Message-ID: <433CF2BA.8030204 at irisa.fr>
Date: Fri, 30 Sep 2005 10:09:30 +0200
From: Sebastien Ferre <ferre at irisa.fr>
Organization: IRISA
MIME-Version: 1.0
To: Olivier Andrieu <oandrieu at nerim.net>, lablgtk at math.nagoya-u.ac.jp
Cc: =?ISO-8859-1?Q?S=E9bastien_Ferre?= <ferre at irisa.fr>
Subject: Re: GTree: delaying the computation of a pixbuf upon visibility
References: <43355ED4.5000004 at inria.fr>	<433A46AE.8000004 at irisa.fr> <17211.57896.40053.753344 at karryall.dnsalias.org>
In-Reply-To: <17211.57896.40053.753344 at karryall.dnsalias.org>
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Hi,

Olivier Andrieu wrote:
>  Sebastien Ferre [Wednesday 28 September 2005] :
>  >
>  > 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.
> 
> Why don't you use GdkPixbuf for this ? It can load JPEG pictures. 

this is what I used at the beginning. But I noticed there was something
like a memory leak as the process rapidly grew to more than 1Gb of
memory, while I checked the loaded images were no more reachable.
Also, CamlImages allows for loading directly a thumbnail from JPEG
pictures, which is lighter.

But if you know another way to do it directly with Lablgtk2, I am
quite interested.

>  > 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
> 
> I see you're doing a pixmap_of_image, ie you're sending your image to
> the server, then you do a GdkPixbuf.get_from_drawable, ie you're
> asking the server to send the image data back. And GTK will send the
> data to the server again when displaying the pixbuf. This doesn't seem
> very efficient.

I could not find a simpler way to do it. Is there a way to translate
directly an image to a 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.
> 
> But why don't you have a pixbuf column in you model ?
> I'd do it this way:

Well, my knowledge of the library is quite limited. All I can do
is scroll through the documentation, and guess the meaning of
methods and functions from their name and type. The given examples
are most helpful, but still limited...

>  - have a string column and a pixbuf column in your model

What type should I use for creating a pixbuf column ?

     let thumb_pixbuf = cols_extent#add ???

>  - setup the TreeViewColumn to display the pixbuf column with
>    CellRendererPixbuf
> 
>  - compute a small, fixed number of thumbnails (say, 10) and store
>    them in the pixbuf column of model
> 
>  - handle the rest of the thumbnailing in a Glib.Idle callback and
>    update the model as more thumbnails are completed.

Thank you! I will try this.

Sebastien