Create a custom blend type

Many of the blend types available in with_blend() are variations over the formula: a*src*dst + b*src + c*dst + d, where src stands for the channel value in the source image and dst stands for the destination image (the background). Multiply is e.g. defined as a:1, b:0, c:0, d:0. This filter gives you free reign over setting the coefficient of the blend calculation.

with_blend_custom(
  x,
  bg_layer,
  a = 0,
  b = 0,
  c = 0,
  d = 0,
  flip_order = FALSE,
  alpha = NA,
  ...
)

Arguments

x

A ggplot2 layer object, a ggplot, a grob, or a character string naming a filter

bg_layer

The background layer to use. Can either be a string identifying a registered filter, or a raster object. The map will be resized to match the dimensions of x.

a, b, c, d

The coefficients defining the blend operation

flip_order

Should the order of the background and the overlay be flipped so that bg_layer is treated as being on top and x being below.

alpha

For non-Duff-Porter blends the alpha channel may become modified. This argument can be used to set the resulting alpha channel to that of the source ("src") or destination ("dst")

...

Arguments to be passed on to methods. See the documentation of supported object for a description of object specific arguments.

Value

Depending on the input, either a grob, Layer, list of Layers, guide, or element object. Assume the output can be used in the same context as the input.

See also

Other blend filters: with_blend(), with_interpolate(), with_mask()

Examples

library(ggplot2)
ggplot(mpg, aes(class, hwy)) +
  as_reference(geom_boxplot(fill = 'green'), 'box') +
  with_blend_custom(geom_point(colour = 'red'),
                    bg_layer = 'box', a = -0.5, b = 1, c = 1)