97 lines
3.2 KiB
Bash
97 lines
3.2 KiB
Bash
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#!/bin/bash
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# Tom Hale, 2016. MIT Licence.
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# Print out 256 colours, with each number printed in its corresponding colour
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# See http://askubuntu.com/questions/821157/print-a-256-color-test-pattern-in-the-terminal/821163#821163
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set -eu # Fail on errors or undeclared variables
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printable_colours=256
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# Return a colour that contrasts with the given colour
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# Bash only does integer division, so keep it integral
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function contrast_colour {
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local r g b luminance
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colour="$1"
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if (( colour < 16 )); then # Initial 16 ANSI colours
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(( colour == 0 )) && printf "15" || printf "0"
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return
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fi
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# Greyscale # rgb_R = rgb_G = rgb_B = (number - 232) * 10 + 8
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if (( colour > 231 )); then # Greyscale ramp
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(( colour < 244 )) && printf "15" || printf "0"
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return
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fi
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# All other colours:
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# 6x6x6 colour cube = 16 + 36*R + 6*G + B # Where RGB are [0..5]
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# See http://stackoverflow.com/a/27165165/5353461
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# r=$(( (colour-16) / 36 ))
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g=$(( ((colour-16) % 36) / 6 ))
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# b=$(( (colour-16) % 6 ))
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# If luminance is bright, print number in black, white otherwise.
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# Green contributes 587/1000 to human perceived luminance - ITU R-REC-BT.601
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(( g > 2)) && printf "0" || printf "15"
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return
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# Uncomment the below for more precise luminance calculations
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# # Calculate percieved brightness
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# # See https://www.w3.org/TR/AERT#color-contrast
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# # and http://www.itu.int/rec/R-REC-BT.601
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# # Luminance is in range 0..5000 as each value is 0..5
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# luminance=$(( (r * 299) + (g * 587) + (b * 114) ))
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# (( $luminance > 2500 )) && printf "0" || printf "15"
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}
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# Print a coloured block with the number of that colour
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function print_colour {
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local colour="$1" contrast
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contrast=$(contrast_colour "$1")
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printf "\e[48;5;%sm" "$colour" # Start block of colour
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printf "\e[38;5;%sm%3d" "$contrast" "$colour" # In contrast, print number
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printf "\e[0m " # Reset colour
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}
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# Starting at $1, print a run of $2 colours
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function print_run {
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local i
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for (( i = "$1"; i < "$1" + "$2" && i < printable_colours; i++ )) do
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print_colour "$i"
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done
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printf " "
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}
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# Print blocks of colours
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function print_blocks {
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local start="$1" i
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local end="$2" # inclusive
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local block_cols="$3"
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local block_rows="$4"
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local blocks_per_line="$5"
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local block_length=$((block_cols * block_rows))
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# Print sets of blocks
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for (( i = start; i <= end; i += (blocks_per_line-1) * block_length )) do
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printf "\n" # Space before each set of blocks
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# For each block row
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for (( row = 0; row < block_rows; row++ )) do
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# Print block columns for all blocks on the line
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for (( block = 0; block < blocks_per_line; block++ )) do
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print_run $(( i + (block * block_length) )) "$block_cols"
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done
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(( i += block_cols )) # Prepare to print the next row
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printf "\n"
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done
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done
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}
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print_run 0 16 # The first 16 colours are spread over the whole spectrum
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printf "\n"
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print_blocks 16 231 6 6 3 # 6x6x6 colour cube between 16 and 231 inclusive
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print_blocks 232 255 12 2 1 # Not 50, but 24 Shades of Grey
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