-
- /* orthonormal basis */
- Vec3 vk = hair[i].spawn_dir;
- Vec3 vi = Vec3(1, 0, 0);
- if(fabs(vk.x > 0.99)) {
- vi = Vec3(0, -1, 0);
- }
- Vec3 vj = normalize(cross(vk, vi));
- vi = cross(vj, vk);
-
- /* identity when the hair points to the z axis */
- Mat4 basis = Mat4(vi, vj, vk);
-
- for(int j=0; j<3; j++) {
- float angle = (float)j / 3.0 * 2 * M_PI;
- /* dir of each anchor relative to hair root */
- Vec3 dir = Vec3(cos(angle), sin(angle), 0);
- dir = basis * dir;
- hair[i].anchor_dirs[j] = hair[i].pos + dir - hair[i].spawn_pt;
- }