Add isaffine trait (#708)

* Add 'isaffine' trait

* Fix typo

* Apply suggestions

src/Meshes.jl

@@ -498,6 +498,7 @@ export
   LambdaMuSmoothing,
   LaplaceSmoothing,
   TaubinSmoothing,
+  isaffine,
 
   # miscellaneous
   signarea,

src/transforms.jl

@@ -11,6 +11,15 @@ See [https://en.wikipedia.org/wiki/Geometric_transformation]
 """
 abstract type GeometricTransform <: Transform end
 
+"""
+    isaffine(transform)
+
+Tells whether or not the geometric `transform` is Affine,
+i.e. it can be defined as a muladd operation (`Ax + b`).
+"""
+isaffine(t::GeometricTransform) = isaffine(typeof(t))
+isaffine(::Type{<:GeometricTransform}) = false
+
 # fallback with raw vector of geometries for convenience
 function apply(t::GeometricTransform, g::AbstractVector{<:Geometry})
   n, c = apply(t, GeometrySet(g))

src/transforms/affine.jl

@@ -34,6 +34,8 @@ end
 
 parameters(t::Affine) = (A=t.A, b=t.b)
 
+isaffine(::Type{<:Affine}) = true
+
 isrevertible(t::Affine) = isinvertible(t)
 
 function isinvertible(t::Affine)

src/transforms/rotate.jl

@@ -53,6 +53,8 @@ Rotate(θ) = Rotate(Angle2d(θ))
 
 parameters(t::Rotate) = (; rot=t.rot)
 
+isaffine(::Type{<:Rotate}) = true
+
 isrevertible(::Type{<:Rotate}) = true
 
 isinvertible(::Type{<:Rotate}) = true

src/transforms/stretch.jl

@@ -30,6 +30,8 @@ Stretch(factors...) = Stretch(factors)
 
 parameters(t::Stretch) = (; factors=t.factors)
 
+isaffine(::Type{<:Stretch}) = true
+
 isrevertible(::Type{<:Stretch}) = true
 
 isinvertible(::Type{<:Stretch}) = true

src/transforms/translate.jl

@@ -16,6 +16,8 @@ Translate(offsets...) = Translate(offsets)
 
 parameters(t::Translate) = (; offsets=t.offsets)
 
+isaffine(::Type{<:Translate}) = true
+
 isrevertible(::Type{<:Translate}) = true
 
 isinvertible(::Type{<:Translate}) = true

test/transforms.jl

@@ -1,5 +1,6 @@
 @testset "Transforms" begin
   @testset "Rotate" begin
+    @test isaffine(Rotate)
     @test TB.isrevertible(Rotate)
     @test TB.isinvertible(Rotate)
     @test TB.inverse(Rotate(Angle2d(T(π / 2)))) == Rotate(Angle2d(-T(π / 2)))
@@ -201,6 +202,7 @@
   end
 
   @testset "Translate" begin
+    @test isaffine(Translate)
     @test TB.isrevertible(Translate)
     @test TB.isinvertible(Translate)
     @test TB.inverse(Translate(T(1), T(2))) == Translate(T(-1), T(-2))
@@ -363,6 +365,7 @@
 
   @testset "Affine" begin
     f = Affine(Angle2d(T(π / 2)), T[1, 1])
+    @test isaffine(f)
     @test TB.isrevertible(f)
     @test TB.isinvertible(f)
     @test TB.inverse(f) == Affine(Angle2d(-T(π / 2)), Angle2d(-T(π / 2)) * -T[1, 1])
@@ -535,6 +538,7 @@
   end
 
   @testset "Stretch" begin
+    @test isaffine(Stretch)
     @test TB.isrevertible(Stretch)
     @test TB.isinvertible(Stretch)
     @test TB.inverse(Stretch(T(1), T(2))) == Stretch(T(1), T(1 / 2))
@@ -686,6 +690,7 @@
   end
 
   @testset "Expand" begin
+    @test !isaffine(Expand)
     @test TB.isrevertible(Expand)
     @test TB.isinvertible(Expand)
     @test TB.inverse(Expand(T(1), T(2))) == Expand(T(1), T(1 / 2))
@@ -837,6 +842,7 @@
   end
 
   @testset "StdCoords" begin
+    @test !isaffine(StdCoords)
     @test TB.isrevertible(StdCoords)
 
     # ---------
@@ -872,6 +878,7 @@
   end
 
   @testset "Repair{0}" begin
+    @test !isaffine(Repair)
     poly = PolyArea(P2[(0, 0), (1, 0), (1, 0), (1, 1), (0, 1), (0, 1)])
     rpoly = poly |> Repair{0}()
     @test nvertices(rpoly) == 4
@@ -950,6 +957,7 @@
   end
 
   @testset "Bridge" begin
+    @test !isaffine(Bridge)
     δ = T(0.01)
     f = Bridge(δ)
     @test TB.parameters(f) == (; δ)
@@ -1021,6 +1029,7 @@
   end
 
   @testset "Smoothing" begin
+    @test !isaffine(LambdaMuSmoothing)
     n, λ, μ = 30, T(0.5), T(0)
     f = LambdaMuSmoothing(n, λ, μ)
     @test TB.parameters(f) == (; n, λ, μ)