Legend is missing for type "mesh3d" unless some surface trace is added

plotly.js added support for more trace legends but, for mesh3d, there is no legend below unless showlegend = TRUE for the mesh and a surface is added.

GH issue for more trace legends
merge for above

library(plotly)
library(rmarchingcubes)

R <- 2
f1 <- function(x, y, z){
  x^2 + y^2 + z^2 - R^2
}
f2 <- function(x, y, z){
  (x-2)^2 + (y-2)^2 + (z-2)^2 - R^2
}
g <- function(x, y, z) {
  pmax(f1(x, y, z), f2(x, y, z))
}

n <- 100
x_ <- y_ <- z_ <- seq(-R, R, length.out = n) 
Grid <- expand.grid(X = x_, Y = y_, Z = z_)
voxel <- with(Grid, array(g(X, Y, Z), dim = c(n, n, n)))
surf <- contour3d(voxel, level = 0, x_, y_, z_)
vertices <- surf$vertices
indices  <- surf$triangles - 1L

plot_ly(
  x = vertices[, 1], y = vertices[, 2], z = vertices[, 3],
  i = indices[, 1], j = indices[, 2], k = indices[, 3],
  type = "mesh3d",
  name = "hello world",
  showlegend = TRUE
) %>% layout(scene = list(aspectmode = "data"))

z <- c(
  c(8.83,8.89,8.81,8.87,8.9,8.87),
  c(8.89,8.94,8.85,8.94,8.96,8.92),
  c(8.84,8.9,8.82,8.92,8.93,8.91),
  c(8.79,8.85,8.79,8.9,8.94,8.92),
  c(8.79,8.88,8.81,8.9,8.95,8.92),
  c(8.8,8.82,8.78,8.91,8.94,8.92),
  c(8.75,8.78,8.77,8.91,8.95,8.92),
  c(8.8,8.8,8.77,8.91,8.95,8.94),
  c(8.74,8.81,8.76,8.93,8.98,8.99),
  c(8.89,8.99,8.92,9.1,9.13,9.11),
  c(8.97,8.97,8.91,9.09,9.11,9.11),
  c(9.04,9.08,9.05,9.25,9.28,9.27),
  c(9,9.01,9,9.2,9.23,9.2),
  c(8.99,8.99,8.98,9.18,9.2,9.19),
  c(8.93,8.97,8.97,9.18,9.2,9.18)
)
dim(z) <- c(15,6)

plot_ly(
  x = vertices[, 1], y = vertices[, 2], z = vertices[, 3],
  i = indices[, 1], j = indices[, 2], k = indices[, 3],
  type = "mesh3d",
  name = "hello",
  showscale = FALSE,
  showlegend = TRUE
) %>% 
  plotly::layout(scene = list(aspectmode = "data")) %>% 
  add_surface(z = ~z, name = "placeholder")

Commencez par reproduire les exemples mesh3d de l’issue et comparez le comportement avec l’issue 2642 et la pull request 4386 référencés de plotly.js. Suivez la manière dont plotly.R transmet les traces mesh3d à plotly.js ; le travail est terminé lorsqu’une trace mesh3d affiche sa légende sans nécessiter l’ajout d’une trace surface.