Actually, I'm dumb! colorAlphaPercent is the correct value to read it from.
HOWEVER, if the alpha is tweened, it won't be read correctly. It will only refer to the alpha value at the keyframes of the animation, not in between it.
So for simple linear, easeIn and easeOut tweens, I've developed this MathUtils class that may be of help to others who are trying to read alpha AND other values (x,y,scale,skew,rotation) from a tween animation.
You can put the following in it's own JSFL file, and load it wherever you need it.
MathUtils = {
pi2: Math.PI/2,
easeValue: function( pStart, pFinish, pRatio, pEasing ) {
var diff = pFinish - pStart;
var eased = pEasing > 0 ? this.easeOut( pRatio ) : this.easeIn( pRatio );
var linear = pRatio;
var blendRatio = Math.abs(pEasing);
var easeBlend = blendRatio * eased;
var linearBlend = (1 - blendRatio) * linear;
return pStart + diff * (easeBlend + linearBlend);
},
easeIn: function( pRatio ) {
return 1 - Math.sin((1-pRatio) * this.pi2);
},
easeOut: function( pRatio ) {
return Math.sin(pRatio * this.pi2);
}
};
How to use this:
pStart, pFinish: Provide the start value and end value of the element you are trying to read from (in other words, it's alpha from the start keyframe and the next one).
pRatio: A value from 0.0 to 1.0 indicating how far into the tween the given frame is. Usually, this value can be calculated with (currentFrameID - startFrameID) / (endFrameID - startFrameID).
pEasing: The easing value given for the startFrame, usually between -100 and 100 (0 = linear).