Re: GtkImageView

[muppet <scott asofyet org>]

On Dec 18, 2007, at 7:05 AM, Jeffrey Ratcliffe wrote:

> gtk2-perl does not have separate typemaps for every event type.  There
> is just one for GdkEvent which looks at the event's type at run-time
> to decide how to represent it.

As an aside, the reason for this is the way that GdkEvent is  
implemented.  GdkEvent is the structure type, which contains a union  
of all the event types, and a type code that tells you which of the  
union members is valid.


> Once you have the converters newSVStructName and SVStructName, you can

That should be SvStructName() -- note the lower-case "v".  (Blame the  
perlapi, not me.)


> > You're trying to use a GdkRectangle where a GdkRectangle* is  
> > wanted.  I
> > think this should work:
>
> Thanks, Torsten and Muppet. I briefly had the same but discarded it
> when I got the error message:
>
> IImageTool.xs: In function `SvDrawSettings':
> IImageTool.xs:62: warning: dereferencing `void *' pointer
> IImageTool.xs:62: error: void value not ignored as it ought to be
>
>  if (svp) settings->zoom_rect = *SvGdkRectangle (*svp);
>
> Which leaves me pretty much in the dark.


In general, the "dereferencing a `void*' pointer warning means that  
your pointer isn't cast to a valid type.  I notice now that  
gperl_get_boxed_check() returns a void*, and Glib::CodeGen creates  
macros like this:

  #define SvGtkBorder(sv)   (gperl_get_boxed_check ((sv),  
GTK_TYPE_BORDER))

That is, the generated SvStructType() macros don't contain the cast  
like you'd expect.  In the general case of

    Foo * foo = SvFoo (sv);

this works fine, because C (unlike C++) says that a void* may be used  
where any pointer type is wanted; that is, the conversion is implicit  
in C.  But, the construct

       Foo foo = *SvFoo (sv);

turns into

       Foo foo = * ((void*) something)

which is *not* valid.  The two solutions are

a)   Foo * foo = * (Foo*) SvFoo (sv);

b)   change Glib::CodeGen to insert the cast into the macro like this:

     #define SvFoo(sv)    ((Foo*) gperl_get_boxed_check ((sv),  
TYPE_FOO))

In reality, you may as well go for a) to make things work until we get  
b) vetted and rolled out.



Now, the error message,

> IImageTool.xs:62: error: void value not ignored as it ought to be

makes me go back and realize that you are using a hand-written  
function for SvDrawSettings() instead of a Glib::CodeGen-created  
macro.  I don't see anything related to this at http://trac.bjourne.webfactional.com/browser/plgtkimageview/ 
, so, from the message, it sounds like your function has the prototype

    void SvDrawSettings (SV * sv);

That means that it returns nothing, and the compiler will complain  
that you're attempting to use a non-existent value.  This is  
incorrect.  Change it to

    DrawSettings * SvDrawSettings (SV * sv);

(note the parallel with the discussion of the macro definitions,  
above), and everything should Just Work.


If that still doesn't work, give us the url of an svn branch that has  
the current code.


--
It's all very complicated and would take a scientist to explain it.
  -- MST3K