val accum : op:[ `accum | `add | `load | `mult | `return ] -> float -> unit
val alpha_func : Gl.cmp_func -> ref:Gl.clampf -> unit
type sfactor =
    [ `dst_alpha
    | `dst_color
    | `one
    | `one_minus_dst_alpha
    | `one_minus_dst_color
    | `one_minus_src_alpha
    | `src_alpha
    | `src_alpha_saturate
    | `zero ]
type dfactor =
    [ `dst_alpha
    | `one
    | `one_minus_dst_alpha
    | `one_minus_src_alpha
    | `one_minus_src_color
    | `src_alpha
    | `src_color
    | `zero ]
val blend_func : src:sfactor -> dst:dfactor -> unit
val color_mask :
  ?red:bool -> ?green:bool -> ?blue:bool -> ?alpha:bool -> unit -> unit
val depth_func : Gl.cmp_func -> unit
val depth_mask : bool -> unit
val depth_range : near:float -> far:float -> unit
val index_mask : int -> unit
val stencil_func : Gl.cmp_func -> ref:int -> mask:int -> unit
val stencil_mask : int -> unit
type stencil_op = [ `decr | `incr | `invert | `keep | `replace | `zero ]
val stencil_op :
  ?fail:stencil_op -> ?zfail:stencil_op -> ?zpass:stencil_op -> unit -> unit
type logic_op =
    [ `And
    | `Or
    | `and_inverted
    | `and_reverse
    | `clear
    | `copy
    | `copy_inverted
    | `equiv
    | `invert
    | `nand
    | `noop
    | `nor
    | `or_inverted
    | `or_reverse
    | `set
    | `xor ]
val logic_op : logic_op -> unit
type draw_buffer =
    [ `aux of int
    | `back
    | `back_left
    | `back_right
    | `front
    | `front_and_back
    | `front_left
    | `front_right
    | `left
    | `none
    | `right ]
val draw_buffer : draw_buffer -> unit
type read_buffer =
    [ `aux of int
    | `back
    | `back_left
    | `back_right
    | `front
    | `front_left
    | `front_right
    | `left
    | `right ]
val read_buffer : read_buffer -> unit