-Providing direct memory access to SDL_Surface's pixels +SDL RC 2.5 decides to play with PDL
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In an attempt to make pixel access easier on SDL_Surface pixels. I have started work on SDLx::Surface. So far I have only start on the 32 bpp surfaces.
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The general idea is to make Pointer Values (PV) of each pixel in the surface and place them into a 2D matrix. First I make pointer values like this:
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SV * get_pixel32 (SDL_Surface *surface, int x, int y) -{ - //Convert the pixels to 32 bit - Uint32 *pixels = (Uint32 *)surface->pixels; - - //Get the requested pixel - Uint32* u_ptr = pixels + ( y * surface->w ) + x ; - - SV* sv = newSVpv("a",1); //Make a temp SV* value on the go - SvCUR_set(sv, sizeof(Uint32)); //Specify the new CUR length - SvLEN_set(sv, sizeof(Uint32)); //Specify the LEN length - SvPV_set(sv,(char*)u_ptr); // set the actual pixel's pointer as the memory space to use - - return sv; //make a modifiable reference using u_ptr's place as the memory :) - -} +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;
-Next I loop through all the pixels and put them in a 2D array format, shown below:
AV * construct_p_matrix ( SDL_Surface *surface ) -{ - AV * matrix = newAV(); - int i, j; - for( i =0 ; i < surface->w; i++) - { - AV * matrix_row = newAV(); - for( j =0 ; j < surface->h; j++) - { - av_push(matrix_row, get_pixel32(surface, i,j) ); - } - av_push(matrix, newRV_noinc((SV*) matrix_row) ); - } - - return matrix; -} +Suppose you want a surface of size (200,400) and 32 bit (RGBA).
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+my ( $bytes_per_pixel, $width, $height ) = ( 4, 200, 400 );
-You can see the complete here.
-In Perl I can do a get access on this pixel using:
+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 $surf32_matrix = SDLx::Surface::pixel_array($screen_surface); - print unpack 'b*', $surf32_matrix->[0][0]; # pixel value at x = 0 and y =0 -#OUTPUT: -# 11111111000000000000000000000000 +my $piddle = zeros( byte, $bytes_per_pixel, $width, $height );
-The structure of the PV is using Devel::Peek is :
-print Dump $surf32_matrix->[0][0]; -#OUTPUT: -#SV = PV(0xed0dbc) at 0xeb5344 -# REFCNT = 1 -# FLAGS = (POK,pPOK) -# PV = 0x9e04ac "\0\0\377\0" -# CUR = 4 -# LEN = 4 +Create a normal $piddle with zeros, byte format and the Bpp x width x height dimensions.
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+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 * $bytes_per_pixel );
-The problem is in setting the value of this pointer value. I have tried the following things with no success:
-if ( SDL::Video::MUSTLOCK($screen_surface) ) { - return if ( SDL::Video::lock_surface($screen_surface) < 0 ); #required for pixel operations -} - -#USING pack - -my $green = pack 'b*', '11111111000000000000000000000000'; -substr( $surf32_matrix->[0][0], 0, 8 * 4, $green); #no change -#substr( $surf32_matrix->[0][0], 0, 8 * 4, 0xFF000000); segfault -substr( ${$surf32_matrix->[0][0]}, 0, 8 * 4, 0xFF000000); #no change -#$surf32_matrix->[0][0] = $green; SEGFAULT's cannot write to memory -${$surf32_matrix->[0][0]} = $green; #no change - - -SDL::Video::unlock_surface($screen_surface) - if ( SDL::Video::MUSTLOCK($screen_surface) ); +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.
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+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.
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+NOTE: $surface->format->BytesPerPixel must return 1,2,3,4. !!
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+Now you can blit and use the surface as needed; and do PDL operations as required.
+
+Operating on the Surface safely
+To make sure SDL is in sync with the data. You must call SDL::Video::lock before doing PDL operations on the piddle.
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+SDL::Video::lock_surface($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 );
-You can see an example here.
-Any help will be greatly appreciated.
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