Flash MX 2004 Games : Art to ActionScript

and if the curve section is between the penultimate and the final keyframe then
T2 = 0.5 ∗ (K2.value − K1.value) ∗ ((1 − K2.tn)(1 + K2.bs)(1 − K1.ct)
+ (1 − K2.tn)(1 − K2.bs)(1 + K2.ct))
Appendix B
In the tweening function we first test to see if the time passed as a parameter is within range. If not
then we set the motion to either the first or last keyframe. Then we look through the keyframe
list to see which section to interpolate. If the current time is an exact match with a keyframe time
then no interpolation is required and so the position is set directly and the function returns. If
interpolation is required then we precalculate the value of tcb coefficients and store them in the
variables a − d. These are used to derive the values of T1 and T2. A section of the curve can be set
to be linear if required in which case the interpolation calculation is simplified to starting position
plus the product of delta time and the offset value for the curve section. This arithmetic is applied
to all the channels in the keyframe.
function tween_keyframe(name, channels, millisecs)
{
if (millisecskeys[keys.length-1].millisecs){
setDirect(name, keys.length - 1);
return;
}
//Must be within range
var index = 0, i;
for (i=0; ikeys[i].millisecs) index = i;
if (millisecs == keys[index].millisecs){
setDirect(name, index);
return;
}
//Interpolation required
var t, tt, ttt, h1, h2, h3, h4, a, b, c, d;
var secDur, s1, s2, dd0, ds1, result, p0, p1, p2, p3, d10;
secDur = keys[index+1].millisecs - keys[index].millisecs;
t = (millisecs - keys[index].millisecs)/secDur;
//Hermite coefficients
tt = t*t; ttt = t*tt;
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