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- #!/usr/bin/ruby
- #
- ## https://rosettacode.org/wiki/Animate_a_pendulum
- #
- require('Tk')
- var root = %s<MainWindow>.new('-title' => 'Pendulum Animation')
- var canvas = root.Canvas('-width' => 320, '-height' => 200)
- canvas.createLine( 0, 25, 320, 25, '-tags' => <plate>, '-width' => 2, '-fill' => :grey50)
- canvas.createOval(155, 20, 165, 30, '-tags' => <pivot outline>, '-fill' => :grey50)
- canvas.createLine( 1, 1, 1, 1, '-tags' => <rod width>, '-width' => 3, '-fill' => :black)
- canvas.createOval( 1, 1, 2, 2, '-tags' => <bob outline>, '-fill' => :yellow)
- canvas.raise(:pivot)
- canvas.pack('-fill' => :both, '-expand' => 1)
- var(θ = 45, Δθ = 0, length = 150, homeX = 160, homeY = 25)
- func show_pendulum() {
- var angle = θ.deg2rad
- var x = (homeX + length*sin(angle))
- var y = (homeY + length*cos(angle))
- canvas.coords(:rod, homeX, homeY, x, y)
- canvas.coords(:bob, x - 15, y - 15, x + 15, y + 15)
- }
- func recompute_angle() {
- var scaling = 3000/(length**2)
- # first estimate
- var firstΔΔθ = (-sin(θ.deg2rad) * scaling)
- var midΔθ = (Δθ + firstΔΔθ)
- var midθ = ((Δθ + midΔθ)/2 + θ)
- # second estimate
- var midΔΔθ = (-sin(midθ.deg2rad) * scaling)
- midΔθ = ((firstΔΔθ + midΔΔθ)/2 + Δθ)
- midθ = ((Δθ + midΔθ)/2 + θ)
- # again, first
- midΔΔθ = (-sin(midθ.deg2rad) * scaling)
- var lastΔθ = (midΔθ + midΔΔθ)
- var lastθ = ((midΔθ + lastΔθ)/2 + midθ)
- # again, second
- var lastΔΔθ = (-sin(lastθ.deg2rad) * scaling)
- lastΔθ = ((midΔΔθ + lastΔΔθ)/2 + midΔθ)
- lastθ = ((midΔθ + lastΔθ)/2 + midθ)
- # Now put the values back in our globals
- Δθ = lastΔθ
- θ = lastθ
- }
- func animate(Ref id) {
- recompute_angle()
- show_pendulum()
- *id = root.after(15 => { animate(id) })
- }
- show_pendulum()
- var after_id = root.after(500 => { animate(\after_id) })
- canvas.bind('<Destroy>' => { after_id.cancel })
- %S<Tk>.MainLoop()
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