Correct way to save Makie plot to IOBuffer

Specific Domains Visualization
1

I am generating a web page including a data URL for a Makie plot. I would like to avoid saving the plot to a file if possible. I figured this out but I would like to know if there is a better way.

using Makie, CairoMakie, Base64

# test data 
t=0:0.1:2π
y=sin.(t)

# make a plot
CairoMakie.activate!(type="png")
fig = Figure()
ax = Axis(fig[1,1], title="test", ylabel="value", xlabel="time")
xlims!(ax, 0, t[end])
ylims!(ax, -1.1, 1.1)
lns = lines!(ax, t, y)
fig[1,2] = Legend(fig, [lns], ["lines"])

# save to IOBuffer
io = IOBuffer()
Makie.backend_show(Makie.current_backend[], io, MIME"image/png"(), fig.scene)
# extract bytes and create data uri
img_data_uri = "data:image/png;base64,$(base64encode(take!(io)))";

Specifically, backend_show looks like something I shouldn’t be messing with.

2 Likes
2

show(io, MIME"image/png"(), fig) should work I think

3

Huh, that works great in the REPL but fails when called in the full code with

MethodError: no method matching show(::IOBuffer, ::Type{MIME{Symbol("image/png")}}, ::Makie.Figure)

Adding a call to methods immediately before the call to show only makes me more confused, the method is right there!

methods(show, [IO, MIME"image/png", Any]) = # 2 methods for generic function "show":
[1] show(io::IO, m::MIME, figlike::Union{Makie.Figure, Makie.FigureAxisPlot, Makie.Scene}) in Makie at /home/user/.julia/packages/Makie/Ppzqh/src/display.jl:114
[2] show(io::IO, ::MIME{Symbol("image/png")}, surface::Cairo.CairoSurface) in Cairo at /home/user/.julia/packages/Cairo/smWIA/src/Cairo.jl:441

I’ll continue to investigate.

4

Take care to do MIME"..."() with the parentheses, the dispatch is not defined for the Type so you need to instantiate the MIME object

5

That was it, thank you very much!

6

What about for svg?

    buf = IOBuffer()
    show(buf, MIME"image/svg"(), fig)
ERROR: Unsupported mime: image/svg
Stacktrace:
      ⋮ internal @ Base, CairoMakie, Makie
  [6] show(io::IOBuffer, m::MIME{Symbol("image/svg")}, figlike::Figure)
    @ Makie ~/.julia/packages/Makie/z2T2o/src/display.jl:258
7

The mime type of svg is “image/svg+xml”