[Caml-list] Why I cannot open a graph with a specific title

[Caml-list] Why I cannot open a graph with a specific title

[Andy Yang]

Hi, all

I found that with the following  code is OK:

open Graphics;;
let _ = open_graph "";;

However, if I set a title for a widnow

open Graphics;;
let _ = open_graph "hello";;

Ocaml will report "Fatal error: exception
Graphics.Graphic_failure("Cannot open display hello").

open_graph has a signature  string -> unit.


Thanks a lot!

Andy


		
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Re: [Caml-list] Why I cannot open a graph with a specific title

[Christophe TROESTLER]

On Mon, 28 Jun 2004, Andy Yang <yyu08@yahoo.com> wrote:
> 
> let _ = open_graph "hello";;
> Ocaml will report "Fatal error: exception
> Graphics.Graphic_failure("Cannot open display hello").

Please read the manual:

           open_graph "foo:0"  connects to the display foo:0 and creates a
             window with the default geometry 
           open_graph "foo:0 300x100+50-0"  connects to the display foo:0
             and creates a window 300 pixels wide by 100 pixels tall, at
             location (50,0) 
           open_graph " 300x100+50-0"  connects to the default display and
             creates a window 300 pixels wide by 100 pixels tall, at
             location (50,0) 
           open_graph ""  connects to the default display and creates a
             window with the default geometry. 

(this is specific to Unix).

Cheers,
ChriS

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Re: [Caml-list] Why I cannot open a graph with a specific title

[Matt Gushee]

On Mon, Jun 28, 2004 at 12:57:34PM -0700, Andy Yang wrote:
> 
> I found that with the following  code is OK:
> 
> open Graphics;;
> let _ = open_graph "";;
> 
> However, if I set a title for a widnow
> 
> open Graphics;;
> let _ = open_graph "hello";;
> 
> Ocaml will report "Fatal error: exception
> Graphics.Graphic_failure("Cannot open display hello").
> 
> open_graph has a signature  string -> unit.

Yes, and did you read what the manual says about that string? The string
is not supposed to be the window title. On X11, it's the the name of an
X display and/or a geometry specification. I'm not sure what it's
supposed to be on Win32 platforms.

Nonetheless, the behavior of open_graph leaves something to be desired.
For example,

  # open_graph " 400x600" (* Note the leading space. *);;
  - : unit = ()
  # open_graph "400x600";;      
  Exception: Graphics.Graphic_failure "Cannot open display 400x600".

So the function distinguishes a display name from a geometry spec by
whether there is a leading space? Yech. Maybe the signature should be

  open_graph : ?display:string -> ?geometry:string -> unit -> unit

And at least one of the following should work:

  # open_graph "0";;  
  Exception: Graphics.Graphic_failure "Cannot open display 0".
  # open_graph "0.0";;  
  Exception: Graphics.Graphic_failure "Cannot open display 0.0".
  # open_graph "localhost:0.0";;
  Exception: Graphics.Graphic_failure "Cannot open display localhost:0.0".
  # open_graph "127.0.0.1:0.0";;
  Exception: Graphics.Graphic_failure "Cannot open display 127.0.0.1:0.0".
  # open_graph "localhost:0";;
  Signal 13
  bash-2.05a$ 
  
Brilliant.

P.S. When asking questions of this sort, it would be helpful if you gave
  some information about your system, e.g. the platform and version of
  OCaml--especially with libraries like Graphics that have
  platform-dependent features.

-- 
Matt Gushee                 When a nation follows the Way,
Englewood, Colorado, USA    Horses bear manure through
mgushee@havenrock.com           its fields;
http://www.havenrock.com/   When a nation ignores the Way,
                            Horses bear soldiers through
                                its streets.
                                
                            --Lao Tzu (Peter Merel, trans.)

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Re: [Caml-list] Why I cannot open a graph with a specific title

[Matt Gushee]

On Mon, Jun 28, 2004 at 10:50:22PM +0200, Christophe TROESTLER wrote:
> 
> Please read the manual:
> 
>            open_graph "foo:0"  connects to the display foo:0 and creates a
>              window with the default geometry 

Okay, but can you explain why

  # open_graph "localhost:0";;

fails on my Linux box? If I do 

  $ xhost +localhost

before starting the OCaml toplevel, it raises an exception. If not, it
causes OCaml to die with Signal 13 (SIGPIPE).

I suppose it's redundant to specify "localhost:0," but I don't see a
good reason why it shouldn't work.

-- 
Matt Gushee                 When a nation follows the Way,
Englewood, Colorado, USA    Horses bear manure through
mgushee@havenrock.com           its fields;
http://www.havenrock.com/   When a nation ignores the Way,
                            Horses bear soldiers through
                                its streets.
                                
                            --Lao Tzu (Peter Merel, trans.)

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Re: [Caml-list] Why I cannot open a graph with a specific title

[Christophe TROESTLER]

On Mon, 28 Jun 2004, Matt Gushee <mgushee@havenrock.com> wrote:
> 
> Okay, but can you explain why
> 
>   # open_graph "localhost:0";;
> 
> fails on my Linux box?

For the same reason that

$ xterm -display localhost:0.0
xterm Xt error: Can't open display: localhost:0.0

My guess (not tested) is that this ask for a TCP connection while your
Linux distribution starts the server with "-nolisten tcp" (e.g. in
/etc/X11/xdm/Xservers).

Cheers,
ChriS

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