termtris

by tylerneylon

tylerneylon /termtris

A text-based game inspired by tetris.

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--[[

termtris: A Game like Tetris in Ten Functions

This is a literate implementation of a tetris-like game called

termtris
. You may be reading this as an html-ified version - but the original,
termtris.lua
, is simultaneously a Lua file and a markdown file. In the original file, all the text between the --[​[ and --]​] comment delimiters are markdown while everything else is code.
-- This is an example of a code block. Taken together, all the code
-- blocks in this document compose the complete termtris game.

This code has been written with an emphasis on readability and learn-from-ability. I hope these comments are useful to anyone interested in how a game like tetris can be made. I've put some effort into making this document friendly to coders who are new to Lua.

On github.com, the

readme.md
is a symbolic link to
termtris.lua
to enable easy reading from the repo's home page. A nonliterate version of the code is in the file
plain_termtris.lua
.

I'll tell you how you can download and play

termtris
, and then we'll dive into the code.

Playing the game

You can play

termtris
on Mac OS X or linux/unix using a Lua interpreter.

On macOS, you can install Lua via

brew install lua
; for any OS, you can download Lua here. Download the
luarocks
package manager here. From there:
  • sudo luarocks install luaposix
  • sudo luarocks install lcurses
  • Ensure Lua can see your installed modules. On macOS, you can do this via (from your shell)
    eval $(luarocks path)
  • git clone https://github.com/tylerneylon/termtris.git
  • lua termtris/termtris.lua

Here are the game controls:

| key | action | |--------------------|----------------------------------| | left, right arrows | move the piece left or right | | up arrow | rotate the piece | | down arrow | drop and lock the piece in place | |

p
| pause or unpause | |
q
| quit |

Reading Lua

Even if you're new to Lua, I think you'll find it easy to understand the code. I'll mention a few things that may not be obvious:

  • Block comments are between
    --[​[
    and
    --]​]
    . Line-tail comments start with
    --
    .
  • An assignment like
    a, b, c = f()
    calls
    f
    and assigns all of
    f
    's return values to
    a
    ,
    b
    , and
    c
    in order — not just to
    c
    .
  • The token
    ~=
    is the not-equal-to operator.
  • The only compound data structure is called a table. It's an associative array that can map any non-nil Lua value to any other.
  • Things inside curly braces
    {}
    are table literals. The literal
    a = {x, y}
    has values
    a[1] == x
    and
    a[2] == y
    . Table literals can be nested: if
    a = {{x}, {y}}
    , then
    a[2][1] == y
    .
  • If
    pi == 3.141
    , then the literal
    b = {w = 1, [pi] = 2}
    results in
    b.w == b['w'] == 1
    and
    b[pi] == 2
    ; that is, identifiers to the left of
    =
    are string keys and keys inside brackets
    []
    are treated as general expressions.
  • Using an undefined table key is not an error — it just returns
    nil
    , which is falsy. For example, if
    a = {key1 = 'hi', key2 = 'there'}
    , then
    a.key3
    is a valid expression with value
    nil
    .
  • We can iterate over the keys and values of table
    t
    with the pattern
    for k, v in pairs(t) do my_fn(k, v) end
    . If
    t
    is treated as an array — if it has sequential integer keys starting at 1 — then
    ipairs
    can be used instead of
    pairs
    to ensure the keys are given in order:
    for i, v in ipairs(t) do my_fn(i, v) end
    .

Armed with that lightning flash of a Lua introduction, I believe you can understand all of the code. For a tad more depth, some crazy guy claims you can learn the language in 15 minutes.

The Code

This code has been written to maximize readability. This is hard to measure. We can get a quantifiable hint that the code is not too daunting by consider its line count and function count.

The code we'll examine has a total of 10 functions, and a little over 200 non-blank, non-comment lines of code:

$ # (This is a bash line, not part of the Lua code!)
$ egrep -v '^\s*(--|$)' nonliterate/plain_termtris.lua | wc -l
231

This is small for a game. We could have used even fewer functions or fewer lines, but beyond a certain point the compressed code becomes more cryptic than simple. The trick is to find a balance between brevity and clarity.

Overview

Here's the complete call graph for

termtris
:

The

main
function initializes our data and then enters a game loop in which we consistently check for input, drop the moving piece if the time is right, and update what is drawn on the screen.

We'll understand the full code by looking at the libraries used for drawing and timing, then going through the code more-or-less in the order that it's executed.

Libraries

curses: Tetris is a visually-oriented game, so we need a way to draw. A simple and somewhat-portable way to do this is to draw colored space characters in the terminal. We can do this using a time-tested library called

curses
.

posix: We also need accurate timing information. Lua comes with functions like

os.clock()
and
os.time()
, but neither of these are appropriate for a game clock. The
os.clock()
function returns cpu time, rather than wall-clock time; the difference is that cpu time only passes when our process is actually running on the cpu, while wall-clock marches on no matter what process is running. Users think in wall-clock time, so that's what we want.

The

os.time()
function gives us the wall-clock time, but only in seconds. We'd like pieces to move faster than once per second! To achieve this, we import the
posix
library, which gives us access to more advanced posix functions, including higher-resolution timestamps.

Both of these libraries are installed together by running the

luarocks install luaposix
command mentioned in the installation section above.

Below are our module imports. This is the first "real" code block, unlike the non-running example code sections above. From here till the end, all code blocks are part of the official program.

--]]

local curses = require 'curses'
local posix  = require 'posix'

--[[


Function 1: The Main Loop

Let's take a look at our game loop, which lives in a function called

main
.

This function will initialize the game state by calling

init
, then enter a seemingly-infinite
while true
loop that executes the game. The loop isn't really infinte because we can call
os.exit
when the player presses
q
to quit.

A few local variables are going to be used:

| local var | what it does | |--------------|-------------------------------------------------------| |

stats
| Track the player's line count, level and score. | |
fall
| Track the speed and timing of the falling piece. | |
colors
| A table to conveniently access text color attributes. | |
next_piece
| Track which piece is coming up next. |

All of these are tables so that they can be modified by functions as parameters, and have those changes persist after the function has completed. This makes the code less functional in style, but since most parameters are used as both input and output, it simplifies the code nicely.

We'll also use a small number of globals. It's considered good practice to minimize global variable use. The global variables in this file either act as constants or are used so widely that passing them to many functions felt messier to me than leaving them as globals.

Our main game loop takes three actions: check for any input, lower the current piece if the time is right, and redraw the screen. We also have a short delay to avoid using 100% of the cpu.

Below is the main function. We'll examine each of the called functions as we define them.

--]]

function main()
  local stats, fall, colors, next_piece = init()

while true do -- Main loop. handle_input(stats, fall, next_piece) lower_piece_at_right_time(stats, fall, next_piece) draw_screen(stats, colors, next_piece)

-- Don't poll for input much faster than the display can change.
local sec, nsec = 0, 5e6  -- 0.005 seconds.
posix.nanosleep(sec, nsec)

end end

--[[

Shape data

Next let's set up all possible shape pieces. We'll use a global table called

shapes
for this.

There are seven possibilities:

The

shapes
table will be indexed first by shape number (1-7), and then by a rotation number (1-4). So
s = shapes[5][1]
represents shape number 5 in its first rotation orientation. This variable
s
represents the shape so that
s[x][y]
is either 0 or 1; its value is 1 if the shape exists in the given
(x, y)
cell.

There are 7 shapes and 4 rotated orientations for each, giving 28 possible shape grids. Instead of initializing all of them by hand, we'll set up one orientation of each shape, and include some code in

init
that expands the
shapes
variable to include all 28 possibilities.

Even though the

shape
variable - and others defined below - are global to this file, we declare them with the
local
keyword so that any other Lua code importing this file won't have these variables in scope. In a sense, they become 'locally global.'

--]]

-- Set up one orientation of each shape.

local shapes = { { {0, 1, 0}, {1, 1, 1} }, { {0, 1, 1}, {1, 1, 0} }, { {1, 1, 0}, {0, 1, 1} }, { {1, 1, 1, 1} }, { {1, 1}, {1, 1} }, { {1, 0, 0}, {1, 1, 1} }, { {0, 0, 1}, {1, 1, 1} } }

--[[

Global game state

We'll use globals to conceptually track the following items:

| global var | description | |---------------------|---------------------------------------------------------------------------------| |

game_state
| Whether the game is playing, paused, or over. | |
board
| Where pieces have already been placed on the game board. | |
board_size
,
val
| Effectively, board-related constants to reduce magic numbers in the code. | |
stdscr
| A
curses
-library window object for drawing to the screen. | |
moving_piece
| Which piece is currently falling: it has keys
shape
,
rot_num
,
x
, and
y
. |

The name

rot_num
is used for rotation numbers.

Game state

We'll use strings values to track if the game is playing, paused, or over. This would be a good place to use an enum, but Lua doesn't have an enum equivalent.

--]]

local game_state = 'playing'  -- Could also be 'paused' or 'over'.

--[[

What's on the board

We'll use an 11x20 board size. Traditional tetris games are usually 10x20, but I'm purposefully putting in some differences in hopes of not getting sued.

The game area where pieces may live is represented by values in

board[x][y]
where 1 ≤ x ≤
board_size.x
and 1 ≤ y ≤
board_size.y
. The
board
variable also includes a U-shaped border with
board[x][y] == -1
when any of the following are true: *
x == 0
, *
x == board_size.x + 1
, or *
y == board_size.y + 1
.

When a shape is locked in place — that is, after it's done falling — we update the affected cells in

board
by setting them to the shape number. This works since our shape numbers are all > 0, so that 0 itself can represent empty cells.

It's very handy to keep the border of -1 values in the

board
itself since it simplifies testing to see if a potential piece placement might go off the edge of the playing area.

We actually start with an empty

board
table that is filled in by the
init
function below.

The

val
variable exists so we can write code like
board[x][y] == val.border
instead of the more cryptic
board[x][y] == -1
; and similarly for
val.empty
instead of 0.

--]]

local board_size = {x = 11, y = 20}
local board = {}                      -- board[x][y] = shape_num; 0=empty; -1=border.
local val = {border = -1, empty = 0}  -- Shorthand to avoid magic numbers.

--[[

Next are the remaining globals for the

curses
library's standard screen object and tracking the currently moving piece.

--]]

local stdscr = nil  -- This will be the standard screen from the curses library.
local moving_piece = {}  -- Keys will be: shape, rot_num, x, y.

--[[


Function 2: Initialization

A number of things must happen before the player can start playing. The

init
function takes care of all of these:
  • Seed the random number generator.
  • Expand the
    shapes
    table to include all shape rotations.
  • Initialize the
    curses
    library and enable colored text rendering.
  • Set up the
    board
    variable.
  • Set up the player stats and the next and currently-moving piece.

Let's see how each of these happen.

Seed the random number generator

This is important since otherwise the player will see the same piece sequence every game.

--]]

function init()
  -- Use the current time's microseconds as our random seed.
  math.randomseed(posix.gettimeofday().usec)

--[[

Set up the shapes table

Before this code,

shapes[shape_index][rot_num]
exists only when
rot_num == 1
. So we have to take
shapes[shape_index][1]
and rotate it into
shapes[shape_index][i]
for
i
= 2, 3, 4.

A simple mathematical way to perform a 90 degree rotation is to treat the point

(x, y)
as the value rotated from
(y, -x)
. In our case, these coordinates are table indexes, such as
shapes[shape_index][rot_num][x][y]
, so
x
and
y
are only meaningful when they're positive integers. Instead of starting at
(y, -x)
to rotate to
(x, y)
, we'll start at
(y, max_x + 1 - x)
. Mathematically, this is like a rotation around
(0, 0)
followed by a translation to keep us in positive
(x, y)
space.

This rotation method is captured in the line

new_shape[x][y] = s[y][x_end - x]
in the loop below.

--]]

  -- Set up the shapes table.
  for s_index, s in ipairs(shapes) do
    shapes[s_index] = {}
    for rot_num = 1, 4 do
      -- Set up new_shape as s rotated by 90 degrees.
      local new_shape = {}
      local x_end = #s[1] + 1  -- Chosen so that x_end - x is in [1, x_max].
      for x = 1, #s[1] do      -- Coords x & y are indexes for the new shape.
        new_shape[x] = {}
        for y = 1, #s do
          new_shape[x][y] = s[y][x_end - x]
        end
      end
      s = new_shape
      shapes[s_index][rot_num] = s
    end
  end

--[[

Start curses

The curses library requires initialization by calling its

initscr
function, and by setting a number of options appropriate for a terminal-based game. The individual comments in the code describe what each function does.

--]]

  -- Start up curses.
  curses.initscr()    -- Initialize the curses library and the terminal screen.
  curses.cbreak()     -- Turn off input line buffering.
  curses.echo(false)  -- Don't print out characters as the user types them.
  curses.nl(false)    -- Turn off special-case return/newline handling.
  curses.curs_set(0)  -- Hide the cursor.

--[[

Set up colors

Each piece in

termtris
has its own color. The
curses
library requires registering an integer for each foreground/background color pair that we want to use. This is done by calling
curses.init_pair(, , )
; the input colors are based on constants such as
curses.COLOR_RED
.

For clearer code, we'll use a table called

colors
to refer to the color indexes we register with
curses.init_pair
. Later we'll define a
set_color
function so that we can simply call
set_color(colors.red)
in order to print red characters to the screen, for example.

--]]

  -- Set up colors.
  curses.start_color()
  if not curses.has_colors() then
    curses.endwin()
    print('Bummer! Looks like your terminal doesn\'t support colors :\'(')
    os.exit(1)
  end
  local colors = { white = 1, blue = 2, cyan = 3, green = 4,
                   magenta = 5, red = 6, yellow = 7, black = 8 }
  for k, v in pairs(colors) do
    curses_color = curses['COLOR_' .. k:upper()]
    curses.init_pair(v, curses_color, curses_color)
  end
  colors.text, colors.over = 9, 10
  curses.init_pair(colors.text, curses.COLOR_WHITE, curses.COLOR_BLACK)
  curses.init_pair(colors.over, curses.COLOR_RED,   curses.COLOR_BLACK)

--[[

Set up the standard screen object

All of our character drawing happens through this object. It is also the object we use to make character input non-blocking, and to accept arrow keys.

--]]

  -- Set up our standard screen.
  stdscr = curses.stdscr()
  stdscr:nodelay(true)  -- Make getch nonblocking.
  stdscr:keypad()       -- Correctly catch arrow key presses.

--[[

Set up the board

As mentioned above, the board is mostly 0's with a U-shaped border of -1 values along the left, right, and bottom edges.

--]]

  -- Set up the board.
  local border = {x = board_size.x + 1, y = board_size.y + 1}
  for x = 0, border.x do
    board[x] = {}
    for y = 1, border.y do
      board[x][y] = val.empty
      if x == 0 or x == border.x or y == border.y then
        board[x][y] = val.border  -- This is a border cell.
      end
    end
  end

--[[

Set up player stats and the next and falling pieces

We track the position, orientation, and shape number of the currently moving piece in the

moving_piece
table. The
next_piece
table needs only track the shape of the next piece. The
stats
table tracks lines, level, and score; the
fall
table tracks when and how quickly the moving piece falls.

--]]

  -- Set up the next and currently moving piece.
  moving_piece = {shape = math.random(#shapes), rot_num = 1, x = 4, y = 0}

-- Use a table so functions can edit its value without having to return it. next_piece = {shape = math.random(#shapes)}

local stats = {level = 1, lines = 0, score = 0} -- Player stats.

-- fall.interval is the number of seconds between downward piece movements. local fall = {interval = 0.7} -- A 'last_at' time is added to this table later.

--[[

Return local values

--]]

  return stats, fall, colors, next_piece
end

--[[


Function 3: Handling Input

Our main game loop is set up so that the

handle_input
function gets called at most once every 0.005 seconds - that is, up to 200 times each second. Most of the time, the player will not have pressed a key between since the last time we called
handle_input
, in which case our
stdscr:getch
call returns
nil
, and
handle_input
can return immediately.

Otherwise, we want to listen for and respond to the arrow keys and the

p
or
q
keys. The
getch
function returns an integer key code which is a standard ascii value for conventional keys, and a value like
curses.KEY_LEFT
for the arrow keys.

First is the code to collect the

key
value and handle quitting or pausing/unpausing.

--]]

function handle_input(stats, fall, next_piece)
  local key = stdscr:getch()  -- Nonblocking; returns nil if no key was pressed.
  if key == nil then return end

if key == tostring('q'):byte(1) then -- The q key quits. curses.endwin() os.exit(0) end

if key == tostring('p'):byte(1) then -- The p key pauses or unpauses. local switch = {playing = 'paused', paused = 'playing'} if switch[game_state] then game_state = switch[game_state] end end

--[[

Next we handle the arrow keys.

Our first action is to return from

handle_input
if the game is not in a state that responds to arrow keys — that is, we ignore arrow keys when the game is paused or over.

After that, we can handle left, right, or up arrow keys with a simple incremental-change table sent in to the

set_moving_piece_if_valid
function. This function will only perform valid moves, and leaves the piece alone if the suggested move was invalid.

The down arrow action is less obvious, as we want to move the piece down as far as we can until it hits something. A simple loop achieves this by using the return value from

set_moving_piece_if_valid
to know when the piece has hit the bottom, at which point it's locked in palce.

--]]

  if game_state ~= 'playing' then return end  -- Arrow keys only work if playing.

-- Handle the left, right, or up arrows. local new_rot_num = (moving_piece.rot_num % 4) + 1 -- Map 1->2->3->4->1. local moves = {[curses.KEY_LEFT] = {x = moving_piece.x - 1}, [curses.KEY_RIGHT] = {x = moving_piece.x + 1}, [curses.KEY_UP] = {rot_num = new_rot_num}} if moves[key] then set_moving_piece_if_valid(moves[key]) end

-- Handle the down arrow. if key == curses.KEY_DOWN then while set_moving_piece_if_valid({y = moving_piece.y + 1}) do end lock_and_update_moving_piece(stats, fall, next_piece) end end

--[[


Functions 4 and 5: Working with Pieces

The

set_moving_piece_if_valid
function accepts a table that suggests new values for the
moving_piece
. If those new values are valid,
moving_piece
is updated and the function returns
true
; otherwise it returns
false
.

This function is used for all piece movements: left, right, rotation, dropping, and even when setting up a new piece after the previous piece has hit the bottom. A new piece may be in an invalid position if the board has filled to the top, in which case the game is over.

Because the board's border is included in the

board
variable, the only check we have to make is that
board[x][y] == val.empty
for every cell occupied by the new piece values.

We'll rely on a function called

call_fn_for_xy_in_piece
that helpfully iterates over all
(x, y)
values occupied by a given piece.

--]]

-- Returns true if and only if the move was valid.
function set_moving_piece_if_valid(piece)
  -- Use values of moving_piece as defaults.
  for k, v in pairs(moving_piece) do
    if piece[k] == nil then piece[k] = moving_piece[k] end
  end
  local is_valid = true
  call_fn_for_xy_in_piece(piece, function (x, y)
    if board[x] and board[x][y] ~= val.empty then is_valid = false end
  end)
  if is_valid then moving_piece = piece end
  return is_valid
end

--[[

The function

call_fn_for_xy_in_piece
makes it easy to draw the piece or check if it's in a valid location. It accepts a callback that is called with each
(x, y)
value in the given piece.

It also accepts an optional

param
value that is passed straight through to the callback with every call. In Lua, if you omit parameters when making a function call, the left-out values are seen as
nil
by the function. If you call a function with extra values set to
nil
, it is functionally the same as if those parameters were not sent in, regardless of how many parameters a function officially accepts. This is how
param
works as an optional parameter.

There are other ways this could have been implemented. We could have instead named this function

piece_coords
and defined it as a Lua iterator. In that case, we could have used the syntax
for x, y in piece_coords(piece) 
. I made the subjective decision to use a callback since I would like non-Lua-experts to find the code readable, and I consider Lua's iterator system to be less readable to Lua newbies.

--]]

-- This function calls callback(x, y) for each x, y coord
-- in the given piece. Example use using draw_point(x, y):
-- call_fn_for_xy_in_piece(moving_piece, draw_point)
function call_fn_for_xy_in_piece(piece, callback, param)
  local s = shapes[piece.shape][piece.rot_num]
  for x, row in ipairs(s) do
    for y, val in ipairs(row) do
      if val == 1 then callback(piece.x + x, piece.y + y, param) end
    end
  end
end

--[[


Function 6: When a Piece Hits the Bottom

The next function handles everything that needs to happen when a piece hits bottom. Once we define this function, we'll have completed all the code that might be called - directly or indirectly - from

handle_input
.

There are three things that happen when a piece hits the bottom:

  1. The moving piece becomes part of the board.
  2. Any full lines are removed and scored, possibly moving us to a new level.
  3. The next piece begins falling from the top of the playing area.

The code to make the moving piece part of the board is simple:

--]]

function lock_and_update_moving_piece(stats, fall, next_piece)
  call_fn_for_xy_in_piece(moving_piece, function (x, y)
    board[x][y] = moving_piece.shape  -- Lock the moving piece in place.
  end)

--[[

Next we look for affected rows of

board
which have no empty cells; we call these full lines. Each one is cleared, dropping anything above it downward by iterating over the line
board[x][y] = board[x][y - 1]
.

We finish by incrementing the line count, the level if appropriate, and the score.

--]]

  -- Clear any lines possibly filled up by the just-placed piece.
  local num_removed = 0
  local max_line_y = math.min(moving_piece.y + 4, board_size.y)
  for line_y = moving_piece.y + 1, max_line_y do
    local is_full_line = true
    for x = 1, board_size.x do
      if board[x][line_y] == val.empty then is_full_line = false end
    end
    if is_full_line then
      -- Remove the line at line_y.
      for y = line_y, 2, -1 do
        for x = 1, board_size.x do
          board[x][y] = board[x][y - 1]
        end
      end
      -- Record the line and level updates.
      stats.lines = stats.lines + 1
      if stats.lines % 10 == 0 then  -- Level up when lines is a multiple of 10.
        stats.level = stats.level + 1
        fall.interval = fall.interval * 0.8  -- The pieces will fall faster.
      end
      num_removed = num_removed + 1
    end
  end
  if num_removed > 0 then curses.flash() end
  stats.score = stats.score + num_removed * num_removed

--[[

Finally,

next_piece
begins to fall, and a new
next_piece
value is set up.

Even though

board[x][y]
is only valid for y ≥ 1, we want to set up new pieces with
y=0
because
call_fn_for_xy_in_piece
uses the expression
piece.y + y
to determine a piece's
y
values, and the
y
in that expression ranges from 1 up to the height of the piece. In other words,
(moving_piece.x, moving_piece.y)
is the coordinate of the cell just to the upper-left of where the moving piece will be drawn.

--]]

  -- Bring in the waiting next piece and set up a new next piece.
  moving_piece = {shape = next_piece.shape, rot_num = 1, x = 4, y = 0}
  if not set_moving_piece_if_valid(moving_piece) then
    game_state = 'over'
  end
  next_piece.shape = math.random(#shapes)
end

--[[


Function 7: Making Pieces Fall

The game is no fun unless the pieces fall at a reliably constant speed that increases with the level.

If we called

sleep
or
posix.nanosleep
to wait until the next falling moment, the piece wouldn't respond to user key presses quickly enough. That's why the game cycle is much faster than the fall cycle.

The fall speed is tracked by these values:

  • fall.interval
    - The floating-point number of seconds between falling motions.
  • fall.last_at
    - The timestamp of the last fall motion, also in floating-point seconds.

We use

posix.gettimeofday()
to get microsecond-resolution timestamps.

It's also up to the piece-falling function to do nothing if the game is over or paused, and to call

lock_and_update_moving_piece
if the piece has hit bottom.

--]]

function lower_piece_at_right_time(stats, fall, next_piece)
  -- This function does nothing if the game is paused or over.
  if game_state ~= 'playing' then return end

local timeval = posix.gettimeofday() local timestamp = timeval.sec + timeval.usec * 1e-6 if fall.last_at == nil then fall.last_at = timestamp end -- Happens at startup.

-- Do nothing until it's been fall.interval seconds since the last fall. if timestamp - fall.last_at < fall.interval then return end

if not set_moving_piece_if_valid({y = moving_piece.y + 1}) then lock_and_update_moving_piece(stats, fall, next_piece) end fall.last_at = timestamp end

--[[


Functions 8-10: Drawing the Screen

The last function called from

main
is
draw_screen
, which renders the board, player stats, and next piece to the terminal window.

Before defining

draw_screen
itself, we'll set up two convenience functions to make drawing easier.

The first is the one-line

set_color
function, which wraps the not-as-clearly-named
stdscr:attron
function. The input to
stdscr:attron
is an output value from
curses.color_pair
, which accepts the same integer values we sent in to
curses.init_pair
back in our
init
function. The entire purpose of
set_color
is to clarify the act of setting a color.

--]]

-- Accepts integer values corresponding to the 'colors' table
-- created by init. For example, call 'set_color(colors.black)'.
function set_color(c)
  stdscr:attron(curses.color_pair(c))
end

--[[

The

draw_point
function essentially draws a simple sprite on the screen. This sprite is usually a solid-color square. A sqaure is rendered as two adjacent space characters since most terminals draw a single space as a tall rectangle with an aspect ratio near 1:2.

This function works with a coordinate system whose origin is offset by a given

x_offset
column value. In this program,
x_offset
is always going to be the left edge of the game board as determined in
draw_screen
. The code is set up to accept
x_offset
as a parameter because:
  • It depends on
    board_size
    , and it's nice to make the rest of the code "just work" if
    board_size
    is changed.
  • We can avoid a global variable by accepting
    x_offset
    as a parameter.

The last two parameters to

draw_point
are optional. If present, the
color
parameter sets the color, and the
point_char
parameter sets the character drawn. The only time we don't draw space characters is when rendering the border, where we use the '|' vertical bar character. Since
curses
only guarantees 7 non-black colors, those 7 have been used for the pieces, and the border is rendered with a different character to visually clarify the edge of the board.

If the game is paused and a space character is being drawn, then

draw_piece
returns early. This way no pieces — including the next piece — are rendered when the game is paused; the border is still drawn.

--]]

function draw_point(x, y, x_offset, color, point_char)
  point_char = point_char or ' '  -- Space is the default point_char.
  if color then set_color(color) end
  -- Don't draw pieces when the game is paused.
  if point_char == ' ' and game_state == 'paused' then return end
  stdscr:mvaddstr(y, x_offset + 2 * x + 0, point_char)
  stdscr:mvaddstr(y, x_offset + 2 * x + 1, point_char)
end

--[[

The

draw_screen
function begins by erasing the screen and recalculating the x coordinates of the left edge of the game board - which we call the
x_margin
- and of the stats on the right side of the board - which we call
x_labels
. These are constantly recalculated because it's cheap to do so and because the player may resize their terminal at any time.

It may be worth explaining this line ahead of time:

  • local win_width = 2 * (board_size.x + 2) + 16

The

win_width
value represents the width, in characters, that we may render to. We want it to be smaller than
scr_width
. The
board_size.x + 2
value is the board width in cells, plus 2 border cells; this value is converted to characters by being doubled. The
+ 16
is meant to give 16 characters of room in which to render the player stats and next piece. The updated screen dimensions are illustrated here:

--]]

function draw_screen(stats, colors, next_piece)
  stdscr:erase()

-- Update the screen dimensions. local scr_width = curses.cols() local win_width = 2 * (board_size.x + 2) + 16 local x_margin = math.floor((scr_width - win_width) / 2) local x_labels = x_margin + win_width - 10

--[[

Next we draw the board, including all previously-fallen pieces. Because the currently-moving piece is not represented in

board
, it's not drawn yet. The
draw_point
function avoids drawing pieces for us if the game is paused.

--]]

  -- Draw the board's border and non-falling pieces if we're not paused.
  local color_of_val = {[val.border] = colors.text, [val.empty] = colors.black}
  local char_of_val = {[val.border] = '|'}  -- This is the border character.
  if game_state == 'over' then color_of_val[val.border] = colors.over end
  for x = 0, board_size.x + 1 do
    for y = 1, board_size.y + 1 do
      local board_val = board[x][y]
      -- Draw ' ' for shape & empty points; '|' for border points.
      local pt_char = char_of_val[board_val] or ' '
      draw_point(x, y, x_margin, color_of_val[board_val] or board_val, pt_char)
    end
  end

--[[

We either draw the string 'paused' in the middle of the board or render the moving piece, depending on if the game state is paused or playing.

--]]

  -- Write 'paused' if the we're paused; draw the moving piece otherwise.
  if game_state == 'paused' then
    set_color(colors.text)
    local x = x_margin + board_size.x - 1  -- Slightly left of center.
    stdscr:mvaddstr(math.floor(board_size.y / 2), x, 'paused')
  else
    set_color(moving_piece.shape)
    call_fn_for_xy_in_piece(moving_piece, draw_point, x_margin)
  end

--[[

Now we draw the player's lines, score, and level stats, along with a Game Over message if the game is over.

--]]

  -- Draw the stats: level, lines, and score.
  set_color(colors.text)
  stdscr:mvaddstr( 9, x_labels, 'Level ' .. stats.level)
  stdscr:mvaddstr(11, x_labels, 'Lines ' .. stats.lines)
  stdscr:mvaddstr(13, x_labels, 'Score ' .. stats.score)
  if game_state == 'over' then
    stdscr:mvaddstr(16, x_labels, 'Game Over')
  end

--[[

Finally we render the next piece between top and bottom lines to suggest a next piece box. The function ends with a call to

stdscr:refresh
, which tells the
curses
library to batch up all our drawing operations and send them to the terminal.

--]]

  -- Draw the next piece.
  stdscr:mvaddstr(2, x_labels, '----------')
  stdscr:mvaddstr(7, x_labels, '---Next---')
  local piece = {shape = next_piece.shape, rot_num = 1, x = board_size.x + 5, y = 3}
  set_color(piece.shape)
  call_fn_for_xy_in_piece(piece, draw_point, x_margin)

stdscr:refresh() end

--[[

Until now, we have only defined variables and functions. No code has been executed. It's time to call the main function!

--]]

main()

--[[

That's the whole game.

Learning More

If you enjoyed this, you might like further exploration of Lua and my favorite 2D game engine, Löve, which adds modern 2D graphics capabilities to Lua. Here are some diving boards into more game-making goodness:

One More Thing

I'm working on an original large-scale game called Apanga. If you're interested in independently-developed games, you could send me your email addy to find out more about Apanga. I'm looking for early-stage testers and any help/interest would be greatly appreciated!

--]]

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