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back.go
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back.go
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package easing
const (
defaultOvershoot = 1.70158
magicOvershootInOutScalar = 1.525
)
var _ EaseFunctionProvider = &BackOutEaseProvider{}
var _ EaseFunctionProvider = &BackInEaseProvider{}
var _ EaseFunctionProvider = &BackInOutEaseProvider{}
type BackOutEaseProvider struct{}
func (*BackOutEaseProvider) New(params []float64) func(float64) float64 {
params = ensureBackParams(params)
overshoot := params[0]
back := func(v float64) float64 {
return v*v*((overshoot+1)*v+overshoot) + 1
}
return back
}
type BackInEaseProvider struct{}
func (*BackInEaseProvider) New(params []float64) func(float64) float64 {
params = ensureBackParams(params)
overshoot := params[0]
back := func(v float64) float64 {
return v * v * ((overshoot+1)*v - overshoot)
}
return back
}
type BackInOutEaseProvider struct{}
func (*BackInOutEaseProvider) New(params []float64) func(float64) float64 {
params = ensureBackParams(params)
overshoot := params[0]
back := func(v float64) float64 {
v *= 2
s := overshoot * magicOvershootInOutScalar
if v < 1 {
return 0.5 * (v * v * ((s+1)*v - s))
}
return 0.5 * ((v-2)*v*((s+1)*v+s) + 2)
}
return back
}
func ensureBackParams(params []float64) []float64 {
if params == nil {
params = []float64{defaultOvershoot}
}
switch len(params) {
case 0:
params = []float64{defaultOvershoot}
}
return params
}