Support length on Gray StepRanges (#177)

Author: timholy

src/ColorVectorSpace.jl

@@ -216,6 +216,7 @@ end
 
 for f in (:mod, :rem, :mod1)
     @eval $f(x::Gray, m::Gray) = Gray($f(gray(x), gray(m)))
+    @eval $f(x::Gray, m::Real) = Gray($f(gray(x), m))
 end
 
 dotc(x::T, y::T) where {T<:Real} = acc(x)*acc(y)
@@ -477,6 +478,9 @@ function stdmult(op, itr; kwargs...)
     return isa(result, Union{Real,Colorant,RGBRGB}) ? _sqrt(result) : _sqrt.(result)
 end
 
+Base.length(r::StepRange{<:AbstractGray,<:AbstractGray}) = length(StepRange(gray(r.start), gray(r.step), gray(r.stop)))
+Base.length(r::StepRange{<:AbstractGray})                = length(StepRange(gray(r.start), r.step,       gray(r.stop)))
+
 function __init__()
     if isdefined(Base, :Experimental) && isdefined(Base.Experimental, :register_error_hint)
         Base.Experimental.register_error_hint(MethodError) do io, exc, argtypes, kwargs

test/runtests.jl

@@ -825,4 +825,22 @@ ColorTypes.comp2(c::RGBA32) = alpha(c)
         @test copy(c) === c
     end
 
+    @testset "ranges" begin
+        T = Gray{N0f8}
+        for r in (zero(T):eps(T):oneunit(T),
+                  zero(T):eps(N0f8):oneunit(T),
+                  zero(N0f8):eps(T):oneunit(N0f8),
+                  StepRangeLen(zero(T), eps(T), 256),
+                  StepRangeLen(zero(T), eps(N0f8), 256),
+                  LinRange(zero(T), oneunit(T), 256))
+            @test length(r) == 256
+            @test step(r) == eps(T)
+        end
+
+        r = LinRange(RGB(1, 0, 0), RGB(0, 0, 1), 256)
+        @test length(r) == 256
+        @test step(r) == RGB(-1.0f0/255, 0, eps(N0f8))
+        @test r[2] == RGB(254.0f0/255, 0, 1.0f0/255)
+    end
+
 end