cleanup easing functions

include/fggl/math/easing.hpp

@@ -6,14 +6,15 @@
 #define FGGL_MATH_EASING_H
 
 #include <fggl/math/types.hpp>
+#include <functional>
 
 namespace fggl::math {
 
-	inline float lerp(float a, float b, float w) {
+	constexpr inline float lerp(float a, float b, float w) {
 		return (b - a) * w + a;
 	}
 
-	inline float scale(float in, float inMin, float inMax, float outMin, float outMax) {
+	constexpr inline float scale(float in, float inMin, float inMax, float outMin, float outMax) {
 		return ((in - inMin) * (outMax - outMin)) / (inMax - inMin);
 	}
 
@@ -22,42 +23,42 @@ namespace fggl::math {
 	//
 	using transformF = std::function<float(float)>;
 
-	inline float scaleFilter(float in, float inMin, float inMax, float outMin, float outMax, transformF filter) {
+	inline float scaleFilter(float in, float inMin, float inMax, float outMin, float outMax, const transformF& filter) {
 		float out = in - inMin;
 		out /= (inMax - inMin);
-		out = f(out);
-		out *= (outEnd - outStart);
+		out = filter(out);
+		out *= (outMax - outMin);
 		return out + outMin;
 	}
 
-	inline float mix(transformF a, transformF b, float weightB, float t) {
-		return ((1 - weightB) * a(t)) + (weightB * b(t));
+	inline float mix(const transformF& funcA, const transformF& funcB, float weightB, float t) {
+		return ((1 - weightB) * funcA(t)) + (weightB * funcB(t));
 	}
 
-	inline float crossFade(transformF a, transformF b, float t) {
-		return ((1 - t) * a(t)) + (t * b);
+	inline float crossFade(transformF funcA, transformF funcB, float t) {
+		return ((1 - t) * funcA(t)) + (t * funcB(t));
 	}
 
 	//
 	// building blocks
 	//
-	inline float scale(transformF a, float t) {
+	inline float scale(transformF f, float t) {
 		return t * f(t);
 	}
 
-	inline float reverseScale(transformF a, float t) {
-		return (1 - t) * a(t);
+	inline float reverseScale(transformF f, float t) {
+		return (1 - t) * f(t);
 	}
 
-	inline float Arch2(float t) {
+	constexpr inline float Arch2(float t) {
 		return t * (1 - t);
 	}
 
-	inline float BounceClampBottom(float t) {
+	constexpr inline float BounceClampBottom(float t) {
 		return fabs(t);
 	}
 
-	inline float BounceClampTop(float t) {
+	constexpr inline float BounceClampTop(float t) {
 		return 1.f - fabs(1.f - t);
 	}
 
@@ -66,39 +67,39 @@ namespace fggl::math {
 	// see Math for Game Programmers: Fast and Funky 1D Nonlinear Transformations, GDC 2015
 	//
 
-	inline float SmoothStart2(float t) {
+	constexpr inline float SmoothStart2(float t) {
 		return t * t;
 	}
 
-	inline float SmoothStart3(float t) {
+	constexpr inline float SmoothStart3(float t) {
 		return t * t * t;
 	}
 
-	inline float SmoothStart4(float t) {
+	constexpr inline float SmoothStart4(float t) {
 		return t * t * t * t;
 	}
 
-	inline float SmoothStart5(float t) {
+	constexpr inline float SmoothStart5(float t) {
 		return t * t * t * t * t;
 	}
 
-	inline float SmoothStop2(float t) {
-		constexpr tFlip = 1 - y;
+	constexpr inline float SmoothStop2(float t) {
+		const auto tFlip = 1 - t;
 		return 1 - (tFlip * tFlip);
 	}
 
-	inline float SmoothStop3(float t) {
-		constexpr tFlip = 1 - y;
+	constexpr inline float SmoothStop3(float t) {
+		const auto tFlip = 1 - t;
 		return 1 - (tFlip * tFlip);
 	}
 
-	inline float SmoothStop4(float t) {
-		constexpr tFlip = 1 - y;
+	constexpr inline float SmoothStop4(float t) {
+		const auto tFlip = 1 - t;
 		return 1 - (tFlip * tFlip * tFlip * tFlip);
 	}
 
-	inline float SmoothStop5(float t) {
-		constexpr tFlip = 1 - y;
+	constexpr inline float SmoothStop5(float t) {
+		const auto tFlip = 1 - t;
 		return 1 - (tFlip * tFlip * tFlip * tFlip * tFlip);
 	}
 
@@ -106,7 +107,7 @@ namespace fggl::math {
 	// Bezier curves
 	//
 
-	inline float NormalizedBezier3(float B, float C, float t) {
+	constexpr inline float NormalizedBezier3(float B, float C, float t) {
 		const float s = 1.f - t;
 		const float t2 = t * t;
 		const float s2 = s * s;