Size revamp3: ContinuousSizeScale

[Mattriks]

• I've updated the documentation to reflect these changes
• I've added an entry to NEWS.md
• I've added and/or updated the unit tests
• I've run the regression tests
• I've built the docs and confirmed these changes don't cause new errors

This PR

• the third PR in a set of 3 (Size revamp 1: Scale.size_discrete2 #1376, Size revamp 2: Guide.sizekey #1379)
• adds Scale.size_radius. This should become the default Scale.size_continuous in Gadfly 2.0 (Scale.size_radius can also be kept as an alias)
• adds Scale.size_area

Design

There are three possible types of continuous sizes:

• sizes in plot units e.g. size=[s], where s is in x,y units
• sizes in Measure units e.g. size=[xmm] i.e. absolute size (these are deferred to Scale.size_identity)
• Real numbers where -∞ < s < ∞ are mapped to absolute sizes

Scale.size_radius and Scale.size_area have a default_continuous_sizes(p) function where 0≤p≤1. This maps proportions to absolute sizes (the default sizes are 0mm-2mm).
If maxvalue is specified, the continuous sizes are converted to a proportion (between minvalue and maxvalue), and then mapped to absolute sizes using the function f(p).

Examples

theme = Theme(key_swatch_shape=Shape.circle, alphas=[0.1],
  discrete_highlight_color=identity)

y, size = [0.55, 0.7, 0.9, 0.99, 0.9], [0.4, 0.5, 0.6, 0.68, 0.63]
juliaclrs = Gadfly.parse_colorant(["forestgreen", "brown3", "mediumorchid"])

p1 = plot(x=[2,1.13,2.87], y=[3,1.5,1.5], size=[0.75],
    Scale.size_radius, color=juliaclrs, Coord.cartesian(fixed=true),
    alpha=[0.8], Guide.title("size=[0.75]"))
p2 = plot(x=[2,4], y=[2,4], size=[20pt], Guide.title("size=[20pt]"))
p3 = plot(x=1:5, y=y, size=10^5*size, Scale.size_radius(maxvalue=10^5),
     Guide.title("size=10⁵⋅rand(5)"), theme)
p4 = plot(x=1:5, y=y, size=10^5*size, Scale.size_area(maxvalue=10^5),
     Guide.title("size=10⁵⋅rand(5)"), theme)
gridstack([p1 p2; p3 p4]))

Note plot p3 and p4 use Scale.size_radius and Scale.size_area respectively.

Wrt the size aesthetic, the only outstanding issue is to get the axis scales to take into account the absolute sizes when calculating the axis limits e.g., in plot p2 above. This will be done in a future PR (see #1385)

[codecov-io]

Codecov Report

Merging #1386 into master will decrease coverage by 0.01%.
The diff coverage is 88.57%.

@@            Coverage Diff             @@
##           master    #1386      +/-   ##
==========================================
- Coverage   90.27%   90.26%   -0.02%     
==========================================
  Files          39       39              
  Lines        4207     4242      +35     
==========================================
+ Hits         3798     3829      +31     
- Misses        409      413       +4

Impacted Files	Coverage Δ
src/scale.jl	97.46% <ø> (ø)	⬆️
src/theme.jl	69.49% <ø> (ø)	⬆️
src/scale/scales.jl	88.7% <88.57%> (-0.18%)	⬇️

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[bjarthur]

looks good. is it ready to merge?

[Mattriks]

Yes