blocks|key|658665|text|首先，您应该告诉任何导出工具不要导出具有那么多顶点的面。面应该有3个顶点，句号。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|658666|如果你的导出工具不能做到这一点，那么你的加载工具应该将多边形分解为3个顶点面。我相当肯定the+Asset+Importer+library可以做到这一点。|offset|length|658667|entityMap|0|LINK|mutability|MUTABLE|url|http://assimp.sourceforge.net/^0|0|18|Q|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

First, you should tell any exporting tool to not export faces with that many vertices. Faces should have 3 vertices, period.

If your exporting tool can't do that, then your loading tool should break the polygons down into 3 vertex faces. I'm fairly certain that <a href="http://assimp.sourceforge.net/">the Asset Importer library</a> can do that.

blocks|key|444353|text|OBJ导出器将以合理的顺序导出每个面的顶点(逆/顺时针)，只要你的面是共面和凸面(他们血腥应该是！)-你可以使用GL_TRIANGLE_FAN。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|444354|我不同意Nicol+Bolas的观点，面部应该总是有3个顶点，尽管很简单，如果你的多边形遵循上面的规则，使用GL_TRIANGLE_FAN可以简化你的代码并减少系统内存消耗。没有什么会改变GPU的一面，因为多边形将被分解成三角形。|offset|length|style|CODE|444355|entityMap^0|0|1I|F|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

OBJ exporters will export the vertices in a sane order for each face (anti-/clockwise), and long as your faces are coplanar and convex (which they bloody should be!) - you can use GL_TRIANGLE_FAN.

I disagree with Nicol Bolas' point that faces should always have 3 vertices, although fool proof, if your polygons follow the above rules, using <code>GL_TRIANGLE_FAN</code> simplifies your code and reduces system memory consumption. Nothing will change GPU side as the polygons will be decomposed to triangles anyway.

blocks|key|658802|text|实际上，大多数wavefront-obj面都是共面和凸面的，但我在original+OBJ+specification中找不到任何可以保证这一点的东西。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|658803|如果面是共面和凸面，则可以使用GL_TRIANGLE_FAN，也可以使用GL_TRIANGLE并手动评估风扇。扇形的所有三角形共享第一个顶点。如下所示：|658804|//+manually+generate+a+triangle-fan
for+(int+x+=+1;+x+<+(faceIndicies.Length-1);+x%2B%2B)+{
++++renderIndicies.Add(faceIndicies[0]);
++++renderIndicies.Add(faceIndicies[x]);
++++renderIndicies.Add(faceIndicies[x%2B1]);
}|code-block|syntax|javascript|658805|如果n边形中的顶点数量较多，则使用GL_TRIANGLE_STRIP或手动形成您自己的三角形条带可以产生更好的视觉效果。但这在wavefront+OBJ文件中很少见。|658806|如果面是共面的但是凹的，则需要使用某种算法对面进行三角剖分，例如耳朵修剪法。|658807|http://en.wikipedia.org/wiki/Polygon_triangulation#Ear_clipping_method|658808|如果垂直不是共面的，你就完蛋了，因为OBJ没有保留足够的信息来知道想要的是什么形状的镶嵌。|658809|entityMap|0|LINK|mutability|MUTABLE|url|http://www.martinreddy.net/gfx/3d/OBJ.spec|1^0|X|Q|0|0|0|0|0|0|0|1Y|1|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@]|9|@$A|12|B|13|1|14]]|C|$]]|$1|D|3|E|5|6|7|15|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|16|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|17|8|@]|9|@]|C|$]]|$1|M|3|N|5|6|7|18|8|@]|9|@]|C|$]]|$1|O|3|P|5|6|7|19|8|@]|9|@$A|1A|B|1B|1|1C]]|C|$]]|$1|Q|3|R|5|6|7|1D|8|@]|9|@]|C|$]]|$1|S|3|-4|5|6|7|1E|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]|10|$5|V|W|X|C|$Y|P]]]]

In practice, most wavefront-obj faces are coplanar and convex, but I can't find anything in the <a href="http://www.martinreddy.net/gfx/3d/OBJ.spec" rel="nofollow noreferrer">original OBJ specification</a> saying this is guaranteed.

If the face is coplanar and convex, you can either use GL_TRIANGLE_FAN, or you can use GL_TRIANGLE and manually evaluate the fan yourself. A fan has all triangles share the first vertex. Like this:

<pre><code>// manually generate a triangle-fan
for (int x = 1; x &lt; (faceIndicies.Length-1); x++) {
 renderIndicies.Add(faceIndicies[0]);
 renderIndicies.Add(faceIndicies[x]);
 renderIndicies.Add(faceIndicies[x+1]);
}
</code></pre>

If the number of vertices in an n-gon is large, using GL_TRIANGLE_STRIP, or manually forming your own triangle strips, can produce better visual results. But this is very uncommon in wavefront OBJ files.

If the face is co-planar but concave, then you need to triangulate the face using an algorithm, such as the Ear-Clipping Method..

<a href="http://en.wikipedia.org/wiki/Polygon_triangulation#Ear_clipping_method" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Polygon_triangulation#Ear_clipping_method</a>

If the verticies are not-coplanar, you are screwed, because OBJ doesn't preserve enough information to know what shape tessellation was intended.

So using a <a href="http://en.wikipedia.org/wiki/Wavefront_.obj_file" rel="nofollow noreferrer">Wavefront object file</a> how am i supposed to render faces that have more than 4 vertices in OpenGL?

I understand that if it has 3 vertices I use <code>GL_TRIANGLES</code>, if it has 4 I use <code>GL_QUADS</code>, but if it has 5 or more, what am I supposed to use? Is there a standard?

in a wavefront object file (.obj) how am i supposed to render faces with more than 4 vertices in opengl?

那么在OpenGL中如何使用来渲染顶点超过4个的面呢？我知道如果它有3个顶点我使用GL_TRIANGLES，如果它有4个我使用GL_QUADS，但如果它有5个或更多，我应该使用什么？有没有标准？

问在一个波前对象文件(.obj)中，我应该如何在opengl中渲染超过4个顶点的面？
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问在一个波前对象文件(.obj)中，我应该如何在opengl中渲染超过4个顶点的面？
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