add annulus, docs update, and replace Sprintf with Appendf in Array

cpu_evaluators.go

@@ -883,3 +883,19 @@ func (s *symmetry2D) Evaluate(pos []ms2.Vec, dist []float32, userData any) error
 	}
 	return nil
 }
+
+func (s *annulus2D) Evaluate(pos []ms2.Vec, dist []float32, userData any) error {
+	sdf, err := gleval.AssertSDF2(s.s)
+	if err != nil {
+		return err
+	}
+	err = sdf.Evaluate(pos, dist, userData)
+	if err != nil {
+		return err
+	}
+	r := s.r
+	for i, d := range dist {
+		dist[i] = math32.Abs(d) - r
+	}
+	return nil
+}

gsdf2d.go

@@ -923,3 +923,40 @@ func (s *symmetry2D) AppendShaderBody(b []byte) []byte {
 	b = append(b, "(p);"...)
 	return b
 }
+
+// Annulus makes a 2D shape annular by emptying it's center. It is the equivalent of the 3D Shell operation but in 2D.
+func Annulus(s glbuild.Shader2D, sub float32) (glbuild.Shader2D, error) {
+	if s == nil {
+		return nil, errors.New("nil argument to Annulus")
+	} else if sub <= 0 {
+		return nil, errors.New("invalid annular parameter")
+	}
+	return &annulus2D{s: s, r: sub}, nil
+}
+
+type annulus2D struct {
+	s glbuild.Shader2D
+	r float32
+}
+
+func (u *annulus2D) Bounds() ms2.Box {
+	return u.s.Bounds()
+}
+
+func (s *annulus2D) ForEach2DChild(userData any, fn func(userData any, s *glbuild.Shader2D) error) error {
+	return fn(userData, &s.s)
+}
+
+func (s *annulus2D) AppendShaderName(b []byte) []byte {
+	b = append(b, "annulus"...)
+	b = append(b, '_')
+	b = s.s.AppendShaderName(b)
+	return b
+}
+
+func (s *annulus2D) AppendShaderBody(b []byte) []byte {
+	b = glbuild.AppendFloatDecl(b, "r", s.r)
+	b = glbuild.AppendDistanceDecl(b, "d", "p", s.s)
+	b = append(b, "return abs(d)-r;"...)
+	return b
+}

operations.go

@@ -387,7 +387,7 @@ func (s *offset) AppendShaderBody(b []byte) []byte {
 	return b
 }
 
-// Array is the domain repetition operation. It repeats domain centered around (x,y,z)=(0,0,0)
+// Array is the domain repetition operation. It repeats domain centered around the origin (x,y,z)=(0,0,0).
 func Array(s glbuild.Shader3D, spacingX, spacingY, spacingZ float32, nx, ny, nz int) (glbuild.Shader3D, error) {
 	if nx <= 0 || ny <= 0 || nz <= 0 {
 		return nil, errors.New("invalid array repeat param")
@@ -434,7 +434,7 @@ func (s *array) AppendShaderBody(b []byte) []byte {
 	// o is neighbor offset direction (which neighboring tile is closest in 3 directions)
 	// s is scaling factors in 3 directions.
 	// rid is the neighboring tile index, which is then corrected for limited repetition using clamp.
-	body := fmt.Sprintf(`
+	b = fmt.Appendf(b, `
 vec3 s = vec3(%f,%f,%f);
 vec3 n = vec3(%d.,%d.,%d.);
 vec3 minlim = vec3(0.,0.,0.);
@@ -453,9 +453,7 @@ for( int i=0; i<2; i++ )
 }
 return d;`, s.d.X, s.d.Y, s.d.Z,
 		s.nx-1, s.ny-1, s.nz-1,
-		largenum, sdf,
-	)
-	b = append(b, body...)
+		largenum, sdf)
 	return b
 }