Filled contour plots

[jhidding]

Hi, I once created a demo for filled contour plots in the terminal. When I saw this package I thought I might contribute it. The original was in Rust, but I created a small demo in Julia to show what I had in mind: https://github.com/jhidding/UnicodeContour.jl

This code could also be adapted for the fill_between feature that was requested earlier in #254.

If you like the idea, I could invest some more time to see if this works.

[t-bltg]

Great, I wasn't aware of the extra Symbols for Legacy Computing block of Unicode.

UnicodePlots is definitively the right place for this kind of addition.

Even if we use opaque characters instead of braille characters, this could be our implementation for the missing contourf (or maybe contourplot with a filled kwarg).

Could also be useful for drawing polar heatmaps: I wonder if it's possible to render a perfect circle using these characters.

I like this ;)

[t-bltg]

I guess that the first step is creating a new canvas type (Name t.b.d. <: LookupCanvas), similar to https://github.com/JuliaPlots/UnicodePlots.jl/blob/master/src/canvas/blockcanvas.jl#L7-L23, with an adjusted lookup table.

[jhidding]

Started fork at jhidding/UnicodePlots.jl.

[t-bltg]

Great, I would for the moment (subject to evolution) hijack contourplot by replacing this line with something like:

if canvas === FilledCanvas
   # TODO: process levels, and fill the canvas

   # Note that displaying the characters is not done here (delayed to using `show`, `display` or `savefig` on the plot)
   # and that is handled in `src/show.jl`: https://github.com/JuliaPlots/UnicodePlots.jl/blob/master/src/show.jl#L301

   # There, each canvas row is printed: since `FilledCanvas` is a subtype of the abstract type `LookupCanvas`,
   # `lookup_decode` must be implemented such that decoding can occur in here:
   # https://github.com/JuliaPlots/UnicodePlots.jl/blob/master/src/canvas/lookupcanvas.jl#L75

   # I would suggest taking inspiration from `src/interface/heatmap.jl` for filling the grid and colors:
   # https://github.com/JuliaPlots/UnicodePlots.jl/blob/master/src/interface/heatmap.jl#L192-L196
else
   contourplot!(plot, x, y, A; colormap, okw...)  # other canvases (BrailleCanvas, ...)
end
plot

, so that you can work your mwe out (TIL himmelblau):

julia> using UnicodePlots
julia> himmelblau(x, y) = (x^2 + y - 11)^2 + (x + y^2 - 7)^2
julia> contourplot(himmelblau; canvas = FilledCanvas, levels = ...)  # would need to adjust `levels` kw to take a vector of levels

It's unlikely a miracle will happen but that's a start ...

You can also open a draft PR here so that it would be easier to review and add comments.

[t-bltg]

Also note that filling FILLED_DECODE[(N_FILLED + 1):typemax(N_FILLED)] = UNICODE_TABLE[1:(typemax(N_FILLED) - N_FILLED)] is un-needed since for this canvas, since we don't plan to add other characters than those from the Symbols for Legacy Computing block (the whole canvas will be filled, and colored).

This means that the FilledCanvas.grids eltype can probably be restricted to UInt8: grid::Transpose{UInt8,Matrix{UInt8}} as what is currently done for the HeatmapCanvas.