PDL provides great number crunching capabilities to Perl and SDL provides game-developer quality real-time bitmapping and sound.
You can use PDL and SDL together to create real-time,
responsive animations and simulations.
In this section we will go through the pleasures and pitfalls of working with both powerhouse libraries. -- David Mertnes
Creating a SDL Surface piddle
PDL's core type is a piddle.
Once a piddle is provided to PDL it can go do a numerous amounts of things.
Please see the example in '
examples/cookbook/pdl.pl' in github.
Creating a simple piddle
First lets get the right modules.
use PDL;
use SDL::Rect;
use SDL::Video;
use SDL::Surface;
use SDL::PixelFormat;
Suppose you want a surface of size (200,400) and 32 bit (RGBA).
my ( $bytes_per_pixel, $width, $height ) = ( 4, 200, 400 );
Define the
$width,
$height and
$bytes_per_pixel. Your
$bytes_per_pixel is the number of bits (in this case 32) divided by 8 bits per byte. Therefore for our 32 bpp we have 4 Bpp;
my $piddle = zeros( byte, $bytes_per_pixel, $width, $height );
Create a normal $piddle with zeros, byte format and the Bpp x width x height dimensions.
my $pointer = $piddle->get_dataref();
Here is where we get the acutal data the piddle is pointing to. We will have SDL create a new surface from this function.
my $surface = SDL::Surface->new_from( $pointer, $width, $height, 32,
$width * $bytes_per_pixel );
Using the same dimensions we create the surface using
SDL::Surface->new_form(). The
$width * $Bpp is the scanline (pitch) of the surface in bytes.
warn "Made surface of $width, $height and ". $surface->format->BytesPerPixel;
return ( $piddle, $surface );
Finally make sure that the surface acutally has the correct dimensions we gave.
NOTE: $surface->format->BytesPerPixel must return 1,2,3,4. !!
Now you can blit and use the surface as needed; and do PDL operations as required.
Operating on the Surface safely
To make sure SDL is in sync with the data. You must call SDL::Video::lock
before doing PDL operations on the piddle.
SDL::Video::lock_surface($surface);
$piddle ( :, 0 : rand(400), 0 : rand(200) ) .= pdl( rand(225), rand(225), rand(255), 255 );
After that you can unlock the surface to blit.
SDL::Video::unlock_surface($surface);
Errors due to BPP at blitting
When blitting the new surface check for the return value to see if there has been a problem.
my $b = SDL::Video::blit_surface(
$surface, SDL::Rect->new( 0, 0, $surface->w, $surface->h ),
$app, SDL::Rect->new( ( $app->w - $surface->w ) / 2, ( $app->h - $surface->h ) / 2, $app->w, $app->h )
);
die "Could not blit: " . SDL::get_error() if ( $b == -1 );
If the error message is 'Blit combination not supported' that means that the BPP is incorrect or incosistent with the dimensions. After that a simple update_rect will so your new surface on the screen.