Added ThresholdFilter

Author: jphsd

thresh.go

@@ -0,0 +1,22 @@
+package texture
+
+// ThresholdFilter returns B if src < A, and C if equal or greater.
+// See also [ThresholdCombiner].
+type ThresholdFilter struct {
+	Name    string
+	Src     Field
+	A, B, C float64
+}
+
+func NewThresholdFilter(src Field, a, b, c float64) *ThresholdFilter {
+	return &ThresholdFilter{"ThresholdFilter", src, a, b, c}
+}
+
+// Eval2 implements the Field interface.
+func (f *ThresholdFilter) Eval2(x, y float64) float64 {
+	v := f.Src.Eval2(x, y)
+	if v < f.A {
+		return f.B
+	}
+	return f.C
+}