>double dist = distRayPlane(Pos, velocity, pl.Normal, Dplane);

>if(dist < distRayPlane(Pos, velocity, pl.Normal, Dplane))

dist is never going to be less than itself

This is a discussion on *Ray tracer and collision detection* within the **Game Programming** forums, part of the General Programming Boards category; >double dist = distRayPlane(Pos, velocity, pl.Normal, Dplane);
>if(dist < distRayPlane(Pos, velocity, pl.Normal, Dplane))
dist is never going to be less ...

- 01-11-2006 #16
>double dist = distRayPlane(Pos, velocity, pl.Normal, Dplane);

>if(dist < distRayPlane(Pos, velocity, pl.Normal, Dplane))

dist is never going to be less than itself

- 01-11-2006 #17

- Join Date
- May 2005
- Posts
- 964

score 1 for perspective

I was thinking about telling him that in class today.... but... I decided it was best he find out his silly mistake for himself

No, I'm just kidding, I was just as oblivious as he was .Sometimes I forget what I am doing when I enter a room, actually, quite often.

- 01-11-2006 #18

- Join Date
- Sep 2005
- Location
- I'm lost!!!
- Posts
- 200

Originally Posted by**Perspective**Hello, testing testing. Everthing is running perfectly...for now

- 01-11-2006 #19
There is a ray-to-triangle intersection algo somewhere on this board. Bob and I talked about it extensively in several posts. I would recommend searching for posts either started by Bubba or by Bob.

- 01-17-2006 #20

- Join Date
- Sep 2005
- Location
- I'm lost!!!
- Posts
- 200

Yes, finally i've made it work. This is how it goes:

Code:bool checkPointTriangle(vect3 Point, vect3 Pa, vect3 Pb, vect3 Pc) { double totalAngle = 0.0f; vect3 v1 = Point - Pa; vect3 v2 = Point - Pb; vect3 v3 = Point - Pc; NormalizeVect(v1); NormalizeVect(v2); NormalizeVect(v3); totalAngle += acos(dot(v1, v2)); totalAngle += acos(dot(v2, v3)); totalAngle += acos(dot(v3, v1)); if(fabs(totalAngle - 2*PI) < 0.005) return true; else return false; }

Is there anything else i should add into my collision code to make it faster?

EDIT:

If i have a model with multiple triangles, what vector on the model should i check for the collide triangles? A point in a model's triangle or a point on its face?Last edited by hdragon; 01-17-2006 at 09:29 AM.

Hello, testing testing. Everthing is running perfectly...for now

- 01-18-2006 #21
That acos() looks quite nasty. Anything you can do to get rid of it?

- 01-18-2006 #22

- Join Date
- May 2005
- Posts
- 1,041

If i have a model with multiple triangles, what vector on the model should i check for the collide triangles? A point in a model's triangle or a point on its face?

I wrote this for determining if a point resides in a triangle...but this is also pretty nasty, and might actually be more expensive, but it works.

Code:#include "CollisionDetectionPrimitives.h" extern std::ofstream trace; #define CCWPITDEBUG(x) x //Fixme: investigate to see how vector length plays into uncertainty here //Normal x DiffVector = InwardVector //InwardVector Dot Point >= 0 or >= -.0001 BOOL CCWPointInTri(float P1X,float P1Y,float P1Z, float P2X,float P2Y,float P2Z, float P3X,float P3Y,float P3Z, float NormalX,float NormalY,float NormalZ, float PointX,float PointY,float PointZ) { Vector3 Point1(P1X,P1Y,P1Z); Vector3 Point2(P2X,P2Y,P2Z); Vector3 Point3(P3X,P3Y,P3Z); Vector3 Normal(NormalX,NormalY,NormalZ); Vector3 Point(PointX,PointY,PointZ); Vector3 LocalPoint = Point - Point1; //The point in local coordintes with respect to a vertex Vector3 DiffVector = Point2 - Point1; Vector3 InwardVector(0,0,0); InwardVector = CrossProduct(&Normal,&DiffVector); if(DotProduct(&InwardVector,&LocalPoint) < -.0001f) { CCWPITDEBUG( trace << "Returning on first point" << "\n"; ) return FALSE; } LocalPoint = Point - Point2; DiffVector = Point3 - Point2; InwardVector = CrossProduct(&Normal,&DiffVector); if(DotProduct(&InwardVector,&LocalPoint) < -.0001f) { CCWPITDEBUG( trace << "Returning on seconed point" << "\n"; ) return FALSE; } LocalPoint = Point - Point3; DiffVector = Point1 - Point3; InwardVector = CrossProduct(&Normal,&DiffVector); if(DotProduct(&InwardVector,&LocalPoint)<-.0001f) { CCWPITDEBUG( trace << "Returning on third point" << "\n"; ) return FALSE; } return TRUE; }

I'm not immature, I'm refined in the opposite direction.

- 01-18-2006 #23
That doesn't look so nasty. It's only subtraction's and cross product's. Shouldn't hit too hard.

- 01-18-2006 #24
while we're all in the mood for posting ray-triangle intersection algo's, here's mine. (I was forced to use this prototype, thats why i set the u, v, t params by reference). Also, this scence always had one object, that's why i just grab objects[0]. A better implimentation would pass the triangle as a paramater.

edit: oh btw: u and v are the "UV Coordinates" of the intersected triangle and t is the magnitude along the direction of the ray that the intersection takes place. So this algo doesn't just tell you if there is an intersection, it tells you the point on the triangle that the intersection takes place by setting the u,v, and t params (handy for phong shading or other types of lighting). Returns 0 if there is no intersection and 1 if there is.

Code:// calculate ray - triangle intersection with backface culling int RayTracer::calcTriangleIntersection(const Ray& ray, const VertexList* face, float *t, float *u, float *v) { Point3f vert1 = scene->objects[0].vertices[(face->vertex)-1]; Point3f vert0 = scene->objects[0].vertices[(face->next->vertex)-1]; Point3f vert2 = scene->objects[0].vertices[(face->next->next->vertex)-1]; Vector3f edge1, edge2, tvec, pvec, qvec; float det, inv_det; // find vectors for two edges sharing vert0 edge1 = vert1 - vert0; edge2 = vert2 - vert0; // begin calculating determinant - also used to calculate U parameter pvec = ray.dir.cross(edge2); // if determinant is near zero, ray lies in plane of triangle det = edge1.dot(pvec); if (det < EPSILON) return 0; // calculate distance from vert0 to ray origin tvec = ray.start - vert0; // calculate U parameter and test bounds *u = tvec.dot(pvec); if (*u < -EPSILON || *u > det) return 0; // prepare to test V parameter qvec = tvec.cross(edge1); // calculate V parameter and test bounds *v = ray.dir.dot(qvec); if (*v < -EPSILON || (*u + *v) > det) return 0; // calculate t, scale parameters, ray intersects triangle *t = -edge2.dot(qvec); inv_det = 1.0f / det; *t *= inv_det; *u *= inv_det; *v *= inv_det; return 1; }

Last edited by Perspective; 01-18-2006 at 10:43 AM.

- 01-18-2006 #25

- Join Date
- Sep 2005
- Location
- I'm lost!!!
- Posts
- 200

Originally Posted by**Bubba**

Code:totalAngle += (acos(dot(v1, v2)) + acos(dot(v2, v3)) + acos(dot(v3, v1)));

Originally Posted by**BobMcGee123**Last edited by hdragon; 01-18-2006 at 09:26 PM.

Hello, testing testing. Everthing is running perfectly...for now

- 01-18-2006 #26
>>

I meant like this, I use a vector Pos, which i put in the glTranslatef() for testing. So all it does is check the Pos coordinate (x, y, z). Then i draw a triangle moved by the Pos coordinates. So, when i have more than one triangle, what point should i check so that all the triangle of the model can determine if it is inside/hit another objects.

<<

Well, I didn't post the question but anywho...

You can ray trace against every triangle in the model, you can ray trace against a bounding volume of the model, or you can use a space partitioning algorithm to determine which triangles are in the same volume of space as your ray and test the triangles in that volume.

Those 3 options range from easy to difficult while simultaniously ranging from innefficient to efficient

- 01-18-2006 #27

- Join Date
- Sep 2005
- Location
- I'm lost!!!
- Posts
- 200

That was suppose to be Bob, i messed up.

Anyway, if i ray trace every triangle of a model, it would be slow right?

About the bounding volume, if my model is really complex (curve, rectangles, all kind of stuff that make it look complex), do i have to find the center of the model? If the model is an aircraft with 2 wings on the side, would the bounding volume will make it look realistic.

The partitioning algorithm is something i have no idea, could you talk about it more.Hello, testing testing. Everthing is running perfectly...for now

- 01-18-2006 #28

- Join Date
- May 2005
- Posts
- 964

I think he means something along the lines of checking whether or not two objects are even close to each other whatsoever...

If not they don't need to check collision between each other, saving valuable computation time .

How to do it? You could just as well ask a monkey for the answer :d.Sometimes I forget what I am doing when I enter a room, actually, quite often.

- 01-19-2006 #29

- Join Date
- Sep 2005
- Location
- I'm lost!!!
- Posts
- 200

Originally Posted by**Shamino**Hello, testing testing. Everthing is running perfectly...for now

- 01-19-2006 #30
Well you could probably use an octree. Each leaf in the tree holds the vertices for that volume and each leaf is responsible for drawing itself. I'm not sure how to do this in a raytracer except that you wouldn't ray-intersect test any of the tri's in a leaf unless it passed certain tests.

I have very little experience with pure ray-tracing but I'm very experienced with ray-casting and vertical ray coherence. However ray-tracing is a whole nuther ball game since you basically are tracing a ray of light through pixel at x,y to completion.

I hope you get it working because I'm looking forward to seeing the final result.

Also a curve is simply a ray-to-sphere intersection test and you would want to break down the geometry into vertices if the sphere passed the test. Again I'm pretty much in the dark here with little experience in ray-tracing.

- Exactly how to get started with C++ (or C) today
- C Tutorial
- C++ Tutorial
- 5 ways you can learn to program faster
- The 5 Most Common Problems New Programmers Face
- How to set up a compiler
- 8 Common programming Mistakes
- What is C++11?
- Creating a game, from start to finish

- How to create a shared library on Linux with GCC - December 30, 2011
- Enum classes and nullptr in C++11 - November 27, 2011
- Learn about The Hash Table - November 20, 2011
- Rvalue References and Move Semantics in C++11 - November 13, 2011
- C and C++ for Java Programmers - November 5, 2011
- A Gentle Introduction to C++ IO Streams - October 10, 2011