add smart fillto to enable logscale y-axis histogram barplot

ReferenceTests/src/tests/examples2d.jl

@@ -909,6 +909,23 @@ end
     f
 end
 
+@reference_test "Log y-scale histogram (barplot)" begin
+    hist(
+        randn(10^6); 
+        axis=(; yscale=log2)
+    )
+    current_figure()
+end
+
+@reference_test "Log y-scale histogram (barplot) with gap" begin
+    # make a gap in histogram as edge case
+    hist(
+        filter!(x-> x<0 || x > 1.5, randn(10^6)); 
+        axis=(; yscale=log10)
+    )
+    current_figure()
+end
+
 @reference_test "Stephist" begin
     stephist(RNG.rand(10000))
     current_figure()

src/basic_recipes/barplot.jl

@@ -2,6 +2,36 @@ function bar_label_formatter(value::Number)
     return string(round(value; digits=3))
 end
 
+"""
+    bar_default_fillto(tf, ys, offset)::(ys, offset)
+
+Returns the default y-positions and offset positions for the given transform `tf`.  
+
+In order to customize this for your own transformation type, you can dispatch on 
+`tf`.
+
+Returns a Tuple of new y positions and offset arrays.
+
+## Arguments
+- `tf`: `plot.transformation.transform_func[]`. 
+- `ys`: The y-values passed to `barplot`.
+- `offset`: The `offset` parameter passed to `barplot`.
+"""
+function bar_default_fillto(tf, ys, offset)
+    return ys, offset
+end
+
+# `fillto` is related to `y-axis` transofrmation only, thus we expect `tf::Tuple`
+function bar_default_fillto(tf::Tuple, ys, offset)
+    if tf[2] isa Union{typeof(log), typeof(log2), typeof(log10), Base.Fix1{typeof(log), <: Real}}
+        # use the minimal non-zero y divided by 2 as lower bound for log scale
+        smart_fillto = minimum(y -> y<=0 ? oftype(y, Inf) : y, ys) / 2
+        return clamp.(ys, smart_fillto, Inf), smart_fillto
+    else
+        return ys, offset
+    end
+end
+
 """
     barplot(x, y; kwargs...)
 
@@ -190,7 +220,7 @@ function Makie.plot!(p::BarPlot)
     label_aligns = Observable(Vec2f[])
     label_offsets = Observable(Vec2f[])
     label_colors = Observable(RGBAf[])
-    function calculate_bars(xy, fillto, offset, width, dodge, n_dodge, gap, dodge_gap, stack,
+    function calculate_bars(xy, fillto, offset, transformation, width, dodge, n_dodge, gap, dodge_gap, stack,
                             dir, bar_labels, flip_labels_at, label_color, color_over_background,
                             color_over_bar, label_formatter, label_offset)
 
@@ -217,7 +247,7 @@ function Makie.plot!(p::BarPlot)
 
         if stack === automatic
             if fillto === automatic
-                fillto = offset
+                y, fillto = bar_default_fillto(transformation, y, offset)
             end
         elseif eltype(stack) <: Integer
             fillto === automatic || @warn "Ignore keyword fillto when keyword stack is provided"
@@ -249,7 +279,7 @@ function Makie.plot!(p::BarPlot)
         return bar_rectangle.(x̂, y .+ offset, barwidth, fillto, in_y_direction)
     end
 
-    bars = lift(calculate_bars, p, p[1], p.fillto, p.offset, p.width, p.dodge, p.n_dodge, p.gap,
+    bars = lift(calculate_bars, p, p[1], p.fillto, p.offset, p.transformation.transform_func, p.width, p.dodge, p.n_dodge, p.gap,
                 p.dodge_gap, p.stack, p.direction, p.bar_labels, p.flip_labels_at,
                 p.label_color, p.color_over_background, p.color_over_bar, p.label_formatter, p.label_offset)