sass_layer: Bundling Sass layers

Description Usage Arguments Functions Examples

View source: R/layers.R

Description

Sass layers are a way to group a set of related Sass variable definitions, function/mixin declarations, and CSS rules into a single object. Use sass_layer() to create these objects, and sass_bundle() to combine two or more layers or bundles objects into a Sass bundle; this ability to be merged is the main benefit of using Sass layers versus lower-level forms of sass input. At a later time, Sass layers may be removed from Sass bundles by referencing the same name that was used when creating the Sass bundle.

Usage

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sass_layer(
  defaults = NULL,
  declarations = NULL,
  rules = NULL,
  html_deps = NULL,
  file_attachments = character(0),
  tags = NULL
)

sass_bundle(...)

sass_bundle_remove(bundle, name)

is_sass_bundle(x)

Arguments

defaults

A suitable as_sass() input. Intended for declaring variables with !default. When layers are combined, defaults are merged in reverse order; that is, sass_bundle(layer1, layer2) will include layer2$defaults before layer1$defaults.

declarations

A suitable as_sass() input. Intended for function and mixin declarations, and variable declarations without !default; not intended for actual CSS rules. These will be merged in forward order; that is, sass_bundle(layer1, layer2) will include layer1$declarations before layer2$declarations.

rules

A suitable as_sass() input. Intended for actual CSS rules. These will be merged in forward order; that is, sass_bundle(layer1, layer2) will include layer1$rules before layer2$rules.

html_deps

An HTML dependency (or a list of them).

file_attachments

A named character vector, representing file assets that are referenced (using relative paths) from the sass in this layer. The vector names should be a relative path, and the corresponding vector values should be absolute paths to files or directories that exist; at render time, each value will be copied to the relative path indicated by its name. (For directories, the contents of the source directory will be copied into the destination directory; the directory itself will not be copied.) You can also omit the name, in which case that file or directory will be copied directly into the output directory.

tags

Deprecated. Preserve meta information using a key in sass_bundle(KEY = val). preserve simple metadata as layers are merged.

...

A collection of sass_layer()s and/or objects that as_sass() understands. Arguments should be provided in reverse priority order: defaults, declarations, and rules in later layers will take precedence over those of previous layers. Non-layer values will be converted to layers by calling sass_layer(rules = ...).

bundle

Output value from sass_layer() or sass_bundle()

name

If a Sass layer name is contained in name, the matching Sass layer will be removed from the bundle

x

object to inspect

Functions

Examples

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blue <- list(color = "blue !default")
red <- list(color = "red !default")
green <- list(color = "green !default")

# a sass_layer() by itself is not very useful, it just defines some
# SASS to place before (defaults) and after (declarations, rules)
core <- sass_layer(defaults = blue, rules = "body { color: $color; }")
core
sass(core)

# However, by stacking sass_layer()s, we have ability to place
# SASS both before and after some other sass (e.g., core)
# Here we place a red default _before_ the blue default and export the
# color SASS variable as a CSS variable _after_ the core
red_layer <- sass_layer(red, rules = ":root{ --color: #{$color}; }")
sass(sass_bundle(core, red_layer))
sass(sass_bundle(core, red_layer, sass_layer(green)))

# Example of merging layers and removing a layer
# Remember to name the layers that are removable
core_layers <- sass_bundle(core, red = red_layer, green = sass_layer(green))
core_layers # pretty printed for console
core_slim <- sass_bundle_remove(core_layers, "red")
sass(core_slim)


# File attachment example: Create a checkboard pattern .png, then
# use it from a sass layer

tmp_png <- tempfile(fileext = ".png")
grDevices::png(filename = tmp_png, width = 20, height = 20,
  bg = "transparent", antialias = "none")
par(mar = rep_len(0,4), xaxs = "i", yaxs = "i")
plot.new()
rect(c(0,0.5), c(0,0.5), c(0.5,1), c(0.5,1), col = "#00000044", border=NA)
dev.off()

layer <- sass_layer(
  rules = ".bg-check { background-image: url(images/demo_checkboard_bg.png) }",
  file_attachments = c("images/demo_checkboard_bg.png" = tmp_png)
)

output_path <- tempfile(fileext = ".css")
sass(layer, output = output_path, write_attachments = TRUE)

sass documentation built on Jan. 25, 2021, 1:06 a.m.