added an extension method to auto-reverse an easing function

Demos/EasingsDemo.cs

@@ -17,6 +17,7 @@ namespace Demos {
             .Select(f => (Easings.Easing) f.GetValue(null)).ToArray();
         private Group group;
         private int current;
+        private float progress;
 
         public EasingsDemo(MlemGame game) : base(game) {
         }
@@ -26,7 +27,10 @@ namespace Demos {
 
             this.group = new Group(Anchor.TopCenter, Vector2.One) {SetWidthBasedOnChildren = true};
             this.group.AddChild(new Button(Anchor.AutoCenter, new Vector2(30, 10), "Next") {
-                OnPressed = e => this.current = (this.current + 1) % Easings.Length
+                OnPressed = e => {
+                    this.current = (this.current + 1) % Easings.Length;
+                    this.progress = 0;
+                }
             });
             this.group.AddChild(new Paragraph(Anchor.AutoCenter, 1, p => EasingFields[this.current].Name, true));
             this.UiRoot.AddChild(this.group);
@@ -42,11 +46,20 @@ namespace Demos {
 
             this.SpriteBatch.Begin(SpriteSortMode.Deferred, null, SamplerState.PointClamp);
             var view = this.GraphicsDevice.Viewport;
-            var easing = Easings[this.current].ScaleInput(0, view.Width).ScaleOutput(-view.Height / 3, view.Height / 3);
+
+            // graph the easing function
+            var graphEase = Easings[this.current].ScaleInput(0, view.Width).ScaleOutput(-view.Height / 3, view.Height / 3);
             for (var x = 0; x < view.Width; x++) {
-                var area = new RectangleF(x - 2, view.Height / 2 - easing(x) - 2, 4, 4);
+                var area = new RectangleF(x - 2, view.Height / 2 - graphEase(x) - 2, 4, 4);
                 this.SpriteBatch.Draw(this.SpriteBatch.GetBlankTexture(), area, Color.Green);
             }
+
+            // draw a little dot to show what it would look like
+            this.progress = (this.progress + (float) time.ElapsedGameTime.TotalSeconds / 2) % 1;
+            var dotEase = Easings[this.current].AndReverse().ScaleOutput(0, view.Height / 4);
+            var pos = new RectangleF(view.Width / 2 - 4, view.Height - 20 - dotEase(this.progress), 8, 8);
+            this.SpriteBatch.Draw(this.SpriteBatch.GetBlankTexture(), pos, Color.Red);
+
             this.SpriteBatch.End();
         }
 

MLEM/Misc/Easings.cs

@@ -100,6 +100,16 @@ namespace MLEM.Misc {
             return p => easing(p) * (max - min) + min;
         }
 
+        /// <summary>
+        /// Causes the easing functino to play fully, and then play fully in reverse, in the span between an input of 0 and 1.
+        /// In some places, this behavior is also called "auto-reversing".
+        /// </summary>
+        /// <param name="easing">The easing function to play in reverse as well</param>
+        /// <returns>An auto-reversing version of the easing function</returns>
+        public static Easing AndReverse(this Easing easing) {
+            return p => p <= 0.5F ? easing(p * 2) : easing(1 - (p - 0.5F) * 2);
+        }
+
         /// <summary>
         /// A delegate method used by <see cref="Easings"/>.
         /// </summary>