Adobe After Effects - Manual (Page 677)

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Writing expressions for source text
The Source Text property of a text layer is interpreted by expressions as a JavaScript String. You can use the pick whip to retrieve the source text
from another text layer; however, only the style of the first character of the destination layer is used.
For more information on the JavaScript String object, consult a JavaScript reference resource.
You can use "\r" in a string expression to start a new line of text. For example, to copy the original text from one layer onto the same layer and
repeat it in all uppercase characters on a new line, use the following expression:
text.sourceText + "\r" + text.sourceText.toUpperCase()
Adding a text layer to a composition and adding an expression to its Source Text property can be a great way to examine the property values of
other layers. For example, the following expression on a Source Text property reports the name and value of the Opacity property for the next
layer in the layer stacking order:
thisComp.layer(index + 1).name + "\rOpacity = " + thisComp.layer(index + 1).opacity.value
The following example reports the name of the footage item used as the source of the topmost image layer in the stacking order at the current
time that has its Video switch set.
source_footage_name = "";
for (i = 1; i <= thisComp.numLayers; i++){
if (i == index) continue;
my_layer = thisComp.layer(i);
if (! (my_layer.hasVideo && my_layer.active)) continue;
if (time >= my_layer.inPoint && time < my_layer.outPoint){
try{
source_footage_name = my_layer.source.name;
}catch(err1){
source_footage_name = my_layer.name
}
break;
}
}
source_footage_name
Aharon Rabinowitz provides a video tutorial and example expressions on Red Giant TV that show how to animate a video game score with the
Source Text property and a Slider effect (an Expression Controls effect).
Harry Frank provides a tutorial on his graymachine website that shows how to use expressions to read data from an external text file.
Add comments to an expression
If you write a complex expression and intend for you or someone else to use it later, you should add comments that explain what the expression
does and how its pieces work.
Type // at the beginning of the comment. Any text between // and the end of the line is ignored. For example: // This is a
comment.
For examples of this type of comment, see Expression example: Fade opacity of a 3D layer based on distance from camera.
Type /* at the beginning of the comment and */ at the end of the comment. Any text between /* and */ is ignored. For
example: /* This is a multiline comment. */
For examples of this type of comment, see Save and reuse expressions .
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