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surprised by sporatic result in expression
Hi everyone.
I’m using the code below to make a wing flap.
The problem is when i ramp the sliders up it the wing goes crazy until it hits its destination frequency/amplitude.
Does anyone have any idea why? Does it need to calculate integers and not decimals? my sliders are as follows:
frequency: 0.32 -> 3.3
amplitude: 10 -> 77Also, how would i add in the ease(…) code to it?
Thanks!
/jay(ps, the decay element is not needed in the expression)
freq = thisComp.layer("Null: Angle Wing Slider").effect("Frequency Slider")("Slider");
amplitude = thisComp.layer("Null: Angle Wing Slider").effect("Amplitude Slider")("Slider");
decay = 0; //no decayamplitude*Math.sin(freq*time*2*Math.PI)
jay
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1 Reply
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It’s hard to explain, but any time you try and change the speed or frequency of an expression you can run into trouble. In this case, because expressions have no info about what has happened in the past, at each frame the calculation behaves as if the frequency has always been at the current value. This can cause discontinuities, speeding up and slowing down, until the frequency stabilizes.
One approach is to create a loop that integrates how much the frequency at each frame affects the total phase angle of the wave. This isn’t a great solution for a long piece, because the calculation takes longer at each frame, but it works OK for short pieces. Try this:
freq = thisComp.layer(“Null: Angle Wing Slider”).effect(“Frequency Slider”)(“Slider”);
amplitude = thisComp.layer(“Null: Angle Wing Slider”).effect(“Amplitude Slider”)(“Slider”);phase = 0;
f = timeToFrames(time);
for (i = 1; i <= f; i++){ phase += (thisComp.frameDuration*freq.valueAtTime(framesToTime(i)))*Math.PI*2; } amplitude*Math.sin(phase) Dan
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