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exponential scale expression not matching 3D move
hi all
I’ve been using Dan’s exponential scale expression for ages. I’d always assumed it was replicating a 3D camera tracking in or out of a scene. Today I actually tested it out and was surprised to find it doesn’t ??? While markedly better than a straight linear scale the exponential scale still accelerates a little too quickly at the start and the decelerates a little too slowly at the end.
I’m hoping someone with better maths skills than myself can illuminate what might be going on…
I’ve attached a test comp here to illustrate: 6772_scaleexptest.aep.zip
//applyTo: scale
n = 0;
if (numKeys > 0){
n = nearestKey(time).index;
if (key(n).time > time){
n--;
}
}
if (n == 0 || n == numKeys){
value
}else{
d = 1
try{
value[1];
d++;
value[2];
d++;
value[3];
d++;
}catch (err){
}
t1 = key(n).time;
t2 = key(n+1).time;
if (d == 1){
v1 = key(n).value;
if (v1 == 0) v1 = .0001;
v2 = key(n+1).value;
if (v2 == 0) v2 = .0001;
k = Math.log(v1/v2)/(t2-t1);
v1/Math.exp((time-t1)*k)
}else{
v = [];
for(i = 0; i < d; i++){
v1 = key(n).value[i];
if (v1 == 0) v1 = .0001;
v2 = key(n+1).value[i];
if (v2 == 0) v2 = .0001;
k = Math.log(v1/v2)/(t2-t1);
v[i] = v1/Math.exp((time-t1)*k)
}
v
}
} -
1 Reply
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If you’re manipulating scale to represent 3D distance change, you generally want to pick a distance that represents a scale of 100%. Then a ratio of that distance to your current distance will give you the scale multiplier you need. So, for example, if you pick 500 pixels as the 100% distance, your formula becomes
value*500/distance_from_camera
So at 1000 pixels, your scale will be 50%, at 250 pixels it will be 200%.
I hope that helps.
Dan
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