tetris-spinner.sh

#!/usr/bin/env bash

# Tiny 2×4 Tetris in one Braille character
# With slow-motion bomb explosion reset

field=0

# Braille layout:
# 1 4
# 2 5
# 3 6
# 7 8

dotbit() {
    case "$1,$2" in
        0,0) echo 1 ;;
        0,1) echo 2 ;;
        0,2) echo 4 ;;
        0,3) echo 64 ;;
        1,0) echo 8 ;;
        1,1) echo 16 ;;
        1,2) echo 32 ;;
        1,3) echo 128 ;;
    esac
}

getbit() {
    local bit
    bit=$(dotbit "$1" "$2")
    (( field & bit ))
}

setbit() {
    local bit
    bit=$(dotbit "$1" "$2")
    (( field |= bit ))
}

piece_fits() {
    local x=$1 y=$2 w=$3 h=$4

    (( x < 0 || y < 0 || x + w > 2 || y + h > 4 )) && return 1

    local dx dy
    for ((dy=0; dy<h; dy++)); do
        for ((dx=0; dx<w; dx++)); do
            getbit $((x+dx)) $((y+dy)) && return 1
        done
    done

    return 0
}

explode() {
    local frames=(
        "💣"
        "💣"
        "💥"
        "🔥"
        "✨"
        " "
    )

    # half-speed animation (was ~0.10–0.15)
    local delays=(
        0.20
        0.30
        0.30
        0.20
        0.20
        0.10
    )

    local i
    for ((i=0; i<${#frames[@]}; i++)); do
        printf '\r%s ' "${frames[i]}"
        sleep "${delays[i]}"
    done
}

spawn_piece() {
    while :; do
        case $((RANDOM % 4)) in
            0) pw=1; ph=1 ;;
            1) pw=1; ph=2 ;;
            2) pw=2; ph=1 ;;
            3) pw=2; ph=2 ;;
        esac

        px=$(( RANDOM % (3 - pw) ))
        py=0

        if piece_fits "$px" "$py" "$pw" "$ph"; then
            return 0
        fi

        explode
        field=0
    done
}

lock_piece() {
    local dx dy
    for ((dy=0; dy<ph; dy++)); do
        for ((dx=0; dx<pw; dx++)); do
            setbit $((px+dx)) $((py+dy))
        done
    done
}

clear_rows() {
    local old=$field
    local newfield=0
    local dest=3
    local x y

    for ((y=3; y>=0; y--)); do
        local full=1

        for x in 0 1; do
            local bit
            bit=$(dotbit "$x" "$y")
            (( old & bit )) || full=0
        done

        (( full )) && continue

        for x in 0 1; do
            local bit
            bit=$(dotbit "$x" "$y")
            if (( old & bit )); then
                local dbit
                dbit=$(dotbit "$x" "$dest")
                (( newfield |= dbit ))
            fi
        done

        ((dest--))
    done

    field=$newfield
}

render() {
    local mask=$field
    local dx dy

    for ((dy=0; dy<ph; dy++)); do
        for ((dx=0; dx<pw; dx++)); do
            local bit
            bit=$(dotbit $((px+dx)) $((py+dy)))
            (( mask |= bit ))
        done
    done

    perl -CS -e '
        print "\r";
        print chr(0x2800 + shift);
        print " ";
    ' "$mask"
}

cleanup() {
    tput cnorm 2>/dev/null
    printf '\n'
}

trap cleanup EXIT INT TERM

tput civis 2>/dev/null

spawn_piece

while true; do
    render
    sleep 0.20   # half-speed main loop

    if piece_fits "$px" $((py + 1)) "$pw" "$ph"; then
        ((py++))
    else
        lock_piece
        clear_rows
        spawn_piece
    fi
done