Date: Tue, 21 Oct 2003 17:14:41 +0100
To: Olivier Andrieu <andrieu at ijm.jussieu.fr>
Cc: lablgtk at kaba.or.jp
Subject: Re: Crashing bug in lablgtk2 2.2.0 when reading image from pixmap (Windows only)
Message-ID: <20031021161441.GD5277 at redhat.com>
References: <20031021123817.GA5277 at redhat.com> <20031021124207.GB5277 at redhat.com> <20031021124824.GC5277 at redhat.com> <16277.22158.816434.308669 at akasha.ijm.jussieu.fr>
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In-Reply-To: <16277.22158.816434.308669 at akasha.ijm.jussieu.fr>
From: Richard Jones <rich at annexia.org>

On Tue, Oct 21, 2003 at 05:53:50PM +0200, Olivier Andrieu wrote:
>  Richard Jones [Tuesday 21 October 2003] :
>  >
>  > 
>  > OK, ignore the previous version. Here is a much more minimal way to
>  > reproduce the bug. After compiling & running it, click on the button a
>  > few times and notice the console error messages.
> 
> which GTK+ version are you using ? In the NEWS file of GTK+-2.2.4
> there's :
> 
> * Win32
>  - Fix GdkImage memory leak
> 
> might fix your pb.

We're using 2.2.2, so this might be the problem.

> On a side note, I don't know how GdkImage and GdkPixmap are
> implemented on Windows but on Unix your program is a bit weird : you
> have a client-side pixel buffer (pixbuf), then you send it to the
> server (pixmap), then you send it back to the client (image) ...  

Yes, that's because this program is just a demonstration of the
bug. In reality our big program draws complex stuff into a drawable on
the "server" side, and then tries to copy this into an image on the
client side so it can write it out to a file.

> 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.

I worked around that ...

Rich.

-- 
Richard Jones. http://www.annexia.org/ http://freshmeat.net/users/rwmj
Merjis Ltd. http://www.merjis.com/ - all your business data are belong to you.
"I wish more software used text based configuration files!"
 -- A Windows NT user, quoted on Slashdot.