From: Olivier Andrieu <andrieu at ijm.jussieu.fr>
Message-ID: <16278.44802.299222.468101 at akasha.ijm.jussieu.fr>
Date: Wed, 22 Oct 2003 18:23:30 +0200
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To: Richard Jones <rich at annexia.org>
Cc: lablgtk at kaba.or.jp
Subject: Re: Crashing bug in lablgtk2 2.2.0 when reading image from pixmap (Windows only)
In-Reply-To: <20031021161441.GD5277 at redhat.com>
References: <20031021123817.GA5277 at redhat.com>
	<20031021124207.GB5277@redhat.com>
	<20031021124824.GC5277@redhat.com>
	<16277.22158.816434.308669@akasha.ijm.jussieu.fr>
	<20031021161441.GD5277@redhat.com>


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 Richard Jones [Tuesday 21 October 2003] :
 > > For accessing the pixel values I think you should definitively use
 > > pixbufs and the get_pixels function :
 > > 
 > >   val get_pixels : pixbuf -> Gpointer.region
 > 
 > So I changed the program now to copy the drawable into a pixbuf and
 > access the data as you suggest. It now works.
 > 
 > However I did come across a strangeness. Our code looks like this,
 > where width = 800 and height = 600.
 > 
 >       self#paint_drawable (pixmap :> GDraw.drawable) width height;
 > 
 >       (* Create a pixbuf (client side) from the drawable. *)
 >       let pb = GdkPixbuf.create ~width ~height ~has_alpha:false ~bits:8
 > 		 ~colorspace:`RGB () in
 >       GdkPixbuf.get_from_drawable ~dest:pb (pixmap#pixmap);
 > 
 >       (* Get a pointer to the pixels. *)
 >       let ptr = GdkPixbuf.get_pixels pb in
 > 
 >       let length = Gpointer.length ptr in
 > 
 > At this point, length = 1438400, which is 1600 bytes short of what
 > it should be.

Yeah, this one's a bug in lablgtk.

-- 
   Olivier

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Index: src/gdkPixbuf.ml
===================================================================
RCS file: /staff2/garrigue/repos/lablgtk/src/gdkPixbuf.ml,v
retrieving revision 1.6
diff -u -r1.6 gdkPixbuf.ml
--- src/gdkPixbuf.ml	6 Aug 2003 00:12:39 -0000	1.6
+++ src/gdkPixbuf.ml	22 Oct 2003 16:20:36 -0000
@@ -34,7 +34,7 @@
 let get_pixels pixbuf =
   let obj, pos = _get_pixels pixbuf in
   let get_length (_, pixbuf) =
-    get_rowstride pixbuf * (get_height pixbuf - 1) + get_width pixbuf + pos
+    get_rowstride pixbuf * (get_height pixbuf - 1) + (get_width pixbuf * get_n_channels pixbuf) + pos
   in
   let r =
     Gpointer.unsafe_create_region ~path:[|0|] ~get_length (obj, pixbuf) in

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