Fix compiler errors

color/frgba.go

@@ -71,5 +71,5 @@ func (c FRGBA) Scale(v float64) FRGBA {
 
 // IsBlack returns true if the color is black.
 func (c FRGBA) IsBlack() bool {
-	return c.R < 0.0001 && c.G < 0.0001 && c.B < 0.0001
+	return c.A < 0.0001 || (c.R < 0.0001 && c.G < 0.0001 && c.B < 0.0001)
 }

fractal.go

@@ -21,6 +21,7 @@ type Fractal struct {
 // NewFractal returns a new Fractal instance.
 func NewFractal(src Field, xfm *g2d.Aff3, comb OctaveCombiner, octaves float64) *Fractal {
 	oct := int(octaves)
+	oct++
 	w := make([]float64, oct)
 	for i := 0; i < oct; i++ {
 		w[i] = 1

shape.go

@@ -124,7 +124,7 @@ type ShapeCombinerVF struct {
 	Shape *graphics2d.Shape
 }
 
-func NewShapeCombinerVF(src1, src2 ColorField, shape *graphics2d.Shape) *ShapeCombinerVF {
+func NewShapeCombinerVF(src1, src2 VectorField, shape *graphics2d.Shape) *ShapeCombinerVF {
 	return &ShapeCombinerVF{"ShapeCombinerVF", src1, src2, shape}
 }
 

value.go

@@ -73,12 +73,13 @@ func (d *Direction) Eval2(x, y float64) float64 {
 
 // Magnitude converts a VectorField to a Field based on the vector's magnitude.
 type Magnitude struct {
-	Name string
-	Src  VectorField
+	Name  string
+	Src   VectorField
+	Scale float64
 }
 
-func NewMagnitude(src VectorField) *Magnitude {
-	return &Magnitude{"Magnitude", src}
+func NewMagnitude(src VectorField, scale float64) *Magnitude {
+	return &Magnitude{"Magnitude", src, scale}
 }
 
 // Eval2 implements the Field interface. Always >= 0
@@ -88,24 +89,26 @@ func (m *Magnitude) Eval2(x, y float64) float64 {
 	for _, f := range v {
 		s += f * f
 	}
-	return math.Sqrt(s)
+	r := math.Sqrt(s) * m.Scale
+	return clamp(r)
 }
 
 // Select converts a VectorField to a field by selecting one of its components.
 type Select struct {
-	Name string
-	Src  VectorField
-	Chan int
+	Name  string
+	Src   VectorField
+	Chan  int
+	Scale float64
 }
 
-func NewSelect(src VectorField, ch int) *Select {
-	return &Select{"Select", src, ch}
+func NewSelect(src VectorField, ch int, scale float64) *Select {
+	return &Select{"Select", src, ch, scale}
 }
 
 // Eval2 implements the Field interface.
 func (s *Select) Eval2(x, y float64) float64 {
-	v := s.Src.Eval2(x, y)[s.Chan]
-	return v
+	v := s.Src.Eval2(x, y)[s.Chan] * s.Scale
+	return clamp(v)
 }
 
 // Weighted converts a VectorField to a field by selecting one of its components.
@@ -130,5 +133,5 @@ func (w *Weighted) Eval2(x, y float64) float64 {
 	for i := 0; i < n; i++ {
 		s += v[i] * w.Weights[i]
 	}
-	return s
+	return clamp(s)
 }