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Odd/Even Markers
Is there a way to distinguish odd and even numbered markers?
I trying to do a cascading text like in Stranger Than Fiction. I keyframes a #D text layer’s x orientation to flop the text, then moving the anchor point, flopping again, and the text cascades down the screen. There is a pause of time so the text pause after each flop, so that I can apply the following dampening expression to X Rotation.
amp=70; //amplitude (pixels)
freq=2; //frequency (cycles per second)
decay=2.5; //decay time (seconds)// find previous marker
n = 0; // assume haven’t reached a marker yet
if (marker.numKeys > 0){
n = marker.nearestKey(time).index;
if (marker.key(n).time > time){
n–;
}
}if (n > 0) t = time – marker.key(n).time else t =0;
a = amp*Math.sin(freq*t*Math.PI*2)/Math.exp(decay*t);
aIf I could have the last line be “a” on odd numbered markers, and be “- a” on even numbered markers, the dampening would look right. With only “a” as the last line, the text always kicks out in the same direction, and I want it to kick out first toward the viewer, then on the next marker kick out away from the viewer.
Can expression differentiate odd or even numbered markers?
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6 Replies
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Something like this should do it:
if ((marker.key(n).index % 2) > 0) a else -a
Dan
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Works a charm, except before the first keyframe where I get this error message:-(
After Effects warning: Bad method arguments: This property has no keyframe number 0.
Error occurred on line 17.
Expression disabled. -
OK – try this:
amp=70; //amplitude (pixels)
freq=2; //frequency (cycles per second)
decay=2.5; //decay time (seconds)// find previous marker
n = 0; // assume haven’t reached a marker yet
if (marker.numKeys > 0){
n = marker.nearestKey(time).index;
if (marker.key(n).time > time){
n–;
}
}if (n > 0) t = time – marker.key(n).time else t =0;
a = amp*Math.sin(freq*t*Math.PI*2)/Math.exp(decay*t);
if ((n > 0) && ((marker.key(n).index % 2) == 0)) a = -a;
aDan
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Thank you berry, berry much (the blackberries are blooming here).
Works a charm.
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This quite interesting.. I was curious what’s causing the positive and then negative motion.. I know it’s in this
if ((n > 0) && ((marker.key(n).index % 2) == 0)) a = -a;
aI’d love an explanation on this last line. Im trying to dive in a deeper understanding of altering and creating my own expressions. Thanks, you guys are the best.
= = victor = =
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The next-to-last line basically says if there are any markers AND the previous marker index is an even number, flip the sign of variable a.
The test for odd/even is made by using the JavaScript modulus operator “%”. This operator gives you the remainder of a division operation. So, use you can use %2 to find out if an integer is odd or even.
0%2 = 0
1%2 = 1
2%2 = 0
3%2 = 1
4%2 = 0etc.
Dan
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