Re: Simple alpha fade

"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
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