-Providing direct memory access to SDL_Surface's pixels +The Build Process of SDL Perl
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:
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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.
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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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