-SDL RC 2.5 decides to play with PDL +The Build Process of SDL Perl
-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
+
A while ago I had a long chat with mst on why SDL uses Module::Build rather then Make. I told him it is a simple matter of code inertia. The existing Module::Build system has worked well for us so far. Never the less, he convinced me that switching to Make will improve debugging the Build system. But to be able to switch we will need to completely replace the Build system. I am not prepared to do that so I will just present the requirements so mst or someone else can at least attempt to switch.
+
The Build Process
+ Alien::SDL
-
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.
+
SDL Perl depends on a few C libraries for a complete install. This is handled by Alien::SDL. First we look for existing SDL libraries and dependencies by doing a File::Find for headers. If these headers are found we present and option for the user to use those. We then store these locations in Alien::SDL->config options 'cflags', 'prefix' and 'libs'. If we do not have libraries available even for a minimum SDL installed ( SDL.h is not found). We provide several platform specific options.
+
For windows we have a simpler process. We download prebuilt binaries ( and checksum ) based on the user's selection and just copy them in to the right location. Again the 'prefix', 'cflags', and 'libs' is saved in Alien::SDL->config.
+
For *nix/MacOSX we download sources and attempt to compile them. To be able to do this we download several other dependencies like libpng, jpeg and pango. You can see how we do this using hashes here. During the compile process we also apply patches as needed for the sources. Once this is done we can head to SDL Build.PL
+ SDL Perl dependency resolution
-
Creating a simple piddle
-First lets get the right modules.
+SDL's Build is responsible for linking the right libraries to the correct XS. If libraries are missing it will disable the component (not put it in SDL->config).
-
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).
+
For example to build Image.xs we require libsdl, libsdl_image and lib[jpg|png|tiff]. So we would check for these headers in the prefix provided by Alien::SDL->config. If they are not provided we will disable the SDL::Image module.
+
More over the availability of each library is specified as a -DMACRO to the gcc compiler. This way we can prevent XS failures due to missing libraries using #DEFINES. Here the SDL_image macro is defined and used. The availability of the module is then available from SDL::Config->has()
-
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.
-
