<div class="blog">
<h1 id="NAME">
-My milestones (itches) for gaming in Perl
+Providing direct memory access to SDL_Surface's pixels
</h1>
<div class="CONTENT">
-<div style="text-align: right;"><br /><blockquote><blockquote><i>As a young sprout in spring, </i><br /><i>the soil is moist,</i><br /><i>and the sun bright. </i><br /><i><br /></i><br /><i>But as fall comes,</i><br /><i>with fading leaves,</i><br /><i>my roots keep me standing. </i></blockquote></blockquote></div><br /><br /><br />As a new Perl developer I am able to contribute with <a href="http://github.com/kthakore/SDL_perl/commits/">great enthusiasm</a> due to the <a href="http://www.irc.perl.org/">great community</a> and the fancies of the language. However I know that these things will fade and I will need something else to take the place. Usually what has worked for me in the past was to set milestones. These will act as roots, keeping me interested in being involved. After all in words better than mines.<br /><blockquote><i>We all “scratch our own itches”. It’s why I started Linux, it’s why I started git, and it’s why I am still involved. --<a href="http://www.linux-mag.com/cache/7439/1.html">Linus</a><br /></i></blockquote><br />So here are my evolving milestones for Gaming in Perl:<br /><ul><li> Make Tetris,Pong, so on [soon-ish]<br /></li><ul><li>Hack it until its Perly (shows the power Perl can provide for games) </li></ul><li>Do game-a-thon [Starting January 2010]<br /></li><ul><li>Simply</li><ul><li> Get two random words (Warp + hole = portal)<br /></li><li> Make a small game</li><li>Every week for 52 weeks</li></ul></ul><li>Use the results from this to make some Perl specific tools [Parallel to game-a-thon]<br /></li><ul><li>SDL::Game </li></ul></ul>--signed YAPGH<div class="blogger-post-footer"><img width='1' height='1' src='https://blogger.googleusercontent.com/tracker/3102167581424744259-215619435826309735?l=yapgh.blogspot.com'/></div></div></div>
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+<p>In an attempt to make pixel access easier on SDL_Surface pixels. I have started work on <a href="http://github.com/kthakore/SDL_perl/commit/7ee1a1a7f162080a6fa5274e95b80961486e21e5">SDLx::Surface</a>. So far I have only start on the 32 bpp surfaces.</p><br />
+<p>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: </p><br />
+<pre style='color:#d1d1d1;background:#000000;'>SV <span style='color:#d2cd86; '>*</span> get_pixel32 <span style='color:#d2cd86; '>(</span>SDL_Surface <span style='color:#d2cd86; '>*</span>surface<span style='color:#d2cd86; '>,</span> <span style='color:#e66170; font-weight:bold; '>int</span> x<span style='color:#d2cd86; '>,</span> <span style='color:#e66170; font-weight:bold; '>int</span> y<span style='color:#d2cd86; '>)</span>
+<span style='color:#b060b0; '>{</span>
+ <span style='color:#9999a9; '>//Convert the pixels to 32 bit </span>
+ Uint32 <span style='color:#d2cd86; '>*</span>pixels <span style='color:#d2cd86; '>=</span> <span style='color:#d2cd86; '>(</span>Uint32 <span style='color:#d2cd86; '>*</span><span style='color:#d2cd86; '>)</span>surface<span style='color:#d2cd86; '>-</span><span style='color:#d2cd86; '>></span>pixels<span style='color:#b060b0; '>;</span>
+
+ <span style='color:#9999a9; '>//Get the requested pixel </span>
+ Uint32<span style='color:#d2cd86; '>*</span> u_ptr <span style='color:#d2cd86; '>=</span> pixels <span style='color:#d2cd86; '>+</span> <span style='color:#d2cd86; '>(</span> y <span style='color:#d2cd86; '>*</span> surface<span style='color:#d2cd86; '>-</span><span style='color:#d2cd86; '>></span>w <span style='color:#d2cd86; '>)</span> <span style='color:#d2cd86; '>+</span> x <span style='color:#b060b0; '>;</span>
+
+ SV<span style='color:#d2cd86; '>*</span> sv <span style='color:#d2cd86; '>=</span> newSVpv<span style='color:#d2cd86; '>(</span><span style='color:#02d045; '>"</span><span style='color:#00c4c4; '>a</span><span style='color:#02d045; '>"</span><span style='color:#d2cd86; '>,</span><span style='color:#008c00; '>1</span><span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span> <span style='color:#9999a9; '>//Make a temp SV* value on the go</span>
+ SvCUR_set<span style='color:#d2cd86; '>(</span>sv<span style='color:#d2cd86; '>,</span> <span style='color:#e66170; font-weight:bold; '>sizeof</span><span style='color:#d2cd86; '>(</span>Uint32<span style='color:#d2cd86; '>)</span><span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span> <span style='color:#9999a9; '>//Specify the new CUR length</span>
+ SvLEN_set<span style='color:#d2cd86; '>(</span>sv<span style='color:#d2cd86; '>,</span> <span style='color:#e66170; font-weight:bold; '>sizeof</span><span style='color:#d2cd86; '>(</span>Uint32<span style='color:#d2cd86; '>)</span><span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span> <span style='color:#9999a9; '>//Specify the LEN length</span>
+ SvPV_set<span style='color:#d2cd86; '>(</span>sv<span style='color:#d2cd86; '>,</span><span style='color:#d2cd86; '>(</span><span style='color:#e66170; font-weight:bold; '>char</span><span style='color:#d2cd86; '>*</span><span style='color:#d2cd86; '>)</span>u_ptr<span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span> <span style='color:#9999a9; '>// set the actual pixel's pointer as the memory space to use</span>
+
+ <span style='color:#e66170; font-weight:bold; '>return</span> sv<span style='color:#b060b0; '>;</span> <span style='color:#9999a9; '>//make a modifiable reference using u_ptr's place as the memory :)</span>
+
+<span style='color:#b060b0; '>}</span>
+</pre><br />
+<p>Next I loop through all the pixels and put them in a 2D array format, shown below: </p><pre style='color:#d1d1d1;background:#000000;'>AV <span style='color:#d2cd86; '>*</span> construct_p_matrix <span style='color:#d2cd86; '>(</span> SDL_Surface <span style='color:#d2cd86; '>*</span>surface <span style='color:#d2cd86; '>)</span>
+<span style='color:#b060b0; '>{</span>
+ AV <span style='color:#d2cd86; '>*</span> matrix <span style='color:#d2cd86; '>=</span> newAV<span style='color:#d2cd86; '>(</span><span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
+ <span style='color:#e66170; font-weight:bold; '>int</span> i<span style='color:#d2cd86; '>,</span> j<span style='color:#b060b0; '>;</span>
+ <span style='color:#e66170; font-weight:bold; '>for</span><span style='color:#d2cd86; '>(</span> i <span style='color:#d2cd86; '>=</span><span style='color:#008c00; '>0</span> <span style='color:#b060b0; '>;</span> i <span style='color:#d2cd86; '><</span> surface<span style='color:#d2cd86; '>-</span><span style='color:#d2cd86; '>></span>w<span style='color:#b060b0; '>;</span> i<span style='color:#d2cd86; '>+</span><span style='color:#d2cd86; '>+</span><span style='color:#d2cd86; '>)</span>
+ <span style='color:#b060b0; '>{</span>
+ AV <span style='color:#d2cd86; '>*</span> matrix_row <span style='color:#d2cd86; '>=</span> newAV<span style='color:#d2cd86; '>(</span><span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
+ <span style='color:#e66170; font-weight:bold; '>for</span><span style='color:#d2cd86; '>(</span> j <span style='color:#d2cd86; '>=</span><span style='color:#008c00; '>0</span> <span style='color:#b060b0; '>;</span> j <span style='color:#d2cd86; '><</span> surface<span style='color:#d2cd86; '>-</span><span style='color:#d2cd86; '>></span>h<span style='color:#b060b0; '>;</span> j<span style='color:#d2cd86; '>+</span><span style='color:#d2cd86; '>+</span><span style='color:#d2cd86; '>)</span>
+ <span style='color:#b060b0; '>{</span>
+ av_push<span style='color:#d2cd86; '>(</span>matrix_row<span style='color:#d2cd86; '>,</span> get_pixel32<span style='color:#d2cd86; '>(</span>surface<span style='color:#d2cd86; '>,</span> i<span style='color:#d2cd86; '>,</span>j<span style='color:#d2cd86; '>)</span> <span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
+ <span style='color:#b060b0; '>}</span>
+ av_push<span style='color:#d2cd86; '>(</span>matrix<span style='color:#d2cd86; '>,</span> newRV_noinc<span style='color:#d2cd86; '>(</span><span style='color:#d2cd86; '>(</span>SV<span style='color:#d2cd86; '>*</span><span style='color:#d2cd86; '>)</span> matrix_row<span style='color:#d2cd86; '>)</span> <span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
+ <span style='color:#b060b0; '>}</span>
+
+ <span style='color:#e66170; font-weight:bold; '>return</span> matrix<span style='color:#b060b0; '>;</span>
+<span style='color:#b060b0; '>}</span>
+</pre><br />
+<p>You can see the complete <a href="http://github.com/kthakore/SDL_perl/blob/7ee1a1a7f162080a6fa5274e95b80961486e21e5/src/SDLx/Surface.xs">here</a>.</p><br />
+<p>In Perl I can do a get access on this pixel using: </p><br />
+<br />
+<pre style='color:#d1d1d1;background:#000000;'><span style='color:#e66170; font-weight:bold; '>my</span> $surf32_matrix <span style='color:#d2cd86; '>=</span> <span style='color:#904050; '>SDLx</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>Surface</span><span style='color:#d2cd86; '>:</span><span style='color:#d2cd86; '>:</span>pixel_array<span style='color:#d2cd86; '>(</span>$screen_surface<span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
+ <span style='color:#e66170; font-weight:bold; '>print</span> <span style='color:#e66170; font-weight:bold; '>unpack</span> <span style='color:#00c4c4; '>'b*'</span><span style='color:#d2cd86; '>,</span> $surf32_matrix<span style='color:#d2cd86; '>-></span><span style='color:#d2cd86; '>[</span><span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>]</span><span style='color:#d2cd86; '>[</span><span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>]</span><span style='color:#b060b0; '>;</span> <span style='color:#9999a9; '># pixel value at x = 0 and y =0</span>
+<span style='color:#9999a9; '>#OUTPUT:</span>
+<span style='color:#9999a9; '># 11111111000000000000000000000000</span>
+</pre><br />
+<p>The structure of the PV is using Devel::Peek is : </p><br />
+<pre style='color:#d1d1d1;background:#000000;'><span style='color:#e66170; font-weight:bold; '>print</span> Dump $surf32_matrix<span style='color:#d2cd86; '>-></span><span style='color:#d2cd86; '>[</span><span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>]</span><span style='color:#d2cd86; '>[</span><span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>]</span><span style='color:#b060b0; '>;</span>
+<span style='color:#9999a9; '>#OUTPUT:</span>
+<span style='color:#9999a9; '>#SV = PV(0xed0dbc) at 0xeb5344</span>
+<span style='color:#9999a9; '># REFCNT = 1</span>
+<span style='color:#9999a9; '># FLAGS = (POK,pPOK)</span>
+<span style='color:#9999a9; '># PV = 0x9e04ac "\0\0\377\0"</span>
+<span style='color:#9999a9; '># CUR = 4</span>
+<span style='color:#9999a9; '># LEN = 4</span>
+</pre><br />
+<p>The problem is in setting the value of this pointer value. I have tried the following things with no success:</p><br />
+<pre style='color:#d1d1d1;background:#000000;'><span style='color:#e66170; font-weight:bold; '>if</span> <span style='color:#d2cd86; '>(</span> <span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>Video</span><span style='color:#d2cd86; '>:</span><span style='color:#d2cd86; '>:</span>MUSTLOCK<span style='color:#d2cd86; '>(</span>$screen_surface<span style='color:#d2cd86; '>)</span> <span style='color:#d2cd86; '>)</span> <span style='color:#b060b0; '>{</span>
+ <span style='color:#e66170; font-weight:bold; '>return</span> <span style='color:#e66170; font-weight:bold; '>if</span> <span style='color:#d2cd86; '>(</span> <span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>Video</span><span style='color:#d2cd86; '>:</span><span style='color:#d2cd86; '>:</span>lock_surface<span style='color:#d2cd86; '>(</span>$screen_surface<span style='color:#d2cd86; '>)</span> <span style='color:#d2cd86; '><</span> <span style='color:#00a800; '>0</span> <span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span> <span style='color:#9999a9; '>#required for pixel operations</span>
+<span style='color:#b060b0; '>}</span>
+
+<span style='color:#9999a9; '>#USING pack</span>
+
+<span style='color:#e66170; font-weight:bold; '>my</span> $green <span style='color:#d2cd86; '>=</span> <span style='color:#e66170; font-weight:bold; '>pack</span> <span style='color:#00c4c4; '>'b*'</span><span style='color:#d2cd86; '>,</span> <span style='color:#00c4c4; '>'11111111000000000000000000000000'</span><span style='color:#b060b0; '>;</span>
+<span style='color:#e66170; font-weight:bold; '>substr</span><span style='color:#d2cd86; '>(</span> $surf32_matrix<span style='color:#d2cd86; '>-></span><span style='color:#d2cd86; '>[</span><span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>]</span><span style='color:#d2cd86; '>[</span><span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>]</span><span style='color:#d2cd86; '>,</span> <span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>,</span> <span style='color:#00a800; '>8</span> <span style='color:#d2cd86; '>*</span> <span style='color:#00a800; '>4</span><span style='color:#d2cd86; '>,</span> $green<span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span> <span style='color:#9999a9; '>#no change</span>
+<span style='color:#9999a9; '>#substr( $surf32_matrix->[0][0], 0, 8 * 4, 0xFF000000); segfault</span>
+<span style='color:#e66170; font-weight:bold; '>substr</span><span style='color:#d2cd86; '>(</span> ${$surf32_matrix<span style='color:#d2cd86; '>-></span><span style='color:#d2cd86; '>[</span><span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>]</span><span style='color:#d2cd86; '>[</span><span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>]</span>}<span style='color:#d2cd86; '>,</span> <span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>,</span> <span style='color:#00a800; '>8</span> <span style='color:#d2cd86; '>*</span> <span style='color:#00a800; '>4</span><span style='color:#d2cd86; '>,</span> <span style='color:#00a800; '>0xFF000000</span><span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span> <span style='color:#9999a9; '>#no change</span>
+<span style='color:#9999a9; '>#$surf32_matrix->[0][0] = $green; SEGFAULT's cannot write to memory</span>
+${$surf32_matrix<span style='color:#d2cd86; '>-></span><span style='color:#d2cd86; '>[</span><span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>]</span><span style='color:#d2cd86; '>[</span><span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>]</span>} <span style='color:#d2cd86; '>=</span> $green<span style='color:#b060b0; '>;</span> <span style='color:#9999a9; '>#no change</span>
+
+
+<span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>Video</span><span style='color:#d2cd86; '>:</span><span style='color:#d2cd86; '>:</span>unlock_surface<span style='color:#d2cd86; '>(</span>$screen_surface<span style='color:#d2cd86; '>)</span>
+ <span style='color:#e66170; font-weight:bold; '>if</span> <span style='color:#d2cd86; '>(</span> <span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>Video</span><span style='color:#d2cd86; '>:</span><span style='color:#d2cd86; '>:</span>MUSTLOCK<span style='color:#d2cd86; '>(</span>$screen_surface<span style='color:#d2cd86; '>)</span> <span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
+</pre><br />
+<p>You can see an example <a href="http://paste.scsys.co.uk/45111">here</a>.</p><br />
+<p>Any help will be greatly appreciated. </p><div class="blogger-post-footer"><img width='1' height='1' src='https://blogger.googleusercontent.com/tracker/3102167581424744259-1929043568015240773?l=yapgh.blogspot.com' alt='' /></div>
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