add stem (#643)

docs/src/plotting_functions.md

@@ -420,6 +420,38 @@ current_figure()
 ```
 
 
+## `stem`
+
+```@docs
+stem
+```
+
+### Examples
+
+```@example
+using GLMakie
+AbstractPlotting.inline!(true) # hide
+
+xs = LinRange(0, 4pi, 30)
+
+f = Figure()
+stem(f[1, 1], xs, sin.(xs))
+stem(f[1, 2], xs, sin,
+    offset = 0.5, trunkcolor = :blue, marker = :rect,
+    stemcolor = :red, color = :orange,
+    markersize = 15, strokecolor = :red, strokewidth = 3,
+    trunklinestyle = :dash, stemlinestyle = :dashdot)
+stem(f[2, 1], xs, sin.(xs),
+    offset = LinRange(-0.5, 0.5, 30),
+    color = LinRange(0, 1, 30), colorrange = (0, 0.5),
+    trunkcolor = LinRange(0, 1, 30), trunkwidth = 5)
+stem(f[2, 2], 0.5xs, 2 .* sin.(xs), 2 .* cos.(xs),
+    offset = Point3f0.(0.5xs, sin.(xs), cos.(xs)),
+    stemcolor = LinRange(0, 1, 30), stemcolormap = :Spectral, stemcolorrange = (0, 0.5))
+f
+```
+
+
 ## `surface`
 
 ```@docs

src/AbstractPlotting.jl

@@ -112,6 +112,7 @@ include("basic_recipes/poly.jl")
 include("basic_recipes/scatterlines.jl")
 include("basic_recipes/series.jl")
 include("basic_recipes/spy.jl")
+include("basic_recipes/stem.jl")
 include("basic_recipes/streamplot.jl")
 include("basic_recipes/timeseries.jl")
 include("basic_recipes/title.jl")

src/basic_recipes/stem.jl

@@ -0,0 +1,83 @@
+"""
+    stem(xs, ys, [zs]; kwargs...)
+
+Plots markers at the given positions extending from `offset` along stem lines.
+
+`offset` can be a number, in which case it sets y for 2D and also z for 3D stems.
+It can be a Point2 for 2D plots and 3D plots, as well as a Point3 for 3D plots.
+It can also be an iterable of any of these at the same length as xs, ys, zs.
+
+The conversion trait of stem is `PointBased`.
+
+## Attributes
+$(ATTRIBUTES)
+"""
+@recipe(Stem) do scene
+    Attributes(
+        stemcolor = :black,
+        stemcolormap = :viridis,
+        stemcolorrange = automatic,
+        stemwidth = 1,
+        stemlinestyle = nothing,
+        trunkwidth = 1,
+        trunklinestyle = nothing,
+        trunkcolor = :black,
+        trunkcolormap = :viridis,
+        trunkcolorrange = automatic,
+        offset = 0,
+        marker = :circle,
+        markersize = 10,
+        color = :gray65,
+        colormap = :viridis,
+        colorrange = automatic,
+        strokecolor = :black,
+        strokewidth = 1,
+        visible = true,
+    )
+end
+
+
+conversion_trait(::Type{<:Stem}) = PointBased()
+
+
+trunkpoint(stempoint::P, offset::Number) where P <: Point2 = P(stempoint[1], offset)
+trunkpoint(stempoint::P, offset::Point2) where P <: Point2 = P(offset...)
+trunkpoint(stempoint::P, offset::Number) where P <: Point3 = P(stempoint[1], offset, offset)
+trunkpoint(stempoint::P, offset::Point2) where P <: Point3 = P(stempoint[1], offset[1], offset[2])
+trunkpoint(stempoint::P, offset::Point3) where P <: Point3 = P(offset...)
+
+
+function plot!(s::Stem{<:Tuple{<:AbstractVector{<:Point}}})
+    points = s[1]
+
+    stemtuples = lift(points, s.offset) do ps, to
+        tuple.(ps, trunkpoint.(ps, to))
+    end
+
+    trunkpoints = @lift(last.($stemtuples))
+
+    lines!(s, trunkpoints,
+        linewidth = s.trunkwidth,
+        color = s.trunkcolor,
+        colormap = s.trunkcolormap,
+        colorrange = s.trunkcolorrange,
+        visible = s.visible,
+        linestyle = s.trunklinestyle)
+    linesegments!(s, stemtuples,
+        linewidth = s.stemwidth,
+        color = s.stemcolor,
+        colormap = s.stemcolormap,
+        colorrange = s.stemcolorrange,
+        visible = s.visible,
+        linestyle = s.stemlinestyle)
+    scatter!(s, s[1],
+        color = s.color,
+        colormap = s.colormap,
+        colorrange = s.colorrange,
+        markersize = s.markersize,
+        marker = s.marker,
+        strokecolor = s.strokecolor,
+        strokewidth = s.strokewidth,
+        visible = s.visible)
+    s
+end