Re: Simple alpha fade

On 12 Sep 2006 11:43:25 +0200, Guillaume Cottenceau <[email protected]> wrote:
>
> "Karl Dane" <karl 'at' rince.net> writes:
>
> > Hi all,
> >
> > I'm trying to write a simple alpha cross-fade app: basically a slideshow
> > that fades one image in and the other out. However, can not get alpha
> fades
> > to work.
> >
> > I'm very new to SDL, so please don't laugh at my code! But I'd be very
> > grateful if anyone could point out where I'm going wrong. The code
> snippet
> > below results in the image being displayed without any change.
> >
> > Many thanks,
> >
> > Karl Dane
> >
> >
> > #!/usr/bin/perl
> >
> > use warnings;
> > use SDL::App;
> >
> > our $app = SDL::App->new(
> >     -width => 640,
> >     -height => 480,
> >     -depth => 24,
> >     -fullscreen => 0,
> >     );
> >
> > for ($i=260; $i >=0; $i-=1) {
> >         print "$i\n";
> >
> >         my $img1 = SDL::Surface->new( -name => "./img1.png" );
> >
> >         $img1->display_format();
> >
> >         $img1->set_alpha(SDL_SRCALPHA, $i);
>
> /usr/include/SDL/SDL_video.h says for this method:
>
> * The 'alpha' parameter is ignored for surfaces that have an alpha
> channel.
>
> One solution might be to remove the alpha by converting the
> surface or creating a new surface with proper properties then
> blitting the original surface to it.
>
> >         $img1->blit( SDL::Rect->new(
> >             -width => 640, -height => 480), $app, undef);
> >
> >         $app->sync;
> >         }
>
> --
> Guillaume Cottenceau
> Create your personal SMS or WAP Service - visit http://mobilefriends.ch/
>


Hi Guillaume -

Thanks for your prompt reply. You mention converting the surface, I assume
to remove the alpha channel. Any ideas how I'd go about doing this? Is there
an appropriate method?


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