- Creating a SDL Surface piddle
SDL::CookBook::PDL -- CookBook for SDL + PDL
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.
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' that came with this module.
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 actual 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 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 actually has the correct dimensions we gave.
NOTE: $surface->format->BytesPerPixel must return 1,2,3,4. !!
Now you can blit and use the surface as needed; and do PDL operations as required.
To make sure SDL is in sync with the data. You must call SDL::Video::lock before doing PDL operations on the piddle.
SDL::Video::lock_surface($surface); $piddle->mslice( 'X', [ rand(400), rand(400), 1 ], [ rand(200), rand(200), 1 ] ) .= pdl( rand(225), rand(225), rand(255), 255 );
After that you can unlock the surface to blit.
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 inconsistent with the dimensions. After that a simple update_rect will so your new surface on the screen.
See "AUTHORS" in SDL.