• Adobe After Effects Expressions

  Custom language parse, compiler

  Posted by Dinesh Salunke on October 19, 2014 at 2:09 pm

  Hello All,

  I have written a small script to automate my and my colleagues usual day to day work, it involves creating keyframes on markers and at specific time.

  I was looking at possibility to include a small expression kind of system where I can write small peice of codes to set the keyframe values based on other factors.

  Below I have explained my requirement with pseudo code of the script.
  
function setKeyAt ( property, time, value, expression )
{
var keyIndex = property.addKey( time );
if ( value )
property.setValueAtKey ( keyIndex, val );

  if ( expression )
  {
  var val = eval( expression );
  property.setValueAtKey ( keyIndex, val );
  }
  }

  var prop = PROPERTY_REFERENCE;
var nTime = 1;
var exp = "property.keyValue( keyIndex -2 )";
setKeyAt( prop, nTime, undefined, exp );


  above code works for me and creates keys at given time, and assings value which is equal to the value at current index – 2.

  I want to extend this and implement a way to incorporate something similar to expressions, so that I can create keys using code

  currently what I have is, I am looking for key words in the expression string and then replace those with values based on the current property,
  EXAMPLE :
  currComp.width
  is replaced by evaluated value of below string
  
var layer = property.propertyGroup( property.propertyDepth );
var comp = layer.containingComp;
comp.width;


  Hope I was able to explain my problem, and also hope I am not expecting or attempting too much 😉

  Thanks,

  Dinesh Salunke replied 11 years, 11 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Dan Ebberts

  October 19, 2014 at 6:11 pm

  I’m not sure this is what you’re talking about, but when I need a script to construct an expression where certain elements are not known at the time the script is written, I use an identifiable string like $PARM1, $PARM2, etc. Then I create a function that will substitute the actual string for a placeholder parm at run time.

  Dan
• 

  Dinesh Salunke

  October 19, 2014 at 7:02 pm

  Hello Dan,

  I am talking on the similar lines, currently I am also doing pretty much the same way you do, but its really dirty way, and i am still learning the whole coding thing.

  currently, I am using a string.contains to find keywords, then using a switch statement I am calculating and substituting the keyswords with calculated values

  this works but is surely not the best way to do it. also I want to be able to write keywords for functions for example

  
/*
Key Object which represents each keyframe in property
*/
function Key ( args )
{

  }

  //This functions takes care of setting the key and assigning the values
  Key.prototype.setAt = function ( property, time )
  {
  var _layer = property.propertyGroup( property.propertyDepth );
  var _comp = _layer.containingComp;

  if ( this.ValueType == undefined || this.ValueType !== property.propertyValueType )
  return 0;
  if ( this.nTimeOffset == undefined )
  return 0;

  var keyIndex = property.addKey ( time + this.nTimeOffset );
  if ( this.nValue !== undefined )
  property.setValueAtKey ( keyIndex, this.nValue );

  if ( this.Expression !== undefined || this.Expression !== "" )
  {
  var val = eval( this.Expression );
  if ( val !== undefined )
  property.setValueAtKey ( keyIndex, val );
  }
  }

  //helper function which can be called from the script to get the value of certain key frame
  function _KeyValueAt ( index )
  {

  }


  Sample Expression :
  
"_keyValueAt ( -2 );"

  this expression will be evaluated in the setAt function,

  this works but I want the function to know the 3 variables
  1. property
  2. _layer
  3. _comp

  so that it can use these to calculate the values

  hope I was right to the point this time

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