add delete and empty for axis and delete for lscene (#679)

Author: jkrumbiegel

docs/src/makielayout/axis.md

@@ -36,6 +36,30 @@ scatobject = scatter!(0:0.5:10, cos, color = :orange)
 f
 ```
 
+## Deleting plots
+
+You can delete a plot object directly via `delete!(ax, plotobj)`.
+You can also remove all plots with `empty!(ax)`.
+
+```@example
+using CairoMakie
+CairoMakie.activate!() # hide
+AbstractPlotting.inline!(true) # hide
+
+f = Figure(resolution = (1200, 500))
+
+axs = [Axis(f[1, i]) for i in 1:3]
+
+scatters = map(axs) do ax
+    [scatter!(ax, 0:0.1:10, x -> sin(x) + i) for i in 1:3]
+end
+
+delete!(axs[2], scatters[2][2])
+empty!(axs[3])
+
+f
+```
+
 
 ## Setting Axis limits and reversing axes
 
@@ -596,4 +620,5 @@ scene
 ```@eval
 using GLMakie
 GLMakie.activate!()
-```
+```
+

src/makielayout/layoutables/axis.jl

@@ -989,4 +989,16 @@ end
 
 function limits!(args...)
     limits!(current_axis(), args...)
-end
+end
+
+function Base.delete!(ax::Axis, plot::AbstractPlot)
+    delete!(ax.scene, plot)
+    ax
+end
+
+function Base.empty!(ax::Axis)
+    for plot in copy(ax.scene.plots)
+        delete!(ax, plot)
+    end
+    ax
+end

src/makielayout/layoutables/scene.jl

@@ -43,3 +43,8 @@ function layoutable(::Type{LScene}, fig_or_scene; bbox = nothing, scenekw = Name
 
     ls
 end
+
+function Base.delete!(ax::LScene, plot::AbstractPlot)
+    delete!(ax.scene, plot)
+    ax
+end

test/unit_tests/makielayout.jl

@@ -16,4 +16,18 @@
     tb = layout[end + 1, :] = Textbox(scene)
     is = layout[end + 1, :] = IntervalSlider(scene)
     @test true
+end
+
+@testset "deleting from axis" begin
+    f = Figure()
+    ax = Axis(f[1, 1])
+    sc = scatter!(ax, randn(100, 2))
+    li = lines!(ax, randn(100, 2))
+    hm = heatmap!(ax, randn(20, 20))
+    @test length(ax.scene.plots) == 3
+    delete!(ax, sc)
+    @test length(ax.scene.plots) == 2
+    @test sc ∉ ax.scene.plots
+    empty!(ax)
+    @test isempty(ax.scene.plots)
 end