Size revamp 2: Guide.sizekey

[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 second in a set of 3 PRs. This PR adds Guide.sizekey
• is another step towards closing issues Feature request: map multiple numerical and categorical data to plots #766, making scatter plots with different shaped markers (issues) #1366

This PR makes changes to the layout of shapekey and sizekey, via render_discrete_key. This doesn't affect colorkey, which currently uses render_discrete_color_key. render_discrete_color_key contains bugs (#859), that become worse with larger swatch sizes. The long-term plan is that all discrete aesthetics (including color) will use render_discrete_key.

Examples

labels = rand(randstring.(fill(8, 5)), 100) 
datas, aes = Gadfly.Data(size=labels), Gadfly.Aesthetics()
sc1 = Scale.size_discrete2(n->range(4pt, 8pt, length=n))
Scale.apply_scale(sc1, [aes], datas)
 gsk = Guide.sizekey(title="Size key")
theme = Theme(key_swatch_shape=Shape.hexagon, key_label_font_size=10pt, 
    discrete_highlight_color=identity, alphas=[0.1], key_max_columns=5)
ctxs =  Guide.render(gsk, theme, aes)[1].ctxs
vstack(hstack(ctxs[1:2]...), ctxs[5]) 

Example from gallery/guides.md (in this PR):

plot(Titanic, Scale.x_log10,  Scale.y_log10,
    x=:Freq, y=:prcnt, color=:Age, shape=:Sex,  size=:Class,
    Scale.size_discrete2(sizemap), Guide.sizekey(title="Passenger\n Class"),
    Guide.colorkey(pos=[0.1, -0.3h]), Guide.shapekey(pos=[0.5, -0.31h]),
    Guide.ylabel("% of Passenger Class"),
 Theme(discrete_highlight_color=identity, alphas=[0.1], key_swatch_color="grey",
    key_swatch_shape=Shape.circle, point_size=3pt) )

[codecov-io]

Codecov Report

Merging #1379 into master will decrease coverage by 0.25%.
The diff coverage is 77.58%.

@@            Coverage Diff             @@
##           master    #1379      +/-   ##
==========================================
- Coverage   90.57%   90.31%   -0.26%     
==========================================
  Files          39       39              
  Lines        3988     4028      +40     
==========================================
+ Hits         3612     3638      +26     
- Misses        376      390      +14

Impacted Files	Coverage Δ
src/theme.jl	69.49% <ø> (ø)	⬆️
src/Gadfly.jl	78.14% <100%> (ø)	⬆️
src/guide/keys.jl	85.34% <76.78%> (-9.4%)	⬇️
src/scale/scales.jl	88.88% <0%> (-3.71%)	⬇️

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[Mattriks]

To do:

• change the key swatch stroke width (to theme.highlight_width)
• Theme(key_swatch_size= ) to override point_size
• Update discrete scale table in the Tutorial

[Mattriks]

I completed my To do list, and updated the figures in my OP. I also refactored some unit tests so that the key item order is always consistent (which makes it easier to regression test the keys). In the regression testing, small changes occur in any test with a shapekey (8 in total). The small changes occur because of the updated layout, and because the key swatch size (for render_discrete_key) now defaults to the default point_size.

I would also like to suggest raising the default point_size from 0.95mm to 3pt (~1mm), you can see 3pt swatch size in the Titanic example above (compare the color and shape keys inside the plot).

[bjarthur]

looks great! thanks for all your work on keys recently. looking forward to the third installment. in addition to the two comments in the code, it'd be nice if you could give the second commit a more informative message.

[Mattriks]

The only q remaining for me in this PR is: can the default point size be changed from 0.95mm to 3pt (~1mm).? The reason is that with this PR the key swatch size defaults to Theme(point_size), and 3pt is closer to the current key swatch size (0.95mm is slightly smaller than the current key swatch size).

[bjarthur]

the only difference i can see between render_key_title and render_key_title2 is the use of 4mm in the former here. to eliminate such code duplication, would it be possible to pass in title_padding as an argument?

[Mattriks]

I would prefer to keep the two functions separate for the moment, as I'm working towards separating the keys for discrete and continuous aesthetics. After I complete that I'm happy to tidy up whatever's remaining.

[Mattriks]

Please answer my question above about the default point size.