1、鉴于本人英语水平有限以及对 Houdini 的学习还不是很深入，所以拿来集思广益， 恳求完美正解! 希望您在修改的时候使用红色标记或者补充说明，发至 ，我会再次修改，发给大家！先谢谢各位兄台的大力支持与帮助!-satandancing 2010/2/26EXPRESSION SYNTAX(表达式语法)Here are some of the main syntax elements which you will encounter again and again when using expression functions:（以下是主要的语法元素，你会一次又一次地遇到一些使用表达式函数： ）
2、() Brackets Brackets are used in order to list all of the arguments that will be contained within a function. Whenever a function is used, there must be an open bracket and a closed bracket. One of the easiest mistakes to make when creating expressions is to accidentally have the incorrect number of
3、 brackets.()括号 括号的使用是为了列举出所有的将要包含在函数中的参数。每当使用一个函数，必须有一个开放的括号和一个封闭的括号。最简单的错误之一就是当你创建表达式时，意外的有多个数目不正确的括号。“”Quotation When a string must be used as an argument inside a function, it must be contained within quotation marks. This can include parameter names, and file paths.“”引号 当一个字符串必须被用作在一个函数的参数，它必须包含
4、在引号内。 这可以包括参数名，和文件路径。 Back Ticks When an HScript expression has been entered into a string type parameter, it must be enclosed in backticks in order to be evaluated as an expression. For example, if you are attempting to use an expression function inside a file path, you will need to include the bac
5、kticks on either end of your function.返回标记 当 HScript 表达式中已经输入了一个字符串类型的参数，它必须包含在返回标记内，以便作为一个表达式的 计算。例如，如果您正试图使用在一个文件路径表达式功能，您需要在您的函数结束包含一个返回标记。 Apostrophe Text inside apostrophes are not expanded. It may be necessary at times to use these characters inside strings to prevent a variable from being rec
6、ognized as a variable.单引号 文本中的单引号不是大写的。可能有必要在有的时候字符串内使用这些字符，以防止一个变量被承认为一个变量。TYPES OF DATA(数据类型)There are four main types of data that exist within Houdini（在 Houdini 中存在有四个主要的数据类型）：Float: Floating point numbers are single numerical values which may contain decimals i.e.: 15.5. It is possible to break
7、 this down further into integers, which do not contain decimals. An Alpha attribute/channel would be a good example of a float value.浮点 浮点数单一数值可能包含小数，即： 15.5。很可能打破这种进一步下降为整数，不包含小数。一个 Alpha 属性/ 通道是一个很好的 float 值的例子。Vectors: Three floating point values. These values can be used to represent positions,
8、directions, normals or colors (RGB or HSV).矢量（向量）： 三浮点值。这些 值可以用来代表的位置，方向，法线或颜色（RGB 或 HSV）。Strings: Strings are data which are not numbers, but text. A number is not represented as numerical in a string but as a text symbol. You can enclose strings in double quotes (“) or apostrophes (). Variables in
9、side double-quotes are expanded. Strings inside apostrophes are not expanded. It is possible to create custom variables which make use of strings. 字符串： 字符串的数据不是数字，而是文字。一个数字并不表示为一个字符串中的数值，而是一个文本符号。你可以在双引号（“ ）或单引号（）中放入字符串。内双引号内的变量会被展开。单引号内的字符串是不会展开的。它可以利用字符串 创建自定义的变量。Matrix: Sixteen floating point val
10、ues representing a 3D transformation matrix. 矩阵： 16 个浮点值描述了一个三维变化矩阵。SIMPLE MATH+ - Add, subtract（加，减）* / % Multiply, Divide（乘，除）% Modulo returns the remainder after division has occured i.e. 4%3=1, 4%20=4百分号返回除法发生之后的剩余，即 i.e. 4%3=1, 4%20=4 Raise to exponent i.e. 33=9（提高指数，例如 33=9）e Exponential notat
11、ion is a concise way of representing large numbers with a minimal amount of digits, for example 3.2e-5 (equivalent to 0.000032).指数符号是一个代表了最少量的数字的简洁方式，例如 3.2e - 5（相当于 0.000032）。() Grouping（群集）COMPARISONSLess than, greater than（小于，大于）= inquire as to whether it is equal（询问它是否等于）!= not equal to（不等于）| or
12、（或）& and（和）GLOBAL VARIABLES（全局变量）Data that is accessible in all contexts. There are different types of global variables, which have various purposes.在任何情况下可访问的数据。不同的全局 变量用于不同的目的。Environment Variables: Useful for setting up your Houdini environment.（环境变量：用于设定你的Houdini 环境。 ）$HIP This defaults to the d
13、irectory containing the current Houdini file.（这个默认值的目录包含了当前的 Houdini 文件。 ）$HIPNAME The name of the current .hip file（当前.hip 文件的名称）$WEDGE The current wedge information（当前的 wedge 信息）$OS Operator String - contains the current OPs name（运算符字符串 - 包含运算符字符串的名称）$JOB A custom variable that determines where yo
14、ur jobs are located（自定义变量取决于您工作的位置）$HOME Your Home environment variable - specify in OS environment variables（你的 home 环境变量 - 指定运算符字符串的环境变量）$ACTIVETAKE Contains the name of the current take（包含当前的名称）$CH Current channel name（当前通道的名称）$TEMP Where temporary (crash) files are saved - specify in OS environm
15、ent variables（临时（崩溃）文件保存的位置-指定运算符字符串环境变量）PLAYBAR VARIABLES：There are various variables that are associated with time in Houdini:（播放条变量：一些与 Houdini 时间有关的各种变量：）$F The current frame.（当前帧） This is very useful, especially for filename numbering.（这对于文件名的编号方式尤其有用。） It allows us to introduce the element of
16、time into our expressions. （它允许我们的表达式可以引入到时间的元素中去。） In the case of file naming we can add padding to $F （因此我们能够在文件的名称中添加到$F）$F3 gives us a padding of 3 meaning that Frame 1 = 001(给我们 提供了3个填充帧 1=001) We can also use $F on a translation parameter tell it to move over time （我们还可以使用$F把翻译参数告诉它移到那个时间）We c
17、an offset $F with simple math. $F-1 tells frame 1 to return a value of 0（我们可以使用简单的数字补充$F. $F-1 表示 帧 1 的返回值为 0）Certain elements, work in units of “Time” which refers to seconds rather than frames:（在某些情况下，工作时所指的“时间” 是秒而不是帧）$FPS Playback speed in frames/second (set in Global Animation Options)（播放速度 帧/秒
18、（设定全局动画选项）$T Current time in seconds（当前时间 秒）We can use ($F-1)/$FPS to determine the current frames time in seconds. This can be useful to know when we see parameters like start time on a particle network and want to be able to determine the start frame. By telling the Start Time to be 40/$FPS, the p
19、article simulation will begin on frame 40.（我们可以使用($F-1)/$FPS 取决于当前帧的时间是秒。当我们看到类似于在一个粒子网络结构上的起始时间，并希望可以确定起始帧，知道这些对我们是有用的。设定开始时间为 40/$FPS，粒子将以40FPS 进 行模拟。 ）Particle and dynamic networks use time rather than frames because we often need subframe data:（粒子和动力学网络的使用时间不是帧，因为我们经常需要子帧数据：）$FF Floating point f
20、rame number（浮点帧数）$SF Simulated frame number（模拟帧数）These become important variables to remember when we adjust the over sampling. i.e.: if collision geometry isnt sampling between frames, we can have problems with accuracy therefore we want to over sample (sample more than once per frame).（谨记，当我 们调节超过
21、采样值，这些都成为重要的变量。换言之：如果一个碰撞几何体之 间没有采样值，我 们会引起一个我 们无法超过采样值精确度的问题（采样值将多次超过每帧）。 ）It is important to cache out simulations using $SF for DOPs and $FF in POPs so that we keep subframe data.（给 DOP 和 POP 做缓存 要使用$SF 为 DOPnetwork 的子帧参数，pop 使用$FF floatframe 为计算单位 这样变量去储存子帧数据。注： KID 的解释）It may also become essent
22、ial when using longer expressions to use the Expression Editor (Alt + e) or right click menu on a parameter.（在表达式编辑器（ALT + e）或在右键菜单中的参数中使用长的表达式时，这是不可或缺的。 ）OTHER PLAYBAR VARIRBLES(其他的播放条变量)$NFRAMES The number of frames in the animation（在动画中的帧数）$RFSTART Frame number of the first frame shown in the pla
23、ybar. The playbar can show a subset of the total number of frames, allowing you to focus on a particular section of a longer sequence（在播放条中 显示第一帧的帧数。播放条可以显示所有总数帧的子帧，让你专注较长序列的 单个部分）$RFEND Frame number of the last frame shown in the playbar（在播放条中显示最后帧的帧数）$FSTART Frame number of the first frame of anim
24、ation (set in Global Animation Options)（在动画中第一帧的帧数）$FEND Frame number of the last frame of animation (set in Global Animation Options)（在动画中最后帧的帧数）$RFSTART and $RFEND control the subset of frames shown in the playbar（$RFSTART and $RFEND 控制着在播放条中 显 示的子帧）$TLENGTH Total length of animation in seconds（总长
25、度在几秒钟的动画）$TSTART Start time of animation in seconds（动画在几秒开始）$TEND End time of animation in seconds（动画在几秒结束）STANDARD VARIABLES（标准变量）Commonly used variables that are unique to specific contexts, however are common enough that they may be recognized across multiple contexts. Note that some variables su
26、ch as $CR, $CG, $CB, $CA are actually attributes: Cd and Alpha. Attributes are data that are easy to lock down, and you can see that they exist if you MMB onto a node.$TX,$TY,$TZ Point Position（点的位置）$BBX,$BBY,$BBZ Point Position within bounding box (ranges 0-1)（在 bounding box 中的位置（范围 0-1）$YMAX,$YMIN
27、 The max/min values of the geometry on the Y-Axis. Note this goes for X,Y, & Z（几何体 Y 轴上的最大/最小值。注意 标记是 X,Y,Z）$CEX,$CEY,$CEZ Centroid of the input geometry（输入几何体的质心）$CR,$CG,$CB,$CA Diffuse Point Color, and Point Alpha（点的漫反射 颜色和点的 alpha）$NX,$NY,$NZ Point Normal Direction(点的法线方向)$PT,$PR Point Number or
28、Primitive Number（点的数量或者面的数量）$NPTS,$NPRIMS Total number of points or primitives（点或者面的总数）VOLUMES AS ATTRIBUTES（体积属性）Each volume primitive may be used to represent a set of data. This is important to note when working with fluid dynamics to understand what purpose the various fields serve.（每个几何体的体积都有可能
29、被用于说明一组数据。用于流体动力学中了解每组数据所对应 服务的记录， 这一点是尤为重要的。）$X,$Y,$Z Bounding Box Information in Volumes（Bounding Box 在体积中的信息）PARTICLE VARIABLES(粒子 变量)There are some very commonly used Standard Variables that are usually associated with particles. Many of the standard variables can be found on the Point SOP.（有一些很
30、常用的标准变量通常与粒子有关。许多标准变量可以在 SOP 下找到。 ）$VX,$VY,$VZ Point Velocity values（点的速度 值）$ID Particle ID（粒子 ID）$PSCALE Particle Scale（粒子缩放）$LIFE Percent of total life used (from 0 to 1)（已使用生命总数的百分之一（从 0 到 1）LOCAL VARIABLES(局部变量)Many variables that are common to one context are not necessarily common to another c
31、ontext. Not all variables are standard. In fact, some nodes have local variables, which will be listed in the help cards on a node-by-node basis.（不是所有的变量都是标准的。事实上，一些节点有局部变量，将在一个节 点上的帮助卡中列出了节点的基础。 ）We can also use functions designed specifically for accessing attributes: point() detail() vertex() or prim()
