Misc/abrash-black-book
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Retidy, removing align=left from headings and empty paragraphs

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James Gregory 2013-12-30 15:37:13 +11:00
commit a96a114403
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@ -1,5 +1,4 @@
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
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<center>
<table border="1">
<tr>
<td><a href="31-03.html">Previous</a></td>
<td>
<a href="31-03.html">Previous</a>
</td>
<td><a href="index.html">Table of Contents</a></td>
<td>
<a href="index.html">Table of Contents</a>
</td>
<td><a href="31-05.html">Next</a></td>
<td>
<a href="31-05.html">Next</a>
</td>
</tr>
</table>
</center>
<p><br /></p>
<p>The interesting aspects of Listing 31.1 are three. First, the <b>Set320x400Mode</b> subroutine selects 320x400 256-color mode. This is accomplished by performing a mode 13H mode set followed by then putting the VGA into standard planar byte mode. <b>Set320x400Mode</b> zeros display memory as well. It&rsquo;s necessary to clear display memory even after a mode 13H mode set because the mode 13H mode set clears only the 64K of display memory that can be accessed in that mode, leaving 192K of display memory untouched.</p>
<p>The second interesting aspect of Listing 31.1 is the <b>WritePixel</b> subroutine, which draws a colored pixel at any <i>x,y</i> addressable location on the screen. Although it may not be obvious because I&rsquo;ve optimized the code a little, the process of drawing a pixel is remarkably simple. First, the pixel&rsquo;s display memory address is calculated as</p>
@ -66,16 +69,20 @@
<p>The color bar routines don&rsquo;t use the <b>WritePixel</b> subroutine from Listing 31.1; they go straight to display memory instead for improved speed. As I mentioned above, better speed yet could be achieved by a color-bar algorithm that draws all the pixels in plane 0, then all the pixels in plane 1, and so on, thereby avoiding the overhead of constantly reprogramming the Map Mask register.</p>
<p><br /></p>
<center>
<table border="1">
<tr>
<td><a href="31-03.html">Previous</a></td>
<td>
<a href="31-03.html">Previous</a>
</td>
<td><a href="index.html">Table of Contents</a></td>
<td>
<a href="index.html">Table of Contents</a>
</td>
<td><a href="31-05.html">Next</a></td>
<td>
<a href="31-05.html">Next</a>
</td>
</tr>
</table>
</center>