bm_compress: Compress bitmaps by a factor of two

Description

Compresses bm_bitmap() objects by a factor of two by re-mapping to a “block elements” scheme. For pixmap objects like bm_pixmap() we simply shrink the pixmap by a factor of two using bm_distort().

Usage

bm_compress(x, direction = "vertical", ...)
# S3 method for bm_bitmap
bm_compress(x, direction = "vertical", ...)
# S3 method for bm_pixmap
bm_compress(x, direction = "vertical", ..., filter = "Point")
# S3 method for `magick-image`
bm_compress(x, direction = "vertical", ..., filter = "Point")
# S3 method for nativeRaster
bm_compress(x, direction = "vertical", ..., filter = "Point")
# S3 method for raster
bm_compress(x, direction = "vertical", ..., filter = "Point")
# S3 method for bm_list
bm_compress(x, ...)

Value

Depending on x either a bm_bitmap(), bm_font(), bm_list(), magick-image, "nativeRaster", bm_pixmap(), or raster object.

Arguments

x: Either a bm_bitmap(), bm_font(), bm_list(), "magick-image", "nativeRaster", bm_pixmap(), or "raster" object.
direction: Either "vertical" or "v", "horizontal" or "h", OR "both" or "b".
...: Additional arguments to be passed to or from methods.
filter: Passed to magick::image_resize(). Use magick::filter_types() for list of supported filters. The default "Point" filter will maintain your sprite's color palette. NULL will give you the magick's default filter which may work better if you are not trying to maintain a sprite color palette.

Details

Depending on direction we shrink the bitmaps height and/or width by a factor of two and re-encode pairs/quartets of pixels to a “block elements” scheme. If necessary we pad the right/bottom of the bitmap(s) by a pixel. For each pair/quartet we determine the most-common non-zero element and map them to a length twenty set of integers representing the “block elements” scheme. For integers greater than zero we map it to higher twenty character sets i.e. 1's get mapped to 0:19, 2's get mapped to 20:39, 3's get mapped to 40:59, etc. Using the default px_unicode will give you the exact matching “Block Elements” glyphs while px_ascii gives the closest ASCII approximation. Hence print.bm_bitmap() should produce reasonable results for compressed bitmaps if either of them are used as the px argument.

Examples

Run this code

font_file <- system.file("fonts/spleen/spleen-8x16.hex.gz", package = "bittermelon")
font <- read_hex(font_file)
r <- font[[str2ucp("R")]]
print(r)
print(bm_compress(r, "vertical"))
print(bm_compress(r, "horizontal"))
print(bm_compress(r, "both"))

img <- png::readPNG(system.file("img", "Rlogo.png", package="png"))
logo <- as_bm_pixmap(img)
if (cli::is_utf8_output() &&
    cli::num_ansi_colors() > 256L &&
    requireNamespace("magick", quietly = TRUE)) {
  logo_c <- bm_compress(pm, "both", filter = NULL)
  print(logo_c, compress = "v")
}