90               GLfloat z0, GLfloat z1, GLfloat plane[4])  in compute_plane()
104    plane[0] = a;  in compute_plane()
105    plane[1] = b;  in compute_plane()
106    plane[2] = c;  in compute_plane()
107    plane[3] = d;  in compute_plane()
118       plane[0] = 0.0;  in compute_plane()
119       plane[1] = 0.0;  in compute_plane()
120       plane[2] = 1.0;  in compute_plane()
121       plane[3] = 0.0;  in compute_plane()
124       plane[0] = a;  in compute_plane()
125       plane[1] = b;  in compute_plane()
126       plane[2] = c;  in compute_plane()
127       plane[3] = d;  in compute_plane()
134 constant_plane(GLfloat value, GLfloat plane[4])  in constant_plane()
136    plane[0] = 0.0;  in constant_plane()
137    plane[1] = 0.0;  in constant_plane()
138    plane[2] = -1.0;  in constant_plane()
139    plane[3] = value;  in constant_plane()
144 solve_plane(GLfloat x, GLfloat y, const GLfloat plane[4])  in solve_plane()
146    const GLfloat z = (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];  in solve_plane()
158 solve_plane_recip(GLfloat x, GLfloat y, const GLfloat plane[4])  in solve_plane_recip()
160    const GLfloat denom = plane[3] + plane[0] * x + plane[1] * y;  in solve_plane_recip()
164       return -plane[2] / denom;  in solve_plane_recip()
172 solve_plane_chan(GLfloat x, GLfloat y, const GLfloat plane[4])  in solve_plane_chan()
174    const GLfloat z = (plane[3] + plane[0] * x + plane[1] * y) / -plane[2];  in solve_plane_chan()