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   1 <div class="blog">
   2 <h1 id="NAME">
   3 SDL RC 2.5 decides to play with PDL
   4 </h1>
   5 <div class="CONTENT">
   6 <i>PDL provides great number crunching capabilities to Perl and SDL provides game-developer quality real-time bitmapping and sound.<br />
   7 You can use PDL and SDL together to create real-time,<br />
   8 responsive animations and simulations.<br />
   9 In this section we will go through the pleasures and pitfalls of working with both powerhouse libraries.</i> <b>-- David Mertnes</b><br />
  10 <br />
  11 <br />
  12 <h1>Creating a SDL Surface piddle</h1><br />
  13 PDL's core type is a piddle.<br />
  14 Once a piddle is provided to PDL it can go do a numerous amounts of things.<br />
  15 Please see the example in '<a href="http://github.com/kthakore/SDL_perl/blob/master/examples/cookbook/pdl.pl">examples/cookbook/pdl.pl</a>' in github.<br />
  16 <br />
  17 <h3>Creating a simple piddle</h3><br />
  18 First lets get the right modules.<br />
  19 <br />
  20 <pre style='color:#d1d1d1;background:#000000;'>  <span style='color:#e66170; font-weight:bold; '>use</span> <span style='color:#b060b0; '>PDL;</span>
  21   <span style='color:#e66170; font-weight:bold; '>use</span> <span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>Rect</span><span style='color:#b060b0; '>;</span>
  22   <span style='color:#e66170; font-weight:bold; '>use</span> <span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>Video</span><span style='color:#b060b0; '>;</span>
  23   <span style='color:#e66170; font-weight:bold; '>use</span> <span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>Surface</span><span style='color:#b060b0; '>;</span>
  24   <span style='color:#e66170; font-weight:bold; '>use</span> <span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>PixelFormat</span><span style='color:#b060b0; '>;</span>
  25 </pre><br />
  26 Suppose you want a surface of size (200,400) and 32 bit (RGBA).<br />
  27 <br />
  28 <pre style='color:#d1d1d1;background:#000000;'><span style='color:#e66170; font-weight:bold; '>my</span> <span style='color:#d2cd86; '>(</span> $bytes_per_pixel<span style='color:#d2cd86; '>,</span> $width<span style='color:#d2cd86; '>,</span> $height <span style='color:#d2cd86; '>)</span> <span style='color:#d2cd86; '>=</span> <span style='color:#d2cd86; '>(</span> <span style='color:#00a800; '>4</span><span style='color:#d2cd86; '>,</span> <span style='color:#00a800; '>200</span><span style='color:#d2cd86; '>,</span> <span style='color:#00a800; '>400</span> <span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
  29 </pre><br />
  30 Define the <b>$width</b>, <b>$height</b> and <b>$bytes_per_pixel</b>. Your <b>$bytes_per_pixel</b> is the number of bits (in this case 32) divided by 8 bits per byte. Therefore for our 32 bpp we have 4 Bpp;<br />
  31 <br />
  32 <pre style='color:#d1d1d1;background:#000000;'><span style='color:#e66170; font-weight:bold; '>my</span> $piddle  <span style='color:#d2cd86; '>=</span> zeros<span style='color:#d2cd86; '>(</span> byte<span style='color:#d2cd86; '>,</span> $bytes_per_pixel<span style='color:#d2cd86; '>,</span> $width<span style='color:#d2cd86; '>,</span> $height <span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
  33 </pre><br />
  34 Create a normal $piddle with zeros, byte format and the Bpp x width x height dimensions.<br />
  35 <br />
  36 <pre style='color:#d1d1d1;background:#000000;'><span style='color:#e66170; font-weight:bold; '>my</span> $pointer <span style='color:#d2cd86; '>=</span> $piddle<span style='color:#d2cd86; '>-></span>get_dataref<span style='color:#d2cd86; '>(</span><span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
  37 </pre><br />
  38 Here is where we get the acutal data the piddle is pointing to. We will have SDL create a new surface from this function.<br />
  39 <br />
  40 <pre style='color:#d1d1d1;background:#000000;'><span style='color:#e66170; font-weight:bold; '>my</span> $surface <span style='color:#d2cd86; '>=</span> <span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>Surface</span><span style='color:#d2cd86; '>-></span>new_from<span style='color:#d2cd86; '>(</span> $pointer<span style='color:#d2cd86; '>,</span> $width<span style='color:#d2cd86; '>,</span> $height<span style='color:#d2cd86; '>,</span> <span style='color:#00a800; '>32</span><span style='color:#d2cd86; '>,</span>
  41         $width <span style='color:#d2cd86; '>*</span> $bytes_per_pixel <span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
  42 </pre><br />
  43 Using the same dimensions we create the surface using <b>SDL::Surface->new_form()</b>. The <b>$width * $Bpp</b> is the scanline (pitch) of the surface in bytes.<br />
  44 <br />
  45 <pre style='color:#d1d1d1;background:#000000;'><span style='color:#e66170; font-weight:bold; '>warn</span> <span style='color:#00c4c4; '>"Made surface of </span><span style='color:#00c4c4; '>$width</span><span style='color:#00c4c4; '>, </span><span style='color:#00c4c4; '>$height</span><span style='color:#00c4c4; '> and "</span><span style='color:#d2cd86; '>.</span> $surface<span style='color:#d2cd86; '>-></span>format<span style='color:#d2cd86; '>-></span>BytesPerPixel<span style='color:#b060b0; '>;</span>
  46    <span style='color:#e66170; font-weight:bold; '>return</span> <span style='color:#d2cd86; '>(</span> $piddle<span style='color:#d2cd86; '>,</span> $surface <span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
  47 </pre><br />
  48 Finally make sure that the surface acutally has the correct dimensions we gave.<br />
  49 <br />
  50 <b>NOTE:</b> <b>$surface->format->BytesPerPixel</b> must return 1,2,3,4. !!<br />
  51 <br />
  52 Now you can blit and use the surface as needed; and do PDL operations as required.<br />
  53 <br />
  54 <h3>Operating on the Surface safely</h3><br />
  55 To make sure SDL is in sync with the data. You must call SDL::Video::lock <b>before</b> doing PDL operations on the piddle.<br />
  56 <br />
  57 <pre><pre style='color:#d1d1d1;background:#000000;'><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>$surface<span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
  58
  59     $piddle <span style='color:#d2cd86; '>(</span> <span style='color:#d2cd86; '>:</span><span style='color:#d2cd86; '>,</span> <span style='color:#00a800; '>0</span> <span style='color:#d2cd86; '>:</span> <span style='color:#e66170; font-weight:bold; '>rand</span><span style='color:#d2cd86; '>(</span><span style='color:#00a800; '>400</span><span style='color:#d2cd86; '>)</span><span style='color:#d2cd86; '>,</span> <span style='color:#00a800; '>0</span> <span style='color:#d2cd86; '>:</span> <span style='color:#e66170; font-weight:bold; '>rand</span><span style='color:#d2cd86; '>(</span><span style='color:#00a800; '>200</span><span style='color:#d2cd86; '>)</span> <span style='color:#d2cd86; '>)</span> <span style='color:#d2cd86; '>.</span><span style='color:#d2cd86; '>=</span>   pdl<span style='color:#d2cd86; '>(</span> <span style='color:#e66170; font-weight:bold; '>rand</span><span style='color:#d2cd86; '>(</span><span style='color:#00a800; '>225</span><span style='color:#d2cd86; '>)</span><span style='color:#d2cd86; '>,</span> <span style='color:#e66170; font-weight:bold; '>rand</span><span style='color:#d2cd86; '>(</span><span style='color:#00a800; '>225</span><span style='color:#d2cd86; '>)</span><span style='color:#d2cd86; '>,</span> <span style='color:#e66170; font-weight:bold; '>rand</span><span style='color:#d2cd86; '>(</span><span style='color:#00a800; '>255</span><span style='color:#d2cd86; '>)</span><span style='color:#d2cd86; '>,</span> <span style='color:#00a800; '>255</span> <span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
  60 </pre></pre><br />
  61 After that you can unlock the surface to blit.<br />
  62 <br />
  63 <pre style='color:#d1d1d1;background:#000000;'><span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>Video</span><span style='color:#d2cd86; '>:</span><span style='color:#d2cd86; '>:</span>unlock_surface<span style='color:#d2cd86; '>(</span>$surface<span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
  64 </pre><br />
  65 <h3>Errors due to BPP at blitting</h3><br />
  66 When blitting the new surface check for the return value to see if there has been a problem.<br />
  67 <br />
  68 <pre style='color:#d1d1d1;background:#000000;'><span style='color:#e66170; font-weight:bold; '>my</span> $b <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>blit_surface<span style='color:#d2cd86; '>(</span>
  69         $surface<span style='color:#d2cd86; '>,</span>  <span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>Rect</span><span style='color:#d2cd86; '>-></span>new<span style='color:#d2cd86; '>(</span> <span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>,</span> <span style='color:#00a800; '>0</span><span style='color:#d2cd86; '>,</span> $surface<span style='color:#d2cd86; '>-></span>w<span style='color:#d2cd86; '>,</span> $surface<span style='color:#d2cd86; '>-></span>h <span style='color:#d2cd86; '>)</span><span style='color:#d2cd86; '>,</span>
  70         $app<span style='color:#d2cd86; '>,</span> <span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>Rect</span><span style='color:#d2cd86; '>-></span>new<span style='color:#d2cd86; '>(</span>  <span style='color:#d2cd86; '>(</span> $app<span style='color:#d2cd86; '>-></span>w <span style='color:#d2cd86; '>-</span> $surface<span style='color:#d2cd86; '>-></span>w <span style='color:#d2cd86; '>)</span> <span style='color:#d2cd86; '>/</span> <span style='color:#00a800; '>2</span><span style='color:#d2cd86; '>,</span> <span style='color:#d2cd86; '>(</span> $app<span style='color:#d2cd86; '>-></span>h <span style='color:#d2cd86; '>-</span> $surface<span style='color:#d2cd86; '>-></span>h <span style='color:#d2cd86; '>)</span> <span style='color:#d2cd86; '>/</span> <span style='color:#00a800; '>2</span><span style='color:#d2cd86; '>,</span> $app<span style='color:#d2cd86; '>-></span>w<span style='color:#d2cd86; '>,</span> $app<span style='color:#d2cd86; '>-></span>h <span style='color:#d2cd86; '>)</span>
  71        <span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
  72
  73     <span style='color:#e66170; font-weight:bold; '>die</span> <span style='color:#00c4c4; '>"Could not blit: "</span> <span style='color:#d2cd86; '>.</span> <span style='color:#904050; '>SDL</span><span style='color:#d2cd86; '>::</span><span style='color:#904050; '>get_error</span><span style='color:#d2cd86; '>(</span><span style='color:#d2cd86; '>)</span> <span style='color:#e66170; font-weight:bold; '>if</span> <span style='color:#d2cd86; '>(</span> $b <span style='color:#d2cd86; '>=</span><span style='color:#d2cd86; '>=</span> <span style='color:#d2cd86; '>-</span><span style='color:#00a800; '>1</span> <span style='color:#d2cd86; '>)</span><span style='color:#b060b0; '>;</span>
  74 </pre><br />
  75 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.<div class="blogger-post-footer"><img width='1' height='1' src='https://blogger.googleusercontent.com/tracker/3102167581424744259-3580429408870545769?l=yapgh.blogspot.com' alt='' /></div>
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