OGRE 3D 1.7 Beginner's Guide 第二章 中文翻译

[声明：本人仅仅英语四级水平，因为喜欢翻译和喜欢 Ogre，翻译以下文字，如果哪里有错误或不足还望

大虾们见谅，如果您发现有什么错误，请把问题发送到 whistleofmysong@gmail.com ，我将尽快的改正。

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2 The Ogre Scene Graph

【 第二章 Ogre 之场景绘图】

This chapter will introduce us to the concept of a scene graph and how we can use its functions to

create complex scenes

【 这章将会介绍给我们场景绘图的一些概念和如何使用函数创造一个复杂的场景。 】

在这章，我们将会：

 学习在 3D 空间中三个基本的操作。

 一个场景绘图是如何被组织的。

 我们可以操作的不同的 3D 空间。

那么，就让我们开始吧。

】

Creating a scene node

【 创建一个场景结点。 】

In the last chapter, Chapter 1, Installing Ogre 3D, we loaded a 3D model and attached it to our

scene. Now we will learn how to create a new scene node and attach our 3D model to it.

node, and attach it to the scene. We will follow these steps:

【 我们将会使用第一章的代码，修改第一章的代码以创建一个新的场景结点，并且把他绑

定到一个场景结点上。我们将会做以下步骤：】

1.In the old version of our code, we had the following two lines in the createScene() function:

【 在我们老版本的代码中，我们在 createScene() 函数中存在以下两行。】

Ogre::Entity* ent = mSceneMgr->createEntity("MyEntity","Sinbad.mesh");

mSceneMgr->getRootSceneNode()->attachObject(ent);

2. Replace the last line with the following:

【 用以下代码替换函数中的最后一行。 】

Ogre::SceneNode* node = mSceneMgr->createSceneNode("Node1");

the resulting scene:

【 当你运行应用程序，你应会看到和你第一章一样的场景。】

What just happened?

【 刚刚发生了什么？】

We created a new scene node named Node1. Then we added the scene node to the root

scene node. After this, we attached our previously created 3D model to the newly created

scene node so it would be visible.

【 我们创建了一个新的命名为 Node1 的场景结点。然后我们添加这个场景结点到根结点。

在这之后，我们绑定之前的 3D 模型到我们新创建的结点上面，这样就可以看到效果了。

】

How to work with the RootSceneNode

The call mSceneMgr->getRootSceneNode() returns the root scene node. This scene node is a

member variable of the scene manager. When we want something to be visible, we need to attach

it to the root scene node or a node which is a child or a descendent in any way. In short, there

organize the scene.

【 调用 mSceneMgr->getRootSceneNode() 函数将会返回场景的根结点。这个场景结点是场

景管理器的一个成员变量。当我们想要什么显示的时候，我们需要以一种方式把它绑定到

场景根结点是场景的根。因此整个场景将会以某种方式绑定到场景的根结点上。Ogre 3D

it has one root, the root scene node, and each node can have children. We already have used this

characteristc when we called mSceneMgr->getRootSceneNode()->addChild(node);. There we

added the created scene node as a child to the root. Directly afterwards, we added another kind of

child to the scene node with node->attachObject(ent);. Here, we added an entity to the scene node.

nodes, which can be added as children and have children themselves. Secondly, we have entity

that we want rendered. Entity aren't children and can't have children themselves. They are data

点 都 可 以 有 子 结 点 。 我 们 已 经 使 用 了 这 一 特 性 当 我 们 调 用 mSceneMgr-

>getRootSceneNode()->addChild(node) 的时候。我们把创建好的场景结点当做场景根结点的

里，我们添加一个实体到场景结点。我们现在有两种不同的可以添加到场景结点的对象。

首先，创建可以被添加为子结点或者可以继续为自己添加子结点的结点。然后，我们我们

创建我们想要渲染的实体。实体不是子结点，它们也不可能有子结点。它们有数据对象可

以被关联上结点也可以被认为是树上的叶子。我们稍晚将会学习它们到底是什么和如何使

用它们。现在，我们只需要实体。我们当前的场景绘图方式就好像下图一样。】

The first thing we need to understand is what a scene graph is and what it does. A scene graph is

used to represent how different parts of a scene are related to each other in 3D space.

3D space

Ogre 3D is a 3D rendering engine, so we need to understand some basic 3D concepts. The

【 Ogre 3D 是一个 3D 渲染引擎，所以我们需要一些基本的 3D 概念。在 3D 上最基础的结

构就是向量，这个向量中有次序的包含着(x,y,z)。 】

Each position in a 3D space can be represented by such a triple using the Euclidean coordinat ion

system for three dimensions. It is important to know that there are different kinds of coordinate

and the right-handed versions. In the following image, we see both systems—on the left side, we

see the left-handed version; and on the right side, we see the right-handed one.

一下在 3D 表示方面有不同的坐标体系。而这些体系之间的不同就是主轴的方向和选装的

正方向。现在主流的有两种体系，左手坐标系和右手坐标系。在下面的图中，我们看到两

种体系— 在左边我们看到的是左手坐标系;在右边我们看到的是右手坐标系。 】

The names left-and right-handed are based on the fact that the orientation of the axis can be

reconstructed using the left and right hand. The thumb is the x-axis, the index finger the y-axis,

and the middle finger the z-axis. We need to hold our hands so that we have a ninety-degree angle

hand, we get a right-handed coordination system. When using the left hand, we get the left-handed

指之间保持 90 度角。当使用右手时，我们就可以得到一个右手坐标系。当使用左手时，我

们就可以得到一个右手坐标系】

Ogre uses the right-handed system, but rotates it so that the positive part of the x-axis is pointing

right and the negative part of the x-axis points to the left. The y-axis is pointing up and the z-axis

but we will soon learn to think in this coordinate system. The Website

http://viz.aset.psu.edu/gho/sem_notes/3d_fundamentals/html/3d_coordinates.html contains a

【 Ogre 使用的是右手坐标系，但是旋转坐标系使 X 轴的正半轴指向右并且 X 轴的负半轴

指 向 左 。 Y 轴 ( 正 半 轴 ) 指 向 上 ， Z 轴 （ 正 半 轴 ） 垂 直 于 屏 幕 向 外 ， 这 被 称 为 y-up

Ogre 。 这 个 网 址 http://viz.aset.psu.edu/gho/sem_notes/3d_fundamentals/html/

3d_coordinates.html 有能更好展示不同坐标系之间的不同和联系的图片解释。 】

Scene graph

【场景绘图】

store information about a scene. We already discussed that a scene graph has a root and is

organized like a tree. But we didn't touch on the most important function of a scene graph. Each

node of a scene graph has a list of its children as well as a transformation in the 3D space. The

transformation is composed of three aspects, namely, the position, the rotation, and the scale. The

position is a triple (x,y,z), which obviously describes the position of the node in the scene. The

rotation is stored using a quaternion, a mathematical concept for storing rotations in 3D space, but

we can think of rotations as a single floating point value for each axis, describing how the node is

rotated using radians as units. Scaling is quite easy; again, it uses a triple (x,y,z), and each part of

the triple is simply the factor to scale the axis with.

没有涉及场景绘图中最重要的函数。每个场景结点既可有子结点也可以在 3D 空间变换的

函数。这些变换可以说由三方面组成，就是—— 位置变换(position)，旋转变换(rotation)和

The important thing about a scene graph is that the transformation is relative to the parent

by this change. When we move the parent 10 units along the x-axis, all children will also be

orientation of all parents. This fact will become clearer with the next diagram.