Added Ceil, Floor and Remap filters

doc.go

@@ -121,15 +121,18 @@ Filters are nodes that do something with the value supplied by their source.
 They map values in [-1,1] to another in [-1,1].
 Some filters take A and B parameters, in which case the value filtered is A*value+B
   - [AbsFilter] applies [math.Abs] so the value will be in [0,1]
+  - [CeilFilter] limits the value to [-1,C]
   - [ClipFilter] limits the value to [-1,1]
   - [Convolution] calculates value by applying a kernel to the source
+  - [FloorFilter] limits the value to [C,1]
   - [FoldFilter] 'folds' a value outside of [-1,1] back in on itself
   - [InvertFilter] applies 0 - value
   - Morphological [Erode], [Dilate], [EdgeIn], [EdgeOut], [Edge], [Close], [Open], [TopHat], [BottomHat]
   - [NLFilter] applies a [NonLinear] to value
   - [OffsScaleFilter] applies A * (B + value)
   - [QuantizeFilter] quantizes the value
   - [RandQuantFilter] like [QuantizeFilter] but the values are scrambled
+  - [RemapFilter] maps the value to the new domain [A,B]
 
 # 5.2 Vector Filters (VF)
   - [UnitVector] modifies the magnitude of the vector to 1

example_decay_test.go

@@ -20,7 +20,7 @@ func Example_decay() {
 	f2 := texture.NewLinearGradient(w3)
 
 	// Remap [-1,1] => [0,1]
-	f4 := texture.NewOffsScaleFilter(f2, 0.5, 1)
+	f4 := texture.NewRemapFilter(f2, 0, 1)
 
 	// Combine waves to get decay waveform
 	f3 := texture.NewMulCombiner(f, f4)

filter.go

@@ -211,6 +211,70 @@ func (f *RandQuantFilter) Eval2(x, y float64) float64 {
 	return f.M[k]
 }
 
+// RemapFilter holds the parameters for a linear filter remapping [-1,1] => [a,b].
+type RemapFilter struct {
+	Name string
+	Src  Field
+	A, B float64
+}
+
+func NewRemapFilter(src Field, a, b float64) *RemapFilter {
+	return &RemapFilter{"RemapFilter", src, a, b}
+}
+
+// Eval2 implements the Field interface.
+func (f *RemapFilter) Eval2(x, y float64) float64 {
+	v := f.Src.Eval2(x, y)
+	t := (v + 1) / 2
+	return clamp(f.A*(1-t) + f.B*t)
+}
+
+// FloorFilter maps Av+B to [C, 1]
+type FloorFilter struct {
+	Name string
+	Src  Field
+	A, B float64
+	C    float64
+}
+
+func NewFloorFilter(src Field, a, b float64, c float64) *FloorFilter {
+	return &FloorFilter{"FloorFilter", src, a, b, c}
+}
+
+// Eval2 implements the Field interface.
+func (f *FloorFilter) Eval2(x, y float64) float64 {
+	v := f.Src.Eval2(x, y)
+	v *= f.A
+	v += f.B
+	if v < f.C {
+		return f.C
+	}
+	return clamp(v)
+}
+
+// CeilFilter maps Av+B to [-1,C]
+type CeilFilter struct {
+	Name string
+	Src  Field
+	A, B float64
+	C    float64
+}
+
+func NewCeilFilter(src Field, a, b float64, c float64) *CeilFilter {
+	return &CeilFilter{"CeilFilter", src, a, b, c}
+}
+
+// Eval2 implements the Field interface.
+func (f *CeilFilter) Eval2(x, y float64) float64 {
+	v := f.Src.Eval2(x, y)
+	v *= f.A
+	v += f.B
+	if v > f.C {
+		return f.C
+	}
+	return clamp(v)
+}
+
 func clamp(v float64) float64 {
 	if v < -1 {
 		return -1