[changeset] - improve clf() compatibility

[David Bateman]

John W. Eaton wrote:
> I still see some strange behavior.
>
>
> * Try
>
>     demo plotyy
>     demo quiver3
>
>   Both of these demos seem to work OK if run separately in fresh Octave
>   sessions, but plotyy seems to be leaving some state that causes
>   quiver3 to fail with
>
>   octave:2> demo quiver3
>   quiver3 example 1:
>    [x,y]=meshgrid (-1:0.1:1); 
>    z=sin(2*pi*sqrt(x.^2+y.^2)); 
>    theta=2*pi*sqrt(x.^2+y.^2)+pi/2;
>    quiver3(x,y,z,sin(theta),cos(theta),ones(size(z)));
>    hold on; 
>    mesh(x,y,z); 
>    hold off;
>
>   quiver3 example 1: failed
>   get: invalid handle (= -1.22961)Press <enter> to continue: 
>   quiver3 example 2:
>    [x, y, z] = peaks (25);
>    surf (x, y, z);
>    hold on;
>    [u, v, w] = surfnorm (x, y, z / 10);
>    h = quiver3 (x, y, z, u, v, w);
>    set (h, "maxheadsize", 0.33);
>
>   quiver3 example 2: failed
>   get: invalid handle (= -1.22961)error: get: invalid handle (= -14.6238)
>   error: called from:
>   error:   /home/jwe/src/octave/scripts/plot/__go_draw_axes__.m at line 60, column 9
>   error:   /home/jwe/src/octave/scripts/plot/__go_draw_figure__.m at line 58, column 8
>   error:   /home/jwe/src/octave/scripts/plot/gnuplot_drawnow.m at line 66, column 5
>
>   
Ok, this one is subtle.. The problem is that the callback function that 
is associated with the plotyy axes is not removed by the newplot call in 
quiver3 -> __quiver__ -> plot3. Therefore, as one of the axes of the 
plotyy object remains and the other is destroyed, the update_position 
callback in plotyy.m tries to update a non existent axis with the change 
of view.

There are two solutions to this

1) The simple and wrong solution is to just test if the axis to update 
in the plotyy callback still exists before trying to update it. A patch 
as simple as

diff --git a/scripts/plot/plotyy.m b/scripts/plot/plotyy.m
--- a/scripts/plot/plotyy.m
+++ b/scripts/plot/plotyy.m
@@ -203,7 +203,7 @@
   persistent recursion = false;
 
   ## Don't allow recursion
-  if (! recursion)
+  if (! recursion && ishandle (ax2) && strcmp (get (ax2, "type"), "axes"))
     unwind_protect
       recursion = true;
       position = get (h, "position");

will do that and will prevent the error. However, the callback is 
continually called while the axis exists..

2) The correct solution is to have a means of removing callback 
functions in the deletefcn of plotyy. So we need a dellistener function 
that corresponds to the existing addlistener function.. I'm working on a 
patch along these lines.

D.

-- 
David Bateman                                David.Bateman at motorola.com
Motorola Labs - Paris                        +33 1 69 35 48 04 (Ph) 
Parc Les Algorithmes, Commune de St Aubin    +33 6 72 01 06 33 (Mob) 
91193 Gif-Sur-Yvette FRANCE                  +33 1 69 35 77 01 (Fax) 

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