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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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61-03.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="61-02.html">Previous</a></td>
<td>
<a href="61-02.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="61-04.html">Next</a></td>
<td>
<a href="61-04.html">Next</a>
</td>
</tr>
</table>
</center>
<p><br /></p>
<p>Why does this matter? It matters because, on average, half the polygons in any scene are facing away from the viewer, and hence shouldn&rsquo;t be drawn. One way to identify such polygons is to see whether they&rsquo;re facing toward or away from the viewer; that is, whether their normals have negative z values (so they&rsquo;re visible) or positive z values (so they should be culled). However, we&rsquo;re talking about screenspace normals here, because the perspective projection can shift a polygon relative to the viewpoint so that although its viewspace normal has a negative z, its screenspace normal has a positive z, and vice-versa, as shown in Figure 61.3. So we need screenspace normals, but those can&rsquo;t readily be generated by transformation from worldspace.</p>
<p><a id="Fig3"><img src="images/61-03.jpg" /><br />
@ -37,8 +40,6 @@
<p>The solution is to use the cross product of two of the polygon&rsquo;s edges to generate a normal. The formula for the cross product is:</p>
<p align="left"></p>
<p align="center"><img src="images/61-07d.jpg" /></p>
<p align="right">(eq. 7)</p>
@ -73,16 +74,20 @@
<p><a id="Fig5"><img src="images/61-05.jpg" /><br />
<b>Figure 61.5</b></a>&nbsp;&nbsp;<i>Backface culling with the dot product.</i></p>
<p><br /></p>
<center>
<table border="1">
<tr>
<td><a href="61-02.html">Previous</a></td>
<td>
<a href="61-02.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="61-04.html">Next</a></td>
<td>
<a href="61-04.html">Next</a>
</td>
</tr>
</table>
</center>