Message-ID: <433A46AE.8000004 at irisa.fr>
Date: Wed, 28 Sep 2005 09:30:54 +0200
From: Sebastien Ferre <ferre at irisa.fr>
Organization: IRISA
MIME-Version: 1.0
To: lablgtk at math.nagoya-u.ac.jp
Subject: GTree: delaying the computation of a pixbuf upon visibility
References: <43355ED4.5000004 at inria.fr>
In-Reply-To: <43355ED4.5000004 at inria.fr>
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Hi,

I'm working on a GUI in which there is a 'GTree.list_store'
of thumbnails (look at http://www.irisa.fr/lande/ferre/camelis
for screen captions). I use the library CamlImages for computing
these thumbnails from JPEG pictures.

The problem is that computing these thumbnails is really slow.
For example it takes about 20s for 100 thumbnails, whereas only
a few are visible at one time. So I wonder if it is possible to
delay these computations upon the visibility of a row of the list
inside the scrolling window ? What I want is also to keep control on
the scrolling and selecting while thumbnails are being computed
and displayed.

Here is the code I use to build a pixbuf from a JPEG file. Can it be
made more efficient ?

     let pixbuf_of_jpeg =
       let ht = Hashtbl.create 100 in
       fun ~maxside filename ->
	try Hashtbl.find ht filename
	with Not_found ->
	  let spec = {
	    spec_width = Scale 0.2;
	    spec_height = Scale 0.2;
	    spec_aspect = Keep_at_most;
	    spec_switch = Smaller_only;
	    spec_x = 0;
	    spec_y = 0} in
	  let _, _, img = OJpeg.load_thumbnail filename [] spec in
	  let img = OImages.rgb24 img in
	  let w = img#width in
	  let h = img#height in
	  let scale = max maxside (max w h) / maxside in
	  let width = w / scale in
	  let height = h / scale in
	  let newimage = img#resize None width height in
	  let pixmap = OXimage2.pixmap_of_image (Gdk.Window.root_parent ()) 
None newimage#coerce in
	  let pixbuf = GdkPixbuf.create ~width ~height () in
	  GdkPixbuf.get_from_drawable ~dest:pixbuf pixmap#pixmap;
	  Hashtbl.add ht filename pixbuf;
	  pixbuf

And now, here is the code I use for building the list. In the model I
put the filename of the source picture, and in the view I use a
'cell_renderer_pixbuf' and redefine the cell_data_func.

     let cell_thumb = GTree.cell_renderer_pixbuf[]
     let col_thumb = GTree.view_column ~title:"Thumbnail" ()
	~renderer:(cell_thumb, [])
     let _ = col_thumb#set_sizing `AUTOSIZE
     let _ = col_thumb#set_cell_data_func
	cell_thumb
	(fun model iter ->
	  let colormap = Gdk.Color.get_system_colormap () in
	  let black = Gdk.Color.alloc ~colormap `BLACK in
	  let thumbname = model#get ~row:iter ~column:thumb in
	  try
	    if thumbname = "" then raise Not_found;
	    let pixbuf = pixbuf_of_jpeg ~maxside:150 thumbname in
	    let height = GdkPixbuf.get_height pixbuf in
	    let width = GdkPixbuf.get_width pixbuf in
	    cell_thumb#set_properties [`HEIGHT (height+20); `PIXBUF pixbuf; 
`VISIBLE true]
	  with _ -> cell_thumb#set_properties [`VISIBLE false])
      [...]
      let make_list nbobj =
         model_extent#clear;
	for oid=1 to nbobj do
	    let item = model_extent#append () in
	    model_extent#set ~row:item ~column:id oid;
             model_extent#set ~row:item ~column:thumb (file_of_oid oid);
	done

Thanks for your help,
Sebastien