gallery/noise: Initial commit

gallery/noise/config.sh

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+# Config for the 'noise' screensaver
+
+# Name of the screensaver (12 chars max)
+name="noise"
+# Tagline for the screensaver (40 chars max)
+tagline="Retro CRT static noise screensaver"
+description="Relive the analog static noise of the yester-years."
+authors="Rawiri Blundell"
+license="MIT"
+settings=""

gallery/noise/noise.sh

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+#!/usr/bin/env bash
+# Replicate old-school CRT static noise
+
+# Handler for SIGINT (Ctrl‑C)
+_handle_cleanup_and_exit() {
+  # show the cursor again
+  tput cnorm       
+  tput sgr0
+  echo
+  clear
+  exit 0
+}
+
+# Handler for SIGWINCH (window resize)
+_handle_window_resize() {
+  width="$(tput cols)"
+  height="$(tput lines)"
+  clear
+}
+
+# Capture Ctrl‑C
+trap _handle_cleanup_and_exit SIGINT 
+# Capture SIGWINCH
+trap _handle_window_resize SIGWINCH
+
+# Get terminal dimensions
+width="${COLUMNS:-$(tput cols)}"
+height="${LINES:-$(tput lines)}"
+
+# For portability, we use these UTF codes
+block100="\xe2\x96\x88"  # u2588\0xe2 0x96 0x88 Solid Block 100%
+block75="\xe2\x96\x93"   # u2593\0xe2 0x96 0x93 Dark shade 75%
+block50="\xe2\x96\x92"   # u2592\0xe2 0x96 0x92 Half shade 50%
+block25="\xe2\x96\x91"   # u2591\0xe2 0x96 0x91 Light shade 25%
+block00=' '              # Literal space
+
+blocks=( "${block100}" "${block75}" "${block50}" "${block25}" "${block00}" )
+
+tput setab 0 # black background
+clear
+tput civis # no cursor
+
+# Initialise vars for batching
+# This eliminates "one pixel change per loop iteration"
+# Benchmarking led to a batch_size selection of 100
+buffer=""
+count=0
+batch_size=100
+
+emit_with_color() {
+  local color_set x y color_element color_code
+  local block_element block buffer count batch_size
+  color_set=( 0 7 8 15 16 145 188 {231..255} 196 46 21 226 )
+  while true; do
+    # Get random location and color
+    x=$(( ${SRANDOM:-$RANDOM} % width + 1 ))
+    y=$(( ${SRANDOM:-$RANDOM} % height + 1 ))
+    color_element=$(( ${SRANDOM:-$RANDOM} % ${#color_set[@]} ))
+    color_code="${color_set[color_element]}"
+    block_element=$(( ${SRANDOM:-$RANDOM} % ${#blocks[@]} ))
+    block=${blocks[block_element]}
+
+    # Build a buffer of changes to emit
+    buffer+="\e[${y};${x}H\e[38;5;${color_code}m${block}"
+    ((count++))
+
+    # Once the buffer size meets the threshold, dump it and start again
+    if (( count >= batch_size )); then
+      printf -- '%b' "${buffer}"
+      buffer=""
+      count=0
+    fi
+  done
+}
+
+# Uses direct color calculation instead of array lookup
+# Benchmarking shows ~11% improvement over emit_with_color()
+# Generates grey shades from ANSI 231-255 (25 shades)
+emit_with_simple_color() {
+  local x y color_code
+  local block_element block buffer count batch_size
+  while true; do
+    # Get random location
+    x=$(( ${SRANDOM:-$RANDOM} % width + 1 ))
+    y=$(( ${SRANDOM:-$RANDOM} % height + 1 ))
+
+    # Direct color calculation - no array needed
+    color_code=$(( 231 + ${SRANDOM:-$RANDOM} % 25 ))
+
+    block_element=$(( ${SRANDOM:-$RANDOM} % ${#blocks[@]} ))
+    block=${blocks[block_element]}
+
+    # Build a buffer of changes to emit
+    buffer+="\e[${y};${x}H\e[38;5;${color_code}m${block}"
+    ((count++))
+
+    # Once the buffer size meets the threshold, dump it and start again
+    if (( count >= batch_size )); then
+      printf -- '%b' "${buffer}"
+      buffer=""
+      count=0
+    fi
+  done
+}
+
+# In benchmarking, this performs 25-30% faster than emit_with_color()
+# Eliminating the rand calls for color selection clearly has an impact
+# Implicit trust of the terminal color state may have unpredictable results
+# At the end of the day, we're constrained by a shell loop
+# More performance could potentially be gleaned with parallelism (see: forkrun)
+emit_without_color() {
+  local x y color_code
+  local block_element block buffer count batch_size
+  color_code=15
+  while true; do
+    # Get random location and color
+    x=$(( ${SRANDOM:-$RANDOM} % width + 1 ))
+    y=$(( ${SRANDOM:-$RANDOM} % height + 1 ))
+    block_element=$(( ${SRANDOM:-$RANDOM} % ${#blocks[@]} ))
+    block=${blocks[block_element]}
+
+    # Build a buffer of changes to emit
+    buffer+="\e[${y};${x}H\e[38;5;${color_code}m${block}"
+    ((count++))
+
+    # Once the buffer size meets the threshold, dump it and start again
+    if (( count >= batch_size )); then
+      printf -- '%b' "${buffer}"
+      buffer=""
+      count=0
+    fi
+  done
+}
+
+# Randomly select one of the color modes
+# This could be moved to an arg in the future or split to separate screensavers
+# This would allow desired behaviour to be selectable
+while true; do
+  rand="${RANDOM}"
+  # Require range [0, 32765] to evenly divide by 3
+  # Reject 32766 and 32767 to avoid modulo bias
+  if (( rand < 32766 )); then
+    color_mode=$(( rand % 3 ))
+    case "${color_mode}" in
+      (0)
+        # Greys only - use simple direct calculation (fastest with color)
+        emit_with_simple_color
+      ;;
+      (1)
+        # Greys + accent colors - needs array lookup for RGBY
+        emit_with_color
+      ;;
+      (2)
+        # White only - uses emit_without_color (fastest overall)
+        emit_without_color
+      ;;
+    esac
+  fi
+  # If we're at this line, RANDOM hit 32766 or 32767!
+done