-
-// Map a vector onto the plane specified by normal
-void map_vec_onto_cur_surface_plane(MAT3vec normal, MAT3vec v0, MAT3vec vec,
- MAT3vec result)
-{
- MAT3vec u1, v, tmp;
-
- // calculate a vector "u1" representing the shortest distance from
- // the plane specified by normal and v0 to a point specified by
- // "vec". "u1" represents both the direction and magnitude of
- // this desired distance.
-
- // u1 = ( (normal <dot> vec) / (normal <dot> normal) ) * normal
-
- MAT3_SCALE_VEC( u1,
- normal,
- ( MAT3_DOT_PRODUCT(normal, vec) /
- MAT3_DOT_PRODUCT(normal, normal)
- )
- );
-
- // printf(" vec = %.2f, %.2f, %.2f\n", vec[0], vec[1], vec[2]);
- // printf(" v0 = %.2f, %.2f, %.2f\n", v0[0], v0[1], v0[2]);
- // printf(" u1 = %.2f, %.2f, %.2f\n", u1[0], u1[1], u1[2]);
-
- // calculate the vector "v" which is the vector "vec" mapped onto
- // the plane specified by "normal" and "v0".
-
- // v = v0 + vec - u1
-
- MAT3_ADD_VEC(tmp, v0, vec);
- MAT3_SUB_VEC(v, tmp, u1);
- // printf(" v = %.2f, %.2f, %.2f\n", v[0], v[1], v[2]);
-
- // Calculate the vector "result" which is "v" - "v0" which is a
- // directional vector pointing from v0 towards v
-
- // result = v - v0
-
- MAT3_SUB_VEC(result, v, v0);
- // printf(" result = %.2f, %.2f, %.2f\n",
- // result[0], result[1], result[2]);
+// calculate the projection, p, of u along the direction of d.
+void sgProjection(sgVec3 p, const sgVec3 u, const sgVec3 d){
+ double denom = sgScalarProductVec3(d,d);
+ if (denom == 0.) sgCopyVec3(p, u);
+ else sgScaleVec3(p, d, sgScalarProductVec3(u,d) / denom);