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<td align="center" valign="middle" width="75%"><font color="#ffccaa" size="+3"><b><i>第27课</i></b></font></td>
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<td width="75%"><p><font class="head">影子:</font></p>
<p><font size="3">这是一个高级的主题，请确信你已经熟练的掌握了基本的OpenGL，并熟悉蒙板缓存。当然它会给你留下深刻的印象的。</font></p></td>
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<td valign="top" width="100%">欢迎来到另一个有些复杂的课程，阴影。这一课的效果好的有些让人不可思议，阴影可以变形，混合在其他的物体上。<br>
这一课要求你必须对OpenGL比较了解，它假设你知道许多OpenGL的知识，你必须知道蒙板缓存，基本的OpenGL步骤。如果你对这些不太熟悉，我建议你可以看看前面的教程。当然，在这一课里，我们用到了很多数学知识，请准备好一本数学手册在你的身边。<br>
首先我们定义阴影体可以延伸的距离。</td>
<td background="Tutorial_27_files/r.png"><img src="Tutorial_27_files/r.png"></td></tr></tbody></table><table border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td><img src="Tutorial_27_files/bl.png" height="28" width="28"></td><td width="100%"><img src="Tutorial_27_files/bc.png" height="28" width="100%"></td><td><img src="Tutorial_27_files/br.png" height="28" width="28"></td></tr></tbody></table><font color="#aaffaa" size="3"><pre><font color="#ffffaa">// 定义阴影体可以延伸的距离</font>
#define INFINITY 100
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<td valign="top" width="100%">下面定义一个3D顶点结构</td>
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<pre><font color="#ffffaa">// 3D顶点结构</font>
struct sPoint
{
GLfloat x, y, z;
};
</pre>
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<td valign="top" width="100%">定义一个平面结构</td>
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<pre><font color="#ffffaa">// 平面方程为: ax + by + cz + d = 0</font>
struct sPlaneEq
{
GLfloat a, b, c, d;
};
</pre>
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<td valign="top" width="100%">下面定义一个用来投影的三角形的结构
<ul>
<li>3个整形索引指定了模型中三角形的三个顶点</li>
<li>第二个变量指定了三角形面的法线</li>
<li>平面方程描述了三角所在的平面</li>
<li>临近的3个顶点索引，指定了与这个三角形相邻的三个顶点</li>
<li>最后一个变量指定这个三角形是否投出阴影</li>
</ul>
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<pre><font color="#ffffaa">// 描述一个模型表面的结构</font>
struct sPlane
{
unsigned int p[3]; <font color="#ffffaa">// 3个整形索引指定了模型中三角形的三个顶点</font>
sPoint normals[3]; <font color="#ffffaa">// 第二个变量指定了三角形面的法线</font>
unsigned int neigh[3]; <font color="#ffffaa"> // 与本三角形三个边相邻的面的索引</font>
sPlaneEq PlaneEq; <font color="#ffffaa">// 平面方程描述了三角所在的平面</font>
bool visible; <font color="#ffffaa">// 最后一个变量指定这个三角形是否投出阴影?</font>
};
</pre>
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<table border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td><img src="Tutorial_27_files/tl.png" height="28" width="28"></td><td width="100%"><img src="Tutorial_27_files/tc.png" height="28" width="100%"></td><td><img src="Tutorial_27_files/tr.png" height="28" width="28"></td></tr></tbody></table><table border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td background="Tutorial_27_files/l.png"><img src="Tutorial_27_files/l.png"></td>
<td valign="top" width="100%">最后我们用下面的结构描述一个产生阴影的物体。</td>
<td background="Tutorial_27_files/r.png"><img src="Tutorial_27_files/r.png"></td></tr></tbody></table><table border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td><img src="Tutorial_27_files/bl.png" height="28" width="28"></td><td width="100%"><img src="Tutorial_27_files/bc.png" height="28" width="100%"></td><td><img src="Tutorial_27_files/br.png" height="28" width="28"></td></tr></tbody></table>
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<pre>struct glObject{<br> GLuint nPlanes, nPoints;<br> sPoint points[100];<br> sPlane planes[200];<br>};</pre>
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<table border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td><img src="Tutorial_27_files/tl.png" height="28" width="28"></td><td width="100%"><img src="Tutorial_27_files/tc.png" height="28" width="100%"></td><td><img src="Tutorial_27_files/tr.png" height="28" width="28"></td></tr></tbody></table><table border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td background="Tutorial_27_files/l.png"><img src="Tutorial_27_files/l.png"></td>
<td valign="top" width="100%">下面的代码用来读取模型，它的代码本身就解释了它的功能。它从文件中读取数据，并把顶点和索引存储在上面定义的结构中，并把所有的临近顶点初始化为-1，它代表这没有任何顶点与它相邻，我们将在以后计算它。</td>
<td background="Tutorial_27_files/r.png"><img src="Tutorial_27_files/r.png"></td></tr></tbody></table><table border="0" cellpadding="0" cellspacing="0" width="100%"><tbody><tr><td><img src="Tutorial_27_files/bl.png" height="28" width="28"></td><td width="100%"><img src="Tutorial_27_files/bc.png" height="28" width="100%"></td><td><img src="Tutorial_27_files/br.png" height="28" width="28"></td></tr></tbody></table><font color="#aaffaa" size="3">
<pre>bool readObject( const char *filename, glObject*o)
{
FILE *file;
unsigned int i;
file = fopen(st, "r");
if (!file) return FALSE;
<font color="#ffffaa">//读取顶点</font>
fscanf(file, "%d", &(o->nPoints));
for (i=1;i<=o->nPoints;i++){
fscanf(file, "%f", &(o->points[i].x));
fscanf(file, "%f", &(o->points[i].y));
fscanf(file, "%f", &(o->points[i].z));
}
<font color="#ffffaa"> //读取三角形面</font>
fscanf(file, "%d", &(o->nPlanes));
for (i=0;i<o->nPlanes;i++){
fscanf(file, "%d", &(o->planes[i].p[0]));
fscanf(file, "%d", &(o->planes[i].p[1]));
fscanf(file, "%d", &(o->planes[i].p[2]));
<font color="#ffffaa">//读取每个顶点的法线</font>
fscanf(file, "%f", &(o->planes[i].normals[0].x));
fscanf(file, "%f", &(o->planes[i].normals[0].y));
fscanf(file, "%f", &(o->planes[i].normals[0].z));
fscanf(file, "%f", &(o->planes[i].normals[1].x));
fscanf(file, "%f", &(o->planes[i].normals[1].y));
fscanf(file, "%f", &(o->planes[i].normals[1].z));
fscanf(file, "%f", &(o->planes[i].normals[2].x));
fscanf(file, "%f", &(o->planes[i].normals[2].y));
fscanf(file, "%f", &(o->planes[i].normals[2].z));
}
return true;
}
</o-></pre>
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