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easings/README.md

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+## easings [![GoDoc](https://godoc.org/github.com/gen2brain/raylib-go/easings?status.svg)](https://godoc.org/github.com/gen2brain/raylib-go/easings)
+
+Useful easing functions for values animation.
+
+A port of Robert Penner's [easing equations](http://robertpenner.com/easing/).
+
+![screenshot](https://goo.gl/crzRrH)

easings/easings.go

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+// Useful easing functions for values animation
+//
+// A port of Robert Penner's easing equations (http://robertpenner.com/easing/)
+package easings
+
+import (
+	"math"
+)
+
+// Linear Easing functions
+
+func LinearNone(t, b, c, d float32) float32 {
+	return c*t/d + b
+}
+
+func LinearIn(t, b, c, d float32) float32 {
+	return c*t/d + b
+}
+
+func LinearOut(t, b, c, d float32) float32 {
+	return c*t/d + b
+}
+
+func LinearInOut(t, b, c, d float32) float32 {
+	return c*t/d + b
+}
+
+// Sine Easing functions
+
+func SineIn(t, b, c, d float32) float32 {
+	return -c*float32(math.Cos(float64(t/d)*(math.Pi/2))) + c + b
+}
+
+func SineOut(t, b, c, d float32) float32 {
+	return c*float32(math.Sin(float64(t/d)*(math.Pi/2))) + b
+}
+
+func SineInOut(t, b, c, d float32) float32 {
+	return -c/2*(float32(math.Cos(math.Pi*float64(t/d)))-1) + b
+}
+
+// Circular Easing functions
+
+func CircIn(t, b, c, d float32) float32 {
+	t = t / d
+	return -c*(float32(math.Sqrt(float64(1-t*t)))-1) + b
+}
+
+func CircOut(t, b, c, d float32) float32 {
+	return c*float32(math.Sqrt(1-float64((t/d-1)*t))) + b
+}
+
+func CircInOut(t, b, c, d float32) float32 {
+	t = t / d * 2
+
+	if t < 1 {
+		return -c/2*(float32(math.Sqrt(float64(1-t*t)))-1) + b
+	} else {
+		t = t - 2
+		return c/2*(float32(math.Sqrt(1-float64(t*t)))+1) + b
+	}
+}
+
+// Cubic Easing functions
+
+func CubicIn(t, b, c, d float32) float32 {
+	t = t / d
+	return c*t*t*t + b
+}
+
+func CubicOut(t, b, c, d float32) float32 {
+	t = t/d - 1
+	return c*(t*t*t+1) + b
+}
+
+func CubicInOut(t, b, c, d float32) float32 {
+	t = t / d * 2
+	if t < 1 {
+		return (c/2*t*t*t + b)
+	} else {
+		t = t - 2
+		return c/2*(t*t*t+2) + b
+	}
+}
+
+// Quadratic Easing functions
+
+func QuadIn(t, b, c, d float32) float32 {
+	t = t / d
+	return c*t*t + b
+}
+
+func QuadOut(t, b, c, d float32) float32 {
+	t = t / d
+	return (-c*t*(t-2) + b)
+}
+
+func QuadInOut(t, b, c, d float32) float32 {
+	t = t / d * 2
+	if t < 1 {
+		return ((c / 2) * (t * t)) + b
+	} else {
+		return -c/2*((t-1)*(t-3)-1) + b
+	}
+}
+
+// Exponential Easing functions
+
+func ExpoIn(t, b, c, d float32) float32 {
+	if t == 0 {
+		return b
+	} else {
+		return (c*float32(math.Pow(2, 10*float64(t/d-1))) + b)
+	}
+}
+
+func ExpoOut(t, b, c, d float32) float32 {
+	if t == d {
+		return (b + c)
+	} else {
+		return c*(-float32(math.Pow(2, -10*float64(t/d)))+1) + b
+	}
+}
+
+func ExpoInOut(t, b, c, d float32) float32 {
+	if t == 0 {
+		return b
+	}
+	if t == d {
+		return (b + c)
+	}
+
+	t = t / d * 2
+
+	if t < 1 {
+		return (c/2*float32(math.Pow(2, 10*float64(t-1))) + b)
+	} else {
+		t = t - 1
+		return (c/2*(-float32(math.Pow(2, -10*float64(t)))+2) + b)
+	}
+}
+
+// Back Easing functions
+
+func BackIn(t, b, c, d float32) float32 {
+	s := float32(1.70158)
+	t = t / d
+	return c*t*t*((s+1)*t-s) + b
+}
+
+func BackOut(t, b, c, d float32) float32 {
+	s := float32(1.70158)
+	t = t/d - 1
+	return c*(t*t*((s+1)*t+s)+1) + b
+}
+
+func BackInOut(t, b, c, d float32) float32 {
+	s := float32(1.70158)
+	s = s * 1.525
+	t = t / d * 2
+
+	if t < 1 {
+		return c/2*(t*t*((s+1)*t-s)) + b
+	} else {
+		t = t - 2
+		return c/2*(t*t*((s+1)*t+s)+2) + b
+	}
+}
+
+// Bounce Easing functions
+
+func BounceIn(t, b, c, d float32) float32 {
+	return (c - BounceOut(d-t, 0, c, d) + b)
+}
+
+func BounceOut(t, b, c, d float32) float32 {
+	t = t / d
+	if t < (1 / 2.75) {
+		return (c*(7.5625*t*t) + b)
+	} else if t < (2 / 2.75) {
+		t = t - (1.5 / 2.75)
+		return c*(7.5625*t*t+0.75) + b
+	} else if t < (2.5 / 2.75) {
+		t = t - (2.25 / 2.75)
+		return c*(7.5625*t*t+0.9375) + b
+	} else {
+		t = t - (2.625 / 2.75)
+		return c*(7.5625*t*t+0.984375) + b
+	}
+}
+
+func BounceInOut(t, b, c, d float32) float32 {
+	if t < d/2 {
+		return BounceIn(t*2, 0, c, d)*0.5 + b
+	} else {
+		return BounceOut(t*2-d, 0, c, d)*0.5 + c*0.5 + b
+	}
+}
+
+// Elastic Easing functions
+
+func ElasticIn(t, b, c, d float32) float32 {
+	if t == 0 {
+		return b
+	}
+
+	t = t / d
+
+	if t == 1 {
+		return b + c
+	}
+
+	p := d * 0.3
+	a := c
+	s := p / 4
+	postFix := a * float32(math.Pow(2, 10*float64(t-1)))
+
+	return -(postFix * float32(math.Sin(float64(t*d-s)*(2*math.Pi)/float64(p)))) + b
+}
+
+func ElasticOut(t, b, c, d float32) float32 {
+	if t == 0 {
+		return b
+	}
+
+	t = t / d
+
+	if t == 1 {
+		return b + c
+	}
+
+	p := d * 0.3
+	a := c
+	s := p / 4
+
+	return a*float32(math.Pow(2, -10*float64(t)))*float32(math.Sin(float64(t*d-s)*(2*math.Pi)/float64(p))) + c + b
+}
+
+func ElasticInOut(t, b, c, d float32) float32 {
+	if t == 0 {
+		return b
+	}
+
+	t = t / d * 2
+
+	if t == 2 {
+		return b + c
+	}
+
+	p := d * (0.3 * 1.5)
+	a := c
+	s := p / 4
+
+	if t < 1 {
+		t = t - 1
+		postFix := a * float32(math.Pow(2, 10*float64(t)))
+		return -0.5*(postFix*float32(math.Sin(float64(t*d-s)*(2*math.Pi)/float64(p)))) + b
+	} else {
+		t = t - 1
+		postFix := a * float32(math.Pow(2, -10*(float64(t))))
+		return postFix*float32(math.Sin(float64(t*d-s)*(2*math.Pi)/float64(p)))*0.5 + c + b
+	}
+}