1
1) vertices of every mesh in the scene
2) normals of every mesh in the scene
3) the ray starting position
4) the ray direction
What does the general opengl coding look like for picking operations in my case?
I have the code from Recast, but I am not sure how to modify it to suit my needs.
bool intersectSegmentTriangle(const float* sp, const float* sq,
const float* a, const float* b, const float* c,
float &t)
{
float v, w;
float ab[3], ac[3], qp[3], ap[3], norm[3], e[3];
vsub(ab, b, a);
vsub(ac, c, a);
vsub(qp, sp, sq);
// Compute triangle normal. Can be precalculated or cached if
// intersecting multiple segments against the same triangle
vcross(norm, ab, ac);
// Compute denominator d. If d <= 0, segment is parallel to or points
// away from triangle, so exit early
float d = vdot(qp, norm);
if (d <= 0.0f) return false;
// Compute intersection t value of pq with plane of triangle. A ray
// intersects iff 0 <= t. Segment intersects iff 0 <= t <= 1. Delay
// dividing by d until intersection has been found to pierce triangle
vsub(ap, sp, a);
t = vdot(ap, norm);
if (t < 0.0f) return false;
if (t > d) return false; // For segment; exclude this code line for a ray test
// Compute barycentric coordinate components and test if within bounds
vcross(e, qp, ap);
v = vdot(ac, e);
if (v < 0.0f || v > d) return false;
w = -vdot(ab, e);
if (w < 0.0f || v + w > d) return false;
// Segment/ray intersects triangle. Perform delayed division
t /= d;
return true;
}
static bool raycast(rcMeshLoaderObj& mesh, float* src, float* dst, float& tmin)
{
float dir[3];
vsub(dir, dst, src);
int nt = mesh.getTriCount();
const float* verts = mesh.getVerts();
const float* normals = mesh.getNormals();
const int* tris = mesh.getTris();
tmin = 1.0f;
bool hit = false;
for (int i = 0; i < nt*3; i += 3)
{
const float* n = &normals[i];
if (vdot(dir, n) > 0)
continue;
float t = 1;
if (intersectSegmentTriangle(src, dst,
&verts[tris[i]*3],
&verts[tris[i+1]*3],
&verts[tris[i+2]*3], t))
{
if (t < tmin)
tmin = t;
hit = true;
}
}
return hit;
}
You see in this case there is a destination parameter involved. But general picking shouldn't care about the destination, should it?
Any thoughts?
Thanks
Jack
