Fix AA with large linewidth differences

[ffreyer]

Description

This is another fix coming out of #2944. I added per position linewidths with the fixes for line patterns but I didn't think carefully enough about the padding for those cases. Thus we find no anti-aliasing when the change in linewidth from one point to the next is (much) larger than the distance between those points:

scene = Scene(resolution = (400, 400))
campixel!(scene)
lines!(scene, fill(200, 4), [0, 190, 210, 400], linewidth = [2, 2, 202, 202], color = :black)
scene

The pr adds scaling so that this is fixed:

I didn't bother with patterned lines since, well, they do their own weird thing....

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• Added an entry in NEWS.md (for new features and breaking changes)
• Added or changed relevant sections in the documentation
• Added unit tests for new algorithms, conversion methods, etc.
• Added reference image tests for new plotting functions, recipes, visual options, etc.

[ffreyer]

Here's a sketch for the scaling factor

v and n match the names in the shader, describing the line direction and normal. AA is AA_THICKNESS. The factor 1/2 in the linewidth difference comes from that difference existing symmetrically on both sides of the line segment. That factor drops out in the shader because widths are scaled by a factor of 2. y is the final (geometric) padding we apply, which is still representative of a padding by AA_THICKNESS in uv.y causing that to have a reduced linewidth.

[MakieBot]

Compile Times benchmark

Note, that these numbers may fluctuate on the CI servers, so take them with a grain of salt. All benchmark results are based on the mean time and negative percent mean faster than the base branch. Note, that GLMakie + WGLMakie run on an emulated GPU, so the runtime benchmark is much slower. Results are from running:

using_time = @ctime using Backend
# Compile time
create_time = @ctime fig = scatter(1:4; color=1:4, colormap=:turbo, markersize=20, visible=true)
display_time = @ctime Makie.colorbuffer(display(fig))
# Runtime
create_time = @benchmark fig = scatter(1:4; color=1:4, colormap=:turbo, markersize=20, visible=true)
display_time = @benchmark Makie.colorbuffer(display(fig))

	using	create	display	create	display
GLMakie	10.20s (9.99, 10.44) 0.16+-	1.17s (1.13, 1.19) 0.02+-	834.46ms (799.34, 885.99) 32.91+-	10.71ms (10.51, 10.89) 0.13+-	91.35ms (89.97, 92.50) 0.95+-
master	10.15s (9.95, 10.35) 0.18+-	1.16s (1.10, 1.21) 0.04+-	819.48ms (795.38, 836.07) 15.02+-	10.74ms (10.59, 10.93) 0.11+-	92.22ms (91.30, 93.18) 0.76+-
evaluation	+0.51%, 0.05s invariant (0.31d, 0.57p, 0.17std)	+0.98%, 0.01s invariant (0.36d, 0.51p, 0.03std)	+1.80%, 14.98ms invariant (0.59d, 0.30p, 23.96std)	-0.28%, -0.03ms invariant (-0.25d, 0.65p, 0.12std)	-0.95%, -0.87ms invariant (-1.01d, 0.08p, 0.85std)
CairoMakie	10.33s (9.97, 10.73) 0.24+-	1.56s (1.50, 1.59) 0.03+-	345.24ms (330.31, 374.88) 18.82+-	13.79ms (13.50, 14.19) 0.25+-	7.27ms (6.99, 7.74) 0.26+-
master	10.26s (9.90, 10.75) 0.30+-	1.56s (1.51, 1.61) 0.04+-	314.96ms (303.93, 324.12) 8.52+-	13.65ms (13.34, 14.17) 0.30+-	7.27ms (6.95, 7.45) 0.18+-
evaluation	+0.65%, 0.07s invariant (0.25d, 0.65p, 0.27std)	+0.37%, 0.01s invariant (0.15d, 0.78p, 0.04std)	+8.77%, 30.28ms slower❌ (2.07d, 0.00p, 13.67std)	+1.04%, 0.14ms invariant (0.52d, 0.35p, 0.28std)	+0.04%, 0.0ms invariant (0.01d, 0.98p, 0.22std)
WGLMakie	9.15s (9.00, 9.22) 0.08+-	1.24s (1.19, 1.26) 0.02+-	11.13s (11.03, 11.21) 0.07+-	13.39ms (11.71, 20.09) 2.98+-	751.63ms (710.94, 783.74) 25.61+-
master	9.19s (9.12, 9.26) 0.05+-	1.24s (1.21, 1.27) 0.02+-	11.18s (11.02, 11.45) 0.15+-	12.14ms (11.56, 12.50) 0.32+-	734.12ms (712.13, 753.62) 15.42+-
evaluation	-0.44%, -0.04s invariant (-0.59d, 0.29p, 0.07std)	+0.20%, 0.0s invariant (0.10d, 0.85p, 0.02std)	-0.51%, -0.06s invariant (-0.48d, 0.39p, 0.11std)	+9.32%, 1.25ms noisy🤷‍♀️ (0.59d, 0.31p, 1.65std)	+2.33%, 17.51ms invariant (0.83d, 0.15p, 20.52std)