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Newbie
Join Date: Apr 2005
Posts: 1
Rep Power: 0 
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Separating Axis Test. Desperate for help
Hey :-)
Basically, i'm at the end of my tether while trying to get this thing to work. I've tried everything I can think of, and I just can't get it to work. I understand what the test does, and how it works, but when coding it, it just won't do what I want. I can get it to test correctly if two boxes are axis aligned, but as soon as they are oriented, it won't work.
I will follow with my code
This is where the OBB is updated. Its extent and edge vectors are set.
void drawBox()
{
glPushMatrix();
glColor3f(1.0,1.0,1.0);
center.x = center.x + dMove*cos(PI/2+turn1*PI/180.0);
center.y = center.y + dMove*sin(PI/2+turn1*PI/180.0);
glTranslatef(center.x, center.y, center.z);
glRotatef(turn1,0.0,0.0,1.0);
glRotatef(turn2,0.0,1.0,0.0);
//Rotation Vector
Vec3d temp;
temp.Set(0, turn2, turn1);
//Sets extremity vector and edge vectors
extrem.Set(center.x+width/2, center.y+height/2, center.z+depth/2);
edgeX.Set(center.x+width/2, center.y, center.z);
edgeY.Set(center.x, center.y+height/2, center.z);
edgeZ.Set(center.x, center.y, center.z+depth/2);
//Rotates those vectors with the box
extrem.Rotate(center.xyz,temp);
edgeX.Rotate(center.xyz,temp);
edgeY.Rotate(center.xyz,temp);
edgeZ.Rotate(center.xyz,temp);
glScalef(width, height, depth);
glutWireCube(1);
glPopMatrix();
}
This is where the test is performed. Anything with 'this' is the local box (BOX A) and anything with 'box' is the passed in box (BOX B).
bool checkCollision(OBB *box)
{
Vec3d CA;
Vec3d CB;
Vec3d L;
Vec3d centerB, Labs;
//Extent Vectors of Boxes relative to their local axis
CA.Set(this->extrem-this->center);
CB.Set(box->extrem-box->center);
centerB.Set(box->center-this->center);
for (int i = 0; i < 3; ++i)
{
//The 3 edge vectors of the box A (anything with 'this' is box A)
if(i == 0)
{
L.Set(this->edgeX-this->center);
}
else if( i == 1)
{
L.Set(this->edgeY-this->center);
}
else if(i == 2)
{
L.Set(this->edgeZ-this->center);
}
L.Normalize();
//|L|
Labs.Set(fabs(L.x), fabs(L.y), fabs(L.z));
float min1 = L.Dot(this->center-this->center) - Labs.Dot(CA);
float max1 = L.Dot(this->center-this->center) + Labs.Dot(CA);
float min2 = L.Dot(centerB) - Labs.Dot(CB);
float max2 = L.Dot(centerB) + Labs.Dot(CB);
float d0 = min1 - max2;
float d1 = min2 - max1;
if(d0>0 || d1>0)
{
return false;
}
//Edge vectors of box B (anything with 'box->' is box B)
if(i == 0)
{
L.Set((box->edgeX-box->center+centerB));
}
else if( i == 1)
{
L.Set((box->edgeY-box->center+centerB));
}
else if(i == 2)
{
L.Set((box->edgeZ-box->center+centerB));
}
L.Normalize();
Labs.Set(fabs(L.x), fabs(L.y), fabs(L.z));
min1 = L.Dot(this->center-this->center) - Labs.Dot(CA);
max1 = L.Dot(this->center-this->center) + Labs.Dot(CA);
min2 = L.Dot(centerB) - Labs.Dot(CB);
max2 = L.Dot(centerB) + Labs.Dot(CB);
d0 = min1 - max2;
d1 = min2 - max1;
if(d0>0 || d1>0)
{
return false;
}
}
// and now for the cross product axes
for (int i = 0; i < 3; ++i)
{
if(i == 0)
{
L.Set(this->edgeX-this->center);
}
else if( i == 1)
{
L.Set(this->edgeY-this->center);
}
else if(i == 2)
{
L.Set(this->edgeZ-this->center);
}
for (int j = 0; j < 3; ++j)
{
Vec3d temp3;
if(j == 0)
{
temp3.Set((box->edgeX-box->center+centerB));
L.Set(L.Cross(temp3));
}
else if( j == 1)
{
temp3.Set((box->edgeY-box->center+centerB));
L.Set(L.Cross(temp3));
}
else if(j == 2)
{
temp3.Set((box->edgeZ-box->center+centerB));
L.Set(L.Cross(temp3));
}
L.Normalize();
Labs.Set(fabs(L.x), fabs(L.y), fabs(L.z));
float min1 = L.Dot(this->center-this->center) - Labs.Dot(CA);
float max1 = L.Dot(this->center-this->center) + Labs.Dot(CA);
float min2 = L.Dot(centerB) - Labs.Dot(CB);
float max2 = L.Dot(centerB) + Labs.Dot(CB);
float d0 = min1 - max2;
float d1 = min2 - max1;
if(d0>0 || d1>0)
{
return false;
}
}
}
return true;
}
Now, I know this may sound annoying or whatever, but I don't want references or anything to websites or vague descriptions of how the test works, because I have checked every website I can find, and spent hours trying lots of different things to get this test to work. I have Van Den Bergens 'Collision detection in interactive 3d environments' which is where I got the theory from, and I think I understand it.
I really just need help with this code and getting it to work. PLEASE, i'm seriously desperate :-) |