add symlog and pseudolog

docs/src/makielayout/axis.md

@@ -180,6 +180,8 @@ The default tick type is `LinearTicks(n)`, where `n` is the target number of tic
 
 ```@example
 using CairoMakie
+CairoMakie.activate!() # hide
+Makie.inline!(true) # hide
 
 fig = Figure()
 for (i, n) in enumerate([2, 5, 9])
@@ -195,6 +197,8 @@ A common scenario is plotting a trigonometric function which should be marked at
 
 ```@example
 using CairoMakie
+CairoMakie.activate!() # hide
+Makie.inline!(true) # hide
 
 lines(0..20, sin, axis = (xticks = MultiplesTicks(4, pi, "π"),))
 ```
@@ -203,6 +207,8 @@ Here are a couple of examples that show off different settings for ticks and for
 
 ```@example
 using CairoMakie
+CairoMakie.activate!() # hide
+Makie.inline!(true) # hide
 
 scene, layout = layoutscene(resolution = (1200, 900))
 
@@ -240,6 +246,8 @@ The default minor tick type is `IntervalsBetween(n, mirror = true)` where `n` gi
 
 ```@example
 using CairoMakie
+CairoMakie.activate!() # hide
+Makie.inline!(true) # hide
 
 theme = Attributes(
     Axis = (
@@ -271,6 +279,8 @@ To hide spines, you can use `hidespines!`.
 
 ```@example
 using CairoMakie
+CairoMakie.activate!() # hide
+Makie.inline!(true) # hide
 
 f = Figure()
 
@@ -290,6 +300,8 @@ It's common, e.g., to hide everything but the grid lines in facet plots.
 
 ```@example
 using CairoMakie
+CairoMakie.activate!() # hide
+Makie.inline!(true) # hide
 
 f = Figure()
 
@@ -312,6 +324,8 @@ Take care that the axis limits always stay inside the limits appropriate for the
 
 ```@example
 using CairoMakie
+CairoMakie.activate!() # hide
+Makie.inline!(true) # hide
 
 data = LinRange(0.01, 0.99, 200)
 
@@ -330,10 +344,14 @@ end
 f
 ```
 
+### Pseudolog and symlog scales
+
 Some plotting functions, like barplots or density plots, have offset parameters which are usually zero, which you have to set to some non-zero value explicitly so they work in `log` axes.
 
 ```@example
 using CairoMakie
+CairoMakie.activate!() # hide
+Makie.inline!(true) # hide
 
 processors = ["VAX-11/780", "Sun-4/260", "PowerPC 604",
     "Alpha 21164", "Intel Pentium III", "Intel Xeon"]
@@ -347,6 +365,33 @@ ylims!(0.5, 10000)
 current_figure()
 ```
 
+Another option are pseudolog and symlog scales.
+Pseudolog is similar to log, but modified in order to work for zero and for negative values.
+The `pseudolog10` function is defined as `sign(x) * log10(abs(x) + 1)`.
+
+Another option for symmetric log scales including zero is the symmetric log scale `Symlog10`, which combines a normal log scale with a linear scale between two boundary values around zero.
+
+```@example
+using CairoMakie
+CairoMakie.activate!() # hide
+Makie.inline!(true) # hide
+
+f = Figure(resolution = (800, 700))
+
+lines(f[1, 1], -100:0.1:100, axis = (
+    yscale = Makie.pseudolog10,
+    title = "Pseudolog scale",
+    yticks = [-100, -10, -1, 0, 1, 10, 100]))
+
+lines(f[2, 1], -100:0.1:100, axis = (
+    yscale = Makie.Symlog10(10.0),
+    title = "Symlog10 with linear scaling between -10 and 10",
+    yticks = [-100, -10, 0, 10, 100]))
+
+f
+```
+
+
 ## Controlling Axis aspect ratios
 
 If you're plotting images, you might want to force a specific aspect ratio

src/layouting/transformation.jl

@@ -313,12 +313,50 @@ apply_transform(f::typeof(identity), r::Rect) = r
 apply_transform(f::NTuple{2, typeof(identity)}, r::Rect) = r
 apply_transform(f::NTuple{3, typeof(identity)}, r::Rect) = r
 
+
+pseudolog10(x) = sign(x) * log10(abs(x) + 1)
+inv_pseudolog10(x) = sign(x) * (exp10(abs(x)) - 1)
+
+struct Symlog10
+    low::Float64
+    high::Float64
+    function Symlog10(low, high)
+        if !(low < 0 && high > 0)
+            error("Low bound needs to be smaller than 0 and high bound larger than 0. You gave $low, $high.")
+        end
+        new(Float64(low), Float64(high))
+    end
+end
+function Symlog10(x)
+    Symlog10(-x, x)
+end
+function (s::Symlog10)(x)
+    if x > 0
+        x <= s.high ? x / s.high * log10(s.high) : log10(x)
+    elseif x < 0
+        x >= s.low ? x / abs(s.low) * log10(abs(s.low)) : sign(x) * log10(abs(x))
+    else
+        x
+    end
+end
+function inv_symlog10(x, low, high)
+    if x > 0
+        l = log10(high)
+        x <= l ? x / l * high : exp10(x)
+    elseif x < 0
+        l = sign(x) * log10(abs(low))
+        x >= l ? x / l * abs(s.low) : sign(x) * exp10(abs(x))
+    else
+        x
+    end
+end
+
 inverse_transform(::typeof(identity)) = identity
 inverse_transform(::typeof(log10)) = exp10
 inverse_transform(::typeof(log)) = exp
 inverse_transform(::typeof(log2)) = exp2
 inverse_transform(::typeof(sqrt)) = x -> x ^ 2
+inverse_transform(::typeof(pseudolog10)) = inv_pseudolog10
 inverse_transform(F::Tuple) = map(inverse_transform, F)
-
 inverse_transform(::typeof(logit)) = logistic
-inverse_transform(x) = nothing
+inverse_transform(s::Symlog10) = x -> inv_symlog10(x, s.low, s.high)

src/makielayout/layoutables/axis.jl

@@ -1279,8 +1279,13 @@ defaultlimits(::typeof(log)) = (1.0, exp(3.0))
 defaultlimits(::typeof(identity)) = (0.0, 10.0)
 defaultlimits(::typeof(sqrt)) = (0.0, 100.0)
 defaultlimits(::typeof(Makie.logit)) = (0.01, 0.99)
+defaultlimits(::typeof(Makie.pseudolog10)) = (0.0, 100.0)
+defaultlimits(::Makie.Symlog10) = (0.0, 100.0)
 
 defined_interval(::typeof(identity)) = OpenInterval(-Inf, Inf)
 defined_interval(::Union{typeof(log2), typeof(log10), typeof(log)}) = OpenInterval(0.0, Inf)
 defined_interval(::typeof(sqrt)) = Interval{:closed,:open}(0, Inf)
 defined_interval(::typeof(Makie.logit)) = OpenInterval(0.0, 1.0)
+defined_interval(::typeof(Makie.pseudolog10)) = OpenInterval(-Inf, Inf)
+defined_interval(::Makie.Symlog10) = OpenInterval(-Inf, Inf)
+