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filter.go
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filter.go
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package texture
import (
"math"
"math/rand"
)
// Filter functions map [-1,1] -> [-1,1]
// NLFilter holds the parameters for a symmetric non-linear filter mapping.
type NLFilter struct {
Name string
Src Field
NLFunc *NonLinear
A, B float64
}
func NewNLFilter(src Field, nlf *NonLinear, a, b float64) *NLFilter {
return &NLFilter{"NLFilter", src, nlf, a, b}
}
// Eval2 implements the Field interface.
func (f *NLFilter) Eval2(x, y float64) float64 {
v := f.Src.Eval2(x, y)
v *= f.A
v += f.B
flag := v < 0
if flag {
v = -v
}
v = f.NLFunc.NLF.Transform(v)
if flag {
v = -v
}
return v
}
// InvertFilter flips the sign of v.
type InvertFilter struct {
Name string
Src Field
}
func NewInvertFilter(src Field) *InvertFilter {
return &InvertFilter{"InvertFilter", src}
}
// Eval2 implements the Field interface.
func (f *InvertFilter) Eval2(x, y float64) float64 {
return 0 - f.Src.Eval2(x, y)
}
// Quantize maps Av+B into one of C buckets.
type QuantizeFilter struct {
Name string
Src Field
A, B float64
C int
}
func NewQuantizeFilter(src Field, a, b float64, c int) *QuantizeFilter {
return &QuantizeFilter{"QuantizeFilter", src, a, b, c}
}
// Eval2 implements the Field interface.
func (f *QuantizeFilter) Eval2(x, y float64) float64 {
v := f.Src.Eval2(x, y)
v *= f.A
v += f.B
v = clamp(v)
v = (v + 1) / 2
c := float64(f.C)
if c < 2 {
c = 2
}
v *= c
return clamp(2*math.Floor(v)/(c-1) - 1)
}
// Clip limits At+B to [-1,1].
type ClipFilter struct {
Name string
Src Field
A, B float64
}
func NewClipFilter(src Field, a, b float64) *ClipFilter {
return &ClipFilter{"ClipFilter", src, a, b}
}
// Eval2 implements the Field interface.
func (f *ClipFilter) Eval2(x, y float64) float64 {
v := f.Src.Eval2(x, y)
v *= f.A
v += f.B
return clamp(v)
}
// OffsScaleFilter limits A(t+B) to [-1,1].
type OffsScaleFilter struct {
Name string
Src Field
A, B float64
}
func NewOffsScaleFilter(src Field, a, b float64) *OffsScaleFilter {
return &OffsScaleFilter{"OffsScaleFilter", src, a, b}
}
// Eval2 implements the Field interface.
func (f *OffsScaleFilter) Eval2(x, y float64) float64 {
v := f.Src.Eval2(x, y)
v += f.B
v *= f.A
return clamp(v)
}
// Abs returns Abs(At+B) (clamped).
type AbsFilter struct {
Name string
Src Field
A, B float64
}
func NewAbsFilter(src Field, a, b float64) *AbsFilter {
return &AbsFilter{"AbsFilter", src, a, b}
}
// Eval2 implements the Field interface.
func (f *AbsFilter) Eval2(x, y float64) float64 {
v := f.Src.Eval2(x, y)
v *= f.A
v += f.B
if v < 0 {
v = -v
}
return clamp(v)
}
// Fold wraps values (aX+b) outside of the domain [-1,1] back into it.
type FoldFilter struct {
Name string
Src Field
A, B float64
}
func NewFoldFilter(src Field, a, b float64) *FoldFilter {
return &FoldFilter{"FoldFilter", src, a, b}
}
// Eval2 implements the Field interface.
func (f *FoldFilter) Eval2(x, y float64) float64 {
v := f.Src.Eval2(x, y)
v *= f.A
v += f.B
// Map [-1,1] -> [0,1]
v = (v + 1) / 2
if v < 0 {
v = -v
}
if v > 1 {
nv := math.Floor(v)
v -= nv
// if nv is even, we're going up, else odd
if int(nv)%2 != 0 {
v = 1 - v
}
}
// Map [0,1] -> [-1,1]
return v*2 - 1
}
// RandQuantFilter supports a randomized quatization filter.
type RandQuantFilter struct {
Src Field
A, B float64
C int
M []float64
}
// NewRandQuantFilter returns a new RandFilter instance for use in quantization.
func NewRandQuantFilter(src Field, a, b float64, c int) *RandQuantFilter {
if c < 2 {
c = 2
}
mm := make([]float64, c)
dx := 2 / float64(c-1)
mm[0] = -1
for i := 1; i < c; i++ {
mm[i] = clamp(mm[i-1] + dx)
}
rand.Shuffle(c, func(i, j int) { mm[i], mm[j] = mm[j], mm[i] })
return &RandQuantFilter{src, a, b, c, mm}
}
// Eval2 implements the Field interface.
func (f *RandQuantFilter) Eval2(x, y float64) float64 {
v := f.Src.Eval2(x, y)
v *= f.A
v += f.B
v = clamp(v)
v = (v + 1) / 2
v *= float64(f.C)
k := int(math.Floor(v))
if k == f.C {
k--
}
return f.M[k]
}
func clamp(v float64) float64 {
if v < -1 {
return -1
}
if v > 1 {
return 1
}
return v
}