Support antialiasing in pipeline API

[ianthomas23]

Fixes #1204.

In the pipeline API we weren't passing through the antialias flag. With this fix, the OP's example works fine for all values of line_width:

import datashader as ds
import pandas as pd

df = pd.DataFrame(dict(x=[0,1],y=[0,1]))

glyph = ds.glyphs.LineAxis0('x','y')
glyph.set_line_width(1)
pipeline = ds.Pipeline(df, glyph)

image = pipeline(x_range=(0,1), y_range=(0,1), width=400, height=400)

[ianthomas23]

This is now handled in line.py.

[ianthomas23]

This isn't excellent, but is the simplest solution available given that the Glyph class has the antialiased attribute and this _AntiAliasedLine class is a mixin for line glyphs only. In fact the antialiased flag is always available here given how we are using it, so this hasattr isn't really needed but it is good practice to check before setting it.

In the long run, when we add antialiasing to other glyphs such as points it would be better to remove the _AntialisedLine class and move the line_width to the Glyph base class. But it will need a more generic name than line_width (antialiased_spread?) which is TBD.

[codecov]

Codecov Report

Merging #1213 (6fd8d37) into main (31b3182) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1213      +/-   ##
==========================================
+ Coverage   84.63%   84.65%   +0.02%     
==========================================
  Files          35       35              
  Lines        8354     8355       +1     
==========================================
+ Hits         7070     7073       +3     
+ Misses       1284     1282       -2     

Impacted Files	Coverage Δ
datashader/core.py	88.23% <ø> (-0.03%)	⬇️
datashader/glyphs/line.py	93.05% <100.00%> (+0.20%)	⬆️
datashader/pipeline.py	100.00% <100.00%> (ø)

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[jbednar]

Thanks!