From 89312254e3eb1aa496dff15f2d503e97f3c985f2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?David=20W=C3=BChrer?= <def@gmx.at>
Date: Sun, 26 Apr 2026 15:47:41 +0200
Subject: fire

---
 bin/fire        | 173 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 man/man1/fire.1 |  59 +++++++++++++++++++
 2 files changed, 232 insertions(+)
 create mode 100755 bin/fire
 create mode 100644 man/man1/fire.1

diff --git a/bin/fire b/bin/fire
new file mode 100755
index 0000000..b9c6c98
--- /dev/null
+++ b/bin/fire
@@ -0,0 +1,173 @@
+#!/bin/bash
+
+###
+# ASCII fire
+
+# TODO:
+# Better gradient for cooling flame.
+
+r=$'\e[31m'
+y=$'\e[33m'
+br=$'\e[1;31m'
+by=$'\e[1;33m'
+c=$'\e[0m'
+bs=$'\e[1;30m'
+#w=$'\e[37m'
+
+flame_gradient=(
+#	"$w#$c"
+	"$by@$c"
+	"$by#$c"
+	"$y#$c"
+	"$y@$c"
+	"$br@$c"
+	"$br#$c"
+	"$r#$c"
+#	"$bs($c"
+#	"$bs($c"
+#	"$bs)$c"
+#	"$bs.$c"
+	" "
+)
+# TODO: Use 256 color palette.
+
+declare -ia cells=()
+
+##
+# init
+
+tput clear
+n_rows=$(tput lines)
+n_cols=$(tput cols)
+
+printf 'rows: %d\ncols: %d\n' "$n_rows" "$n_cols"
+
+#for cell in $(seq 0 $(((n_rows * n_cols) - 1)))
+for ((cell=0;cell<n_rows*n_cols;++cell))
+do	cells[cell]=0
+done
+
+###
+# It is best if the bottom row is row #0.
+# Even if the terminal is resized,
+# there will always be a row #0.
+# Of course this means the rows will be drawn in reverse order.
+new_base_row(){
+	# TODO: If the terminal is resized, re-evaluate the number of columns.
+#	for cell in $(seq 0 $((n_cols-1)))
+	declare -i delta=32 # ±16
+	for ((cell=0;cell<n_cols;++cell))
+	do	cells[cell]=$(((cells[cell]+RANDOM%delta-(delta/2)+256)%256))
+	done
+	# TODO: Adjust delta to size of terminal? Not sure how.
+}
+
+# end init
+##
+
+num_to_cell(){
+	# Cells have a value between 0 and 255, inclusive.
+	# Arrays are 0-indexed.
+	echo -n "${flame_gradient[(255-$1)*${#flame_gradient[@]}/256]}"
+	# printf makes no apparent difference.
+}
+
+##
+# Compute the values of the indicated row
+# from the values of the row below.
+# Indicated row should not be the bottom row.
+# TODO: Does a lot of repeatedly computing the same numbers; could be avoided.
+burn_row(){
+	declare -i row_number=$1
+	declare -i cell
+	for ((cell=row_number*n_cols;cell<(row_number+1)*n_cols;++cell))
+	do
+		cell_l=${cells[$cell-$n_cols-1]}
+		cell_b=${cells[$cell-$n_cols]}
+		cell_r=${cells[$cell-$n_cols+1]}
+		# The flames cool between rows.
+		cells[cell]=$(((cell_l+cell_b+cell_r)/3-(256/n_rows)))
+		[[ ${cells[cell]} -lt 0 ]] && cells[cell]=0
+	done
+}
+# By burning iteratively, the entire array can be processed at once.
+# It is only a matter of direction.
+
+burn(){
+	declare -i cell cell_l cell_b cell_r
+	for ((cell=${#cells[@]}-1;cell>=n_cols;--cell))
+	do	
+		cell_l=${cells[$cell-$n_cols-1]}
+		cell_b=${cells[$cell-$n_cols]}	# cell_l from previous iteration.
+		cell_r=${cells[$cell-$n_cols+1]}	# cell_b from previous iteration.
+		# The flames cool between rows.
+		cells[cell]=$(((cell_l+cell_b+cell_r)/3-(256/n_rows)))
+		[[ ${cells[cell]} -lt 0 ]] && cells[cell]=0
+	done
+}
+
+print_all(){
+# Wrong order. This burns downwards.
+	declare -i cell
+	for cell in "${cells[@]}"
+	do
+		num_to_cell $cell
+	done
+}
+
+print_rows(){
+	declare -i row
+	for ((row=n_rows-1;row>=0;--row))
+	do
+		# Print rows top to bottom:
+		tput cup $((n_rows-row)) 0
+		print_row $row
+		# Print rows bottom to top:
+	#	tput cup $row 0
+	#	print_row $((n_rows-1-row))
+	done
+	# TODO:
+	# It should be more efficient to print all at once.
+}
+
+print_row(){
+	declare -i row=$1
+	declare -i cell
+	for ((cell=row*n_cols;cell<(row+1)*n_cols;++cell))
+	do
+		num_to_cell "${cells[cell]}"
+	done
+}
+
+test_fire() {
+	# Saturate base row.
+	for ((cell=0;cell<n_cols;++cell))
+	do	cells[cell]=255
+	done
+	# Print buffer.
+	tput cup 0 0
+	print_rows
+	# Burn.
+	for ((counter=0;counter<n_rows;++counter))
+	do
+		burn
+		print_rows
+	done
+}
+
+##
+# main
+
+#test_fire
+#exit
+
+new_base_row
+while :
+do
+	burn
+	print_rows
+	new_base_row
+	tput cup 0 0
+#	sleep 0.2
+#	sleep 1
+done
diff --git a/man/man1/fire.1 b/man/man1/fire.1
new file mode 100644
index 0000000..c3f214f
--- /dev/null
+++ b/man/man1/fire.1
@@ -0,0 +1,59 @@
+.TH fire 1 2026-04-17 utils
+
+.SH NAME
+fire \- exothermic oxygenation
+
+.SH SYNOPSIS
+.SY fire
+.YS
+
+.SH DESCRIPTION
+.B fire
+is a shell script that prints a burning fire into the terminal.
+.P
+If you are cold, you can make a
+.B fire
+to use your computer as an electric heater.
+(Disclaimer:
+While
+.B fire
+may increase the CPU temperature from frequent calculation and printing,
+it is not guaranteed to do so.  Its main purpose is to look pretty.)
+.P
+On a printer or a mechanical teletype terminal, it will only waste your paper and ink.
+
+.SH OPTIONS
+.B fire
+has no options at this time.
+
+.SH EXIT STATUS
+No exit status is defined.
+
+.SH NOTES
+.B fire
+does not use an artificial delay, but prints as fast as it can,
+This may be too slow or too fast to have the desired effect,
+but slowing it down is trivial by commenting out and adjusting the
+.BR sleep (1)
+command in the script, near the botton.
+Making it faster is not as trivial; the bottleneck is almost certainly the terminal.
+
+.SH BUGS
+.B fire
+requires that the terminal supports certain capabilities, such as
+ANSI escape codes for colour.
+It does not check for those capabilities, but it does make use of
+.BR tput (1).
+.P
+.B fire
+currently only uses ASCII characters and the standard 16 colour palette.
+.BR termcap (5)
+permitting, it should support 256 colours
+(there are currently no terminals supporting 16 bit or 24 bit palettes),
+and maybe use glyphs that are better suited for rendering a convincing fire.
+
+.SH EXAMPLES
+.B fire
+
+.SH SEE ALSO
+.BR rain (1)
-- 
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