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Squash and Stretch – Random Seed?
Hello expression experts!
I’m using this wonderful set of expressions for a “Squash and Stretch” animation but I need to know how to modify them to create a random offset. When I duplicate the layers they are applied to, the animation remains the same for each. Many thanks in advance!
-Steve//Bouncing ball with squash and stretch
//Apply to Position
freq = 1.0; //oscillations per second
amplitude = 90;
decay = .5;
posCos = Math.abs(Math.cos(freq*time*2*Math.PI));
y = amplitude*posCos/Math.exp(decay*time);
position - [0,y]//and here's the expression for the scale parameter.
freq = 1.0;
squashFreq = 4.0;
decay = 5.0;
masterDecay = 0.4;
amplitude = 25;
delay = 1/(freq*4);
if (time > delay){
bounce = Math.sin(squashFreq*time*2*Math.PI);
bounceDecay = Math.exp(decay*((time - delay)%(freq/2)));
overallDecay = Math.exp(masterDecay*(time - delay));
x = scale[0] + amplitude*bounce/bounceDecay/overallDecay;
y = scale[0]*scale[1]/x;
[x,y]
}else{
scale
}Steven Kutny
Designer/Compositor
http://www.stevenkutny.com -
7 Replies
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If you have a bunch of parameters in an expression and you want to vary them by say, plus or minus 10% on each layer, you could do something like this:
seedRandom(index,true);
freq = 1.0*random(.9,1.1);
amplitude = 90*random(.9,1.1);
decay = .5*random(.9,1.1);
posCos = Math.abs(Math.cos(freq*time*2*Math.PI));
y = amplitude*posCos/Math.exp(decay*time);
position – [0,y]You would do a similar thing for the scale expression.
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Thanks for the quick response Dan! This works for the subtle variations, but what if I wanted to offset the entire animation by 10 frames without having to pre-comp? No variation, just frame/time offset.
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Ah, that would be more like this:
freq = 1.0;
amplitude = 90;
decay = .5;
delay = .1;
t = (time-inPoint) – delay*(index-1);
posCos = Math.abs(Math.cos(freq*t*2*Math.PI));
y = amplitude*posCos/Math.exp(decay*t);
position – [0,y]Dan
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Perfect! Thanks so much for this Dan, it is a big help 🙂
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Hi Dan,
Grateful if I could get your input one more time with this. I notice that the look of the animation changes depending on the layer order. If I create layers about them, or if I reorder the layers in my comp, their animation shifts.
I removed the (index-1) part from this line: t = (time-inPoint) – delay*(index-1); which fixes that problem, but now I see the bouncing doesn’t always land on the same base line with a 0.1 delay; the hits will be slightly higher than the final resting position, unless I change the delay to 0.5 or something higher. Just making sure my change to that line is correct for this expression.
Also wondering if there is a way to match up the squash & stretch expression on scale to the bouncing? I’m getting varied results. Not sure if I need to match the delay to the delay on position or the difference between the decay and masterDecay…
Many thanks!
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Fixed the scale problem using this code form your site:
maxDev = 13; // max deviation in pixels
spd = 30; //speed of oscillation
decay = 1.0; //how fast it slows downt = time – inPoint;
x = scale[0] + maxDev*Math.sin(spd*t)/Math.exp(decay*t);
y = scale[0]*scale[1]/x;
[x,y]I repositioned my null to where it should have been, at the bottom of my ball, and now the sin wave feels correct. Thanks again!
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Going with this for position… Frame rate must dictate how bounce lands on the base line when tweaking the frequency… Sometimes a higher or lower freq throws off the hit. Trial and error but it’s all good.
freq = 1.0;
amplitude = 500;
decay = 1;
t = time-inPoint;
posCos = Math.abs(Math.cos(freq*t*2*Math.PI));
y = amplitude*posCos/Math.exp(decay*t);
position - [0,y]
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