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
362 changed files with 8472 additions and 5040 deletions
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39-03.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="39-02.html">Previous</a></td>
<td>
<a href="39-02.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="39-04.html">Next</a></td>
<td>
<a href="39-04.html">Next</a>
</td>
</tr>
</table>
</center>
<p><br /></p>
<p>Listing 39.2 shows a C implementation of integer edge tracing. Vertical and diagonal lines, which are trivial to trace, are special-cased. Other lines are broken into two categories: Y-major (closer to vertical) and X-major (closer to horizontal). The handlers for the Y-major and X-major cases operate on the principle of similar triangles: The number of X pixels advanced per scan line is the same as the ratio of the X delta of the edge to the Y delta. Listing 39.2 is more complex than the original floating point implementation, but not painfully so. In return for that complexity, Listing 39.2 is more than 80 times faster at scanning edges&mdash;and, as just mentioned, it&rsquo;s actually more accurate than the floating point code.</p>
<p>Ya gotta love that integer arithmetic.</p>
@ -159,16 +162,20 @@ void ScanEdge(int X1, int Y1, int X2, int Y2, int SetXStart,
<p>Listing 39.3 is an assembly language version of <b>DrawHorizontalLineList</b> . In actual use, it proved to be about 36 percent faster than Listing 39.1; better than a poke in the eye with a sharp stick, but just barely. There&rsquo;s more to these timing results than meets that eye, though. Display memory generally responds much more slowly than system memory, especially in 386 and 486 systems. That means that much of the time taken by Listing 39.3 is actually spent waiting for display memory accesses to complete, with the processor forced to idle by wait states. If, instead, Listing 39.3 drew to a local buffer in system memory or to a particularly fast VGA, the assembly implementation might well display a far more substantial advantage over the C code.</p>
<p><br /></p>
<center>
<table border="1">
<tr>
<td><a href="39-02.html">Previous</a></td>
<td>
<a href="39-02.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="39-04.html">Next</a></td>
<td>
<a href="39-04.html">Next</a>
</td>
</tr>
</table>
</center>