improve linestyles, add "-.-." and (:dash, :loose) variants (#593)

src/conversions.jl

@@ -677,22 +677,29 @@ convert_attribute(A::AbstractVector, ::key"linestyle") = A
 """
     A `Symbol` equal to `:dash`, `:dot`, `:dashdot`, `:dashdotdot`
 """
-function convert_attribute(ls::Symbol, ::key"linestyle")
-    return if ls == :solid
+convert_attribute(ls::Union{Symbol,AbstractString}, ::key"linestyle") = line_pattern(ls, :normal)
+
+function convert_attribute(ls::Tuple{<:Union{Symbol,AbstractString},<:Any}, ::key"linestyle")
+    line_pattern(ls[1], ls[2])
+end
+
+function line_pattern(linestyle, gaps)
+    float.([0.0; cumsum(line_diff_pattern(linestyle, gaps))])
+end
+
+"The linestyle patterns are inspired by the LaTeX package tikZ as seen here https://tex.stackexchange.com/questions/45275/tikz-get-values-for-predefined-dash-patterns."
+
+function line_diff_pattern(ls::Symbol, gaps = :normal)
+    if ls == :solid
         nothing
     elseif ls == :dash
-        [0.0, 1.0, 2.0, 3.0, 4.0]
+        line_diff_pattern("-", gaps)
     elseif ls == :dot
-        tick, gap = 1/2, 1/4
-        [0.0, tick, tick+gap, 2tick+gap, 2tick+2gap]
+        line_diff_pattern(".", gaps)
     elseif ls == :dashdot
-        dtick, dgap = 1.0, 1.0
-        ptick, pgap = 1/2, 1/4
-        [0.0, dtick, dtick+dgap, dtick+dgap+ptick, dtick+dgap+ptick+pgap]
+        line_diff_pattern("-.", gaps)
     elseif ls == :dashdotdot
-        dtick, dgap = 1.0, 1.0
-        ptick, pgap = 1/2, 1/4
-        [0.0, dtick, dtick+dgap, dtick+dgap+ptick, dtick+dgap+ptick+pgap, dtick+dgap+ptick+pgap+ptick,  dtick+dgap+ptick+pgap+ptick+pgap]
+        line_diff_pattern("-..", gaps)
     else
         error(
             """
@@ -705,6 +712,61 @@ function convert_attribute(ls::Symbol, ::key"linestyle")
     end
 end
 
+function line_diff_pattern(ls_str::AbstractString, gaps = :normal)
+    dot = 1
+    dash = 3
+    check_line_pattern(ls_str)
+
+    dot_gap, dash_gap = convert_gaps(gaps)
+
+    pattern = Float64[]
+    for i in 1:length(ls_str)
+        curr_char = ls_str[i]
+        next_char = i == lastindex(ls_str) ? ls_str[begin] : ls_str[i+1]
+        # push dash or dot
+        if curr_char == '-'
+            push!(pattern, dash)
+        else
+            push!(pattern, dot)
+        end
+        # push the gap (use dot_gap only between two dots)
+        if (curr_char == '.') && (next_char == '.')
+            push!(pattern, dot_gap)
+        else
+            push!(pattern, dash_gap)
+        end
+    end
+    pattern
+end
+
+"Checks if the linestyle format provided as a string contains only dashes and dots"
+function check_line_pattern(ls_str)
+    isnothing(match(r"^[.-]+$", ls_str)) &&
+        throw(ArgumentError("If you provide a string as linestyle, it must only consist of dashes (-) and dots (.)"))
+
+    nothing
+end
+
+function convert_gaps(gaps)
+  error_msg = "You provided the gaps modifier $gaps when specifying the linestyle. The modifier must be `∈ ([:normal, :dense, :loose])`, a real number or a collection of two real numbers."
+  if gaps isa Symbol
+      gaps in [:normal, :dense, :loose] || throw(ArgumentError(error_msg))
+      dot_gaps  = (normal = 2, dense = 1, loose = 4)
+      dash_gaps = (normal = 3, dense = 2, loose = 6)
+
+      dot_gap  = getproperty(dot_gaps, gaps)
+      dash_gap = getproperty(dash_gaps, gaps)
+  elseif gaps isa Real
+      dot_gap = gaps
+      dash_gap = gaps
+  elseif length(gaps) == 2 && eltype(gaps) <: Real
+      dot_gap, dash_gap = gaps
+  else
+      throw(ArgumentError(error_msg))
+  end
+  (; dot_gap, dash_gap)
+end
+
 function convert_attribute(f::Symbol, ::key"frames")
     f == :box && return ((true, true), (true, true))
     f == :semi && return ((true, false), (true, false))

test/unit_tests/conversions.jl

@@ -85,3 +85,38 @@ end
     @test ilabels == [1, 2]
     @test AbstractPlotting.categoric_position.(a, Ref(ilabels)) == [1, 1, 2]
 end
+
+using AbstractPlotting: check_line_pattern, line_diff_pattern
+
+@testset "Linetype" begin
+    @test isnothing(check_line_pattern("-."))
+    @test isnothing(check_line_pattern("--"))
+    @test_throws ArgumentError check_line_pattern("-.*")
+
+    # for readability, the length of dash and dot
+    dash, dot = 3.0, 1.0
+
+    @test line_diff_pattern(:dash)             ==
+          line_diff_pattern("-",   :normal)    == [dash, 3.0]
+    @test line_diff_pattern(:dot)              == 
+          line_diff_pattern(".",   :normal)    == [dot, 2.0]
+    @test line_diff_pattern(:dashdot)          ==
+          line_diff_pattern("-.",  :normal)    == [dash, 3.0, dot, 3.0]
+    @test line_diff_pattern(:dashdotdot)       == 
+          line_diff_pattern("-..", :normal)    == [dash, 3.0, dot, 2.0, dot, 3.0]
+
+    @test line_diff_pattern(:dash, :loose)     == [dash, 6.0]
+    @test line_diff_pattern(:dot,  :loose)     == [dot, 4.0]
+    @test line_diff_pattern("-",   :dense)     == [dash, 2.0]
+    @test line_diff_pattern(".",   :dense)     == [dot, 1.0]
+    @test line_diff_pattern(:dash, 0.5)        == [dash, 0.5]
+    @test line_diff_pattern(:dot,  0.5)        == [dot, 0.5]
+    @test line_diff_pattern("-",   (0.4, 0.6)) == [dash, 0.6]
+    @test line_diff_pattern(:dot,  (0.4, 0.6)) == [dot, 0.4]
+    @test line_diff_pattern("-..", (0.4, 0.6)) == [dash, 0.6, dot, 0.4, dot, 0.6]
+
+    # gaps must be Symbol, a number, or two numbers
+    @test_throws ArgumentError line_diff_pattern(:dash, :NORMAL)
+    @test_throws ArgumentError line_diff_pattern(:dash, ()) 
+    @test_throws ArgumentError line_diff_pattern(:dash, (1, 2, 3))
+end