shape_string {systemfonts}

Calculate glyph positions for strings

Description

Do basic text shaping of strings. This function will use freetype to calculate advances, doing kerning if possible. It will not perform any font substitution or ligature resolving and will thus be much in line with how the standard graphic devices does text shaping. Inputs are recycled to the length of strings.

Usage

shape_string(
  strings,
  id = NULL,
  family = "",
  italic = FALSE,
  bold = FALSE,
  size = 12,
  res = 72,
  lineheight = 1,
  align = "left",
  hjust = 0,
  vjust = 0,
  width = NA,
  tracking = 0,
  indent = 0,
  hanging = 0,
  space_before = 0,
  space_after = 0,
  path = NULL,
  index = 0
)

Arguments

strings

A character vector of strings to shape

id

A vector grouping the strings together. If strings share an id the shaping will continue between strings

family

The name of the font families to match

italic

logical indicating the font slant

bold

logical indicating whether the font weight

size

The pointsize of the font to use for size related measures

res

The ppi of the size related mesures

lineheight

A multiplier for the lineheight

align

Within text box alignment, either 'left', 'center', or 'right'

hjust, vjust

The justification of the textbox surrounding the text

width

The requested with of the string in inches. Setting this to something other than NA will turn on word wrapping.

tracking

Tracking of the glyphs (space adjustment) measured in 1/1000 em.

indent

The indent of the first line in a paragraph measured in inches.

hanging

The indent of the remaining lines in a paragraph measured in inches.

space_before, space_after

The spacing above and below a paragraph, measured in points

path, index

path an index of a font file to circumvent lookup based on family and style

Value

A list with two element: shape contains the position of each glyph, relative to the origin in the enclosing textbox. metrics contain metrics about the full strings.

shape is a data.frame with the following columns:

glyph

The glyph as a character

index

The index of the glyph in the font file

metric_id

The index of the string the glyph is part of (referencing a row in the metrics data.frame)

string_id

The index of the string the glyph came from (referencing an element in the strings input)

x_offset

The x offset in pixels from the origin of the textbox

y_offset

The y offset in pixels from the origin of the textbox

x_mid

The x offset in pixels to the middle of the glyph, measured from the origin of the glyph

metrics is a data.frame with the following columns:

string

The text the string consist of

width

The width of the string

height

The height of the string

left_bearing

The distance from the left edge of the textbox and the leftmost glyph

right_bearing

The distance from the right edge of the textbox and the rightmost glyph

top_bearing

The distance from the top edge of the textbox and the topmost glyph

bottom_bearing

The distance from the bottom edge of the textbox and the bottommost glyph

left_border

The position of the leftmost edge of the textbox related to the origin

top_border

The position of the topmost edge of the textbox related to the origin

pen_x

The horizontal position of the next glyph after the string

pen_y

The vertical position of the next glyph after the string

Examples

string <- "This is a long string\nLook; It spans multiple lines\nand all"

# Shape with default settings
shape_string(string)

# Mix styles within the same string
string <- c(
  "This string will have\na ",
  "very large",
  " text style\nin the middle"
)

shape_string(string, id = c(1, 1, 1), size = c(12, 24, 12))