shadowtext: Add text to a plot with a contrasting background.

Description

This is similar to the text function, but it also puts a background shadow (outline) behind the text to make it stand out from the background better.

Usage

shadowtext(x, y = NULL, labels, col = "white", bg = "black",
  theta = seq(pi/32, 2 * pi, length.out = 64), r = 0.1, 
  cex = 1, ...)

Value

This function is run for its side effects, returns NULL.

Arguments

x: x-coordinates for the text
y: y-coordinates for the text
labels: The text labels to plot
col: Color of the text
bg: Color of the background shadow
theta: Angles for plotting the background
r: Thickness of the shadow relative to plotting size
cex: Character expansion passed through to text and used in computing text size.
...: Additional arguments passed on to text

Author

Greg Snow, 538280@gmail.com, with improvements by Thomas Danhorn

Details

When adding text to a plot it is possible that the color of the text may make it difficult to see relative to its background. If the text spans different backgrounds then it may not be possible to find a single color to give proper contrast.

This function creates a contrasting shadow for the text by first plotting several copies of the text at angles theta and distance r in the background color, then plotting the text on top.

This gives a shadowing or outlining effect to the text making it easier to read on any background.

Examples

Run this code

 plot(1:10, 1:10, bg='aliceblue')
 rect(3,3,5,8, col='navy')
 text(5,6, 'Test 1', col='lightsteelblue')
 shadowtext(5,4, 'Test 2', col='lightsteelblue')

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