Build paper-anchored panel border shapes for a faceted plotly figure

Native plotly subplot() figures with shared (shareX/shareY) axes do not render axis border lines on the matched/inner panels, so faceted plots end up with a box around only the first panel. This helper reconstructs each panel's rectangle from the grid of x/y axis domains in the figure layout and returns paper-anchored shapes that draw a uniform border around every panel.

Usage

build_facet_panel_borders(
  fig,
  n_facets,
  showline = TRUE,
  mirror = TRUE,
  linecolor = "black",
  linewidth = 0.5,
  ncol = NULL,
  nrow = NULL
)

Arguments

fig: A plotly figure object whose x$layout contains the per-panel xaxis*/yaxis* domains (typically after subplot() and apply_facet_subplot_spacing()).
n_facets: Integer, number of facet panels.
showline: Logical, whether to draw border lines. Default TRUE.
mirror: Logical, whether to mirror the lines to form a full box. Default TRUE.
linecolor: Character, colour of the border lines. Default "black".
linewidth: Numeric, width of the border lines in pixels. Default 0.5.
ncol: Optional integer. Number of facet columns. If NULL or NA, detected from the distinct x-axis domain starts.
nrow: Optional integer. Number of facet rows. If NULL or NA, detected from the distinct y-axis domain starts.

Value

A list of plotly shape definitions (each paper-anchored). Returns an empty list when borders should not be drawn or panel domains cannot be resolved.

Details

Panel rectangles are derived from the geometry of the subplot grid rather than from a per-panel axis index. With shared axes plotly only keeps one axis per column (x) and one per row (y), so an xaxis{i}/yaxis{i} lookup keyed on the facet index breaks down for grids with more than one row or column. Instead the distinct x-axis domain starts define the columns (left to right) and the distinct y-axis domain starts define the rows (top to bottom), and each facet panel is mapped to a (row, column) cell in row-major fill order — matching how subplot() lays panels out.

The borders honour the same axis styling semantics used for single-panel figures:

showline and mirror both TRUE: full rectangle border around each panel.
only showline TRUE: left and bottom edges only.
showline FALSE: no borders (empty list).

Author

Jacob Martin

Examples

p <- ggplot2::ggplot(mtcars, ggplot2::aes(wt, mpg)) +
    ggplot2::geom_point() +
    ggplot2::facet_wrap(~cyl)
fig <- plotly::ggplotly(p)
build_facet_panel_borders(fig, n_facets = 3)
#> [[1]]
#> [[1]]$type
#> [1] "rect"
#> 
#> [[1]]$xref
#> [1] "paper"
#> 
#> [[1]]$yref
#> [1] "paper"
#> 
#> [[1]]$x0
#> [1] 0
#> 
#> [[1]]$x1
#> [1] 0.3219178
#> 
#> [[1]]$y0
#> [1] 0
#> 
#> [[1]]$y1
#> [1] 1
#> 
#> [[1]]$line
#> [[1]]$line$color
#> [1] "black"
#> 
#> [[1]]$line$width
#> [1] 0.5
#> 
#> 
#> [[1]]$fillcolor
#> [1] "rgba(0,0,0,0)"
#> 
#> [[1]]$layer
#> [1] "above"
#> 
#> 
#> [[2]]
#> [[2]]$type
#> [1] "rect"
#> 
#> [[2]]$xref
#> [1] "paper"
#> 
#> [[2]]$yref
#> [1] "paper"
#> 
#> [[2]]$x0
#> [1] 0.3447489
#> 
#> [[2]]$x1
#> [1] 0.6552511
#> 
#> [[2]]$y0
#> [1] 0
#> 
#> [[2]]$y1
#> [1] 1
#> 
#> [[2]]$line
#> [[2]]$line$color
#> [1] "black"
#> 
#> [[2]]$line$width
#> [1] 0.5
#> 
#> 
#> [[2]]$fillcolor
#> [1] "rgba(0,0,0,0)"
#> 
#> [[2]]$layer
#> [1] "above"
#> 
#> 
#> [[3]]
#> [[3]]$type
#> [1] "rect"
#> 
#> [[3]]$xref
#> [1] "paper"
#> 
#> [[3]]$yref
#> [1] "paper"
#> 
#> [[3]]$x0
#> [1] 0.6780822
#> 
#> [[3]]$x1
#> [1] 1
#> 
#> [[3]]$y0
#> [1] 0
#> 
#> [[3]]$y1
#> [1] 1
#> 
#> [[3]]$line
#> [[3]]$line$color
#> [1] "black"
#> 
#> [[3]]$line$width
#> [1] 0.5
#> 
#> 
#> [[3]]$fillcolor
#> [1] "rgba(0,0,0,0)"
#> 
#> [[3]]$layer
#> [1] "above"
#> 
#>