math: add remap/5, smoothstep/3 and smootherstep/3 implementations + tests

spytheman · spytheman · commit e32283fd1c6d · 2025-03-12T08:53:27.000+02:00
diff --git a/vlib/math/interpolation.v b/vlib/math/interpolation.v
@@ -24,3 +24,38 @@ pub fn clip[T](x T, min_value T, max_value T) T {
 		x
 	}
 }
+
+// remap the input `x`, from the range [`a`,`b`] to [`c`,`d`] .
+// Example: math.remap(20, 1, 100, 50, 5000) == 1000
+// Note: `a` should be != `b`.
+@[inline]
+pub fn remap[T](x T, a T, b T, c T, d T) T {
+	return c + (d - c) * (x - a) / (b - a)
+}
+
+// smoothstep smoothly maps a value between `edge0` and `edge1`. It returns:
+// 0 if `x` is less than or equal to the left `edge0`,
+// 1 if `x` is greater than or equal to the right `edge`,
+// and smoothly interpolates, using a Hermite polynomial, between 0 and 1 otherwise.
+// The gradient of the smoothstep function is zero at both edges. This is convenient
+// for creating a sequence of transitions using smoothstep to interpolate each segment
+// as an alternative to using more sophisticated or expensive interpolation techniques.
+// `smoothstep` is a 1st order smoothing function, using a 3rd order polynomial.
+// See also `smootherstep`, which is slower, but nicer looking.
+// See also https://en.wikipedia.org/wiki/Smoothstep
+@[inline]
+pub fn smoothstep[T](edge0 T, edge1 T, x T) T {
+	v := clip((x - edge0) / (edge1 - edge0), 0, 1)
+	return v * v * (3 - 2 * v)
+}
+
+// smootherstep smoothly maps a value between `edge0` and `edge1`.
+// smootherstep is a 2nd order smoothing function, using a 5th order polynomial.
+// The 1st and 2nd order derivatives of the smootherstep function are 0 at both edges.
+// See also `smoothstep`, which is faster, but has just its gradient being 0 at both edges.
+// See also https://en.wikipedia.org/wiki/Smoothstep
+@[inline]
+pub fn smootherstep[T](edge0 T, edge1 T, x T) T {
+	v := clip((x - edge0) / (edge1 - edge0), 0, 1)
+	return v * v * v * (x * (6 * x - 15) + 10)
+}
diff --git a/vlib/math/interpolation_test.v b/vlib/math/interpolation_test.v
@@ -65,3 +65,40 @@ fn test_cubic_bezier_fa() {
 	assert math.cubic_bezier_fa(0.5, bx_fa, by_fa) == math.BezierPoint{0.35375, 0.5375}
 	assert math.cubic_bezier_fa(1.0, bx_fa, by_fa) == math.BezierPoint{bx_fa[3], by_fa[3]}
 }
+
+fn test_remap() {
+	assert math.remap(20, 1, 100, 50, 5000) == 1000
+	assert math.remap(20.0, 1, 100, 50, 5000) == 1000.0
+
+	assert math.remap(55, 1, 100, 52, 5000) == 2750
+	assert math.remap(55.0, 1, 100, 52, 5000) == 2750.909090909091
+
+	assert math.remap(25, 1, 100, 50, 5000) == 1250
+	assert math.remap(25, 1, 100, -50, -5000) == -1250
+	assert math.remap(25, 1, 100, 5000, 50) == 3800
+	assert math.remap(25, 1, 100, -5000, -50) == -3800
+	assert math.remap(25, 100, 1, 50, 5000) == 3800
+	assert math.remap(25, 100, 1, -50, -5000) == -3800
+	assert math.remap(25, 100, 1, 5000, 50) == 1250
+	assert math.remap(25, 100, 1, -5000, -50) == -1250
+}
+
+fn test_smoothstep() {
+	assert math.smoothstep(0.0, 1, 0) == 0
+	assert math.close(math.smoothstep(0.0, 1, 0.05), 0.00725)
+	assert math.close(math.smoothstep(0.0, 1, 0.1), 0.028)
+	assert math.smoothstep(0.0, 1, 0.5) == 0.5
+	assert math.close(math.smoothstep(0.0, 1, 0.9), 0.972)
+	assert math.close(math.smoothstep(0.0, 1, 0.95), 0.99275)
+	assert math.smoothstep(0.0, 1, 1) == 1
+}
+
+fn test_smootherstep() {
+	assert math.smootherstep(0.0, 1, 0) == 0
+	assert math.close(math.smootherstep(0.0, 1, 0.05), 0.001158125)
+	assert math.close(math.smootherstep(0.0, 1, 0.1), 0.00856)
+	assert math.smootherstep(0.0, 1, 0.5) == 0.5
+	assert math.close(math.smootherstep(0.0, 1, 0.9), 0.99144)
+	assert math.close(math.smootherstep(0.0, 1, 0.95), 0.998841875)
+	assert math.smootherstep(0.0, 1, 1) == 1
+}
diff --git a/vlib/math/math.v b/vlib/math/math.v
@@ -42,6 +42,12 @@ pub fn degrees(radians f64) f64 {
 	return radians * (180.0 / pi)
 }
 
+// radians converts an angle in degrees to a corresponding angle in radians.
+@[inline]
+pub fn radians(degrees f64) f64 {
+	return degrees * (pi / 180.0)
+}
+
 // angle_diff calculates the difference between angles in radians
 @[inline]
 pub fn angle_diff(radian_a f64, radian_b f64) f64 {
@@ -154,12 +160,6 @@ pub fn signi(n f64) int {
 	return int(copysign(1.0, n))
 }
 
-// radians converts an angle in degrees to a corresponding angle in radians.
-@[inline]
-pub fn radians(degrees f64) f64 {
-	return degrees * (pi / 180.0)
-}
-
 // signbit returns a value with the boolean representation of the sign for x
 @[inline]
 pub fn signbit(x f64) bool {
