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Alessandro

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Everything posted by Alessandro

  1. Hello folks, I googled around and I yet can't find a way to get this done. Suppose I have a line segment going from (x1,y1,z1) to (x2,y2,z2). How do I calculate the normal vector perpendicular to this line? Thanks for any help.
  2. Find vector normal to line segment

    Thanks a lot for the explanations!
  3. Hi folks,   I'm trying to search a std::vector declared like this: std::vector<MyItem*> myNodeContainer; where MyItem is looking like this: class MyItem :public QGraphicsItem { public: MyItem(QString QwNodeType, QString iQwFamilyType); int testID; ... Now, I've built a function to search the testID: struct findNodeUUID2 { findNodeUUID2(int i) : id(i) { } bool operator()(const MyItem* &obj) { return (obj->testID==id); } int id; }; and I try to search like this: std::vector<MyItem*>::iterator findNodeIterator; findNodeIterator=std::find_if(myNodeContainer.begin(),myNodeContainer.end(), findNodeUUID2(1234) ); Linker errors as follows:   stl_algo.h.... No matching function for call to object of type 'findNodeUUID2'   What am I doing wrong? I suppose I'm using pointers the wrong way? Thanks for any suggestion    
  4. STL C++: iterator issue

    Thanks a lot for all the precious hints! Changed the XCode build setting as suggested by jwezorek and using lambda functions.
  5. STL C++: iterator issue

    Hi Chris, can't do that since I need to compile on XCode too...
  6. STL C++: iterator issue

    I think I sorted it out: struct findNodeUUID2 { findNodeUUID2(int i) : id(i) { } bool operator()(const MyItem *obj) { return (obj->test==id); } int id; };
  7. Evaluating curve points

    Hi folks, I'd like to ask help about evaluating curve points as displayed in the attached image. I'm be able to discard points if the curve is straight, comparing angles between each vector segment (left part).   I'd like to ask how could I evaluate points so that I can build a spline that passes through initial points (blue ones), and adds a number of green points where needed so that I can get a curve instead of a segmented vector.   Thanks
  8. Vector dot product

    I'm trying to use vector dot product to get the angle between two vectors, but I'm puzzled by the results.   Given two vectors, A and B: A(0.0, 0.2, 0.0) B(0.8, 0.0, 0.0) The angle between those, calculated with the dot product: alpha= (acos(A*B)) * RAD_TO_DEG properly returns 90°. Now, let's have two vectors pointing in the same direction: A(0.2, 0.2, 0.0) B(0.8, 0.8, 0.0) Would you guys explain me why in this case alpha is equal to 9.9°, while I'd expect to return 0°? Thanks    
  9. Hello folks, I've created a basic collision detection routine following this document: http://www.lighthouse3d.com/tutorials/maths/ray-triangle-intersection/ I'd like to monitor the distance from the point P and the triangle being tested for intersection, so that I can stop the routine when the distance falls below a certain value. I tried modifying the 0.00001 values in the code thinking that it was meant to be a tolerance value for such collision "distance", but it seems to be ineffective. What do you think? There is a way to do it? Here below is the routine derived from the document above: [code] int rayIntersectsTriangle(vector3_t orig, vector3_t dir, vector3_t v0, vector3_t v1, vector3_t v2) { float a,f,u,v,t; vector3_t e1= v1-v0; vector3_t e2= v2-v0; vector3_t h=dir^e2; a = e1*h; if (a > -0.00001 && a < 0.00001) return(false); f = 1.0/a; vector3_t s=orig-v0; u = f * (s*h); if (u < 0.0 || u > 1.0) return(false); vector3_t q=s^e1; v = f * (dir*q); if (v < 0.0 || u + v > 1.0) return(false); // at this stage we can compute t to find out where the intersection point is on the line t = f * (e2*q); if (t > 0.00001) // ray intersection return(true); else // this means that there is a line intersection // but not a ray intersection return (false); } [/code]
  10. "Preventing" collision detection

    [quote name='C0lumbo' timestamp='1352970376' post='5001156'] In your function, t is the distance between point p and point c (assuming dir is normalised) So, changing "if (t > 0.00001)" to "if (t > 1.0)" would make the function ignore collisions that occur within one unit of the origin of the ray. [/quote] Thank you very much, that was successful.
  11. "Preventing" collision detection

    [quote name='SimonForsman' timestamp='1353003308' post='5001297'] To get the distance between two points(p and c) just treat them as vectors and you get: distance = ||c-p|| are you trying to prevent collision [b]detection[/b] like the post title says or are you trying to stop actors before a collision occurs ? [/quote] Actually the 2nd option would be perhaps a better option for my needs.
  12. "Preventing" collision detection

    Also, I'd like to ask if there are faster algorithms that do ray triangle intersection, or this is just the way to go.
  13. "Preventing" collision detection

    Sorry for not being more precise. Take a look at the attached image. You see there is a point [size=5][b]p[/b][/size] the is being moved in direction [size=5][i][b]v[/b][/i][/size], and the collision point [size=5][b]C[/b][/size]. I'd like to "monitor" the distance between the point [size=5][b]p[/b][/size] and the collision point [b][size=5]C[/size][/b], so that I can stop the routine before it actually collides.
  14. "Preventing" collision detection

    Sorry for not being more precise. Take a look at the attached image. You see there is a point [size=5][b]p[/b][/size] the is being moved in direction [size=5][i][b]v[/b][/i][/size], and the collision point C. I'd like to "monitor" the distance between the point [size=5][b]p[/b][/size] and the collision point [b][size=5]C[/size][/b], so that I can stop the routine before it actually collides.
  15. Hi, I 've no issues declaring a standard type vector as extern as follows: [code] extern std::vector<int> testVector; // main.h std::vector<int> testVector; // main.cpp [/code] However, if I use a vector containing a custom structure, like follows, I get an "expected class name" error. See below: [code] extern std::vector<myTempObjects::myTempObjectLib> testVector; // main.h std::vector<myTempObjects::myTempObjectLib> testVector; // main.cpp [/code] [code] // myTempObjects.h class myTempObjects : public mainClass { // ERROR expected class name on mainClass Q_OBJECT public: myTempObjects (); ~myTempObjects (); struct myTempObjectLib { vector3_t hairControlPoint; int r,g,b; }; [/code] Would you guys please teach me what's wrong? Thanks
  16. Problem declaring extern std::vector

    Hi guys, I'm still at trouble with this. Following your suggestions, and taking a look at the initial code I posted, I made a forward class declaration like this: [code]class myTempObjects[/code]; But then how do I declare the extern vector? I tried the following and I'm getting a "incomplete type 'myTempObjects' named in nested name specifier" [code]std::vector<myTempObjects::myTempObjectLib> myTmpObject; [/code]
  17. Given a XYZ coordinate system, and a vector AB as represented in the attached image (where A is matching the world center 0,0,0 ), how could I calculate the angles of rotation of AB along the 3 axis? Meaning that if you start with AB at 0,1,0 I'd like to know what angle rotations have been applied to achieve its new position (which is known) in space. To put it into numbers, if AB is at (0,1,0) and later you set it at (1,0.4,0.3), there is a way to calculate the angles that if forms within the x,y,z axis? I don't know if the image are really explanatory, let me know if you need further info. Thanks for any help! [img]http://www.alessandromastronardi.com/axistest.jpg[/img]
  18. Calculating angles of rotation

    Thanks a lot, I'm going to try this as well!
  19. Calculating angles of rotation

    Just to report that thanks to all your suggestions I managed to solve this matter. As you wrote I calculated the rotation axis and the angle between the guide and the object, rotated the object, built up a quaternion from it and extracted the euler angles.
  20. Calculating angles of rotation

    I think I understand what you mean. Sorry to be so stubborn but, in my case, the guide represent both the direction and the orientation, wouldn't it? I mean, I just need to orient and direct a 3d object so that it matches that guide. You're all allowed to insult me if I still can't understand it [img]http://public.gamedev.net//public/style_emoticons/default/biggrin.png[/img] I mean, if that guide has origin at (0,0,0), and aims at (0,1,1), there must be a chance to say "Ok, let get another object, sets its origin at (0,0,0) as well, and aim it at (0,1,1)"...
  21. Calculating angles of rotation

    Well, changing SDK unfortunately is not an option [img]http://public.gamedev.net//public/style_emoticons/default/smile.png[/img] The order of rotation is ZXY. I'm so bad at math that I'm really amazed to realize how something that I figured out a simple operation (place an object at the same base point of a guide, and orient it along it), instead seems to be so complicated. I hope you guys can come up with a solution to help me with this.
  22. Calculating angles of rotation

    I also would like to ask this. Since the application I'm working on is based on a SDK and does not accept direct opengl commands, I need to apply rotation angles separately. So I can't do something like this: glRotatef([b]rotationAngle[/b], CP.x, CP.y, CP.z); // where [b]CP[/b] is a vector representing the axis of rotation but I rather have to: setRotX(angleX); setRotY(angleY); setRotZ(angleZ); I need, to provide the three angle components (that the right term) for each axis, obviously gathered from the [b]rotationAngle[/b] and the [b]CP[/b] vector. Also this is something that I can't figure if and how is possible.
  23. Calculating angles of rotation

    I think I understand what you mean, but then, I'd possibly solve this matter? Would the solution you provided in your first reply do it ? BTW, what means the "constraint was that it was the minimum possible rotation"? Sorry for all these questions, it's just that I'm very bad at math and all these terms and notions puzzle me.
  24. Calculating angles of rotation

    Just to give more details, here is what i'm trying to do. In the first image, I have a guide line, made of two points (whose coordinates are known), and I need to replace that guide with a 3D object (see second image). Placing the 3D object it's simple, since I already know the guide base point coordinates, but I'd like to orient the 3D object so that it matches the guide orientation as well. And the issue I have is to calculate those angles so that I can apply those to the 3D object as well. [img]http://www.alessandromastronardi.com/img1.jpg[/img] [img]http://www.alessandromastronardi.com/img2.jpg[/img]
  25. Calculating angles of rotation

    Reading back what Bob wrote, probably I should to something like this: vector CP = cross product between the original vector and the vector AB rotationAngle = arccosine(dot-product between the original vector and the vector AB) Now I could do something like this: glRotatef(rotationAngle, CP.x, CP.y, CP.z); Am I on the right path?
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