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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
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30-01.html
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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>
@ -19,17 +18,21 @@
<center>
<table border="1">
<tr>
<td><a href="29-06.html">Previous</a></td>
<td>
<a href="29-06.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="30-02.html">Next</a></td>
<td>
<a href="30-02.html">Next</a>
</td>
</tr>
</table>
</center>
<p><br /></p>
<h2 id="Heading1">Chapter 30<br />
Video Est Omnis Divisa</h2>
@ -58,7 +61,7 @@
<p>Turning the split screen on involves nothing more than setting all bits of the split screen start scan line to the scan line after which you want the split screen to start appearing. (Of course, you&rsquo;ll probably want to change the start address before using the split screen; otherwise, you&rsquo;ll just end up displaying the memory at offset zero <i>twice:</i> once in the normal screen and once in the split screen.) Turning off the split screen is a simple matter of setting the split screen start scan line to a value equal to or greater than the last scan line displayed; the safest such approach is to set all bits of the split screen start scan line to 1. (That is, in fact, the split screen start scan line value programmed by the BIOS during a mode set.)</p>
<h4 align="left" id="Heading4">The Split Screen in Action</h4>
<h4 id="Heading4">The Split Screen in Action</h4>
<p>All of these points are illustrated by Listing 30.1. Listing 30.1 fills display memory starting at offset zero (the split screen area of memory) with text identifying the split screen, fills display memory starting at offset 8000H with a graphics pattern, and sets the start address to 8000H. At this point, the normal screen is being displayed (the split screen start scan line is still set to the BIOS default setting, with all bits equal to 1, so the split screen is off), with the pixels based on the contents of display memory at offset 8000H. The contents of display memory between offset 0 and offset 7FFFH are not visible at all.</p>
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<p>Listing 30.1 isn&rsquo;t done just yet, however. After a keypress, Listing 30.1 demonstrates how to turn the split screen off (by setting all bits of the split screen start scan line to 1). After another keypress, Listing 30.1 shows that the split screen can never cover the whole screen, by setting the start address to 0 and then flipping back and forth between the normal screen and the split screen with a split screen start scan line setting of zero. Both the normal screen and the split screen display the same text, but the split screen displays it one scan line lower, because the split screen doesn&rsquo;t start until <i>after</i> the first scan line, and that produces a jittering effect as the program switches the split screen on and off. (On the EGA, the split screen may display <i>two</i> scan lines lower, for reasons I&rsquo;ll discuss shortly.)</p>
<p><br /></p>
<center>
<table border="1">
<tr>
<td><a href="29-06.html">Previous</a></td>
<td>
<a href="29-06.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="30-02.html">Next</a></td>
<td>
<a href="30-02.html">Next</a>
</td>
</tr>
</table>
</center>