Function check_point_to_face

physics/findintersection.cpp:1093–1166

see if a point in inside a face by projecting into 2d

// see if a point in inside a face by projecting into 2d
uint32_t check_point_to_face(vector *colp, vector *face_normal, int nv, vector **vertex_ptr_list) {
  vector_array *colp_array; // Axis-independant version of the collision point
  vector_array *norm;       // Axis-independant version of the plane's normal
  vector t;                 // Temporary vector that holds the magnatude of the normal's x,y,z components (ABS)
  int biggest;              // Index of the largest of the three components (0-x, 1-y, 2-z)  Axis to ignore :)
  int i, j, edge;           // Index for i-axis, Index for j-axis, and the current edge
  uint32_t edgemask;        // Bit-field for which side we are outside of
  float check_i, check_j;   // (i,j) checkpoint for 2d in/out test
  vector_array *v0, *v1;    // Vertices of the current line segment in the 2d in/out check loop

  // Lets look at these vectors as arrays :)
  norm = (vector_array *)face_normal;
  colp_array = (vector_array *)colp;

  // now do 2d check to see if point is in side

  // Get x,y,z components of the normal and put them in array form (so we can pick any two for i,j)
  t.x = fabs(norm->xyz[0]);
  t.y = fabs(norm->xyz[1]);
  t.z = fabs(norm->xyz[2]);

  // Determine which axis will be normal to the plane the points are projected onto
  if (t.x > t.y)
    if (t.x > t.z)
      biggest = 0;
    else
      biggest = 2;
  else if (t.y > t.z)
    biggest = 1;
  else
    biggest = 2;

  // For a plane with a normal that is in the opposite direction of the axis,
  // we should circle the other direction -- i.e. always circle in clockwise direction with normal (left-handed)
  if (norm->xyz[biggest] > 0) {
    i = ij_table[biggest][0];
    j = ij_table[biggest][1];
  } else {
    i = ij_table[biggest][1];
    j = ij_table[biggest][0];
  }

  // now do the 2d problem in the i,j plane

  // Get the i,j check point
  check_i = colp_array->xyz[i];
  check_j = colp_array->xyz[j];

  // Do a simple 2d cross-product between each line segment and the start point to the check point
  // Go in a clockwise direction, if determinant is negative then point is outside of this multi-
  // side polygon.  :)  Only works for concave polygons.
  for (edge = edgemask = 0; edge < nv; edge++) {
    vec2d edgevec, checkvec;
    float d;

    // v0 = (vector_array *)&Vertices[vertex_list[facenum*3+edge]];
    // v1 = (vector_array *)&Vertices[vertex_list[facenum*3+((edge+1)%nv)]];
    v0 = (vector_array *)vertex_ptr_list[edge];