Re: Pixbuf to Cairo and vice versa

[Mario Kemper <mario kemper googlemail com>]

Update:

I've found out that Gtk2::Gdk::Pixbuf->new_from_data is much faster than the Gtk2::Gdk::PixbufLoader 
approach. This is how the code looks right now:

my $width = $surface->get_width;
my $height = $surface->get_height;
my $stride = $surface->get_stride;
my $data = $surface->get_data;
my $pixbuf = Gtk2::Gdk::Pixbuf->new_from_data ($data,'rgb',1,8,$width,$height,$stride);


The problem is that the colors of the resulting pixbuf are not correct. I think I am doing something wrong 
here. Are the parameters above correct? The surface is 'argb32' - this might be the problem, right?



Regards
Mario

----- UrsprÃngliche Mail -----
> Von: "Mario Kemper" <mario kemper googlemail com>
> An: gtk-perl-list gnome org
> Gesendet: Mittwoch, 13. Juli 2011 15:41:23
> Betreff: Pixbuf to Cairo and vice versa
>
> Hi,
>
> I was benchmarking one of my applications today and one of the
> slowest operations I detected is related to the Cairo > Pixbuf
> conversion.
>
> This is what the code is currently doing:
> 1) Get the current screen content as a pixbuf
>
> my $clean_pixbuf = Gtk2::Gdk::Pixbuf->get_from_drawable(
>       $self->{_root}, undef, 0, 0, 0, 0,
>       $self->{_root}->{w},
>       $self->{_root}->{h}
> );
>
> 2) I want to draw something on the pixbuf with Cairo
>
> my $surface = Cairo::ImageSurface->create( 'argb32',
> $self->{_root}->{w}, $self->{_root}->{h} );
> my $cr = Cairo::Context->create($surface);
>
> Gtk2::Gdk::Cairo::Context::set_source_pixbuf( $cr, $clean_pixbuf, 0,
> 0 );
> $cr->paint;
>
> <<< more painting goes here >>>
>
> 3) Show the final image in a widget, i.e. convert the cairo surface
> back to a pixbuf
>
> #write surface to pixbuf
> my $loader = Gtk2::Gdk::PixbufLoader->new;
> $surface->write_to_png_stream(
>       sub {
>               my ( $closure, $data ) = @_;
>               $loader->write($data);
>       }
> );
> $loader->close;
>
> <<< use $loader->get_pixbuf somewhere >>>
>
>
>
> Especially the last operation is pretty slow (the root window is big,
> dual monitor). My question is: Is this the correct workflow to do
> such things? Is there any way to avoid the conversions between
> pixbufs and cairo?
>
>
> Thanks in advance.
>
> Bye
> Mario