Re: newbie question concerning drawing/signals

[Jeffrey Goddard <moosewood mooseroot org>]

i'm a relative newcomer to gtk also, and have discovered that as a general 
rule, when i'm getting segfaults it's because i'm trying to call/operate on 
something that does not exist within the scope of the function i'm playing 
with. my usual response to that scenario is to pack the function full of 
g_print statements, call the program from a pseudo-terminal command line and 
find the offending line. hope that is of some help.
Jeffrey
On Wednesday 18 December 2002 19:21, zebster wrote:
> hi y'all!
>
> i'm developing an application which uses a pixmap
> to draw on which is then "copied" to a drawing_area,
> as suggested by the tutorial. far as that, everything
> works fine.
>
> now, the crucial part is that i have *two* drawing
> routines for the job, a scaled and an unscaled one;
> i.e. the "scaled" routine calculates all graphical
> elements to fit the allocation.width/height while
> the "unscaled" one uses fixed sizes for its elements.
> my drawing_area is within a scrolled window, so that
> scrollbars appear when i'm using "unscaled".
> furthermore, i've assembled a menu with a
> check_menu_item that is to trigger which of the
> drawing routines is used. this of course gives the
> need to redraw the pixmap when this button was
> activated and that's where my problem is:
>
> when my app starts, it
>
> 1) draws all widgets & assigns all handlers
> 2) calls a prepare() function which calculates
>     the needed space (depending on "scaled"/"unscaled"
>     and the actual content of the pixmap of course)
>     and then gtk_widget_size_requests the drawing_area.
> 3) on gtk_main, the configure_event handler calls
>     the corresponding drawing function, which is
>     "unscaled" by default. the graphics appear OK.
>
> now, i hooked that check_menu_item (c_m_i) to another
> handler which is to
>
> 1) call prepare() again to resize the drawing_area (DA)
>     (eg. "unscaled" gives DA dimensions of 2000x3000,
>     while the scrolled window is only about 400x400 -
>     and those 400x400 is the space to use for the
>     "scaled" routine" - gtk_widget_set_size again.)
> 2) then i emit the configure_event signal on the DA
>     to have the appropriate drawing routine do it's
>     job: "scaled" on the 1st activation of the c_m_i.
> 3) return to gtk_main()
>
> when i activate the button, that handler is called, but
> unfortunately it segfaults when returning from
> prepare(). i have really worked around with this
> problem a lot and it seems to me the problem is not
> what i'm doing within prepare() but the call
> itself. when i tell prepare() to do NOTHING on the
> first redraw but to immediately return, the crash
> still happens. and if i omit the call on the 1st
> redraw, everything runs perfectly (but the c_m_i's
> functionality is lost due to the structure of the
> code described above).
>
> my question is - am i stoopid coding this way? using
> configure_event to call the appropriate (re)drawing
> routine saves a seperate redraw() routine.
>
> my prepare() is a void routine without parameters -
> might that be the source of the problem?
>
> any suggestions? i'd be really grateful!
>
> zebster
>
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