once in a trade show somewhere and aren't heard of again. I think it could work great with head tracking and some of today's shooters, flight sims (trackIR is nice but the movement scale translation is awkward) and other games with an FPP POV. Is there any technological reason why decent vr headgear can't be made today, or is it just that nobody really cares/everyone is scared to repeat the '90s failure?

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• How can I better manage far-reaching changes in my code?

  - by neuviemeporte

  In my work (writing scientific software in C++), I often get asked by the people who use the software to get their work done to add some functionality or change the way things are done and organized right now. Most of the time this is just a matter of adding a new class or a function and applying some glue to do the job, but from time to time, a seemingly simple change turns out to have far-reaching consequences that require me to redesign a substantial amount of existing code, which takes a lot of time and effort, and is difficult to evaluate in terms of time required. I don't think it has as much to do with inter-dependence of modules, as with changing requirements (admittedly, on a smaller scale). To provide an example, I was thinking about the recently-added multi-user functionality in Android. I don't know whether they planned to introduce it from the very beginning, but assuming they didn't, it seems hard to predict all the areas that will be affected by the change (apps preferences, themes, need to store account info somehow, etc...?), even though the concept seems simple enough, and the code is well-organized. How do you deal with such situations? Do you just jump in to code and then sort out the cruft later like I do? Or do you do a detailed analysis beforehand of what will be affected, what needs to be updated and how, and what has to be rewritten? If so, what tools (if any) and approaches do you use?

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• Why does the MSCVRT library generate conflicts at link time?

  - by neuviemeporte

  I am building a project in Visual C++ 2008, which is an example MFC-based app for a static C++ class library I will be using in my own project soon. While building the Debug configuration, I get the following: warning LNK4098: defaultlib 'MSVCRT' conflicts with use of other libs; use /NODEFAULTLIB:library After using the recommended option (by adding "msvcrt" to the "Ignore specific library" field in the project linker settings for the Debug configuration), the program links and runs fine. However, I'd like to find out why this conflict occured, why do I have to ignore a critical library, and if I'm to expect problems later I if add the ignore, or what happens if I don't (because the program builds anyway). At the same time, the Release configuration warns: warning LNK4075: ignoring '/EDITANDCONTINUE' due to '/OPT:ICF' specification warning LNK4098: defaultlib 'MSVCRTD' conflicts with use of other libs; use /NODEFAULTLIB:library I'm guessing that the "D" suffix means this is the debug version of the vc++ runtime, no idea why this gets used this time. Anyway, adding "msvcrtd" to the ignore field causes lots of link errors of the form: error LNK2001: unresolved external symbol imp_CrtDbgReportW Any insight greatly appreciated.

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• Using a member function pointer within a class

  - by neuviemeporte

  Given an example class: class Fred { public: Fred() { func = &Fred::fa; } void run() { int foo, bar; *func(foo,bar); } double fa(int x, int y); double fb(int x, int y); private: double (Fred::*func)(int x, int y); }; I get a compiler error at the line calling the member function through the pointer "*func(foo,bar)", saying: "term does not evaluate to a function taking 2 arguments". What am I doing wrong?

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• Why do I have to specify virtual functions in the declaration of a derived class?

  - by neuviemeporte

  Given the base class A and the derived class B: class A { public: virtual void f(); } class B : public A { public: void g(); } I get errors saying that f() is not declared in B while trying do define void B::f(). Do I have to declare f() explicitly in B? I think that if the interface changes I shouldn't have to correct the declarations in every single class deriving from it. Is there no way for B to get all the virtual functions' declarations from A automatically?

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• How can I save and read to XML the new C++ style matrix objects in OpenCV?

  - by neuviemeporte

  The old, C style cvMat matrices could be passed to the cvSave() function for easy writing to an XML file. The new C++ style cv::Mat and cv::Mat_ matrices are not accepted by this function. The OpenCV reference has a section on XML persistence, but the three classes (FileStorage, FileNode and FileNodeIterator) lack any description or example and I can't figure out how to use them from the interface. Thanks.

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• Is there performance to be gained by moving storage allocation local to a member function to its cla

  - by neuviemeporte

  Suppose I have the following C++ class: class Foo { double bar(double sth); }; double Foo::bar(double sth) { double a,b,c,d,e,f a = b = c = d = e = f = 0; /* do stuff with a..f and sth */ } The function bar() will be called millions of times in a loop. Obviously, each time it's called, the variables a..f have to be allocated. Will I gain any performance by making the variables a..f members of the Foo class and just initializing them at the function's point of entry? On the other hand, the values of a..f will be dereferenced through this-, so I'm wondering if it isn't actually a possible performance degradation. Is there any overhead to accessing a value through a pointer? Thanks!

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• Why do I get errors when using unsigned integers in an expression with C++?

  - by neuviemeporte

  Given the following piece of (pseudo-C++) code: float x=100, a=0.1; unsigned int height = 63, width = 63; unsigned int hw=31; for (int row=0; row < height; ++row) { for (int col=0; col < width; ++col) { float foo = x + col - hw + a * (col - hw); cout << foo << " "; } cout << endl; } The values of foo are screwed up for half of the array, in places where (col - hw) is negative. I figured because col is int and comes first, that this part of the expression is converted to int and becomes negative. Unfortunately, apparently it doesn't, I get an overflow of an unsigned value and I've no idea why. How should I resolve this problem? Use casts for the whole or part of the expression? What type of casts (C-style or static_cast<...)? Is there any overhead to using casts (I need this to work fast!)? EDIT: I changed all my unsigned ints to regular ones, but I'm still wondering why I got that overflow in this situation.

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• How to debug an external library (OpenCV) in Visual C++?

  - by neuviemeporte

  I am developing a project in VC++2008. The project uses the OpenCV library (but I guess this applies to any other library). I am working with the Debug configuration, the linker properties include the debug versions of the library .lib's as additional dependencies. In VC++ Directories under Tools|Options i set up the include directory, the .lib directory, the source directories for the library as well. I get an error while calling one of the functions from the library and I'd like to see exactly what that function is doing. The line that produces the error is: double error = cvStereoCalibrate(&calObjPointsM, &img1PointsM, &img2PointsM, &pointCountsM, &cam1M, &dist1M, &cam2M, &dist2M, imgSize, &rotM, &transM, NULL, NULL, cvTermCriteria(CV_TERMCRIT_ITER + CV_TERMCRIT_EPS, 100, 1e-5)); I set up a breakpoint at this line to see how the cvStereoCalibrate() function fails. Unfortunately the debugger won't show the source code for this function when I hit "Step into". It skips immediately to the cvTermCriteria() (which is a simple inline, macro-kinda function) and show its contents. Is there anything else I need to do to be able to enter the external library functions in the debugger? EDIT: I think the cvTermCriteria() function shows in the debugger, because it's defined in a header file, therefore immediately accesible to the project.

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• Why do I have to specify pure virtual functions in the declaration of a derived class in Visual C++?

  - by neuviemeporte

  Given the base class A and the derived class B: class A { public: virtual void f() = 0; }; class B : public A { public: void g(); }; void B::g() { cout << "Yay!"; } void B::f() { cout << "Argh!"; } I get errors saying that f() is not declared in B while trying do define void B::f(). Do I have to declare f() explicitly in B? I think that if the interface changes I shouldn't have to correct the declarations in every single class deriving from it. Is there no way for B to get all the virtual functions' declarations from A automatically? EDIT: I found an article that says the inheritance of pure virtual functions is dependent on the compiler: http://www.objectmentor.com/resources/articles/abcpvf.pdf I'm using VC++2008, wonder if there's an option for this.

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• Should downcasting be avoided while using a class hierarchy in C++?

  - by neuviemeporte

  Let's say I'm writing an application which works with projects, and exposes different functionality depending on the type of the project. I have a hierarchy of classes for the different types of projects: class AbstractProject { }; class ProjectA : public AbstractProject { }; class ProjectB : public AbstractProject { }; class ProjectC : public AbstractProject { }; Now, I was planning to have an AbstractProject *_currentProject pointer as a member in the application's main class, pop up a dialog box on startup and based on the selection, do: _currentProject = new ProjectB(); // e.g. Later, I'll have to downcast the pointer to the specific type to utilize the functionality specific to different Project-s. Somehow this makes me feel uneasy. Is there a Better Way of doing this?

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• Are there any pitfalls when calling functions from a C library in a C++ program?

  - by neuviemeporte

  I'm using a library which has both a C interface and a C++ interface in my C++ program. The C++ one is a bit immature and I must stick with the C one. I was wondering, in more general terms, is there anything specific to keep in mind when mixing C-style binary object files with a C++ project?

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