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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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<!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">
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<center>
<table border="1">
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<td><a href="56-01.html">Previous</a></td>
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<a href="56-01.html">Previous</a>
</td>
<td><a href="index.html">Table of Contents</a></td>
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<a href="index.html">Table of Contents</a>
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<td><a href="56-03.html">Next</a></td>
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<p><br /></p>
<p>Ah, but what is an &ldquo;equivalent amount&rdquo;? Think of it this way. If a destination edge is 100 scan lines high, it will be stepped 100 times. Then, we&rsquo;ll divide the <b>SourceXWidth</b> and <b>SourceYHeight</b> lengths of the source edge by 100, and add those amounts to the source edge&rsquo;s coordinates each time the destination is stepped one scan line. Put another way, we have, as usual, arranged things so that in the destination polygon we step <b>DestYHeight</b> times, where <b>DestYHeight</b> is the height of the destination edge. The this approach arranges to step the source image edge <b>DestYHeight</b> times also, to match what the destination is doing.</p>
<p><a id="Fig3"><img src="images/56-03.jpg" /><br />
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<p><a id="Fig5"><img src="images/56-05.jpg" /><br />
<b>Figure 56.5</b></a>&nbsp;&nbsp;<i>Mapping a texture onto a narrower polygon.</i></p>
<h4 align="left" id="Heading5">Notes on DDA Texture Mapping<br />
<h4 id="Heading5">Notes on DDA Texture Mapping<br />
<br /></h4>
<p>That&rsquo;s all there is to quick-and-dirty texture mapping. This technique basically uses a two-stage digital differential analyzer (DDA) approach to step through the appropriate part of the source image in tandem with the normal scan-line stepping through the destination polygon, so I&rsquo;ll call it &ldquo;DDA texture mapping.&rdquo; It&rsquo;s worth noting that there is no need for any trigonometric functions at all, and only two divides are required per scan line.</p>
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<p>For now, all we need is fast texture mapping of adequate quality, which the straightforward, non-antialiased DDA approach supplies. I&rsquo;m sure there are many other fast approaches, and, as I&rsquo;ve said, there are more accurate approaches, but DDA texture mapping works well, given the constraints of the PC&rsquo;s horsepower. Next, we&rsquo;ll look at code that performs DDA texture mapping. First, though, I&rsquo;d like to take a moment to thank Jim Kent, author of Autodesk Animator and a frequent correspondent, for getting me started with the DDA approach.</p>
<p><br /></p>
<center>
<table border="1">
<tr>
<td><a href="56-01.html">Previous</a></td>
<td>
<a href="56-01.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="56-03.html">Next</a></td>
<td>
<a href="56-03.html">Next</a>
</td>
</tr>
</table>
</center>