Artefacts in meshes with transparency using CairoMakie

[philbit]

When plotting meshes with transparency, line artefacts appear where the triangles are touching.

MWE:

using CairoMakie

points = [Point2f(0.0, 0.0),
          Point2f(0.0, 1.0),
          Point2f(1.0, 1.0),
          Point2f(1.0, 0.0)]

m = Makie.GeometryBasics.Mesh(points, Makie.GeometryBasics.earcut_triangulate([points]))

# m is a Mesh{2, Float32, Triangle}:
# Triangle(Float32[0.0, 1.0], Float32[0.0, 0.0], Float32[1.0, 0.0])
# Triangle(Float32[1.0, 0.0], Float32[1.0, 1.0], Float32[0.0, 1.0])

fig = Figure()
ax = Axis(fig[1,1]; aspect = DataAspect())
mesh!(m)
display(fig)

Result:

It looks similar to issue #2469, which, as far as I understand, was resolved by not plotting as a mesh. But what if we need to explicitly draw a mesh? Is there a different way I am missing?

This is with CairoMakie 0.10.4.

[jkrumbiegel]

This is a limitation of Cairo, which can only draw mesh patterns triangle per triangle, so you're bound to get artifacts at the edges with alpha. In the future, we would like to implement a software renderer that draws meshes to a bitmap more like GLMakie would.

[philbit]

Thanks for the information. It's a pity it's not simply a bug ;), but I understand the limitation. Software rendering would be great!

[jkrumbiegel]

There are also some attempts to insert GLMakie rendered plot objects into CairoMakie vector graphics, maybe that would be an option in the future.