# Brother Bob

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Programming
1. ## Importing .OBJ model to OpenGL

The primary issue is that OBJ files allows you to share the individual attributes; for example, the first vertex of the two faces you showed is 1/3/1 and 1/3/6, so the two faces share position and texture coordinate, which also happens to be different indices (first vertex and third texture coordinate), but use different normal (first vs. sixth). But, OpenGL does not allow that; you can only have one single index to select all attributes of a vertex. You have to rearrange the indices to make sure that all triplets uses the same indices; for example 1/1/1, 2/2/2 and 3/3/3 to make a triangle of the first, second and third vertex. You cannot have mixed indices within a triplet. The important thing to keep in mind that a vertex in OpenGL is a collection of all its attributes. The vertex is not just it's position. Basically, this is your vertex (vec2 and vec3 represent your favourite 2- and 3-dimensional vectors): struct Vertex { vec3 p; // position vec2 t; // texture coordinate vec3 n; // normal }; If two vertices have different normals, then the two vertices are entirely different. You then need two different instances of this structure with the set of positions and normals duplicated. You need to translate your OBJ file's split index structure into OpenGL's shared index structure. If you are learning this and don't feel comfortable doing that, then I suggest you forget about indices and just use a flat non-indexed vertex array instead. Assuming that you have individual lists of each position, texture coordinate and normal attribute from the OBJ file, as well as a list of faces and corresponding sets of indices, you can flatten the arrays by simply iterating over the faces and build a new vertex array from scratch. struct Index { int position_index; int texture_index; int normal_index; } struct Face { Index indices[3]; } std::vector<Face> faces; std::vector<vec3> position; std::vector<vec2> texture; std::vector<vec3> normal; std::vector<Vertex> object; for(auto &&f : faces) { for(auto &&i : f.indices) { Vertex v; v.p = position[i.position_index]; v.t = texture[i.texture_index]; v.n = normal[i.normal_index]; object.push_back(v); } } The vector object now contains the list of vertices forming triangles as specified by the OBJ-file. You can pass this vector, or it's data rather, directly to OpenGL as an interleaved array. No index arrays needed. It is assumed that you have populated position, texture, normal and faces from the OBJ file already.

3. ## C++ General C++ class questions

Static members are initialized once, automatically. struct myclass { myclass(); static int mystatic; }; int myclass::mystatic = 42; If you need to run arbitrary code in the constructor just once there are facilities for that as well; click. #include <mutex> myclass::myclass() { static std::once_flag onceflag; std::call_one(onceflag, []() { // code here will be executed just once }); } Personally I would just do minimal amount of work in the constructor to put the object in a well-defined state. Non-trivial work that can fail goes into separate init functions. But there's nothing technically wrong with throwing from a constructor; the object just isn't constructed and doesn't come into existence in the first place. Maybe the debugger just allows you to continue execution and "bypass" the exception. Run it without the debugger and see what happens instead. That's the wrong solution to the problem. The core of the problem is that your class is not copyable, but you put a copy of it into the vector. Look up resource ownership, the rule of three/five/zero, and how to properly handle dynamic resources. My guess is that the class contains a pointer to some resource (or equivalent; you mention a Release method so perhaps a COM-pointer), but you don't implement a proper copy constructor for your class. When you then make a copy, you have two objects holding a pointer to the same resource, and the first one to destruct will also release the resources. Either implement a proper deep copy (rather than a shallow copy or pointer assignment) so two objects hold separate copies of the actual resource rather than copies of the pointer, or implement proper resource sharing (for example std::shared_ptr), depending on what you want to happen when you copy your objects. Primitive types are not initialized, you have to do that yourself. class MyClass { public: int count = 0; OtherObject *otherObj = nullptr; }
4. ## Some questions about glViewport

I am fairly certain you can do that by applying the translation of card after the projection matrix. Just insert the projection matrix between step 3 and 4 in your previously "incorrect" list: Start with vertices comprising an upright card centered around the origin. Apply a rotation matrix to rotate the card. Apply a translation matrix moving the card forward so its dead center in front of the eye. Apply projection matrix here. Apply another translation matrix moving the card so its in the lower-right corner of the screen. The amount to translate in step 5 is left as an exercise to the reader (i.e., too lazy to check myself) but I believe it has to be done in normalised device units. That is, a translation of 0.5 would translate the card by half the size of the window (or rather the viewport, but I assume you're not changing the viewport in this approach and the viewport is the full size of the window).
5. ## Some questions about glViewport

I see now what you intend to do. If you consider the view of a single card as its own viewport then what you describe here is precisely what glViewport is for; you define the region of the window where you want the scene (your single card) to be drawn. It even gives you possibly positive side effects, such as clipping. Consider for example if you zoom in a little on the card while it's rotating, or if the viewport is too small. If the corners or the card extend beyond the viewport while rotating it, they will be clipped to the viewport region and won't interfere with things outside the defined viewport. For this purpose, the viewport is typically set together with the scissor region; look up glScissor.
6. ## Some questions about glViewport

The parameters x and y can be negative, but the width and height parameters must be non-negative. The viewport transform is just a coordinate transformation from normalised device coordinates to window (or pixel) coordinates. Once all transformations (model, view, perspective, or any other transformation you may have) have been applied, you end up in a coordinate system called normalized device coordinate. It is a coordinate system when the visible coordinates ar in the range [-1, 1] along all three axes. For example, -1 to 1 along the X-axis corresponds to what is visible along the X-axis from left to right, independent of Y and Z-coordinate. This range [-1, 1] along both the X and Y is then transformed by the viewport transform, so that -1 ends up at the pixel coordinates x or y (the parameters to glViewport), and 1 ends up at the pixel coordinates x+width or y+height. The -1 and 1 along the Z-axis is subject to the depth buffer process so will not covered at this stage. So where your point (100,100) ends up in window space depends on all the transformations you apply to it, and what its normalised device coordinates is. But if you move the viewport around by changing the x and y parameters, you will effectively just translate the rendering region around the window, like grabbing the title bar of any window and moving it around. Stencil testing, however, is tied to the actual pixel coordinates. Thus, moving the viewport around will render your scene over a different set of actual pixels within the window, and therefore subject the rendered scene to a different region of the stencil buffer.   As far as I understand what you want to do and the way you want to use the viewport to achieve this, you need negative width or height to achieve the flipping effect. That is not possible in the first place; see Q1.
7. ## Java and C++

Original post has been restored and some replies regarding post history has been hidden. You can continue that discussion in the corresponding thread; clicky. Do not fundamentally change you posts like this again.
8. ## OpenGL doesn't render my triangle

You're drawing the triangle after you have swapped the back and front buffers. You need to first clear, then draw, and then swap the buffers.
9. ## Template argument deduction fails here...

Maybe overloading and SFINAE can help you. Something like this; seems to work on VS2015. Tweak the type trait checks as you like. template <typename T> using is_vector = std::is_same<T, std::vector< typename T::value_type, typename T::allocator_type>>; template<typename T> typename std::enable_if<std::is_arithmetic<T>::value>::type foo(T v) { std::cout << "value: " << v << std::endl; } template<typename T> typename std::enable_if<is_vector<T>::value>::type foo(T const &v) { std::cout << "vector: " << v[0] << std::endl; } template<typename T> typename std::enable_if<std::is_class<T>::value>::type foo(T *v) { std::cout << "pointer: " << v << std::endl; } int main() {     int i = 42;     double d = 3.14;     std::vector<int> v{271};     std::string s = "foo";     foo(i);     /* ok; arithmetic type by value */     foo(d);     /* ok; arithmetic type by value */     foo(v);     /* ok; vector by const reference */     foo(&v);    /* ok; pointer to class type although class happens to be vector */     foo(&s);    /* ok; pointer to class type */ #if 0     foo(&i);    /* not ok; pointer to non-class type */     foo(s);     /* not ok; class type but not called as pointer */ #endif } The value function is enabled only for arithmetic types, the vector function is enabled only for vectors (of any kind) and the pointer function is enabled for classes only. Just be aware that you can pass vectors by pointer to the pointer function  since the vector is a class. There's no way to distinguish user defined classes from standard library classes, as far as I am aware, other than manually excluding them.
10. ## Template argument deduction fails here...

What you want then is for the compiler to find a type Type such that Dummy<Type>::type resolves to int. The type Type is unrelated to the parameter type int and the compiler would have to instantiate Dummy with every possible type in order to find the ones where Dummy<Type>::type is an int. That is, as you can imagine, a quite unreasonable task. There could be some obscure and hidden type, somewhere, that specialize the Dummy template with using Type = int and that would necessarily have to be a legal type for Type.   The template parameter is in a non-deduced context and the language simply doesn't allow deduction in this case. I imagine my argument above would be a reasonable reason for that.   Possible ways around it depends on use case and what other possible constraints you can impose on the types. But as it stands, it simply isn't a context where a template parameter can be deduced. For example, if you pass other parameter types to the function, Type being one of them, then those parameters can deduce the types: template<typename Type> void dummyFunction(typename Dummy<Type>::type type, Type other) { ... } Now the parameter other can deduce the template parameter, and Dummy<Type> is instantiated accordingly.
11. ## Initializing std::string members of a class?

If you don't initialize a member in the initializer list, its default constructor will be executed as a part of the initialization of the object. Once the initializer list is executed (including the default constructor for members you don't explicitly initialize) the constructor body is executed. The difference between constructing a member in the initializer list and "constructing" it in the body of the containing class' constructor is; the former directly calls the proper constructor, while the latter default constructs the object and then calls the assignment operator of whatever you're assigning to it.   If the member type cannot be default initialized, you must initialize it in the constructor body. If the member type is expensive to default construct, then you pay for unnecessary default initialization and then an assignment to override the value from the default constructor.   edit: To expand on the above a little more. Once the constructor body starts executing, all members have had one of their constructors called and they are all properly constructed. I mentioned in my last post that some things cannot be initialized other than in the initializer list. For example, the base class in an inheritance tree must be called from the initializer list; objects without a default constructor cannot be default constructed; const objects cannot be assigned to in the constructor body since that would change a const object.
12. ## Initializing std::string members of a class?

The two are not equivalent in the constructor implementation. In the initializer list, however, they produce equivalent results; the first is value-initialization which for pointers means its value is set to the null pointer, while the second (explicitly) initialises it with a null pointer. Start using the initializer list; some things just cannot be initialized in the constructor body.
13. ## how good is rand() ?

Correct.  In modern math notation this type of function works with [0,x)  meaning it includes zero but stops just short of x.  This is also common in many other systems.  Graphics, for example, typically draw segments in the [A,B) form, starting exactly at A and ending the instant before B.     I tried this in VS2015 and it does return RAND_MAX.. is it not supposed to? #include <iostream> int main() { for(int i = 0; i < 200000; ++i) { int r = rand(); if(r == RAND_MAX) std::cout << "MAX\n"; else if(r == (RAND_MAX - 1)) std::cout << "ALMOST\n"; else if(r == 0) std::cout << "ZERO\n"; } } The range for both rand() and the <random> library (at least the uniform integer distributions when comparing with rand) are inclusive at both ends. The range is therefore [0, RAND_MAX], not [0, RAND_MAX). This is different from, for example, iterator ranges in the standard library which are half-open.
14. ## Generate this kind of 2d burst or pulse

Don't post in multiple forums, your other posts have been removed. If you want it in some other sub-forum then ask a moderator to move it instead.
15. ## Template-related compiler bug or... ?

That may explain why I was surprised there wasn't much information about it. It's in VS 2013 at least where I tried it, but if it was actually removed then it should be fairly easy to make the necessary types to handle the particular problem raised in this thread. template<typename T> struct identity {     using type = T; }; The idea of making the second parameter a non-deduced one still applies.