added a new 256 color testpattern script in bash and nu

coloring/256_color_testpattern.nu

@@ -0,0 +1,77 @@
+
+let printable_colours = 256
+
+def contrast_colour [ colour:int ] {
+    # The first 16 colors
+    if $colour < 16 {
+        if $colour == 0 {
+            15
+        } {
+            0
+        }
+    } {
+      # The gray colors
+      if $colour > 231 {
+          if $colour < 244 {
+              15
+          } {
+              0
+          }
+      } {
+        # The rest
+        let r = ($colour - 16) / 36
+        let g = (($colour - 16) mod 36) / 6
+        let b = ($colour - 16) mod 6
+
+        # if $g > 2 {
+        #     0
+        # } {
+        #     15
+        # }
+
+        let luminance = ($r * 299) + ($g * 587) + ($b * 114)
+        if $luminance > 2500 {
+            0
+        } {
+            15
+        }
+      }
+    }
+}
+
+def print_colour [ colour:int ] {
+    let contrast = (contrast_colour $colour)
+    let bg_color = $"(ansi idx_bg)($colour)m" # Start block of colour
+    let fg_color = $"(ansi idx_fg)($contrast)m" # In contrast, print number
+    let text = $"($colour | into string | str lpad -c ' ' -l 3)(ansi reset)"
+    $bg_color + $fg_color + $text + " "
+}
+
+def print_run [start:int, amount:int] {
+  for i in $start..<($start + $amount) {
+    if $i < $printable_colours {
+      print_colour $i
+    } {
+      ""
+    }
+  } | append "  " | str collect
+}
+
+def print_blocks [start:int, end:int, block-cols:int, block-rows:int, blocks-per-line:int] {
+  let block-length = ($block-cols * $block-rows)
+  let end = (($end - $start) / (($blocks-per-line) * $block-length))
+  for i in 0..<$end {
+    for row in 0..<$block-rows {
+      for block in 0..<$blocks-per-line {
+        print_run ($start + $block * $block-length + $row * $block-cols + $i * $block-length * $blocks-per-line) $block-cols
+      } | append (char nl) | str collect | autoview
+    }
+    char nl | autoview
+  }
+}
+
+print_run 0 16 # The first 16 colours are spread over the whole spectrum
+char nl
+char nl
+print_blocks 16 231 6 6 3 # 6x6x6 colour cube between 16 and 231 inclusive
+print_blocks 232 255 12 2 1 # Not 50, but 24 Shades of Grey

coloring/256_color_testpattern.sh

@@ -0,0 +1,96 @@
+#!/bin/bash
+
+# Tom Hale, 2016. MIT Licence.
+# Print out 256 colours, with each number printed in its corresponding colour
+# See http://askubuntu.com/questions/821157/print-a-256-color-test-pattern-in-the-terminal/821163#821163
+
+set -eu # Fail on errors or undeclared variables
+
+printable_colours=256
+
+# Return a colour that contrasts with the given colour
+# Bash only does integer division, so keep it integral
+function contrast_colour {
+    local r g b luminance
+    colour="$1"
+
+    if (( colour < 16 )); then # Initial 16 ANSI colours
+        (( colour == 0 )) && printf "15" || printf "0"
+        return
+    fi
+
+    # Greyscale # rgb_R = rgb_G = rgb_B = (number - 232) * 10 + 8
+    if (( colour > 231 )); then # Greyscale ramp
+        (( colour < 244 )) && printf "15" || printf "0"
+        return
+    fi
+
+    # All other colours:
+    # 6x6x6 colour cube = 16 + 36*R + 6*G + B  # Where RGB are [0..5]
+    # See http://stackoverflow.com/a/27165165/5353461
+
+    # r=$(( (colour-16) / 36 ))
+    g=$(( ((colour-16) % 36) / 6 ))
+    # b=$(( (colour-16) % 6 ))
+
+    # If luminance is bright, print number in black, white otherwise.
+    # Green contributes 587/1000 to human perceived luminance - ITU R-REC-BT.601
+    (( g > 2)) && printf "0" || printf "15"
+    return
+
+    # Uncomment the below for more precise luminance calculations
+
+    # # Calculate percieved brightness
+    # # See https://www.w3.org/TR/AERT#color-contrast
+    # # and http://www.itu.int/rec/R-REC-BT.601
+    # # Luminance is in range 0..5000 as each value is 0..5
+    # luminance=$(( (r * 299) + (g * 587) + (b * 114) ))
+    # (( $luminance > 2500 )) && printf "0" || printf "15"
+}
+
+# Print a coloured block with the number of that colour
+function print_colour {
+    local colour="$1" contrast
+    contrast=$(contrast_colour "$1")
+    printf "\e[48;5;%sm" "$colour"                # Start block of colour
+    printf "\e[38;5;%sm%3d" "$contrast" "$colour" # In contrast, print number
+    printf "\e[0m "                               # Reset colour
+}
+
+# Starting at $1, print a run of $2 colours
+function print_run {
+    local i
+    for (( i = "$1"; i < "$1" + "$2" && i < printable_colours; i++ )) do
+        print_colour "$i"
+    done
+    printf "  "
+}
+
+# Print blocks of colours
+function print_blocks {
+    local start="$1" i
+    local end="$2" # inclusive
+    local block_cols="$3"
+    local block_rows="$4"
+    local blocks_per_line="$5"
+    local block_length=$((block_cols * block_rows))
+
+    # Print sets of blocks
+    for (( i = start; i <= end; i += (blocks_per_line-1) * block_length )) do
+        printf "\n" # Space before each set of blocks
+        # For each block row
+        for (( row = 0; row < block_rows; row++ )) do
+            # Print block columns for all blocks on the line
+            for (( block = 0; block < blocks_per_line; block++ )) do
+                print_run $(( i + (block * block_length) )) "$block_cols"
+            done
+            (( i += block_cols )) # Prepare to print the next row
+            printf "\n"
+        done
+    done
+}
+
+print_run 0 16 # The first 16 colours are spread over the whole spectrum
+printf "\n"
+print_blocks 16 231 6 6 3 # 6x6x6 colour cube between 16 and 231 inclusive
+print_blocks 232 255 12 2 1 # Not 50, but 24 Shades of Grey