Patterns ‘image’ and ‘placeholder’

suppressPackageStartupMessages({
  library("ggplot2")
  library("ggpattern")
  require("magick", quietly = TRUE)
})

Introduction to the ‘image and ’placeholder’ patterns

The ‘image’ pattern allows filling a geom with an image from file or URL. It is an “array” pattern that depends on the suggested package {magick}.
The ‘placeholder’ pattern fetches images from image placeholder sites. It is an “array” pattern that depends on the suggested package {magick} and additionally requires an internet connect.
For more info on these patterns see their {gridpattern} documentation:
- help("grid.pattern_image", package = "gridpattern")
- help("grid.pattern_placeholder", package = "gridpattern")

The `image` pattern - filling a geom with an image from file or URL

This pattern will load an image from a file or URL (pattern_filename) and display it within the geom.

Because the image will most likely not exactly cover the area of the geom, there are options to specify how the image is used to fill the region.

After expanding to cover the area, the image is then clipped to the boundary of the geom.

The files/URLs are loaded with magick::image_read which means that transparent images and SVGs are supported.

`image` options

Aesthetic	Description	Default
`pattern_filename`	Image filename or URL	’’
`pattern_type`	Image scaling type	‘fit’
`pattern_scale`	Extra scaling	1
`pattern_gravity`	Position of image within area	‘center’
`pattern_filter`	Filter to use when scaling	‘lanczos’
`pattern_alpha`	Alpha	NA
`pattern_aspect_ratio`	Override aspect ratio	NA
`pattern_key_scale_factor`	Additional scale factor for legend	1

`pattern_type`	Description	`pattern_scale`	`pattern_gravity`
squish	distort the image to cover the bounding box of the region
fit	scale the image such that either the width or the height of the image fits in the bounding box.		Yes
expand	scale the image beyond the bounding box and crop it such that the image fully covers the width and the height of the region
none	position a single image in the region without attempting to scale to the bounding box size	Yes	Yes
tile	repeat the image to cover the bounding box.	Yes

Note: not all combinations of aesthetics are useful e.g. if pattern_type = 'fit' is specified, then pattern_scale has no effect.

Example Data

These examples use some of the built-in images in the ggpattern package.

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# filenames of images
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
logo_filename   <- system.file("img", "Rlogo.png" , package="png")
magpie_filename <- system.file("img", "magpie.jpg", package="ggpattern")
bug_filename    <- system.file("img", "bug.jpg"   , package="ggpattern")

seamless1 <- system.file("img", "seamless1.jpg"   , package="ggpattern")
seamless2 <- system.file("img", "seamless2.jpg"   , package="ggpattern")
seamless3 <- system.file("img", "seamless3.jpg"   , package="ggpattern")

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Plotting data
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
df1 <- data.frame(
  trt      = c("a", "b", "c"), 
  outcome  = c(2.3, 1.9, 3.2),
  gravity  = c('South', 'North', 'West'),
  filltype = c('squish', 'fit' , 'expand'),
  scale    = c(1, 2, 0.5),
  filename = c(logo_filename, magpie_filename, bug_filename),
  stringsAsFactors = FALSE
)

Example Data
trt	outcome	gravity	filltype	scale	filename
a	2.3	South	squish	1.0	/usr/local/lib/R/site-library/png/img/Rlogo.png
b	1.9	North	fit	2.0	/usr/local/lib/R/site-library/ggpattern/img/magpie.jpg
c	3.2	West	expand	0.5	/usr/local/lib/R/site-library/ggpattern/img/bug.jpg

Example: `pattern = 'image'` - No Attempt at filling the area (`pattern_type = 'none'`)

If pattern_type = 'none' then no attempt is made at snugly filling the area. Instead a single copy of the image is scaled (pattern_scale) and placed (pattern_gravity) in the geom area.

if (require("magick")) {

ggplot(df1, aes(trt, outcome)) +
  geom_col_pattern(
    aes(
      fill            = trt,
      pattern_gravity = I(gravity),
      pattern_scale   = I(scale)
    ), 
    pattern          = 'image', 
    pattern_filename = logo_filename,
    pattern_type     = 'none',
    colour           = 'black'
  ) +
  theme_bw(15) +
  labs(
    title    = "ggpattern::geom_col_pattern()",
    subtitle = "pattern = 'image', pattern_type = 'none'"
  ) +
  theme(legend.key.size = unit(1.5, 'cm')) +
  coord_fixed(ratio = 1/2)

}

Example: `pattern = 'image'` - Covering the area (`pattern_type = 'fit', 'squish', 'expand'`)

In the plot below, 3 different methods are used to cover the area of the geom. From left-to-right:

pattern_type = 'squish' to force the image to cover the bounding box of the geom.
pattern_type = 'fit' to force the image to cover the width (or height) yet still remain fully visible. pattern_gravity = 'North' floats the image to the top.
pattern_type = 'expand`` scales the image (while preserving aspect ratio) such that the entire geom is covered.pattern_gravity = ‘West’` anchors the image to the left side of the geom.

if (require("magick")) {

ggplot(df1, aes(trt, outcome)) +
  geom_col_pattern(
    aes(
      fill            = trt,
      pattern_gravity = I(gravity),
      pattern_type    = I(filltype)
    ), 
    pattern          = 'image', 
    colour           = 'black',
    pattern_filename = logo_filename,
    
  ) +
  theme_bw(15) +
  labs(
    title    = "ggpattern::geom_col_pattern()",
    subtitle = "pattern = 'image'"
  ) +
  # theme(legend.key.size = unit(1.5, 'cm')) +
  theme(legend.position = 'none') +
  coord_fixed(ratio = 1/2)

}

Example: `pattern = 'image'` - Tiling (`pattern_type = 'tile'`)

When tiled, the image is replicated in order to cover the entire area of the geom. In this example, pattern_scale is also applied to the image so that it appears at different sizes.

if (require("magick")) {

ggplot(df1, aes(trt, outcome)) +
  geom_col_pattern(
    aes(
      fill            = trt,
      pattern_gravity = I(gravity),
      pattern_scale   = I(scale)
    ), 
    pattern          = 'image', 
    pattern_type     = 'tile',
    pattern_filename = logo_filename,
    colour           = 'black'
  ) +
  theme_bw(15) +
  labs(
    title    = "ggpattern::geom_col_pattern()",
    subtitle = "pattern = 'image', pattern_type = 'tile'"
  ) +
  # theme(legend.key.size = unit(1.5, 'cm')) +
  theme(legend.position = 'none') +
  coord_fixed(ratio = 1/2)

}

Example: `pattern = 'image'` - Tiling with seamless patterns

By choosing a seamlessly tiling image, then a tiled fill will not have visible discontinuities.

if (require("magick")) {

ggplot(mtcars) +
  geom_density_pattern(
    aes(
      x = mpg, 
      pattern_filename = as.factor(cyl)
    ), 
    pattern      = 'image',
    pattern_type = 'tile'
  ) +
  theme_bw(15) +
  theme(legend.key.size = unit(1.5, 'cm')) + 
  labs(
    title    = "ggpattern::geom_density_pattern()",
    subtitle = "pattern = 'image', pattern_type = 'tile'"
  ) +
  scale_pattern_filename_manual(values = c(`4` = seamless1, `6` = seamless2, `8` = seamless3)) +
  coord_fixed(ratio = 80)

}

Example: `pattern = 'image'` - Tiling with seamless patterns (with scaling)

if (require("magick")) {

ggplot(mtcars) +
  geom_density_pattern(
    aes(
      x = mpg, 
      pattern_filename = as.factor(cyl)
    ), 
    pattern       = 'image',
    pattern_type  = 'tile',
    pattern_scale = 0.5
  ) +
  theme_bw(15) +
  theme(legend.key.size = unit(2, 'cm')) + 
  labs(
    title    = "ggpattern::geom_density_pattern()",
    subtitle = "pattern = 'image', pattern_type = 'tile'"
  ) +
  scale_pattern_filename_manual(values = c(`4` = seamless1, `6` = seamless2, `8` = seamless3)) +
  coord_fixed(ratio = 80)

}

Example: `pattern = 'image'` - Tiling with fit to width (of element bounding box)

In a common case, the image to be tiled should be first scaled to the width of the bar to be tiled and then tiling appears like a vertical stacking. This is useful for bar charts.

Specify pattern_scale = -1 to fit the width of the geom, and pattern_scale = -2 to fit the height of the geom.

if (require("magick")) {

ggplot(df1, aes(trt, outcome)) +
  geom_col_pattern(
    aes(
      fill             = trt,
      pattern_filename = I(filename)
    ), 
    pattern          = 'image', 
    pattern_type     = 'tile',
    pattern_scale    = -1,
    colour           = 'black'
    
  ) +
  theme_bw(15) +
  labs(
    title    = "ggpattern::geom_col_pattern()",
    subtitle = "pattern = 'image', pattern_type = 'tile',\npattern_scale = -1"
  ) +
  theme(legend.position = 'none') +
  coord_fixed(ratio = 1)

}

`placeholder` - Filling with an image placeholder

Array-based patterns allow the user to specify an RGBA that should be displayed in the geom.

Getting the correct sized image such that it takes up the full space without being distorted can be a time-consuming task.

The placeholder pattern takes out this drudgery by fetching exactly the correct sized image to fit the space. These images come from image placeholder sites which are most often used by web-developers as a stand-in for a final image while they are developing a new site.

`placeholder` options

Aesthetic	Description	Default
`pattern_type`	Image source	‘bear’
`pattern_alpha`	Alpha	NA
`pattern_aspect_ratio`	Override aspect ratio	NA
`pattern_key_scale_factor`	Additional scale factor for legend	1

`placeholder` option `pattern_type`

The following is a list of all the pattern_type values which are valid. If unspecified or unknown, then ggpattern will use pattern_type = 'bear'.

If you would like only greyscale images, append bw to the name, e.g. to display only black and white bears use pattern_type = 'bearbw'.

Click the link to see an example of each placeholder generator

‘bear’ - bears
‘beard’ - beards
‘cage’ - nicholas cage
‘dummy’ - image showing dimensions
‘flickr’ - random picture from flickr
‘keanu’ - Keanu
‘kitten’ - kitten
‘murray’ - bill murray
‘picsum’ - random picture from picsum
‘placeholder’ - placeholder.com
‘seagal’ - steven seagal

All placeholder names are available in gridpattern::names_placeholder.

Example Data

df1 <- data.frame(
  trt     = c("a", "b", "c"), 
  outcome = c(2.3, 1.9, 3.2),
  stringsAsFactors = FALSE
)

Example: `pattern = 'placeholder'` - `pattern_type = 'bear'`

if (require("magick")) { 

ggplot(df1, aes(trt, outcome)) +
  geom_col_pattern(
    aes(fill = trt), 
    pattern      = 'placeholder', 
    pattern_type = 'bear',
    colour       = 'black'
  ) +
  theme_bw(15) +
  labs(
    title    = "ggpattern::geom_col_pattern()",
    subtitle = "pattern='placeholder', pattern_type='bear'"
  ) +
  theme(legend.position = 'none') +
  coord_fixed(ratio = 1/2)

}

Example: `pattern = 'placeholder'` - `pattern_type = 'picsum'`

if (require("magick")) {

ggplot(mtcars) +
  geom_density_pattern(
    aes(x = mpg, group = as.factor(cyl)),
    pattern      = 'placeholder',
    pattern_type = 'picsum'
  ) +
  theme_bw(15) +
  theme(legend.position = 'none') +
  labs(
    title    = "ggpattern::geom_col_pattern()",
    subtitle = "pattern='placeholder', pattern_type='picsum'"
  ) +
  coord_fixed(ratio = 80)

}

Example: `pattern = 'placeholder'` - `pattern_type = 'dummy'`

if (require("magick")) {

ggplot(df1, aes(trt, outcome)) +
  geom_col_pattern(
    aes(fill = trt), 
    pattern       = 'placeholder', 
    pattern_type  = 'dummy',
    colour        = 'black'
  ) +
  theme_bw(15) +
  labs(
    title    = "ggpattern::geom_col_pattern()",
    subtitle = "pattern='placeholder', pattern_type='dummy'"
  ) +
  theme(legend.position = 'none') +
  coord_fixed(ratio = 1/2)

}

Resetting the image cache

{gridpattern} stores the images used by the "image" and "placeholder" patterns in a cache. This is mainly to avoid the risk of re-downloading the same image over and over especially for the "placeholder" pattern. However, this may cause problems if you re-using the same image filename but the images in those files are changing. You may reset this image cache with gridpattern::reset_image_cache().

Patterns ‘image’ and ‘placeholder’ - Parameters and Examples

Introduction to the ‘image and ’placeholder’ patterns

The image pattern - filling a geom with an image from file or URL

image options

Example Data

Example: pattern = 'image' - No Attempt at filling the area (pattern_type = 'none')

Example: pattern = 'image' - Covering the area (pattern_type = 'fit', 'squish', 'expand')

Example: pattern = 'image' - Tiling (pattern_type = 'tile')

Example: pattern = 'image' - Tiling with seamless patterns

Example: pattern = 'image' - Tiling with seamless patterns (with scaling)

Example: pattern = 'image' - Tiling with fit to width (of element bounding box)

placeholder - Filling with an image placeholder

placeholder options

placeholder option pattern_type

Example Data

Example: pattern = 'placeholder' - pattern_type = 'bear'

Example: pattern = 'placeholder' - pattern_type = 'picsum'

Example: pattern = 'placeholder' - pattern_type = 'dummy'

Resetting the image cache

The `image` pattern - filling a geom with an image from file or URL

`image` options

Example: `pattern = 'image'` - No Attempt at filling the area (`pattern_type = 'none'`)

Example: `pattern = 'image'` - Covering the area (`pattern_type = 'fit', 'squish', 'expand'`)

Example: `pattern = 'image'` - Tiling (`pattern_type = 'tile'`)

Example: `pattern = 'image'` - Tiling with seamless patterns

Example: `pattern = 'image'` - Tiling with seamless patterns (with scaling)

Example: `pattern = 'image'` - Tiling with fit to width (of element bounding box)

`placeholder` - Filling with an image placeholder

`placeholder` options

`placeholder` option `pattern_type`

Example: `pattern = 'placeholder'` - `pattern_type = 'bear'`

Example: `pattern = 'placeholder'` - `pattern_type = 'picsum'`

Example: `pattern = 'placeholder'` - `pattern_type = 'dummy'`