interpretor/lib/src/libsndfile-ocaml/Todo.txt

   1
   2 Look at Bigarray module:
   3
   4         http://caml.inria.fr/pub/docs/manual-ocaml/manual043.html
   5         http://pauillac.inria.fr/cdrom/www/caml/ocaml/htmlman/manual042.html
   6         http://jhenrikson.org/forklift/checkout/doc/higher_order.html
   7
   8 From :
   9
  10         http://webcvs.freedesktop.org/cairo/cairo-ocaml/test/basket.ml?revision=1.7&view=markup
  11
  12  begin
  13     prerr_endline "Bigarray, PPM and PNG (ARGB32) " ;
  14     let arr =
  15       Bigarray.Array2.create Bigarray.int32 Bigarray.c_layout
  16         (int_of_float y_inches * 72) (int_of_float x_inches * 72) in
  17     Bigarray.Array2.fill arr 0xffffffl ;
  18     let s = Cairo_bigarray.of_bigarr_32 ~alpha:true arr in
  19     let c = Cairo.create s in
  20     draw c ;
  21     do_file_out "basket.ppm"
  22       (fun oc -> Cairo_bigarray.write_ppm_int32 oc arr) ;
  23     Cairo_png.surface_write_to_file s "basket.png"
  24   end
  25
  26
  27 ===========================================================================
  28
  29 Actually many scientific OCaml libraries use the bigarray module.  It
  30 is also the case of Lacaml (a binding to LAPACK) or FFTW (a binding
  31 to, hum, FFTW!).
  32
  33 Now I do not understand why you could not have a function
  34
  35   val read_array1 : t -> ('a,'b,'c) Bigarray.Array1.t -> int
  36
  37   Sndfile.read_array1 f a read data from the file f into the supplied
  38   bigarray a and return the number of float values read.
  39
  40   For multi-channel files, the array length must be an integer
  41   multiple of the number of channels.
  42
  43 The idea is that the read function adapts the type of the bigarray
  44 passed (if possible; if not, raise an exception).  One could also
  45 require that a Bigarray.Array2.t is used with one of its dimensions
  46 being the number of channels (if possible allowing easy slicing to
  47 extract a given channel).
  48
  49 Same goes for a write function.
  50
  51 BTW, the last part of the comment is a bit laconic: one wonders "or
  52 what ?".  An exception is raised ?  The array slots with higher
  53 indexes are never filled ?  Garbage can be returned ? etc.
  54
  55 > I was particularly interested if there was any utility to providing
  56 > functions for accessing shorts or ints. So far noone has come up
  57 > with a need for these.
  58
  59 I did not follow thoroughly the discussion but there is an Int32
  60 module and the C interface has "Int32_val(v)" and "Int64_val(v)".  To
  61 create a caml Int32.t (resp. Int64.t), you must allocate a custom
  62 block containing an "int32" (resp. int64).  See section 18 of the
  63 manual.
  64
  65
  66
  67 ===========================================================================
  68
  69
  70 (* cairo_bigarray.mli *)
  71 (*
  72
  73 open Bigarray
  74
  75 val of_bigarr :
  76   ('a, 'b, c_layout) Array2.t -> Cairo.format ->
  77   width:int -> height:int -> stride:int -> Cairo.image_surface
  78
  79 val of_bigarr_32 : alpha:bool -> (int32, int32_elt, c_layout) Array2.t -> Cairo.image_surface
  80 val of_bigarr_24 : (int, int_elt, c_layout) Array2.t -> Cairo.image_surface
  81 val of_bigarr_8  : (int, int8_unsigned_elt, c_layout) Array2.t -> Cairo.image_surface
  82
  83 val write_ppm_int32 : out_channel -> (int32, int32_elt, c_layout) Array2.t -> unit
  84 val write_ppm_int   : out_channel -> (int,   int_elt,   c_layout) Array2.t -> unit
  85
  86 *)
  87
  88
  89
  90
  91
  92 (* cairo_bigarray.ml *)
  93 (*
  94
  95 open Bigarray
  96
  97 external bigarray_kind_float : ('a, 'b, c_layout) Array2.t -> bool
  98   = "ml_bigarray_kind_float"
  99 external bigarray_byte_size  : ('a, 'b, c_layout) Array2.t -> int
 100   = "ml_bigarray_byte_size"
 101
 102 external image_surface_create :
 103   ('a, 'b, c_layout) Array2.t ->
 104   Cairo.format -> width:int -> height:int -> stride:int ->
 105   Cairo.image_surface = "ml_cairo_image_surface_create_for_data"
 106
 107
 108 let of_bigarr arr format ~width ~height ~stride =
 109   if bigarray_kind_float arr
 110   then invalid_arg "wrong Bigarray kind" ;
 111   if bigarray_byte_size arr < stride * height
 112   then invalid_arg "Bigarray too small" ;
 113   image_surface_create arr format width height stride
 114
 115 let of_bigarr_32 ~alpha (arr : (int32, int32_elt, c_layout) Array2.t) =
 116   let h = Array2.dim1 arr in
 117   let w = Array2.dim2 arr in
 118   of_bigarr arr
 119     (if alpha then Cairo.FORMAT_ARGB32 else Cairo.FORMAT_RGB24)
 120     w h (4 * w)
 121
 122 let of_bigarr_24 (arr : (int, int_elt, c_layout) Array2.t) =
 123   if Sys.word_size <> 32
 124   then failwith "your ints have 63 bits" ;
 125   let h = Array2.dim1 arr in
 126   let w = Array2.dim2 arr in
 127   of_bigarr arr
 128     Cairo.FORMAT_RGB24
 129     w h (4 * w)
 130
 131 let of_bigarr_8 (arr : (int, int8_unsigned_elt, c_layout) Array2.t) =
 132   let h = Array2.dim1 arr in
 133   let w = Array2.dim2 arr in
 134   of_bigarr arr
 135     Cairo.FORMAT_A8
 136     w h w
 137
 138 let output_pixel oc p =
 139   let r = (p lsr 16) land 0xff in
 140   output_byte oc r ;
 141   let g = (p lsr 8) land 0xff in
 142   output_byte oc g ;
 143   let b = p land 0xff in
 144   output_byte oc b
 145
 146 let write_ppm_int32 oc (arr : (int32, int32_elt, c_layout) Array2.t) =
 147   let h = Array2.dim1 arr in
 148   let w = Array2.dim2 arr in
 149   Printf.fprintf oc "P6 %d %d 255\n" w h ;
 150   for i=0 to pred h do
 151     for j=0 to pred w do
 152       output_pixel oc (Int32.to_int arr.{i, j})
 153     done
 154   done ;
 155   flush oc
 156
 157 let write_ppm_int oc (arr : (int, int_elt, c_layout) Array2.t) =
 158   let h = Array2.dim1 arr in
 159   let w = Array2.dim2 arr in
 160   Printf.fprintf oc "P6 %d %d 255\n" w h ;
 161   for i=0 to pred h do
 162     for j=0 to pred w do
 163       output_pixel oc arr.{i, j}
 164     done
 165   done ;
 166   flush oc
 167
 168 *)