1 files changed, 120 insertions, 0 deletions
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Tweening/EasingFunctions.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Tweening/EasingFunctions.cs
new file mode 100644
index 0000000..f93a5ff
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Tweening/EasingFunctions.cs
@@ -0,0 +1,120 @@
+using System;
+using Microsoft.Xna.Framework;
+
+namespace MonoGame.Extended.Tweening
+{
+    public static class EasingFunctions
+    {
+        public static float Linear(float value) => value;
+
+        public static float CubicIn(float value) => Power.In(value, 3);
+        public static float CubicOut(float value) => Power.Out(value, 3);
+        public static float CubicInOut(float value) => Power.InOut(value, 3);
+
+        public static float QuadraticIn(float value) => Power.In(value, 2);
+        public static float QuadraticOut(float value) => Power.Out(value, 2);
+        public static float QuadraticInOut(float value) => Power.InOut(value, 2);
+
+        public static float QuarticIn(float value) => Power.In(value, 4);
+        public static float QuarticOut(float value) => Power.Out(value, 4);
+        public static float QuarticInOut(float value) => Power.InOut(value, 4);
+
+        public static float QuinticIn(float value) => Power.In(value, 5);
+        public static float QuinticOut(float value) => Power.Out(value, 5);
+        public static float QuinticInOut(float value) => Power.InOut(value, 5);
+
+        public static float SineIn(float value) => (float) Math.Sin(value*MathHelper.PiOver2 - MathHelper.PiOver2) + 1;
+        public static float SineOut(float value) => (float) Math.Sin(value*MathHelper.PiOver2);
+        public static float SineInOut(float value) => (float) (Math.Sin(value*MathHelper.Pi - MathHelper.PiOver2) + 1)/2;
+
+        public static float ExponentialIn(float value) => (float) Math.Pow(2, 10*(value - 1));
+        public static float ExponentialOut(float value) => Out(value, ExponentialIn);
+        public static float ExponentialInOut(float value) => InOut(value, ExponentialIn);
+
+        public static float CircleIn(float value) => (float) -(Math.Sqrt(1 - value * value) - 1);
+        public static float CircleOut(float value) => (float) Math.Sqrt(1 - (value - 1) * (value - 1));
+        public static float CircleInOut(float value) => (float) (value <= .5 ? (Math.Sqrt(1 - value * value * 4) - 1) / -2 : (Math.Sqrt(1 - (value * 2 - 2) * (value * 2 - 2)) + 1) / 2);
+
+        public static float ElasticIn(float value)
+        {
+            const int oscillations = 1;
+            const float springiness = 3f;
+            var e = (Math.Exp(springiness*value) - 1)/(Math.Exp(springiness) - 1);
+            return (float) (e*Math.Sin((MathHelper.PiOver2 + MathHelper.TwoPi*oscillations)*value));
+        }
+
+        public static float ElasticOut(float value) => Out(value, ElasticIn);
+        public static float ElasticInOut(float value) => InOut(value, ElasticIn);
+
+        public static float BackIn(float value)
+        {
+            const float amplitude = 1f;
+            return (float) (Math.Pow(value, 3) - value*amplitude*Math.Sin(value*MathHelper.Pi));
+        }
+
+        public static float BackOut(float value) => Out(value, BackIn);
+        public static float BackInOut(float value) => InOut(value, BackIn);
+
+        public static float BounceOut(float value) => Out(value, BounceIn);
+        public static float BounceInOut(float value) => InOut(value, BounceIn);
+
+        public static float BounceIn(float value)
+        {
+            const float bounceConst1 = 2.75f;
+            var bounceConst2 = (float) Math.Pow(bounceConst1, 2);
+
+            value = 1 - value; //flip x-axis
+
+            if (value < 1/bounceConst1) // big bounce
+                return 1f - bounceConst2*value*value;
+
+            if (value < 2/bounceConst1)
+                return 1 - (float) (bounceConst2*Math.Pow(value - 1.5f/bounceConst1, 2) + .75);
+
+            if (value < 2.5/bounceConst1)
+                return 1 - (float) (bounceConst2*Math.Pow(value - 2.25f/bounceConst1, 2) + .9375);
+
+            //small bounce
+            return 1f - (float) (bounceConst2*Math.Pow(value - 2.625f/bounceConst1, 2) + .984375);
+        }
+
+
+        private static float Out(float value, Func<float, float> function)
+        {
+            return 1 - function(1 - value);
+        }
+
+        private static float InOut(float value, Func<float, float> function)
+        {
+            if (value < 0.5f)
+                return 0.5f*function(value*2);
+
+            return 1f - 0.5f*function(2 - value*2);
+        }
+
+        private static class Power
+        {
+            public static float In(double value, int power)
+            {
+                return (float) Math.Pow(value, power);
+            }
+
+            public static float Out(double value, int power)
+            {
+                var sign = power%2 == 0 ? -1 : 1;
+                return (float) (sign*(Math.Pow(value - 1, power) + sign));
+            }
+
+            public static float InOut(double s, int power)
+            {
+                s *= 2;
+
+                if (s < 1)
+                    return In(s, power)/2;
+
+                var sign = power%2 == 0 ? -1 : 1;
+                return (float) (sign/2.0*(Math.Pow(s - 2, power) + sign*2));
+            }
+        }
+    }
+}
+\ No newline at end of file