Advanced usage

library(munch)
library(grid)
library(flextable)

This vignette covers advanced topics: creating grobs directly, configuring text properties, embedding images, and ‘flextable’ integration.

Creating grobs with md_grob()

md_grob() converts markdown text to a grid graphics object (grob).

Basic usage

gr <- md_grob("This is **bold** and *italic* text.")

grid.newpage()
grid.draw(gr)

Positioning and justification

Control position with x, y, hjust, vjust:

grid.newpage()

gr1 <- md_grob("**Top left**", x = 0, y = 1, hjust = 0, vjust = 1)
gr2 <- md_grob("*Center*", x = 0.5, y = 0.5, hjust = 0.5, vjust = 0.5)
gr3 <- md_grob("`Bottom right`", x = 1, y = 0, hjust = 1, vjust = 0)

grid.draw(gr1)
grid.draw(gr2)
grid.draw(gr3)

Automatic text wrapping

Use width to enable line wrapping:

long_text <- "This is a **long text** that will be automatically
wrapped across multiple lines using the `width` parameter."

gr <- md_grob(long_text, x = 0.1, hjust = 0, width = 3)

grid.newpage()
grid.draw(gr)

Creating grobs with chunks_grob()

chunks_grob() converts ‘flextable’ paragraph objects to grobs. Use this when you need superscripts, subscripts, or custom colors.

chunks <- as_paragraph(
  as_chunk("E = mc"),
  as_sup("2")
)

gr <- chunks_grob(chunks)

grid.newpage()
grid.draw(gr)

Complex formatting

chunks <- as_paragraph(
  as_chunk("The speed of light is "),
  as_b("c"),
  as_chunk(" = 3\u00D710"),
  as_sup("8"),
  as_chunk(" m/s")
)

gr <- chunks_grob(chunks)

grid.newpage()
grid.draw(gr)

Colored and highlighted text

chunks <- as_paragraph(
  as_chunk("Normal "),
  colorize(as_chunk("Red "), color = "red"),
  as_highlight(as_chunk("Yellow bg"), color = "yellow")
)

gr <- chunks_grob(chunks)

grid.newpage()
grid.draw(gr)

Configuring text properties

Use default_text_props() to customize font size, family, and color:

props <- default_text_props(
  font_size = 14,
  font_family = "serif",
  font_color = "darkblue",
  code_font_family = "mono"
)

gr <- md_grob("Custom **styled** text with `code`", text_props = props)

grid.newpage()
grid.draw(gr)

Available parameters

Parameter Description Default
font_size Font size in points 11
font_family Font family “Helvetica”
font_color Text color “black”
code_font_family Font for inline code “mono”
line_spacing Line height multiplier 1.2
img_baseline_ratio Image vertical alignment 0.15

Integration with flextable theming

Text properties can also be set globally via ‘flextable’:

set_flextable_defaults(
  font.size = 14,
  font.color = "darkblue"
)

gr <- md_grob("Text using **flextable** defaults")

grid.newpage()
grid.draw(gr)


# Reset defaults
init_flextable_defaults()

Embedding images

In markdown

Use standard markdown image syntax:

img_path <- system.file("img", "Rlogo.png", package = "png")

text_with_img <- sprintf("The R logo: ![](%s) in text.", img_path)

gr <- md_grob(text_with_img)

grid.newpage()
grid.draw(gr)

With flextable chunks

Use as_image() for explicit size control:

img_path <- system.file("img", "Rlogo.png", package = "png")

chunks <- as_paragraph(
  as_chunk("The R logo "),
  as_image(src = img_path, width = 0.3, height = 0.3),
  as_chunk(" is iconic.")
)

gr <- chunks_grob(chunks)

grid.newpage()
grid.draw(gr)

Image baseline alignment

The img_baseline_ratio parameter controls vertical image alignment:

props <- default_text_props(img_baseline_ratio = 0.35)

gr <- md_grob(
  sprintf("Text ![](%s) centered", img_path),
  text_props = props
)

grid.newpage()
grid.draw(gr)

Using grobs in ggplot2

Use annotation_custom() to add grobs to ggplot2:

library(ggplot2)

stats_grob <- md_grob(
  "**R\u00B2 = 0.87**\n\n*p < 0.001*",
  hjust = 0,
  vjust = 1
)

ggplot(mtcars, aes(mpg, wt)) +
  geom_point() +
  geom_smooth(method = "lm", se = FALSE) +
  annotation_custom(
    grob = stats_grob,
    xmin = 25, xmax = 35,
    ymin = 4.5, ymax = 5.5
  )

Flextable integration

Use as_paragraph_md() for markdown in table cells:

ft <- flextable(head(iris, 3))
ft <- mk_par(ft, j = 1, part = "header",
  value = as_paragraph_md("*Sepal* **Length**"))
autofit(ft)

Sepal Length

Sepal.Width

Petal.Length

Petal.Width

Species

5.1

3.5

1.4

0.2

setosa

4.9

3.0

1.4

0.2

setosa

4.7

3.2

1.3

0.2

setosa