Draw a polyline on a native raster image

Draw a polyline on a native raster image

nr_polyline(
  nr,
  x,
  y,
  color = "black",
  linewidth = 1,
  mitre_limit = linewidth,
  close = FALSE,
  use_alpha = TRUE
)

Arguments

nr

native raster image

x, y

Vectors of point coordinates

color

Color as a character string. Either a standard R color (e.g. 'blue', 'white') or a hex color of the form #rrggbbaa, #rrggbb, #rgba or #rgb

linewidth

Line linewidth. Default: 1. If linewidth = 1 then a naive version of Bresenham is used to draw the points. If linewidth is greater than 1, then the line is convert to a triangle strip and rendered as polygons.

mitre_limit

Limit the size of the mitre when two lines meet at an acute angle and linewidth is greater than 1. Default: same as line linewidth which mostly looks OK.

close

Should the polyline be closed? I.e. should a line be drawn between the last point and the first point? Default: FALSE

use_alpha

Use alpha channel when drawing? Logical. Default: TRUE

Value

Invisibly return the supplied native raster image which was been modified in-place

See also

Other drawing functions: nr_circle(), nr_polygon(), nr_rect(), nr_tri_mesh()

Examples

N <- 20
nr <- nr_new(N, N, 'grey80')
nr_polyline(nr, x = c(0, N-1, 0), y = c(0, 0, N-1), color = 'red')
plot(nr)


N <- 200
nr <- nr_new(N, N, 'grey80')
nr_polyline(nr, x = c(10, N-10, 10), y = c(10, 10, N-10), color = 'red', 
                  linewidth = 5, mitre_limit = 3)
nr_polyline(nr, x = c(10, N-10, 10), y = c(10, 10, N-10), color = 'black')
plot(nr)



N <- 200
nr <- nr_new(N, N, 'grey80')
nr_polyline(nr, x = c(10, N-10, N-10, 10), y = c(10, 10, N-10, N-10), 
                  color = 'red', linewidth = 10, mitre_limit = 5, close = TRUE)
nr_polyline(nr, x = c(10, N-10, N-10, 10), y = c(10, 10, N-10, N-10), 
           color = 'black', close = TRUE)
plot(nr)