Function FindPointUV

Descent3/room.cpp:1027–1061

Finds the uv coords of a given point on a room:face. Fills in u & v. Parameters: u,v - pointers to variables to be filled in pnt - the point we're checking rp - pointer to the room that pnt is in fp - pointer to the face that pnt is on

//					rp - pointer to the room that pnt is in
//					fp - pointer to the face that pnt is on
void FindPointUV(float *u, float *v, const vector *pnt, const room *rp, const face *fp) {
  int roomnum = ROOMNUM(rp);
  int ii, jj;
  vector vec0, vec1;
  float *p1, *checkp, *v0, *v1;
  float k0, k1;
  int t;

  // Make sure we have a valid room
  ASSERT((roomnum >= 0) && (roomnum <= Highest_room_index));

  // Find what plane to project this wall onto to make it a 2d case
  GetIJ(&fp->normal, &ii, &jj);

  // Compute delta vectors
  vec0 = rp->verts[fp->face_verts[0]] - rp->verts[fp->face_verts[1]]; // vec from 1 -> 0
  vec1 = rp->verts[fp->face_verts[2]] - rp->verts[fp->face_verts[1]]; // vec from 1 -> 0

  // Get pointers to referece our vectors as arrays of floats
  p1 = (float *)&rp->verts[fp->face_verts[1]];
  v0 = (float *)&vec0;
  v1 = (float *)&vec1;
  checkp = (float *)pnt;

  // Compute our clipping values along i & j axes
  k1 = -(cross(checkp, v0) + cross(v0, p1)) / cross(v0, v1);
  t = (fabs(v0[ii]) > fabs(v0[jj])) ? ii : jj;
  k0 = ((-k1 * v1[t]) + checkp[t] - p1[t]) / v0[t];

  // Compute u & v values
  *u = fp->face_uvls[1].u + (k0 * (fp->face_uvls[0].u - fp->face_uvls[1].u)) +
       (k1 * (fp->face_uvls[2].u - fp->face_uvls[1].u));
  *v = fp->face_uvls[1].v + (k0 * (fp->face_uvls[0].v - fp->face_uvls[1].v)) +
       (k1 * (fp->face_uvls[2].v - fp->face_uvls[1].v));
}

// Check if a particular point on a wall is a transparent pixel
// Parameters:	pnt - the point we're checking