Autodesk 62205-051408-9001 User Guide - Page 326

13 Creating Expressions Broaden the way you animate using Expressions-a powerful feature that enables you to create elaborate animations quickly. About Expressions An expression is a mathematical formula that you use to animate individual channel properties of layers or operators. Animating using expressions can save you a lot of time since you can create an expression for one channel and use the same expression for other channels so that the other channels automatically behave in relation to the first one. Combustion expressions are based on JavaScript and ECMA (European Computer Manufacturers Association)-script standard that enable you to build simple to complex animations. You can use arithmetic operators, such as addition and multiplication, as well as predefined functions to precisely control the behavior of an animation. Combustion includes predefined expression scripts you can use to start working with expressions. Once you are familiar with how expressions work, you can build your own expressions. Defining an Expression An expression is composed of numeric values, constants, channel references, or combinations of these. Expressions are calculated from left to right, according to a specific order. Scripting expressions in Combustion can be mastered by learning a few basic constructs. You can base your expressions on the current frame number, the current local time of a frame, or the current global time of a frame. The following table lists some of the methods used in Combustion. Method CB.GetCurrentFrame(); CB.GetLocalTime(); CB.GetGlobalTime(); CB.GetChannelValue(path,frame); CB.Random(); Definition Returns the current frame number. Returns the current local time in seconds. Returns the current global time in seconds. Returns a channel value at the specified path and optionally at a specified frame. Returns a random number between 0 and 1. It consistently returns the same random value between replays and for a specific channel. About JavaScript and Expressions One of the best things about JavaScript is that you can create simple to more elaborate expressions with very little programming knowledge. Another advantage in using JavaScript in Combustion is that you don't need any other software than Combustion. JavaScript Syntax Like HTML, JavaScript is just text that can be entered in a word processor. In Combustion, you enter text scripts in the Multi-line Editor. For more information, see Editing an Expression via the Multiline Editor. JavaScript includes variables, if-then statements, link events, JavaScript syntax with loops, arrays, functions, and forms. 310