Bounding Box Collision...not working

Iv'e attempted to add bounding box collision detection to my engine, and it compiles properly (which is farther than I got yesterday), but its not working. It calculates a bounding box for every object (3DS) loaded, and passes the min and max values to a struct array. The input functions then call a loop function when a key is pressed, that cycles through all the bounding boxes, and tests to see if the camera is inside them. If not, the camera can move, if so, don't move the camera. The problem: it dosn't recognize that the camera is in the bounding box for some reason.

Heres some code to aid the explination:

collision.cpp:

Code:

---

extern CCamera gCam;

boundingbox boxP[MAX_OBJECTS];
int num_boxes = 0;

collision::collision()
{
}

collision::~collision()
{
}

char collision::createBbox(float cx, float cy, float cz,
                                                  float minx, float miny, float minz,
                                                  float maxx, float maxy, float maxz)
{
        boxP[num_boxes].min.x = minx+cx;
        boxP[num_boxes].min.y = miny+cy;
        boxP[num_boxes].min.z = minz+cz;

        boxP[num_boxes].max.x = maxx+cx;
        boxP[num_boxes].max.y = maxy+cy;
        boxP[num_boxes].max.z = maxz+cz;

        num_boxes++;
        return (1);
}

bool collision::onBboxCollision(float x, float y, float z,
                                                            float minx, float miny, float minz,
                                                            float maxx, float maxy, float maxz)
{
        if (x > minx)
                return false;
        if (x < maxx)
                return false;

        if (y > miny)
                return false;
        if (y < maxy)
                return false;

        if (z> minz)
                return false;
        if (z < maxz)
                return false;

        return true;
}

int collision::loop(float x, float y, float z)
{
        for (int i = 0; i<num_boxes; i++)
        {
                if(onBboxCollision(x, y, z,
                                                  boxP[i].min.x, boxP[i].min.y, boxP[i].min.z,
                                                  boxP[i].max.x, boxP[i].max.y, boxP[i].max.z)==1)
                {
                        return (i);
                }
        }
        return (-1);
}

---

input.cpp (snippet):

Code:

---

void Input::CheckForInput(float speed)
{
        if(GetKeyState('W') & 0x80){
                if(_peCollision->loop(gCam.m_vView.x, gCam.m_vView.y, gCam.m_vView.z)==!-1)exit(0);
        else if(_peCollision->loop(gCam.m_vView.x, gCam.m_vView.y, gCam.m_vView.z)==-1)gCam.MoveCamera(speed);}
       
        if(GetKeyState('S') & 0x80){ if(_peCollision->loop(gCam.m_vPosition.x, gCam.m_vPosition.y, gCam.m_vPosition.z)==-1)gCam.MoveCamera(-speed); }
       
        if(GetKeyState('A') & 0x80){ /*if(_peCollision->loop()==1)*/gCam.StrafeCamera(-speed); }
       
        if(GetKeyState('D') & 0x80){ /*if(_peCollision->loop()==1)*/gCam.StrafeCamera(speed); }
       
       
       
        if(GetKeyState('O') &0x80){ ShowCursor(false); }

        if(GetKeyState('P') &0x80){        ShowCursor(true); }
}

---

Please help if you can. Let me know if I didn't give enough information.

thanx,
-psychopath

I have only looked at your code briefly, but I think you use the wrong operator for comparison (assuming I read the code correctly).

Assuming maxx - minx describes the length of the box on the x-axis, then the camera is outisde the box if it's x-coordinate is less than minx or greater than maxx. You return false if the x-coord is larger than minx or smaller than maxx, which would suggest it might just lie inside the box. Same with the other axes.

Another thing I noticed, you have an if statement that looks something like this:

Code:

---

if(/*stuff*/ == !-1)

---

As !-1 == 0, what you probably want is:

Code:

---

if(/*stuff*/ != -1)

---

Also, some things you might want to remember:

Code:

---

// This...
if(foo() != -1)
  do_stuff();

if(foo() == -1)
  do_other_stuff();

// ...yields the same results as this (as long as 'foo' doesn't rely on anything but the arguments when returning a value)
if(foo() != -1)
  do_stuff();

else
  do_other_stuff();

// This...
if(foo() == 1)
  stuff1();
else if(foo() == 2)
  stuff2();
else
  stuff3();

// ...is the same as:
int f = foo();
if(f == 1)
  stuff1();
else if(f == 2)
  stuff2();
else
  stuff3();

---

These two examples are especially important to remember if 'foo' is an expensive call or if the code is located in the inner loop of a critical section.

Iv'e made some changes, and now, instead of not colliding, it thinks i'm always colliding!?

heres the modified code:

Code:

---

bool collision::onBboxCollision(float x, float y, float z,
                                                            float minx, float miny, float minz,
                                                            float maxx, float maxy, float maxz)
{
        if (x > minx | x < maxx|
                y > miny | y < maxy|
                z > minz | z < maxz)
                return true; //we collided
        else
                return false; //we didn't
}

int collision::loop(float x, float y, float z)
{
        for (int i = 0; i<num_boxes; i++)
        {
                if(onBboxCollision(x, y, z,
                                                  boxP[i].min.x, boxP[i].min.y, boxP[i].min.z,
                                                  boxP[i].max.x, boxP[i].max.y, boxP[i].max.z))
                {
                        return (i); //we collided
                }
                else
                        return (-1); //we didn't
        }
}

---

Code:

---

void Input::CheckForInput(float speed)
{
        if(GetKeyState('W') & 0x80)
        {
                if(_peCollision->loop(gCam.m_vView.x, gCam.m_vView.y, gCam.m_vView.z)>=0)
                        exit (0);
                else
                        gCam.MoveCamera(speed);
        }
       
        if(GetKeyState('S') & 0x80){ if(_peCollision->loop(gCam.m_vPosition.x, gCam.m_vPosition.y, gCam.m_vPosition.z)==-1)gCam.MoveCamera(-speed); }
       
        if(GetKeyState('A') & 0x80){ /*if(_peCollision->loop()==1)*/gCam.StrafeCamera(-speed); }
       
        if(GetKeyState('D') & 0x80){ /*if(_peCollision->loop()==1)*/gCam.StrafeCamera(speed); }
       
       
       
        if(GetKeyState('O') &0x80){ ShowCursor(false); }

        if(GetKeyState('P') &0x80){        ShowCursor(true); }
}

---

-psychopath

Code:

---

bool collision::onBboxCollision(float x, float y, float z,
                                                        float minx, float miny, float minz,
                                                        float maxx, float maxy, float maxz)
{
        if (x > minx | x < maxx|
                y > miny | y < maxy|
                z > minz | z < maxz)
                return true; //we collided
        else
                return false; //we didn't
}

---

Remember you want to use logical operators and not bitwise operators in this case. Also, you want to use AND not OR logical operator ( && instead of || ).

So your code may look something like:

Code:

---

bool collision::onBboxCollision(float x, float y, float z,
                                                        float minx, float miny, float minz,
                                                        float maxx, float maxy, float maxz)
{
  if (x > minx && x < maxx &&
      y > miny && y < maxy &&
      z > minz && z < maxz)
    return true; //we collided
  else
    return false; //we didn't
}

---

Ok, thanx. Iv'e gotten it to work somewhat, but the calculation of the bounding box objects needs to be fixed, but I think I can handle that on my own.

-psychopath