CGAL开发者手册：英文技术文档

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"CGAL开发者手册，英文版。这是一份专为开发人员设计的CGAL（Computational Geometry Algorithm Library）指南，建议在下载前先查阅。" CGAL（Computational Geometry Algorithm Library）是一个开源库，提供了多种计算几何算法，广泛用于计算机图形学、科学计算、工程应用等领域。开发者手册是CGAL用户和贡献者的重要参考资料，它深入介绍了库的内部工作原理、设计模式以及如何有效地使用和扩展CGAL。在给定的部分内容中，涉及到的是CGAL中的数据结构和类型，特别是与三维几何对象相关的部分。`CGAL_Vertex_max_base`、`CGAL_Halfedge_max_base`和`CGAL_Polyhedron_facet_base_3`这些类是构建三维多面体数据结构的基础组件。它们分别代表顶点、边的半边（halfedge）和面（facet）的基类。`CGAL_Point_3<CGAL_Cartesian<double>>`是一个在笛卡尔坐标系中表示三维点的类，其中坐标值为双精度浮点数。 `CGAL__Hlv`似乎是一个模板类型，可能是用来表示某种树结构的节点，这里的`<CGAL_Vertex_max_base<CGAL_Point_3<CGAL_Cartesian<double>>>, CGAL_Halfedge_max_base, CGAL_Polyhedron_facet_base_3<CGAL_Cartesian<double>>>`是这个类型的参数化实例，表明节点包含了与顶点、边和面相关的数据。 `pair`和`select1st`、`less`是C++标准库中的类型和函数，它们在这里用于组织和比较树结构中的元素。`pair`用来存储两个关联值，而`select1st`是一个选择器，用于从对中提取第一个元素。`less`是一个比较函数对象，用于实现小于关系，通常在排序或查找操作中使用。在CGAL中，这样的数据结构和算法常常用于处理复杂的几何操作，比如构建、遍历和修改多面体网格，执行碰撞检测，进行表面建模等。开发者手册会详细介绍这些概念，以及如何通过CGAL库的接口来使用它们。为了更深入地理解和利用CGAL，开发者需要熟悉C++编程语言，理解计算几何的基本概念，并掌握模板元编程和STL（Standard Template Library）的使用。这份手册将提供必要的指导，帮助开发者高效地利用CGAL解决实际问题。

• All names in the kernel traits have the dimension as a sufﬁx. This is necessary because in some cases

(e.g., the Orientation 2 object) the absence of the sufﬁx would cause a name conﬂict with an existing type

or class (e.g., the enumeration type Orientation).

• The names of generalized predicates are determined by their results. Furthermore, names are as much

as possible consistent with the current kernel and the STL. So, for example, we have objects like Has

on bounded side 2, Is degenerate 2, and Is horizontal 2. According to the current kernel we also have

Left turn 2. For reasons of consistency with STL, all “less-than”-objects start with Less , e.g., Less xy 2.

Further examples are Less distance to point 2 and Less distance to line 2. However, we have Equal

2, whereas the corresponding STL functor is called equal to. Here, we give our dimension rule higher

priority.

• The names of construction objects (category 2 above) follow the pattern Construct type d, where type d

is the type constructed, e.g., Construct point 2 and Construct line 2. The operator() of these functor

classes is overloaded. This reduces the number of names to remember drastically, while replacing one of

the constructions gets more complicated, but is still possible.

• Functors in category 3 above can be further subdivided into two classes:

– constructive procedures that construct objects whose types are known a priori

– procedures that construct objects whose types are not known a priori

The names of functors in the ﬁrst class also start with Construct whenever a geometric object is con-

structed, otherwise they start with Compute . Here, real numbers are not considered to be 1-dimensional

geometric objects. For example, on the one hand we have Construct perpendicular vector 2, Construct

midpoint 3, Construct circumcenter d, Construct bisector 2, and Construct point on 3, while on the

other hand there are Compute area 2 and Compute squared length 3.

For the second class, the names of the objects describe the (generic) action, e.g. Intersect 2.

• The equality operator (operator==()) is replaced by function objects with names of the form Equal k,

where k is the dimension number (i.e., 2, 3, or d). For replacing arithmetic operators, we might also

provide Add 2, Subtract 2, Multiply 2, and Divide 2. (As mentioned above, the action determines the

name, not the result.) We think that these objects are not really needed. They are likely to be part of

primitive operations that have a corresponding function object in the traits.

In addition, for each functor the kernel traits class has a member function that returns an instance of this functor.

The name of this function should be the (uncapitalized) name of the functor followed by the sufﬁx object.For

example, the function that retuns an instance of the Less xy 2 functor is called less xy 2 object.

File names

• File names should be chosen in the “spirit” of the naming rules given above.

• If a single geometric object, data structure, or algorithm is provided in a single ﬁle, its name (and its

capitalization) should be used for the ﬁle name. For example, the ﬁle Triangulation 2.h contains the data

structure Triangulation 2.

• If a ﬁle does not contain a single class, its name should not begin with a capital letter.

• No two ﬁles should have the same names even when capitalization is ignored. This is to prevent over-

writing of ﬁles on operating systems where ﬁle names are not case sensitive. A package that contains ﬁle

names that are the same as ﬁles already in the release will be rejected by the submission script.

• The names of ﬁles should not contain any characters not allowed by all the platforms the library supports.

In particular, it should not contain the characters ‘:’, ‘*’, or ‘ ’.

2.2 Programming conventions

The ﬁrst list of items are meant as rules, i.e., you should follow them.

• Give typedefs for all template arguments of a class that may be accessed later from outside the class.

The template parameter is a concept and should follow the concept naming scheme outlines in the previous

section. As a general rule, the typedef should identify the template parameter with a type of the same name

that follows the naming convention of types. For example

template < class GeometricTraits_2 >

class Something {

public:

typedef GeometricTraits_2 Geometric_traits_2;

};

For one-word template arguments, the template parameter name should be followed by an underscore.

(Note that using a preceding underscore is not allowed according to the C

standard; all such names are

reserved.)

template < class Arg_ >

class Something {

public:

typedef Arg_ Arg;

};

• Use const when a call by reference argument is not modiﬁed, e.g. int f( const A& a).

• Use const to indicate that a member function does not modify the object to which it is applied, e.g., class

A { int f( void) const; };. This should also be done when it is only conceptually const. This means that the

member function f() is const as seen from the outside, but internally it may modify some data members

that are declared mutable. An example is the caching of results from expensive computations. For more

information about conceptually const functions and mutable data members see [Mey97].

• Prefer C

-style to C-style casts, e.g., use static cast<double>( i) instead of (double)i.

• Protect header ﬁles against multiple inclusion, e.g. the ﬁle This is an example.h should begin/end with

#ifndef CGAL_THIS_IS_AN_EXAMPLE_H

#define CGAL_THIS_IS_AN_EXAMPLE_H

...

#endif // CGAL_THIS_IS_AN_EXAMPLE_H

The following items can be seen as recommendations in contrast to the rules of previous paragraph.

• Use #define sparingly.

• Do not rename the base types of C

using typedef.

• When using an overloaded call, always give the exact match. Use explicit casting if necessary.

• Do not call global functions unqualiﬁed, that is, always specify explicitly the namespace where the func-

tion is deﬁned.

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