Re: Gnome2::Canvas --> do I really need to worry about pixels_per_unit?

[walt <w41ter gmail com>]

zentara wrote:

> ...
> Didn't you read the code fragment I sent?
>
> > > $window->set_default_size( 500, 500 );
> > >
> > > #if scrollregion is smaller than default size, odd
> > > # coordinate problems occur
> > > #$canvas->set_scroll_region( 0, 0, 400, 400 ); #bad
> > >
> > > $canvas->set_scroll_region( 0, 0, 700, 700 );   #good and works fine
>
> Your scroll region 50,50 is less than 500,500 so a weird
> coordinate transform occurs...

I understand now what my problem is.  From my perspective there is no
scaling going on at all -- there is just shifting of an object left/right
or up/down on the window.  The rectangle (0,0,500,500) is calibrated in
pixels and the only way to change the physical size of an object on the
screen is to change pixels_per_unit.

That's okay if you are drawing a physical object like a circle or a
triangle, but a plot of data points is not a physical object and thus
needs different units on the x and y axes.  That level of abstraction
is apparently not provided by gtk+ AFAICT, but if I'm wrong please let
me know.

Thanks.