On 29/07/2026 12:41, Bald Eagle wrote:
> "S I R ?" <fra### [at] jaliscoedumx> wrote:
>> kurtz le pirate <kur### [at] freefr> wrote:
> 
>>> // 50 degrees -> +/- 25 deg or something else, of course
>>> #declare Amplitude = 50;
>>> #declare HalfAmplitude = Amplitude*0.50;
> 
> You want the pendulum to swing over a certain amount on both sides.
> kurtz defines the included angle as "Amplitude" and then takes half of that as
> the amount it swings to either side.
> 
>>> Object to animate is "Object"
>>>
>>> object {
>>>     Object
> So now he places the Object in the scene, and to rotate it in the animation, he
> creates an equation using the clock variable.
> 
> if you point at your screen, your arm an finger are in the direction of the z
> axis.  So rotating around z rotates things in the plane of your screen.
> By how much?
> Well the max is "HalfAmlitude".
> And we want to go from 0 to HalfAmplitude to 0 to -HalfAmplitude to 0 to .....
> 
> A circle is 2*pi radians around in angular units. (tau = 2*pi)
> plotting sin on a unit circle goes from 0 to 1 to 0 to -1 to 0 to ....
> 
> So as the clock variable increases from 0 to 1, we take that and multiply it by
> tau.  That gives us a value that goes from 0 to tau.
> Taking the sin of that gives us a value that goes from 0 to 1 to 0 to -1 to 0 to
> .....
> then multiplying that by HalfAmplitude gives us a value that goes from 0 to
> HalfAmplitude to 0 to -HalfAmplitude to 0 to .....
> and of course we need a vector to pass to "rotate", and so we multiply by z
> 
>>>     rotate sin(clock*tau)*HalfAmplitude*z
>>>     }
>>>
>>> 'clock' from 0.0 to 1.0
> 


Perfect BE. I couldn't have said it better myself


-- 
kurtz le pirate
compagnie de la banquise

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