Adobe 12040118 Tutorial - Page 558

4 Color [red, green, blue, alpha] You can access the individual elements of an Array object by using brackets and an index number to indicate which element you want. The elements in an Array object are indexed starting from 0. Using the previous example, myArray[0] is 10 and myArray[1] is 23. The following two expressions are equivalent: [myArray[0], 5] [10, 5] The Position property arrays are indexed as follows: position[0] is the x coordinate of position. position[1] is the y coordinate of position. position[2] is the z coordinate of position. Colors are represented as four-dimensional arrays [red, green, blue, alpha]. In projects with a color depth of 8 bpc or 16 bpc, each value in a color array ranges from 0 (black) to 1 (white). For example, red can range from 0 (no color) to 1 (red). So, [0,0,0,0] is black and transparent, and [1,1,1,1] is white and completely opaque. In projects with a color depth of 32 bpc, values under 0 and over 1 are allowed. If you use an index that is greater than the index of the highest-dimension component in an Array object, After Effects returns an error. For example, myArray[2] causes an error, but position[2] returns the z coordinate of Position. Many of the properties and methods in the After Effects expression language take Array objects as arguments or return them as values. For example, thisLayer.position is an Array object that is either two-dimensional or three-dimensional depending on whether the layer is 2D or 3D. If you want to write an expression that keeps the y value of an animation of Position but fixes the x value at 9, you would use the following: y = position[1]; [9,y] The following is even more succinct: [9, position[1]] This is an important point, so let's look at one more example. If you want to combine the x position value from Layer A with the y position value from Layer B, you would use the following: x = thisComp.layer("Layer A").position[0]; y = thisComp.layer("Layer B").position[1]; [x,y] You can create an expression that refers to just one value within the array of a 2D or 3D property. By default, the first value is used, unless you specify otherwise. For example, if you drag the pick whip from the Rotation property of Layer A to Scale property of Layer B, the following expression appears: thisComp.layer("Layer B").scale[0] By default, this expression uses the first value of the Scale property, which is width. If you prefer to use the height value instead, drag the pick whip directly to the second value instead of the property name, or change the expression as follows: thisComp.layer("Layer B").scale[1] Conversely, if you drag the pick whip from the Scale property of Layer B to the Rotation property of Layer A, After Effects automatically creates a variable, assigns the one-dimensional Rotation property value to it, and then uses that variable for both dimensions of the Scale property: temp = thisComp.layer(1).transform.rotation; [temp, temp] Vectors In After Effects, many properties and methods take or return vectors. After Effects refers to an array as a vector if it represents either a point or direction in space. For example, After Effects describes position as returning a vector. However, though a function like audioLevels does return a two-dimensional value (the left and right channel levels), it is not called a vector because it does not represent a point or direction. Some functions in After Effects accept vector arguments, but they are generally only useful when the values passed represent a direction. For example, cross(vec1, vec2) computes a third vector that is at right angles to the input vectors. The cross product is useful when vec1 and vec2 are two vectors representing directions in space, but not if they just represent two arbitrary collections of numbers.