3d object to screen(vec_for_screen)

I would like this>
1object (3d cylinder) in screen ,as part of my HUD. but when iam moving cylinder not rotating corectly (i tried vec_for_screen)

temp.x =500; (x_pos in screen)
temp.y =50; (y_pos in screen)
temp.z = 8; (i dont understand this parameter ,because if i want to use 2D)
vec_for_screen(temp,CAMERA);
vec_Set(object.x,temp);(set vectors)

but what you mean "not rotating corectly"
temp.x and temp.y are 2d coordinates (on screen position)
temp.z is the distance from camera to point in 3d world.

iam add this

vec_set(temp,camera.x);
vec_sub(temp,rad.x);
vec_to_angle(rad.pan,temp);

now is correct ,but when i moving mouse.y my cylined still rotating (panning)
maybe i post video