Ok, after a while, i figured out the theory about collision detection/ray tracing.

For each triangle, i set a plane normal for it and declared 3 vector points.

Then i create an object vector3d point, as well as velocity.

so this is how it goes:

Code:

struct Plane
{
vect3 Normal;
}
Plane pl;
vect3 Pos, velocity; //position and velocity of player object
vect3 IP; //intersection point;
vect3 p1, p2, p3; //3 points for the triangle
double Dplane;

Then I calculate the distance of the vector to the plane (which will be the triangle i created using p1, p2, p3)

Code:

double DistRayPlane(vect3& Origin, vect3& velocity, vect3& PlaneNormal, double& D)
{
double Delta;
double cosAlpha = dot(velocity, PlaneNormal);
if(cosAlpha == 0) return -1.0; //when it is parallel, do nothing
Delta = D - (dot(Origin, PlaneNormal));
return (Delta/cosAlpha);
}

After that, here will be another function to determine if the Pos vector will be inside the triangle (p1, p2, p3) at the IP point.

Code:

bool PointInTriangle(vect3& Point, vect3& v1, vect3& v2, vect3& v3)
{
double Angle;
vect3 vt1 = NormalizeVect(Point - v1);
vect3 vt2 = NormalizeVect(Point - v2);
vect3 vt3 = NormalizeVect(Point - v3);
Angle = (acos(dot(vt1, vt2))+ acos(dot(vt2, vt3)) + acos(dot(vt3, vt1)));
if(fabs(Angle - 2*PI) < EPSILON)
return true;
else
return false;
}

So this is all set...I think. All i have to do is calculate the direction of the object, then check to see if it is inside the triangle or not when the IP hit the plane.

in the InitGL i set the value for the vectors

Code:

pl.Normal = vect3(-1, 0, 0);
Pos = vect3(0, 0, -50);
velocity = vect3(1, 0, 0);
p1 = vect3(0, 10, -45);
p2 = vect3(0, -10, -40);
p3 = vect3(0, -10, -50);
Dplane = 1;

Then, in the draw function i set up the triangle and set normal for everything i needed to.

Code:

glLoadIdentity();
glTranslatef(10, 0, 0);
glBegin(GL_TRIANGLES);
glColor3f(1, 1, 1);
glNormal3f(-1, 0, 0);
glVertex3d(p1.x, p1.y, p1.z);
glVertex3d(p2.x, p2.y, p2.z);
glVertex3d(p3.x, p3.y, p3.z);
glEnd();
//then draw the rectangle
glLoadIdentity();
glTranslated(Pos.x, Pos.y, Pos.z);
glBegin(GL_QUADS);
glColor3f(1, 0, 0);
glVertex3f(1, 1, 0);
glVertex3f(-1, 1, 0);
glVertex3f(-1, -1, 0);
glVertex3f(1, -1, 0);
glEnd();
double dist = distRayPlane(Pos, velocity, pl.Normal, Dplane);
if(dist > 0)
{
if(dist < distRayPlane(Pos, velocity, pl.Normal, Dplane))
{
IP = Pos + velocity*dist;
if(VertexTriangle(IP, p1, p2, p3))
{
//collision
}
}
}

So when the distance is bigger than 0 and the distance is still smaller than the distance the object has to travel, the Intersection point will be add in. And when the IP point is inside the triangle, collision will occurs.

Well, the problem is it did not work. The object goes right through the triangle. Did i do something wrong or my calculation is wrong?