-Providing direct memory access to SDL_Surface's pixels +Grant Progess Reports 1-3: Sept - Nov
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+As you know I have received a TPF grant to write a SDL Perl Manual.
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+http://news.perlfoundation.org/2010/08/2010q3-grant-proposal-manual-f.html
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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 :) - -} -
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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; -} -
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You can see the complete here.
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In Perl I can do a get access on this pixel using:
+As you know I have received a TPF grant to write a SDL Perl Manual.
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+http://news.perlfoundation.org/2010/08/2010q3-grant-proposal-manual-f.html
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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 -
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The structure of the PV is using Devel::Peek is :
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print Dump $surf32_matrix->[0][0]; -#OUTPUT: -#SV = PV(0xed0dbc) at 0xeb5344 -# REFCNT = 1 -# FLAGS = (POK,pPOK) -# PV = 0x9e04ac "\0\0\377\0" -# CUR = 4 -# LEN = 4 -
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The problem is in setting the value of this pointer value. I have tried the following things with no success:
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if ( SDL::Video::MUSTLOCK($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) ); -
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You can see an example here.
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Any help will be greatly appreciated.
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