CairoMakie heatmap pixels overlap

[maxfreu]

I want to create a heatmap of a non-square matrix with square pixels. I'm trying to achieve this by setting a colsize of defined aspect. This however leads to somehow staggered pixels and strange effects, as CairoMakie seemingly draws the pixels larger than they actually are.

Some demo code and the corresponding PDF opened in inkscape:

fig = Figure(size = mm2pt.((83, 50)))
ax = Axis(fig[1, 1])
r = rand(20,30)
colsize!(fig.layout, 1, Aspect(1, size(r)[1] / size(r)[2]))
heatmap!(ax, r; colorrange = (0, 1))
save("deleteme.pdf", fig)

The problem:

Any idea how I can make the pixels square without this effect?

Makie 0.20.7, CairoMakie 0.11.8, julia 1.10

[jkrumbiegel]

CairoMakie draws heatmap cells larger than they are so that you don't get background-colored artifacts at the seams. It should not draw them larger if the adjacent cells are not fully opaque, but maybe in your case the cells are even spanning across more than one neighbor, so they peek through. So we have to check that the overdrawing width is at most some fraction of the neighboring cell so that this cannot happen.

[maxfreu]

https://github.com/MakieOrg/Makie.jl/blob/f92b2607de3788a6c2b45eb5fd5546fb634fab3a/CairoMakie/src/primitives.jl#L785-L795

here, right?