Re: [AD] Problem with remove_mouse() and video bitmaps.

[Stef <stapostol@xxxxxxxxxx>]

On Fri, 30 Dec 2005 10:55:02 +0200, aj <aj@xxxxxxxxxx> wrote:

> Stef wrote:
>
> > On Fri, 30 Dec 2005 10:24:44 +0200, Peter Wang <tjaden@xxxxxxxxxx>  
> > wrote:
> >
> > > +   Note: you must not be showing a mouse pointer on a bitmap at the   
> > > time that
> > > +   the bitmap is destroyed with destroy_bitmap(). This does not apply  
> > > to
> > > +   `screen' since you never destroy `screen' with destroy_bitmap().
> >
> >
> > If the destroy_bitmap() function automatically nulled out the bitmap   
> > pointer, it would be trivial to add a check to avoid drawing onto an   
> > invalid bitmap. While this wouldn't be the end of this kind of  
> > problems,  it would help allegro become more robust. It wouldn't break  
> > compatibility  either (though programs using an old dll would be more  
> > crash prone).
> >
> > Is there an obvious reason against this that I missed? (very  
> > probable).  Otherwise, I think I could submit a patch for this one if  
> > the following  days.
>
>
> explain how that would work ?

I have a hunch that the crash is caused by the draw_mouse() function  
accessing the _mouse_screen bitmap (which in this case is invalid, since  
it is destroyed). If the destroy_bitmap function nulls automatically nulls  
out the bitmap pointer, the draw_mouse could check if the _mouse_screen  
exists, and do nothing if it doesn't. It would be better though if we had  
a bitmap_exists() function, though it is out of the question now.

For the moment, this is only a theory. I'll try to test is today.