circle radius

pkg/util/map.go

@@ -2,6 +2,32 @@ package util
 
 import "math"
 
+// WrapF maps value into the half-open interval [0, float64(size)).
+// It supports negative input values and is used for torus coordinates
+// when the coordinate is represented as float64.
+//
+// size must be greater than zero.
+func WrapF(value float64, size int) float64 {
+	if size <= 0 {
+		panic("WrapF: size must be > 0")
+	}
+
+	s := float64(size)
+
+	r := math.Mod(value, s)
+	if r < 0 {
+		r += s
+	}
+
+	// Protect against a possible boundary artifact and keep result in [0, s).
+	// In normal cases math.Mod already gives a value with |r| < s.
+	if r >= s {
+		r -= s
+	}
+
+	return r
+}
+
 func ShortDistance(w, h uint32, x1, y1, x2, y2 float64) float64 {
 	return math.Hypot(deltas(w, h, x1, y1, x2, y2))
 }