elevator style easing

Author: FreyaHolmer

Runtime/Splines/Multi-Segment Splines/ElevatorEase.cs

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+using System;
+using Freya;
+
+public class ElevatorEase {
+
+	public enum Mode {
+		FastStartPolynomial,
+		Trigonometric
+	}
+
+	public readonly Mode mode;
+	public readonly float maxDistance;
+	public readonly float contractSpeed;
+	public readonly float accDuration;
+
+	public readonly float t1;
+	public readonly float t2;
+	public readonly float tEnd;
+	public readonly float v;
+
+	// linear section
+	float g_c0, g_c1;
+
+	// polynomial coefficients used by Mode.FastStartPolynomial
+	float f_c3, f_c4, f_c5; // ease in
+	float h_c4, h_c5; // ease out (relative)
+
+	// constants used by Mode.Trigonometric
+	float c_xsq, c_trigScale, c_trigInner;
+
+	public ElevatorEase( Mode mode, float maxDistance, float contractSpeed, float accDuration ) {
+		this.mode = mode;
+		this.maxDistance = maxDistance;
+		this.contractSpeed = contractSpeed;
+		this.accDuration = accDuration;
+
+		// derived things
+		t1 = accDuration;
+		t2 = maxDistance / contractSpeed;
+		tEnd = t1 + t2;
+		v = contractSpeed;
+		float tHalf = tEnd / 2;
+		if( accDuration >= tHalf ) {
+			// no linear section - adjust accordingly
+			t1 = t2 = tHalf;
+			v = 2 * ( maxDistance / tEnd );
+		}
+
+		// calculate coefficients
+		g_c1 = v;
+		if( mode == Mode.FastStartPolynomial ) {
+			g_c0 = -2 * v * t1 / 5;
+			float t1_2 = t1 * t1;
+			float t1_3 = t1_2 * t1;
+			float t1_4 = t1_2 * t1_2;
+			f_c3 = 2 * v / t1_2;
+			f_c4 = 2 * v / -t1_3;
+			f_c5 = 3 * v / ( 5 * t1_4 );
+			h_c4 = v / -t1_3;
+			h_c5 = -3 * v / ( 5 * t1_4 );
+		} else if( mode == Mode.Trigonometric ) {
+			g_c0 = -v * t1 / 2;
+			c_xsq = v / ( 2 * t1 );
+			c_trigScale = v * t1 / ( Mathfs.TAU * Mathfs.TAU );
+			c_trigInner = Mathfs.TAU / t1;
+		}
+	}
+
+	float EaseIn( float t ) {
+		float x2 = t * t;
+
+		if( mode == Mode.FastStartPolynomial ) {
+			float x3 = x2 * t;
+			float x4 = x2 * x2;
+			float x5 = x3 * x2;
+			return f_c3 * x3 + f_c4 * x4 + f_c5 * x5;
+		} else if( mode == Mode.Trigonometric ) {
+			return c_xsq * x2 + c_trigScale * ( MathF.Cos( c_trigInner * t ) - 1 );
+		}
+		throw new NotImplementedException();
+	}
+
+	float Linear( float t ) => g_c0 + g_c1 * t;
+
+	float EaseOut( float t ) {
+		if( mode == Mode.FastStartPolynomial ) {
+			// this one is asymmetric, and needs special handling
+			float x = t - tEnd; // remap to relative
+			float x2 = x * x;
+			float x4 = x2 * x2;
+			float x5 = x4 * x;
+			return h_c4 * x4 + h_c5 * x5 + maxDistance;
+		}
+
+		// same as ease-in but reversed
+		return maxDistance - EaseIn( tEnd - t );
+	}
+
+	public float Eval( float t ) {
+		// check extremes:
+		if( t <= 0 )
+			return 0;
+		if( t >= tEnd )
+			return maxDistance;
+		// check functions:
+		if( t < t1 )
+			return EaseIn( t );
+		if( t > t2 )
+			return EaseOut( t );
+		return Linear( t );
+	}
+
+}