bitty

Reference Manual

Manual

Physics

Operations

Others

Table of Content

• Fundamental
  • Specifications
  • Project Structure
    • In Directory
    • Text-based Archive
    • Binary-based Archive
  • Backup
  • Capturing
    • Screenshot
    • GIF
• Programming
  • Lua
    • Syntax
    • Memory Management
    • Standard Libraries
  • Program Structure
  • Libraries
    • Algorithms
      • Noiser
      • Pathfinder
      • Randomizer
      • Raycaster
      • Walker
    • Archive
    • Bytes
    • Color
    • Date Time
    • Encoding
      • Base64
      • LZ4
    • File
    • Filesystem
    • Image
    • JSON
    • Math
      • Structures
      • Intersection Detection
    • Network
    • Platform
    • Promise
    • Stream
    • Web
  • Assets and Resources
    • Resources
    • Asset
    • Palette Asset
    • Font Asset
    • Texture Asset
    • Sprite Asset
    • Map Asset
    • SFX Asset
    • Music Asset
  • Primitives
    • Basics
    • Shapes
    • Palette
    • Font
    • Texture
    • Sprite
    • Map
    • Audio
      • SFX
      • Music
    • Gamepad
    • Keyboard
    • Mouse
    • Camera
    • Clip
    • Blend
  • Physics
  • Invoking
  • Application
    • Canvas
    • Project
    • Debug
• Import and Export
  • Import
  • Export
• Building
  • Building for Desktop
  • Building for HTML

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Fundamental

Specifications

• Display: configurable resolution
• Code: Lua, supports multiple source files
• Image: either true-color (PNG, JPG, BMP, TGA) or paletted, up to 1024x1024 pixels per file
• Palette: 256 colors with transparency support
• Sprite: up to 1024x1024 pixels per frame, up to 1024 frames per sprite
• Map: up to 4096x4096 tiles per page
• Font: supports Bitmap and TrueType
• Audio: 1 BGM channel, 4 SFX channels; supports MP3, OGG, WAV, etc.
• Gamepad: 6 buttons for each pad (D-Pad + A/B), up to 2 players
• Keyboard and mouse: supported

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Project Structure

A new created project consists of a meta info asset (“info.json”) and an entry source (“main.lua”). The meta info indicates basic information of the project in JSON. The entry is where the project starts to execute. You can add supported existing file or create new blank assets into a project. All text-based assets use Unix LF (‘\n’) for line ending.

Note that it requires external programs to open file dialogs on Linux for opening, saving, exporting, etc. Make sure that at least one of the following is available: “zenity”, “kdialog”, “matedialog”, “qarma”.

In Directory

All assets are stored as raw files under a specific directory in this format.

Text-based Archive

A text-based project archive is a plain text file with the “*.bit” extension, with all assets encoded in printable UTF-8 characters or Base64 string. This format uses Unix LF (‘\n’) for line ending.

Binary-based Archive

A binary-based project archive is just a compressed ZIP package replaced with the “*.bit” extension.

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Backup

Bitty Engine makes backup once you save an asset or a project, click “Project”, “Browse Data Directory…” to locate it.

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Capturing

There are shortcuts to capture canvas during running.

Screenshot

• F6: take a screenshot

GIF

• F7: start recording frames
• F8: stop recording frames

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Programming

Lua

Bitty project is programmable in the Lua programming language.

Syntax

Lua is widely used and validated in the software industry, there are a lot of learning materials about the language on the internet. Click to see on the Wikipedia or read the official documentations.

Lua is 1-based for list accessing, Bitty Engine follows the same convention for sequenced structures, like Bytes, File, etc. Otherwise it is 0-based for coordinates and graphical units, like Noiser, Pathfinder, Image, Sprite, Palette, Map, etc.

This document uses a meta method form to describe operators. Eg. foo:__len() denotes #foo, foo:__add(bar) denotes foo + bar, foo:__unm() denotes -foo, etc. Just write the symbol form #, +, -, etc. in your calculation.

Additionally, this is not about the syntax, but for description convenience in this document, optional parameter is described between square brackets [optional]; default value is appended after an equal sign foo = 42; variadic list is described as ....

Memory Management

Lua uses GC to free unused memory automatically, thus you don’t have to do so manually most of the time. However resources loaded by Resources.load(...) are not, consider unloading them properly. See Resources for details.

Standard Libraries

The ready to use modules, package, coroutine, math, table, string, utf8, debug are reserved from the original language.

The trivial modules, io, os are removed. Bitty Engine offers alternatives.

Bitty Engine offers some handy built-in functions, some are reserved from the original but the behaviour is improved, some are extended.

Functions

• print(...): outputs some values to the console window as message, for debugging purposes
• warn(...): outputs some values to the console window as warn, for debugging purposes

• error(...): outputs some values to the console window as error, and stops execution, for debugging purposes

• msgbox(msg): popups a message box with the specific content
  • msg: the message string
• input(prompt[, default]): popups an input box
  • prompt: the prompt on the box
  • default: the default content
  • returns inputted string, or nil for canceled
• exit(): exits execution of the current program

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Program Structure

A conventional entry program of Bitty project is made up of a setup function which is called once program starts, and an update which is called periodically:

function setup()
end

function update(delta)
end

Define another quit function to run code on execution termination:

function quit()
end

Define focusLost, focusGained functions to run code on focus changed:

function focusLost()
end

function focusGained()
end

Define a fileDropped function to run code on file dropped:

function fileDropped(paths) -- For desktop only.
end

Define a rendererReset function to run code on renderer reset:

function rendererReset()
end

Define a call function for callback from JavaScript to Lua (for HTML build only). See Invoking for details.

function call()
end

Generally setup is used to initial game variables, states, update is where gameplay logic and rendering goes, and quit is for persisting necessary data on disk. All these entries above are optional.

Bitty Engine uses a timeout mechanism to avoid unexpected infinite loops, it raises an error when any invoking to the entries takes more than 10 seconds by default. The timeout value can be changed by Debug.setTimeout(…).

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Libraries

Algorithms

Noiser

This module generates 2D or 3D noise values.

Constructors

• Noiser.new(): constructs a noiser object

Methods

• noiser:setOption(key, val): sets option value of the specific key
  • key: the option key to set
  • val: the value to set

Available options:

Key	Value	Note
“frequency”	Real number	Defaults to 0.01
“noise_type”	Can be one in “open_simplex2”, “open_simplex2s”, “cellular”, “perlin”, “value_cubic”, “value”	Defaults to “open_simplex2”
“rotation_type_3d”	Can be one in “none”, “improve_xy_planes”, “improve_xz_planes”	Defaults to “none”
“fractal_type”	Can be one in “none”, “fbm”, “ridged”, “pingpong”, “domain_warp_progressive”, “domain_warp_independent”	Defaults to “none”
“fractal_octaves”	Integer	Defaults to 3
“fractal_lacunarity”	Real number	Defaults to 2.0
“fractal_gain”	Real number	Defaults to 0.5
“fractal_weighted_strength”	Real number	Defaults to 0.0
“fractal_pingpong_strength”	Real number	Defaults to 2.0
“cellular_distance_function”	Can be one in “euclidean”, “euclidean_sq”, “manhattan”, “hybrid”	Defaults to “euclidean_sq”
“cellular_return_type”	Can be one in “cell_value”, “distance”, “distance2”, “distance2_add”, “distance2_sub”, “distance2_mul”, “distance2_div”	Defaults to “distance”
“cellular_jitter”	Real number	Defaults to 1.0
“domain_warp_type”	Can be one in “open_simplex2”, “open_simplex2_reduced”, “basic_grid”	Defaults to “open_simplex2”
“domain_warp_amplitude”	Real number	Defaults to 1.0

• noiser:seed(seed): seeds the Noiser for all noise types
  • seed: the seed integer
• noiser:get(pos): gets the value at the specific position
  • pos: the position to get, either Vec2 or Vec3
  • returns noise value, with range of values from -1.0 to 1.0
• noiser:domainWarp(pos): applies domain warping at the specific position
  • pos: the position to warp, either Vec2 or Vec3
  • returns warped position

Pathfinder

This module performs a pathfinding algorithm on 2D grids.

Constructors

• Pathfinder.new(w, n, e, s): constructs a pathfinder object with finite borders
  • w: the west edge, minimum in the x direction
  • n: the north edge, minimum in the y direction
  • e: the east edge, maximum in the x direction
  • s: the south edge, maximum in the y direction

Object Fields

• pathfinder.diagonalCost: gets or sets the walking cost of diagonal direction, defaults to 1.414; set to -1 for not walkable

Methods

• pathfinder:get(pos): gets the walking cost of a prefilled grid at the specific position
  • pos: the position to get
  • returns walking cost
• pathfinder:set(pos, cost): sets the walking cost of a grid, initializes a cost matrix with 1 for all grids when first calling to this function
  • pos: the position to set
  • cost: the cost value to set
• pathfinder:clear(): clears prefilled matrix and internal cached data
• pathfinder:solve(beginPos, endPos, eval): resolves for a possible path with the specific evaluator
  • beginPos: the beginning position
  • endPos: the ending position
  • eval: in form of function (pos) return number end, an invokable object which accepts position and returns the walking cost at that point
  • returns an approachable path, in a list of Vec2, could be empty
• pathfinder:solve(beginPos, endPos): resolves for a possible path with the prefilled cost matrix
  • beginPos: the beginning position
  • endPos: the ending position
  • returns an approachable path, in a list of Vec2, could be empty

Grid coordinates can be any integer, with range of values from -32,767 to 32,767. A cost matrix will be prefilled once calling the pathfinder:set(...) function; this data exists until calling pathfinder:clear(). The pathfinder:solve(...) function prefers to use invokable to get grid cost, and falls to use prefilled matrix if no evaluator provided. Call pathfinder:clear() before solving in either way, if any grid data has been changed.

Walking cost is combined with two parts by multiplicative: neighbor cost and map cost. Neighbor cost stands for how much does it cost to walk from the current grid to its neighbor directions as following, in which D defaults to 1.414:

 _________________
|     |     |     |
|  D  |  1  |  D  |
|_____|_____|_____|
|     |     |     |
|  1  |     |  1  |
|_____|_____|_____|
|     |     |     |
|  D  |  1  |  D  |
|_____|_____|_____|

Pathfinder retrieves grid cost from either an evaluator or prefilled matrix. All cost states must be immutable during calling the pathfinder:solve(...) function. It’s not walkable if either part of the cost combination results -1; positive cost means walkable, and the pathfinder prefers lower cost grids.

Randomizer

This module provides a random algorithm organized by object, other than the built-in random function in Lua.

Constructors

• Random.new(): constructs a randomizer object

Methods

• random:seed([seed]): seeds the randomizer
  • seed: the seed; omit to seed with the current time
• random:next(low, up): generates a random number
  • low: the low bound
  • up: the up bound
  • returns a pseudo random integer with uniform distribution in the range [m, n]
• random:next(n): generates a random number
  • returns equivalent to random:next(1, n) for a positive n; returns an integer with all bits random for a zero n
• random:next(): generates a random number
  • returns a pseudo random real number with uniform distribution in the range [0, 1)

Raycaster

This module performs a raycasting algorithm on 2D grids.

Constructors

• Raycaster.new(): constructs a raycaster object

Object Fields

• raycaster.tileSize: gets or sets the tile size as Vec2, defaults to 8x8
• raycaster.offset: gets or sets the Raycaster offset as Vec2, defaults to 0, 0

Methods

• raycaster:solve(rayPos, rayDir, eval): resolves for raycasting
  • rayPos: the ray position
  • rayDir: the ray direction
  • eval: in form of function (pos) return boolean end, an invokable object which accepts position and returns true for blocked, false for pass
  • returns an approximate intersection position as Vec2 or nil, and a secondary value for intersection index as Vec2 or nil

Walker

This module performs a smooth walking algorithm on 2D grids.

Constants

• Walker.None
• Walker.Left
• Walker.Right
• Walker.Up
• Walker.Down

Constructors

• Walker.new(): constructs a walker object

Object Fields

• walker.objectSize: gets or sets the object size as Vec2, defaults to 8x8
• walker.tileSize: gets or sets the tile size as Vec2, defaults to 8x8
• walker.offset: gets or sets the Walker offset as Vec2, defaults to 0, 0

Methods

• walker:solve(objPos, expDir, eval, slidable = 5): resolves for a walking step
  • objPos: the object position
  • expDir: the expected direction
  • eval: in form of function (pos) return boolean, enum end, an invokable object which accepts position and returns true for blocked, false for pass; in addition this evaluator can return a secondary value in Walker.None, Walker.Left, Walker.Right, Walker.Up, Walker.Down for one-way walk
  • slidable: non-zero for slidable at edge, with range of values from 0 to 10
  • returns a resolved directional Vec2, could be zero

Archive

This module offers manipulations of ZIP package.

Constructors

• Archive.new(): constructs an archive object

Methods

• archive:open(path, access = Stream.Read): opens an Archive file for reading or writing
  • path: the Archive file path
  • access: can be one in Stream.Read, Stream.Write, Stream.Append, for reading, truncated writing, non-truncated writing respectively
  • returns true for success, otherwise false
• archive:close(): closes an opened Archive
  • returns true for success, otherwise false
• archive:all(): gets all entry names in the Archive
  • returns an entry list, in a list of string, could be empty or nil
• archive:exists(entry): gets whether the specific entry exists in the Archive
  • entry: the entry name to look for
  • returns true for exists, otherwise false
• archive:make(entry): makes an entry in the Archive
  • entry: the entry name to make
  • returns true for success, otherwise false
• archive:toBytes(entry, bytes): reads the specific entry and writes to Bytes
  • entry: the entry name to read
  • bytes: the Bytes to receive, its cursor will be at the end
  • returns bytes for success, otherwise nil
• archive:fromBytes(entry, bytes): writes the specific entry from Bytes
  • entry: the entry name to write
  • bytes: the Bytes to retrieve from start till end, its cursor won’t be moved
  • returns true for success, otherwise false
• archive:toFile(entry, path): reads the specific entry and writes to file
  • entry: the entry name to read
  • path: the file path to receive
  • returns true for success, otherwise false
• archive:fromFile(entry, path): writes the specific entry from file
  • entry: the entry name to write
  • path: the file path to retrieve
  • returns true for success, otherwise false
• archive:toDirectory(path): reads all the entries and writes to directory
  • path: the directory path to receive
  • returns true for success, otherwise false
• archive:fromDirectory(path): writes all the entries from directory
  • path: the directory path to retrieve
  • returns true for success, otherwise false

Bytes

Being the same as Lua list, a Bytes’ index starts from 1. Implements a Stream protocol as memory buffer.

Constructors

• Bytes.new(): constructs a bytes object

Operators

• =bytes[index]: reads a byte from the specific index
  • index: starts from 1
  • returns byte
• bytes[index]=: writes a byte to the specific index
  • index: starts from 1
• bytes:__len(): gets the length in bytes

Methods

• bytes:peek(): peeks the reading/writing cursor
  • returns the cursor, starts from 1
• bytes:poke(index): pokes the reading/writig cursor
  • index: starts from 1
  • returns true for success, otherwise false
• bytes:count(): gets the length in bytes
  • returns the length in bytes
• bytes:empty(): gets whether the Bytes is empty
  • returns true for empty, otherwise false
• bytes:endOfStream(): gets whether the cursor is at the end
  • returns true for end, otherwise false
• bytes:readByte(): reads a byte and moves the cursor forward
  • returns byte
• bytes:readInt16(): reads a 16-bit signed integer and moves the cursor forward
  • returns 16-bit signed integer
• bytes:readUInt16(): reads a 16-bit unsigned integer and moves the cursor forward
  • returns 16-bit unsigned integer
• bytes:readInt32(): reads a 32-bit signed integer and moves the cursor forward
  • returns 32-bit signed integer
• bytes:readUInt32(): reads a 32-bit unsigned integer and moves the cursor forward
  • returns 32-bit unsigned integer
• bytes:readInt64(): reads a 64-bit signed integer and moves the cursor forward
  • returns 64-bit signed integer
• bytes:readSingle(): reads a single precision real number and moves the cursor forward
  • returns single precision real number
• bytes:readDouble(): reads a double precision real number and moves the cursor forward
  • returns double precision real number
• bytes:readBytes([expSize[, bytes_]]): reads some Bytes and moves the cursor forward
  • expSize: optional, the expected size in bytes to read; omit to read till end
  • bytes_: optional, Bytes to receive, its content will be cleared; omit to return a new Bytes
  • returns the target Bytes, its cursor will be at the end
• bytes:readString([expSize]): reads some text and moves the cursor forward
  • expSize: optional, the expected size in bytes to read; omit to read till end
  • returns the read string
• bytes:readLine(): reads a line of text and moves the cursor forward
  • returns the read line
• bytes:writeByte(val): writes a byte and moves the cursor forward
  • val: the byte to write
  • returns the written size in bytes
• bytes:writeInt16(val): writes a 16-bit signed integer and moves the cursor forward
  • val: the 16-bit signed integer to write
  • returns the written size in bytes
• bytes:writeUInt16(val): writes a 16-bit unsigned integer and moves the cursor forward
  • val: the 16-bit unsigned integer to write
  • returns the written size in bytes
• bytes:writeInt32(val): writes a 32-bit signed integer and moves the cursor forward
  • val: the 32-bit signed integer to write
  • returns the written size in bytes
• bytes:writeUInt32(val): writes a 32-bit unsigned integer and moves the cursor forward
  • val: the 32-bit unsigned integer to write
  • returns the written size in bytes
• bytes:writeInt64(val): writes a 64-bit signed integer and moves the cursor forward
  • val: the 64-bit signed integer to write
  • returns the written size in bytes
• bytes:writeSingle(val): writes a single precision real number and moves the cursor forward
  • val: the single precision real number to write
  • returns the written size in bytes
• bytes:writeDouble(val): writes a double precision real number and moves the cursor forward
  • val: the double precision real number to write
  • returns the written size in bytes
• bytes:writeBytes(bytes_[, expSize]): writes some Bytes and moves the cursor forward
  • bytes_: the Bytes to write from start till end, its cursor won’t be moved
  • expSize: optional, the expected size in bytes to write; omit to write till bytes_’s end
  • returns the written size in bytes
• bytes:writeString(val): writes some text and moves the cursor forward
  • val: the string to write
  • returns the written size in bytes
• bytes:writeLine(val): writes a line of text and moves the cursor forward
  • val: the line to write
  • returns the written size in bytes
• bytes:get(index): gets a byte at the specific index, doesn’t moves the cursor
  • index: the index to get, starts from 1
  • returns byte
• bytes:set(index, val): sets a byte to the specific index, doesn’t moves the cursor
  • index: the index to set, starts from 1
  • val: the byte to set
• bytes:resize(expSize): resizes the Bytes
  • expSize: the expected new size
• bytes:clear(): clears all content and resets the cursor

Color

Constructors

• Color.new(r, g, b, a = 255): constructs a color object
  • r: the red component, with range of values from 0 to 255
  • g: the green component, with range of values from 0 to 255
  • b: the blue component, with range of values from 0 to 255
  • a: the alpha component, with range of values from 0 to 255
• Color.new(): constructs a color object in white

Operators

• color:__add(color_): adds with another Color componentwisely
• color:__sub(color_): subtracts by another Color componentwisely
• color:__mul(num): multiplies with another number
  • num: real number
• color:__mul(color_): multiplies with another Color componentwisely
  • color_: with range of values from 0 to 255 for each component
• color:__mul(vec4): multiplies with another Vec4 componentwisely
  • vec4: real number for each component
• color:__unm(): takes the opposite Color componentwisely
• color:__eq(color_): compares with another Color for equality

Object Fields

• color.r: gets or sets the red component
• color.g: gets or sets the green component
• color.b: gets or sets the blue component
• color.a: gets or sets the alpha component

Methods

• color:toRGBA(): converts the Color to an RGBA integer in little-endian
• color:fromRGBA(int): fills the Color with an RGBA integer in little-endian

Date Time

Static Functions

• DateTime.utc(): gets the current UTC time
  • returns sec (0-based), min (0-based), hr (0-based, since midnight), mday (1-based, day of the month), mo (1-based), yr (since C.E.), wday (1-based, days since Sun.), yday (1-based, days since 1, Jan.), isdst (daylight saving time flag, always 0 for UTC)
• DateTime.now(): gets the current local time
  • returns sec (0-based), min (0-based), hr (0-based, since midnight), mday (1-based, day of the month), mo (1-based), yr (since C.E.), wday (1-based, days since Sun.), yday (1-based, days since 1, Jan.), isdst (daylight saving time flag)
• DateTime.ticks(): gets a high precision timestamp
  • returns timestamp in nanoseconds
• DateTime.toMilliseconds(ticks): converts nanoseconds to milliseconds
  • ticks: nanoseconds
  • returns milliseconds
• DateTime.fromMilliseconds(ms): converts milliseconds to nanoseconds
  • ms: milliseconds
  • returns nanoseconds
• DateTime.toSeconds(ticks): converts nanoseconds to seconds
  • ticks: nanoseconds
  • returns seconds
• DateTime.fromSeconds(sec): converts seconds to nanoseconds
  • sec: seconds
  • returns nanoseconds
• DateTime.sleep(ms): sleeps for the specific milliseconds
  • ms: milliseconds

Encoding

Base64

Static Functions

• Base64.encode(bytes): encodes the specific Bytes to Base64 string
  • bytes: the Bytes to encode from start till end, its cursor won’t be moved
  • returns Base64 string
• Base64.decode(txt): decodes the specific Base64 string to Bytes
  • txt: Base64 string to decode
  • returns Bytes, its cursor will be at the end

LZ4

Static Functions

• Lz4.encode(bytes): encodes the specific Bytes to LZ4 encoded Bytes
  • bytes: the Bytes to encode from start till end, its cursor won’t be moved
  • returns LZ4 encoded Bytes
• Lz4.decode(bytes): decodes the specific LZ4 Bytes to Bytes
  • bytes: LZ4 Bytes to decode
  • returns Bytes, its cursor will be at the end

File

Being the same as Lua list, a File’s index starts from 1. Implements a Stream protocol as file on disk.

Constructors

• File.new(): constructs a file object

Operators

• file:__len(): gets the length in bytes

Methods

• file:open(path, access = Stream.Read): opens a File for reading or writing
  • path: the File path
  • access: can be one in Stream.Read, Stream.Write, Stream.Append, Stream.ReadWrite, for reading, truncated writing, non-truncated writing, reading and writing respectively
  • returns true for success, otherwise false
• file:close() closes an opened File
  • returns true for success, otherwise false
• file:peek(): peeks the reading/writing cursor
  • returns the cursor, starts from 1
• file:poke(index): pokes the reading/writing cursor
  • index: starts from 1
  • returns true for success, otherwise false
• file:count(): gets the length in bytes
  • returns the length in bytes
• file:empty(): gets whether the File is empty
  • returns true for empty, otherwise false
• file:endOfStream(): gets whether the cursor is at the end
  • returns true for end, otherwise false
• file:readByte(): reads a byte and moves the cursor forward
  • returns byte
• file:readInt16(): reads a 16-bit signed integer and moves the cursor forward
  • returns 16-bit signed integer
• file:readUInt16(): reads a 16-bit unsigned integer and moves the cursor forward
  • returns 16-bit unsigned integer
• file:readInt32(): reads a 32-bit signed integer and moves the cursor forward
  • returns 32-bit signed integer
• file:readUInt32(): reads a 32-bit unsigned integer and moves the cursor forward
  • returns 32-bit unsigned integer
• file:readInt64(): reads a 64-bit signed integer and moves the cursor forward
  • returns 64-bit signed integer
• file:readSingle(): reads a single precision real number and moves the cursor forward
  • returns single precision real number
• file:readDouble(): reads a double precision real number and moves the cursor forward
  • returns double precision real number
• file:readBytes([expSize[, bytes]]): reads some Bytes and moves the cursor forward
  • expSize: optional, the expected size in bytes to read; omit to read till end
  • bytes: optional, Bytes to receive, its content will be cleared; omit to return a new Bytes
  • returns the target Bytes, its cursor will be at the end
• file:readString([expSize]): reads some text and moves the cursor forward
  • expSize: optional, the expected size in bytes to read; omit to read till end
  • returns the read string
• file:readLine(): reads a line of text and moves the cursor forward
  • returns the read line
• file:writeByte(): writes a byte and moves the cursor forward
  • val: the byte to write
  • returns the written size in bytes
• file:writeInt16(): writes a 16-bit signed integer and moves the cursor forward
  • val: the 16-bit signed integer to write
  • returns the written size in bytes
• file:writeUInt16(): writes a 16-bit unsigned integer and moves the cursor forward
  • val: the 16-bit unsigned integer to write
  • returns the written size in bytes
• file:writeInt32(): writes a 32-bit signed integer and moves the cursor forward
  • val: the 32-bit signed integer to write
  • returns the written size in bytes
• file:writeUInt32(): writes a 32-bit unsigned integer and moves the cursor forward
  • val: the 32-bit unsigned integer to write
  • returns the written size in bytes
• file:writeInt64(): writes a 64-bit signed integer and moves the cursor forward
  • val: the 64-bit signed integer to write
  • returns the written size in bytes
• file:writeSingle(): writes a single precision real number and moves the cursor forward
  • val: the single precision real number to write
  • returns the written size in bytes
• file:writeDouble(): writes a double precision real number and moves the cursor forward
  • val: the double precision real number to write
  • returns the written size in bytes
• file:writeBytes(bytes[, expSize]): writes some Bytes and moves the cursor forward
  • bytes: the Bytes to write from start till end, its cursor won’t be moved
  • expSize: optional, the expected size in bytes to write; omit to write till bytes’s end
  • returns the written size in bytes
• file:writeString(val): writes some text and moves the cursor forward
  • val: the string to write
  • returns the written size in bytes
• file:writeLine(val): writes a line of text and moves the cursor forward
  • val: the line to write
  • returns the written size in bytes

Note that when open a file as Stream.Append, it always writes data at the end of the file, expanding it, and file:poke(...) are ignored.

Filesystem

Static Functions

• Path.combine(...): combines a number of paths
  • returns combined path
• Path.split(full): splits the specific path into parts
  • returns name, ext, parent
• Path.existsFile(path): gets whether the specific file exists
  • path: the file path
  • returns true for exists, otherwise false
• Path.existsDirectory(path): gets whether the specific directory exists
  • path: the directory path
  • returns true for exists, otherwise false
• Path.copyFile(src, dst): copies the specific file to a new path
  • src: the source path
  • dst: the destination path
  • returns true for success, otherwise false
• Path.copyDirectory(src, dst): copies the specific directory to a new path recursively
  • src: the source path
  • dst: the destination path
  • returns true for success, otherwise false
• Path.moveFile(src, dst): moves the specific file to a new path
  • src: the source path
  • dst: the destination path
  • returns true for success, otherwise false
• Path.moveDirectory(src, dst): moves the specific directory to a new path recursively
  • src: the source path
  • dst: the destination path
  • returns true for success, otherwise false
• Path.removeFile(path, toTrashBin): removes the specific file
  • path: the file path
  • toTrashBin: true to remove to the trash bin, otherwise remove permanently
  • returns true for success, otherwise false
• Path.removeDirectory(path, toTrashBin): removes the specific directory recursively
  • path: the directory path
  • toTrashBin: true to remove to the trash bin, otherwise remove permanently
  • returns true for success, otherwise false
• Path.touchFile(path): tries to create a file at the specific path, will touch its ancestors
  • path: the file path
  • returns true for success, otherwise false
• Path.touchDirectory(path): tries to create a directory at the specific path, will touch its ancestors
  • path: the directory path
  • returns true for success, otherwise false

Static Variables

• Path.executableFile: readonly, gets the executable file path
• Path.documentDirectory: readonly, gets the documents directory path
• Path.writableDirectory: readonly, gets the writable directory path
• Path.savedGamesDirectory: readonly, gets the “Saved Games” directory path on Windows, or same as Path.writableDirectory on other platforms

Constructors

• FileInfo.new(path): constructs a file information object with the specific path
  • path: the file path
• DirectoryInfo.new(path): constructs a directory information object with the specific path
  • path: the directory path

Methods

• fileInfo:fullPath(): gets the full path
  • returns the full path
• fileInfo:parentPath(): gets the path of the parent directory
  • returns the path of the parent directory
• fileInfo:fileName(): gets the file name
  • returns the file name, without extension
• fileInfo:extName(): gets the extension name
  • returns the extension name, without dot
• fileInfo:empty(): gets whether the file represented by the FileInfo is empty
  • returns true if empty, otherwise false
• fileInfo:exists(): gets whether the file represented by the FileInfo exists
  • returns true for exists, otherwise false
• fileInfo:make(): makes a file represented by the FileInfo if it doesn’t exist, fails if its ancestors don’t exist
  • returns true for success, otherwise false
• fileInfo:copyTo(dst): copies the file represented by the FileInfo to a new path
  • dst: the destination path
  • returns true for success, otherwise false
• fileInfo:moveTo(dst): moves the file represented by the FileInfo to a new path
  • dst: the destination path
  • returns true for success, otherwise false
• fileInfo:remove(toTrashBin): removes the file represented by the FileInfo
  • toTrashBin: true to remove to the trash bin, otherwise remove permanently
  • returns true for success, otherwise false
• fileInfo:rename(newName[, newExt]): renames the file represented by the FileInfo
  • newName: the new file name
  • newExt: the new extension name; omit to keep the old
  • returns true for success, otherwise false
• fileInfo:parent(): gets the DirectoryInfo of the FileInfo’s parent
  • returns the DirectoryInfo of its parent
• fileInfo:readAll(): reads all content of the file represented by the FileInfo as string
  • returns the content string
• directoryInfo:fullPath(): gets the full path
  • returns the full path
• directoryInfo:parentPath(): gets the path of the parent directory
  • returns the path of the parent directory
• directoryInfo:dirName(): gets the directory name
  • returns the directory name
• directoryInfo:empty(): gets whether the directory represented by the DirectoryInfo is empty
  • returns true if empty, otherwise false
• directoryInfo:exists(): gets whether the directory represented by the DirectoryInfo exists
  • returns true for exists, otherwise false
• directoryInfo:make(): makes a directory represented by the DirectoryInfo if it doesn’t exist, fails if its ancestors don’t exist
  • returns true for success, otherwise false
• directoryInfo:copyTo(dst): copies the directory represented by the DirectoryInfo to a new path
  • dst: the destination path
  • returns true for success, otherwise false
• directoryInfo:moveTo(dst): moves the directory represented by the DirectoryInfo to a new path
  • dst: the destination path
  • returns true for success, otherwise false
• directoryInfo:remove(toTrashBin): removes the directory represented by the DirectoryInfo
  • toTrashBin: true to remove to the trash bin, otherwise remove permanently
  • returns true for success, otherwise false
• directoryInfo:rename(newName): renames the directory represented by the DirectoryInfo
  • newName: the new directory name
  • returns true for success, otherwise false
• directoryInfo:getFiles(pattern = '*.*', recursive = false): gets sub-files under the directory represented by the DirectoryInfo
  • pattern: lookup pattern, supports wildcards, eg. "*.txt;*.json"
  • recursive: whether lookup its sub-directories
  • returns a list of FileInfo objects
• directoryInfo:getDirectories(recursive = false): gets sub-directories under the directory represented by the DirectoryInfo
  • recursive: whether lookup its sub-directories
  • returns a list of DirectoryInfo objects
• directoryInfo:parent(): gets the DirectoryInfo of this DirectoryInfo’s parent
  • returns the DirectoryInfo of its parent

Image

Constructors

• Image.new(palette): constructs an image object with the specific Palette asset
  • palette: the Palette loaded by Resources.load(...)
• Image.new(): constructs a true-color image object

Object Fields

• image.channels: readonly, gets the channels of the Image, 1 for paletted, 4 for true-color
• image.width: readonly, gets the width of the Image
• image.height: readonly, gets the height of the Image

Methods

• image:resize(width, height, stretch = true): resizes the Image with the specific size
  • width: the width
  • height: the height
  • stretch: true to stretch the Image, otherwise to clip
  • returns true for success, otherwise false
• image:get(x, y): gets the Color or Palette index at the specific index
  • x: starts from 0
  • y: starts from 0
  • returns Color or palette index
• image:set(x, y, val): sets the Color or Palette index at the specific index
  • x: starts from 0
  • y: starts from 0
  • val: Color or Palette index
  • returns true for success, otherwise false
• image:blit(dst, x, y[, w, h[, sx, sy]]): blits the Image to another one
  • dst: the specific destination Image
  • x: the destination x
  • y: the destination y
  • w: the destination width
  • h: the destination height
  • sx: the source x
  • sy: the source y
  • returns true for success, otherwise false
• image:fromImage(img): loads content from another Image
  • img: the specific Image to load
  • returns true for success, otherwise false
• image:fromBlank(width, height, paletted = 0): loads blank content
  • width: the specific width
  • height: the specific height
  • paletted: 0 for true-color, non-zero for paletted
  • returns true for success, otherwise false
• image:toBytes(bytes, type = 'png'): encodes the Image to Bytes
  • bytes: the Bytes to receive, its cursor will be at the end
  • type: can be one in “png”, “jpg”, “bmp”, “tga”, “img”
  • returns bytes for success, otherwise nil
• image:fromBytes(bytes): decodes the specific Bytes
  • bytes: the Bytes to retrieve from start till end, its cursor won’t be moved
  • returns true for success, otherwise false

JSON

Constants

• Json.Null

Constructors

• Json.new(): constructs a JSON object

Methods

• json:toString(pretty = true): serializes the Json to string
  • pretty: whether to serialize in a friendly to read format
  • returns serialized string
• json:fromString(txt): parses Json data from the specific string
  • txt: the text to parse
  • returns true for success, otherwise false
• json:toTable(allowNull = false): serializes the Json to Lua table
  • allowNull: true to convert Json null to Json.Null, otherwise to Lua nil
  • returns serialized Lua table
• json:fromTable(tbl): parses Json data from the specific Lua table, ignores incompatible data types
  • tbl: the table to parse
  • returns true for success, otherwise false

Math

Structures

Constants

• Vec2
  • Vec2.Zero: equals to Vec2.new(0, 0)
  • Vec2.One: equals to Vec2.new(1, 1)
  • Vec2.Left: equals to Vec2.new(-1, 0)
  • Vec2.Right: equals to Vec2.new(1, 0)
  • Vec2.Up: equals to Vec2.new(0, -1)
  • Vec2.Down: equals to Vec2.new(0, 1)
• Vec3
  • Vec3.Zero: equals to Vec3.new(0, 0, 0)
  • Vec3.One: equals to Vec3.new(1, 1, 1)
• Vec4
  • Vec4.Zero: equals to Vec4.new(0, 0, 0, 0)
  • Vec4.One: equals to Vec4.new(1, 1, 1, 1)

Static Functions

• Rect
  • Rect.byXYWH(x, y, w, h): constructs a rectangle object in real numbers by position and size
• Recti
  • Recti.byXYWH(x, y, w, h): constructs a rectangle object in integers by position and size

Constructors

• Vec2
  • Vec2.new([x, y]): constructs a vector object in 2 dimensions
• Vec3
  • Vec3.new([x, y, z]): constructs a vector object in 3 dimensions
• Vec4
  • Vec4.new([x, y, z, w]): constructs a vector object in 4 dimensions
• Rect
  • Rect.new([x0, y0, x1, y1]): constructs a rectangle object in real numbers by points
• Recti
  • Recti.new([x0, y0, x1, y1]): constructs a rectangle object in integers by points
• Rot
  • Rot.new([s, c]): constructs a rotation object

Operators

• Vec2
  • vec2:__add(vec2_): adds with another Vec2 componentwisely
  • vec2:__sub(vec2_): subtracts by another Vec2 componentwisely
  • vec2:__mul(num): multiplies with another number
  • vec2:__mul(vec2_): multiplies with another Vec2 componentwisely
  • vec2:__unm(): takes the opposite Vec2 componentwisely
  • vec2:__len(): gets the length of the Vec2
  • vec2:__eq(vec2_): compares with another Vec2 for equality
• Vec3
  • vec3:__add(vec3_): adds with another Vec3 componentwisely
  • vec3:__sub(vec3_): subtracts by another Vec3 componentwisely
  • vec3:__mul(num): multiplies with another number
  • vec3:__mul(vec3_): multiplies with another Vec3 componentwisely
  • vec3:__unm(): takes the opposite Vec3 componentwisely
  • vec3:__len(): gets the length of the Vec3
  • vec3:__eq(vec3_): compares with another Vec3 for equality
• Vec4
  • vec4:__add(vec4_): adds with another Vec4 componentwisely
  • vec4:__sub(vec4_): subtracts by another Vec4 componentwisely
  • vec4:__mul(num): multiplies with another number
  • vec4:__mul(vec4_): multiplies with another Vec4 componentwisely
  • vec4:__unm(): takes the opposite Vec4 componentwisely
  • vec4:__eq(vec4_): compares with another Vec4 for equality
• Rot
  • rot:__add(rot_): adds with another Rot in angle
  • rot:__sub(rot_): subtracts by another Rot in angle
  • rot:__mul(vec2): rotates another Vec2
  • rot:__mul(rot_): rotates another Rot
  • rot:__unm(): takes the opposite Rot in angle
  • rot:__eq(rot_): compares with another Rot for equality
• Rect
  • rect:__eq(rect_): compares with another Rect for equality
• Recti
• recti:__eq(recti_): compares with another Recti for equality

Object Fields

• Vec2
  • vec2.x: gets or sets the x component
  • vec2.y: gets or sets the y component
  • vec2.normalized: readonly, gets the normalized Vec2
  • vec2.length: readonly, gets the length
  • vec2.angle: readonly, gets the rotated angle in radians as a vector
• Vec3
  • vec3.x: gets or sets the x component
  • vec3.y: gets or sets the y component
  • vec3.z: gets or sets the z component
  • vec3.normalized: readonly, gets the normalized Vec3
  • vec3.length: readonly, gets the length
• Vec4
  • vec4.x: gets or sets the x component
  • vec4.y: gets or sets the y component
  • vec4.z: gets or sets the z component
  • vec4.w: gets or sets the w component
• Rot
  • rot.s: gets or sets the sine component
  • rot.c: gets or sets the cosine component
  • rot.angle: gets or sets the angle in radians denoted by the Rot
• Rect
  • rect.x0: gets or sets the first x component
  • rect.y0: gets or sets the first y component
  • rect.x1: gets or sets the second x component
  • rect.y1: gets or sets the second y component
• Recti
  • recti.x0: gets or sets the first x component
  • recti.y0: gets or sets the first y component
  • recti.x1: gets or sets the second x component
  • recti.y1: gets or sets the second y component

Methods

• Vec2
  • vec2:normalize(): normalizes the Vec2
    • returns the original length before normalization
  • vec2:distanceTo(vec2_): gets the distance between this and another Vec2
    • returns the distance number
  • vec2:dot(vec2_): applies a dot multiplication
    • returns the dot result as number
  • vec2:cross(num): applies a cross multiplication
    • returns the cross Vec2
  • vec2:cross(vec2_): applies a cross multiplication
    • returns the cross result as number
  • vec2:angleTo(vec2_): gets the angle between this and another Vec2 as vectors
    • returns the angle in radians
  • vec2:rotated(angle[, pivot]): gets the rotated Vec2
    • angle: the angle to rotate
    • pivot: the pivot Vec2 to rotate around
    • returns the rotated Vec2
  • vec2:rotated(rot[, pivot]): gets the rotated Vec2
    • rot: the Rot to rotate
    • pivot: the pivot Vec2 to rotate around
    • returns the rotated Vec2
• Vec3
  • vec3:normalize(): normalizes the Vec3
    • returns the original length before normalization
  • vec3:dot(vec3_): applies a dot multiplication
    • returns the dot result as number
• Rect
  • rect:xMin(): gets the minimum x component
  • rect:yMin(): gets the minimum y component
  • rect:xMax(): gets the maximum x component
  • rect:xMax(): gets the maximum y component
  • rect:width(): gets the width, equals to rect:xMax() - rect:xMin()
  • rect:height(): gets the height, equals to rect:yMax() - rect:yMin()
• Recti
  • recti:xMin(): gets the minimum x component
  • recti:yMin(): gets the minimum y component
  • recti:xMax(): gets the maximum x component
  • recti:xMax(): gets the maximum y component
  • recti:width(): gets the width, equals to rect:xMax() - rect:xMin() + 1
  • recti:height(): gets the height, equals to rect:yMax() - rect:yMin() + 1

Intersection Detection

Static Functions

• Math.intersects(shapeA, shapeB): detects whether two shapes intersects with each other
  • shapeA: the first shape
  • shapeB: the second shape
  • returns true for intersects, otherwise false

Both shape parameters can be:

• Point: Vec2
• Line (segment): Vec4, x, y for first point, z, w for second
• Circle: Vec3, x, y for center, z for radius
• AABB: Rect; Recti is supported as well, but converted to Rect internally to determine against other shapes except for another Recti

Network

Constants

• Network.None
• Network.Udp
• Network.Tcp

Constructors

• Network.new(onRecv[, onEstb[, onDisc]]): constructs a network object
  • onRecv: callback on received
  • onEstb: callback on connection established
  • onDisc: callback on connection disconnected

The callback of received event is an invokable in form of function (data, size, addr) end, which accepts three parameters respectively represent for the data has been just received, the data size corresponding to specific types, and the remote adress string. The type of the first parameter is determined by the “data_type” option.

The callback of connection established is an invokable in form of function (addr) end, which accepts a parameter represents for the remote address string; nil for failure for outcoming connection. It’s invoked when either incoming or outcoming connection established; ignored by UDP.

The callback of disconnected is an invokable in form of function (addr) end, which accepts a parameter represents for the remote address string. It’s invoked when either incoming or outcoming connection disconnected; ignored by UDP.

Object Fields

• network.ready: readonly, gets whether the Network is ready

Methods

• network:getOption(key): gets the option value of the specific key
  • key: the option key to get
  • returns option value
• network:setOption(key, val): sets option value of the specific key
  • key: the option key to set
  • val: the value to set

Currently there is only one available option:

Key	Value	Note
“data_type”	Can be one in “stream”, “bytes”, “string”, “json”, defaults to “json”	Data type for transmission/datagram

• network:open(addr[, protocal]): opens a Network as either server or client
  • addr: the address
  • protocal: can be one in Network.Udp, Network.Tcp
  • returns true for success, otherwise false
• network:close(): closes a Network, clears all options; will neither be impossible to send nor receive anything after closing
  • returns true for success, otherwise false

An addr argument is combined with four parts, direction, protocol, address and port:

Part	Value
Direction	> for connecting, < for listening
Protocol	udp://, tcp://
Address	IP address
Port	Port number

For example:

Address string	Connectivity
“>tcp://192.168.0.1:12000”	As client, connects to 192.168.0.1 port 12000 via TCP
“<udp://127.0.0.1:12000”	As server, listens from local host port 12000 via UDP
“udp://192.168.0.1:12000”	As client, sends to 192.168.0.1 port 12000 via UDP
“tcp://12000”	As server, listens from port 12000 via TCP
“192.168.0.1:12000”	As client, connects to 192.168.0.1 port 12000, protocal determined by the explicit protocal parameter
“12000”	As server, listens from port 12000, protocal determined by the explicit protocal parameter

• network:poll([timeoutMs]): polls pending Network events manually; do not need to call this function if a program already entered the update(delta) loop
  • timeoutMs: the timeout value
• network:disconnect(): disconnects from remote peers
• network:send(bytes): sends the specific Bytes
  • bytes: the Bytes to send
  • returns true for success, otherwise false
• network:send(txt): sends the specific string
  • txt: the string to send
  • returns true for success, otherwise false
• network:send(json): sends the specific Json
  • json the Json to send
  • returns true for success, otherwise false
• network:send(tbl): sends the specific Lua table as Json
  • tbl the Lua table to send
  • returns true for success, otherwise false
• network:broadcast(bytes): broadcasts the specific Bytes
  • bytes: the Bytes to broadcast
  • returns true for success, otherwise false
• network:broadcast(txt): broadcasts the specific string
  • txt: the string to broadcast
  • returns true for success, otherwise false
• network:broadcast(json): broadcasts the specific Json
  • json: the Json to broadcast
  • returns true for success, otherwise false
• network:broadcast(tbl): broadcasts the specific Lua table as Json
  • tbl: the Lua table to broadcast
  • returns true for success, otherwise false

A single transmission or datagram cannot be longer than 512KB.

Consider closing and setting a Network object to nil as soon as it’s no longer in use.

For “stream”, it sends and receives raw Bytes, you are free parsing and serializing for your own protocol.

For “bytes”, an extra 32-bit unsigned integer will be automatically packed at head of Bytes before sending, the size head itself also counts; Bytes parameter in the received callback doesn’t contain that head. In short words, it’s transparent between Bitty Engine projects, but it’s helpful to communicate with other endpoints to distinguish different messages, and you have to adapt the rule for other Network endpoints.

For both “string” and “json”, the underneath data flow always end up with a zero byte, vice versa, received string and Json must end up with a terminal zero byte.

Platform

Static Functions

• Platform.surf(url): surfs the Internet via browser
  • url: the URL address to surf
• Platform.browse(dir): browses the filesystem via explorer
  • dir: the directory path to browse
• Platform.hasClipboardText(): gets whether there is text content in the clipboard
  • returns true for nonempty, otherwise false
• Platform.getClipboardText(): gets the text content in the clipboard
  • returns text content
• Platform.setClipboardText(txt): sets the text content in the clipboard
  • txt: the text to set
• Platform.execute(cmd): executes the specific system command; this function invokes native command on desktops, and JavaScript function in browser
  • cmd: the command to execute
• Platform.openFile([title[, filter[, multiselect]]]): popups an open-file-dialog
  • title: the title text
  • filter: the file filter, eg. "Text files (*.txt);*.txt;All files (*.*);*"
  • multiselect: true for multiselect, false for single file select
  • returns selected file path or paths, or nil for canceled
• Platform.saveFile([title[, filter]]): popups a save-file-dialog
  • title: the title text
  • filter: the file filter
  • returns specified file path, or nil for canceled
• Platform.selectDirectory([title]): popups a select-directory-dialog
  • title: the title text
  • returns selected directory path, or nil for canceled

Static Variables

• Platform.os: readonly, gets the current running OS
• Platform.endian: readonly, gets the current endian
  • returns either “little-endian” or “big-endian”

Promise

This module declares a minimal protocol to handle asynchronization.

Constants

• Promise.Pending
• Promise.Resolved
• Promise.Rejected

Object Fields

• promise.state: gets the state of the Promise object, can be one in Promise.Pending, Promise.Resolved, Promise.Rejected
• promise.value: gets the fulfilled value of the Promise object, or nil

Methods

• promise:thus(handler): sets the specific callback to handle on succeeded
  • handler: in form of function (...) end, an invokable object which accepts optional arguments
  • returns this Promise itself
• promise:catch(handler): sets the specific callback to handle on failed
  • handler: in form of function ([err]) end, an invokable object
  • returns this Promise itself
• promise:finally(handler): sets the specific callback to handle on finished
  • handler: in form of function () end, an invokable object
  • returns this Promise itself

Stream

This module contains constants indicating accessibilities for other modules.

Constants

• Stream.Read
• Stream.Write
• Stream.Append
• Stream.ReadWrite

Web

Experimental feature. This module offers fetching via HTTP.

Functions

Implements a Promise protocol for HTTP accessing and manipulating.

• fetch(url[, options]): requests the specific HTTP resource
  • url: the URL to request
  • options: the option Json or Lua table
  • returns Promise object

The thus handler of the returned Promise object takes an invokable object in form of function (rsp) end which accepts the responded content. The catch handler of the returned Promise object takes an invokable object in form of function (err) end. The finally handler of the returned Promise object takes an invokable object in form of function () end.

For example:

fetch('https://github.com', {
    method = 'GET',
    headers = {
      ['Content-Type'] = 'text/html',
      ['User-Agent'] = 'Mozilla/5.0 Gecko/20100101 Firefox/83.0'
    }
  })
  :thus(function (rsp)
    print(rsp)
  end)
  :catch(function (err)
    print('Error.')
  end)
  :finally(function ()
    print('Finished.')
  end)

Option	Values	Description
method	“GET”, “POST”, “PUT”, “DELETE”, etc.	Specific method to perform HTTP request
headers	Valid HTTP headers	Optional. Header data
body	Request body	Optional. Body data
hint	“bytes”, “string”, “json”	Optional, defaults to “string”. Prefers how to interpret respond data
allow_insecure_connection_for_https	true, false	Optional, defaults to false, for desktop only. Specifies whether to allow insecure connection for HTTPS

TOP

Assets and Resources

Resources

Static Functions

• Resources.load(entry[, hint]): loads a resource from the specific asset entry
  • entry: the entry name to load
  • hint: the type hint
  • returns loaded resource, or nil
• Resources.load(path[, hint]): loads a resource from the specific file path
  • path: the file path to load
  • hint: the type hint
  • returns loaded resource, or nil
• Resources.load(bytes[, hint]): loads a resource from the specific Bytes; available for Texture, Sfx, Music
  • bytes: the Bytes to load, its cursor won’t be moved
  • hint: the type hint
  • returns loaded resource, or nil
• Resources.load(str[, hint]): loads a resource from the specific asset content as string
  • str: the asset content as string to load
  • hint: the type hint
  • returns loaded resource, or nil
• Resources.load(json[, hint]): loads a resource from the specific Json object
  • json: the Json to load
  • hint: the type hint
  • returns loaded resource, or nil
• Resources.load(tbl[, hint]): loads a resource from the specific Lua table; similar to the Json version, but in table form
  • tbl: the Lua table to load
  • hint: the type hint
  • returns loaded resource, or nil
• Resources.load(img[, hint]): loads a resource from the specific Image object
  • img: the Image to load
  • hint: the type hint
  • returns loaded resource, or nil
• Resources.wait(res): waits until the resource is loaded or timeout
  • res: the resource to wait for
  • returns true for ready to use, otherwise false
• Resources.unload(res): unloads a resource
  • res: the resource to unload
• Resources.collect(): collects all unused resources

The hint can be one in Palette, Texture, Sprite, Map, Sfx, Music. Bitty Engine can infer asset types from extension or content most of the time. However hint is necessary if there is yet insufficient information to tell a type, or to distinguish as either Sfx or Music when loading an audio asset.

For example:

foo = Resources.load('bar.pal') -- Load a palette.
foo = Resources.load({ width = 128, height = 128 }) -- Load a blank texture.

local data = {
  width = 8, height = 8,
  count = 2,
  data = {
    {
      x = 16, y = 0, width = 8, height = 8,
      interval = 0.25,
      key = 'idle'
    },
    {
      x = 24, y = 0, width = 8, height = 8,
      interval = 0.25,
      key = ''
    }
  },
  ref = baz -- Ref by object.
}
foo = Resources.load(data) -- Load a sprite.

local data = {
  tiles = {
    count = { 8, 8 }
  },
  width = 60, height = 40,
  data = { ... },
  ref = 'baz.png' -- Ref by asset name.
}
foo = Resources.load(data) -- Load a map.

foo = Resources.load('bar.mp3', Sfx) -- Load an SFX.
foo = Resources.load('bar.mp3', Music) -- Load a piece of music.

The asynchronous Resources.load(...) returns a resource handle immediately. It is lazy evaluated, loading is deferred until specific reading and writing access happens. The synchronous Resources.wait(...) also loads it, it returns immediately if the specific resource is already loaded, otherwise it waits until loaded or timeout.

Consider using Resources.unload(...) or Resources.collect() to unload unused resources (loaded by Resources.load(...)) periodically and properly, or there would be memory leak. One possible practice is to call Lua’s GC then collect resources after loading a new level, since the old one is no longer in use:

collectgarbage()
Resources.collect()

Asset

Can be loaded by Resources.load(...), only happens when Bitty Engine cannot determine specific sub asset type.

Palette Asset

Can be loaded by Resources.load(...).

Font Asset

Constructors

• Font.new(entry, size = 14 | Vec2.new(8, 8), permeation = 1): constructs a font object from the specific (TrueType or Bitmap) font asset with the specific size and permeation
  • entry: the entry name to load
  • size: can be either a number for TrueType, or a Vec2 for Bitmap
  • permeation: indicates how to blur glyph edges with the alpha channel, with range of values from 0 to 255
• Font.new(path, size = 14 | Vec2.new(8, 8), permeation = 1): constructs a font object from the specific (TrueType or Bitmap) font file with the specific size and permeation
  • path: the file path to load
  • size: can be either a number for TrueType, or a Vec2 for Bitmap
  • permeation: indicates how to blur glyph edges with the alpha channel, with range of values from 0 to 255
• Font.new(img, size = Vec2.new(8, 8), permeation = 1): constructs a font object from the specific (Bitmap) Image with the specific size and permeation
  • img: the Image to load
  • size: the size as Vec2 for a character
  • permeation: indicates how to blur glyph edges with the alpha channel, with range of values from 0 to 255
• Font.new(nil, size = 14, permeation = 1): constructs a font object from the default font with the specific size and permeation
  • size: the size as number
  • permeation: indicates how to blur glyph edges with the alpha channel, with range of values from 0 to 255

Font is constructed like regular object and managed by GC, do not need to unload it manually. The permeation parameter indicates how to handle font transparency, zero means using values from a font file, while non-zero means a specified threshold for whether a pixel shall pass (non-transparent) or be blocked (transparent).

Texture Asset

Can be loaded by Resources.load(...).

Object Fields

• texture.width: readonly, gets the Texture width
• texture.height: readonly, gets the Texture height

Methods

• texture:blend(mode): sets the blend state of the Texture with the specific mode
  • mode: the blend mode to set; refer to the blend modes of Canvas
  • returns true for success, otherwise false

Sprite Asset

Can be loaded by Resources.load(...).

Object Fields

• sprite.count: readonly, gets the Sprite frame count
• sprite.width: readonly, gets the Sprite width of every frame

• sprite.height: readonly, gets the Sprite height of every frame

• sprite.hFlip: gets or sets whether the Sprite is flipped horizontally
• sprite.vFlip: gets or sets whether the Sprite is flipped vertically

Methods

• sprite:play(beginIndex = -1, endIndex = -1, reset = true, loop = true, async = false): plays the specific animation, use -1 for both begin and end indices to play through all frames
  • beginIndex: the begin frame index, starts from 0
  • endIndex: the end frame index, starts from 0
  • reset: whether resets to the initial animation frame
  • loop: true for loop, otherwise plays once
  • async: true for asynchronously playing, otherwise plays synchronously
  • returns true for success, otherwise false, and a secondary value for estimated duration if plays synchronously; the secondary value would be always -1 if plays asynchronously
• sprite:play(beginStr, reset = true, loop = true, async = false): plays the specific animation
  • beginStr: the animation name string
  • reset: whether resets to the initial animation frame
  • loop: true for loop, otherwise plays once
  • async: true for asynchronously playing, otherwise plays synchronously
  • returns true for success, otherwise false, and a secondary value for estimated duration if plays synchronously; the secondary value would be always -1 if plays asynchronously
• sprite:pause(): pauses playing
  • returns true for success, otherwise false
• sprite:resume(): resumes playing
  • returns true for success, otherwise false
• sprite:stop(): stops playing
  • returns true for success, otherwise false

It communicates across internal threads when play a sprite animation synchronously, this might take lots of time if there are lots of sprites. Consider playing it asynchronously if this matters in your actual project.

Map Asset

Can be loaded by Resources.load(...).

Object Fields

• map.width: readonly, gets the Map width
• map.height: readonly, gets the Map height

SFX Asset

Can be loaded by Resources.load(...).

Music Asset

Can be loaded by Resources.load(...).

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Primitives

The coordinate definition in Bitty Engine is as follow:

The zero point is to the top-left corner, the x, y axises increase in right, bottom respectively.

Basics

Functions

• cls([col]): clears the screen with the specific Color
  • col: optional, defaults to the previous passed value to this function
  • returns the previous clear Color
• color(col): sets the active Color with a specific value
  • col: the Color to set
  • returns the previous active Color
• color(): resets the active Color to white
• sync(): synchronizes commands to graphics manually, also updates Network and Web links
  • returns synchronized command count

Shapes

Functions

• plot(x, y[, col]): draws a point
  • x: the x position
  • y: the y position
  • col: omit to use the active Color
• line(x0, y0, x1, y1[, col]): draws a line
  • x0: the first x position
  • y0: the first y position
  • x1: the second x position
  • y1: the second y position
  • col: omit to use the active Color
• circ(x, y, r, fill = false[, col]): draws a cicle
  • x: the x position
  • y: the y position
  • r: the radius
  • fill: true for fill
  • col: omit to use the active Color
• ellipse(x, y, rx, ry, fill = false[, col]): draws an ellipse
  • x: the x position
  • y: the y position
  • rx: the x radius
  • ry: the y radius
  • fill: true for fill
  • col: omit to use the active Color
• pie(x, y, r, startAngle, endAngle, fill = false[, col]): draws a pie
  • x: the x position
  • y: the y position
  • r: the radius
  • startAngle: the start angle in radians
  • endAngle: the end angle in radians
  • fill: true for fill
  • col: omit to use the active Color
• rect(x0, y0, x1, y1, fill = false[, col[, rad]]): draws a rectangle
  • x0: the first x position
  • y0: the first y position
  • x1: the second x position
  • y1: the second y position
  • fill: true for fill
  • col: omit to use the active Color
  • rad: the radius of the corner arcs of the rectangle
• text(txt, x, y[, col, margin = 1, scale = 1]): draws text
  • txt: the text to draw
  • x: the x position
  • y: the y position
  • col: omit to use the active Color
  • margin: the margin distance
  • scale: the scale factor
• tri(p0, p1, p2, fill = false[, col]): draws a triangle
  • p0: Vec2 for the first point
  • p1: Vec2 for the second point
  • p2: Vec2 for the third point
  • fill: true for fill
  • col: omit to use the active Color

Palette

Functions

• pget(res, index): gets the Color from the specific Palette resource
  • res: the Palette resource
  • index: starts from 0
  • returns Color
• pset(res, index, col): sets the Color to the specific Palette resource
  • res: the Palette resource
  • index: starts from 0
  • col: the Color to set

Font

Functions

• font(font_): sets the active Font for the text(...) function
  • font_: the Font resource
• font(): resets the active Font to default
• measure(txt, font, margin = 1, scale = 1): measures the size of the specific text
  • txt: the text to measure
  • font: the Font to measure with, nil to use default
  • margin: the margin distance
  • scale: the scale factor
  • returns width, height for both dimensions respectively

Texture

Functions

• tex(res, x, y[, w, h[, sx, sy[, sw, sh[, rotAngle, rotCenter = Vec2.new(0.5, 0.5), hFlip = false, vFlip = false, col = Color.new(255, 255, 255, 255)]]]]): draws the specific Texture resource
  • res: the Texture resource
  • x: the destination x position
  • y: the destination y position
  • w: the destination width; omit to use the resource width
  • y: the destination height; omit to use the resource height
  • sx: the source x position to sample, defaults to 0
  • sy: the source y position to sample, defaults to 0
  • sw: the source width to sample, defaults to the resource width
  • sh: the source height to sample, defaults to the resource height
  • rotAngle: the rotation angle in radians
  • rotCenter: the rotation center
  • hFlip: whether to flip horizontally
  • vFlip: whether to flip vertically
  • col: additional Color multiplied to render the Texture

Sprite

Functions

• spr(res, x, y[, w, h[, rotAngle, rotCenter = Vec2.new(0.5, 0.5), col = Color.new(255, 255, 255, 255)]]): draws the specific Sprite resource
  • res: the Sprite resource
  • x: the destination x position
  • y: the destination y position
  • w: the destination width
  • y: the destination height
  • rotAngle: the rotation angle in radians
  • rotCenter: the rotation center
  • col: additional Color multiplied to render the Sprite

Map

Functions

• map(res, x, y, col = Color.new(255, 255, 255, 255), scale = 1): draws the specific Map resource
  • res: the Map resource
  • x: the destination x position
  • y: the destination y position
  • col: additional Color multiplied to render the Map
  • scale: positive integer, the scale factor
• mget(res, x, y): gets the tile index from the specific Map resource
  • res: the Map resource
  • x: starts from 0
  • y: starts from 0
  • returns tile index
• mset(res, x, y, cel): sets the tile index to the specific Map resource
  • res: the Map resource
  • x: starts from 0
  • y: starts from 0
  • cel: the tile index

Audio

Functions

• volume(sfxVol[, musicVol]): sets the audio volume
  • sfxVol: volume for all SFX channels, with range of values from 0.0 to 1.0
  • musicVol: with range of values from 0.0 to 1.0
• volume({ sfxVol1, sfxVol2, sfxVol3, sfxVol4 }[, musicVol]): sets the audio volume
  • { sfxVol1, sfxVol2, sfxVol3, sfxVol4 }: volume for SFX channels respectively, with range of values from 0.0 to 1.0 at each, -1 to leave as is
  • musicVol: with range of values from 0.0 to 1.0

SFX

Functions

• play(sfx, loop = false[, fade[, channel]]): plays the specific Sfx resource
  • sfx: the Sfx resource
  • loop: true for loop, otherwise plays once
  • fade: the fade in time in seconds
  • channel: the specific channel to play this sound, starts from 1; omit to pick an available automatically
• stop(sfx[, fade]): stops the specific Sfx resource
  • sfx: the Sfx resource
  • fade: the fade out time in seconds

Music

Functions

• play(music, loop = false[, fade[, pos]]): plays the specific Music resource
  • music: the Music resource
  • loop: true for loop, otherwise plays once
  • fade: the fade in time in seconds
  • pos: real number, the specific position in seconds to start from; affects MP3, OGG, WAV, FLAC, and some MOD formats
• stop(music[, fade]): stops the specific Music resource
  • music: the Music resource
  • fade: the fade out time in seconds

Gamepad

A gamepad is a virtual entity, its buttons are binded to a keyboard or an actual gamepad hardware.

Functions

• btn([button[, index]]): gets whether the specific gamepad button is pressed
  • button: the button index; omit to get any key
  • index: the gamepad index, starts from 1
  • returns true for pressed, otherwise false
• btnp([button[, index]]): gets whether the specific gamepad button is released from pressing
  • button: the button index; omit to get any key
  • index: the gamepad index, starts from 1
  • returns true for released, otherwise false
• rumble(index, lowHz = 100[, hiHz, ms = 100]): rumbles the specific gamepad, if an actual hardware is binded to any key of the gamepad entity
  • index: the gamepad index, starts from 1

For the button parameter, 0, 1, 2, 3, 4, 5 are for Left, Right, Up, Down, A, B respectively. Seealso the “Gamepad” example under the “Primitives” category.

Keyboard

Functions

• key(code): gets whether the specific key is pressed
  • code: the key code on keyboard
  • returns true for pressed, otherwise false
• keyp(code): gets whether the specific key is released from pressing
  • code: the key code on keyboard
  • returns true for released, otherwise false

See keycodes for more readable presentation. Seealso the “Keyboard” example under the “Primitives” category.

Mouse

Functions

• mouse([index]): gets the current mouse (or touch) states
  • index: always 1 for the mouse, or the finger index with touch screens, starts from 1
  • returns x, y, b1, b2, b3, wheel for the mouse position and the LMB, RMB, MMB, wheel state respectively, x and y could be NaN if the mouse is outside the canvas, wheel can be negative, positive or zero

Seealso the “Mouse” example under the “Primitives” category.

Camera

Functions

• camera(x, y): sets the camera offset, affects all coordinate-based primitives
  • x: the x offset
  • y: the y offset
  • returns the previous camera offset x, y, or both nil for non-offset
• camera(): resets the camera offset to 0, 0
  • returns the previous camera offset x, y, or both nil for non-offset

Clip

Functions

• clip(x, y, w, h): sets the clip area
  • x: the x offset to clip
  • y: the y offset to clip
  • w: the clip width
  • h: the clip height
  • returns the previous clip area x, y, w, h, or all nil for non-clip
• clip(): resets the clip area to none
  • returns the previous clip area x, y, w, h, or all nil for non-clip

Blend

Functions

• blend(mode): sets the blend state with the specific mode
  • mode: the blend mode to set; refer to the blend modes of Canvas
• blend(): resets the blend state to alpha blend

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Physics

Due to space limitation in the page, read Physics for details.

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Invoking

• Invoke.call(func, ...): invokes a function in the host environment with the specific arguments, this feature is available with HTML build only
  • func: the function name to invoke
  • returns the return value of the invoked function in string

The Invoke.call(func, ...) invokes from Lua to the host environment (for HTML build only). It supports up to 16 parameters.

Bitty Engine supports callback from the host environment to Lua (for HTML build only). To use this feature, you need to define a function on the Lua side with the name call, and the function will be called when the host environment invokes the callback. The function accepts variadic arguments, and the arguments are passed as strings. In JavaScript, call Module.call(arg1, arg2, ..., arg16) to invoke the callback with up to 16 arguments.

To call from JavaScript to Lua, make a “ccall” to call1, call2, etc. i.e.

Module.ccall(
	'call2',
	'number',
	[ 'number', 'number' ],
	[ stringToNewUTF8('Hello'), stringToNewUTF8('World') ]
);

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Application

Static Functions

• Application.setOption(key, ...): sets option value of the specific key
  • key: the option key to set

Available options:

Key	Value	Note
“title”	String, title	Sets the title of the application window
“minimum_size”	Integers, width, height	Sets the minimum size of the application window
“maximum_size”	Integers, width, height	Sets the maximum size of the application window
“bordered”	Boolean, bordered	Sets whether the application window is bordered
“resizable”	Boolean, resizable	Sets whether the application window is resizable
“position”	Integers, x, y	Sets the position of the application window
“display_index”	Integers, index	Sets the index where the application window will be displayed on that device
“transparent_color”	Color	nil, color	Experimental, sets the transparent color key of the application window

The “transparent_color” option is an experimental feature, it supports Windows 10 and above. Note that it affects the whole application window.

• Application.setCursor(img[, x, y]): sets the mouse cursor
  • img: the specific Image to set, nil to reset
  • x: the spot x, with range of values from 0.0 to 1.0
  • y: the spot y, with range of values from 0.0 to 1.0
• Application.size(): gets the application window size
  • returns width, height
• Application.resize(w, h): resizes the application window; use canvas:resize(...) to resize canvas (the rendering area)
  • w: the expected width
  • h: the expected height
• Application.resize(size): resizes the application window
  • size: can be one in “fullscreen”, “windowed”
• Application.raise(): raises the application window

Canvas

Constants

• Canvas.BlendModeNone
• Canvas.BlendModeBlend
• Canvas.BlendModeAdd
• Canvas.BlendModeMod

• Canvas.BlendModeMul

• Canvas.BlendFactorZero
• Canvas.BlendFactorOne
• Canvas.BlendFactorSrcColor
• Canvas.BlendFactorOneMinusSrcColor
• Canvas.BlendFactorSrcAlpha
• Canvas.BlendFactorOneMinusSrcAlpha
• Canvas.BlendFactorDstColor
• Canvas.BlendFactorOneMinusDstColor
• Canvas.BlendFactorDstAlpha

• Canvas.BlendFactorOneMinusDstAlpha

• Canvas.BlendOperationAdd
• Canvas.BlendOperationSub
• Canvas.BlendOperationRevSub
• Canvas.BlendOperationMin
• Canvas.BlendOperationMax

Static Functions

• Canvas.compose(srcColFactor, dstColFactor, colOp, srcAlphaFactor, dstAlphaFactor, alphaOp): composes a blend value from the specific parameters
  • srcColFactor: the specific source color factor
  • dstColFactor: the specific destination color factor
  • colOp: the specific color operation
  • srcAlphaFactor: the specific source alpha factor
  • dstAlphaFactor: the specific destination alpha factor
  • alphaOp: the specific alpha operation
  • returns composed blend option

Static Variables

• Canvas.main: readonly, gets the main Canvas

Object Fields

• canvas.target: gets or sets the render target of the Canvas, nil for the main canvas
• canvas.autoCls: gets or sets whether to clear the canvas automatically, either true or false

Methods

• canvas:size(): gets the Canvas size
  • returns width, height
• canvas:resize(width, height): resizes the Canvas; use Application.resize(...) to resize the whole application
  • width: the specific width, 0 to adapt automatically
  • height: the specific height, 0 to adapt automatically
  • returns true for success, otherwise false

Project

Project accepts strategies, add a “strategies” field in “info.json” to enable specific options, eg.

{
  ...
  "strategies": [
    "batch_map"
  ]
}

Currently there is only one available strategy, change and try if it’s needed:

Strategy	Description	Note
“batch_map”	Hints to batch map for better rendering performance, but occupies more memory	Always on for HTML build
“linear_canvas”	Hints to set canvas filtering as linear
“anisotropic_canvas”	Hints to set canvas filtering as anisotropic

Constants

• Project.new(): constructs a project object

Static Variables

• Project.main: readonly, gets the main Project

Methods

• project:fullPath(): gets the full path of the Project
  • returns the full path of the Project, or nil
• project:getAssets([pattern]): gets all asset names in the Project
  • pattern: lookup pattern, supports wildcards
  • returns a list of asset entries, or nil
• project:load(path): loads this Project from the specific path; for user constructed Project only
  • path: the specific path to load from
  • returns true for success, otherwise false
• project:save(path): saves this Project to the specific path; for user constructed Project only
  • path: the specific path to save to
  • returns true for success, otherwise false
• project:exists(name): gets whether the specific asset exists in the Project
  • name: the asset name to look for
  • returns true for exists, otherwise false
• project:read(name): reads the content of the specific asset; this method can read all asset types except for code
  • name: the asset name to read
  • returns asset content as Bytes and its cursor will be at the end, or nil
• project:write(name, bytes, overwrite = true): writes the specific Bytes to the Project; for user constructed Project only
  • name: the asset name to write
  • bytes: the Bytes to write
  • overwrite: true to overwrite
  • returns true for success, otherwise false
• project:remove(name): removes the specific asset from the Project; for user constructed Project only
  • name: the asset name to remove
  • returns true for success, otherwise false
• project:strategies(): gets all effective strategies
  • returns a strategy list, in a list of string, could be empty or nil

Debug

This module is used for debugging purposes.

Static Functions

• Debug.setBreakpoint(src, ln, brk = true): sets or unsets a breakpoint programmingly
  • src: the source file
  • ln: the line number
  • brk: whether to set or unset
  • returns true for success, otherwise false
• Debug.clearBreakpoints([src]): clears breakpoints programmingly
  • src: the source file to clear; omit to clear all in project
  • returns true for success, otherwise false
• Debug.clearConsole(): clears the console output programmingly
• Debug.getTimeout(): gets the invoking timeout value
  • returns invoking timeout value
• Debug.setTimeout(val): sets the invoking timeout value to the specific seconds
  • val: the timeout value in seconds, 0 to disable timeout
• Debug.setTimeout(): resets the invoking timeout value to default (10 seconds)
• Debug.trace([message[, level]]): gets the stack trace
  • returns the traceback string

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Import and Export

Import

Click “Project”, “Import…” to browse and import some assets from a “.bit”, “.txt”, “*.zip” archive. This operation doesn’t overwrite conflictions in your editing project.

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Export

Click “Project”, “Export…” to select and export some assets to a “.bit”, “.txt”, “*.zip” archive.

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Building

Building for Desktop

Click “Project”, “Build”, then “Windows”/”MacOS”/”Linux” to make an executable for Windows/MacOS/Linux respectively with the current opened project.

It might require execution permission to launch an exported desktop binary, to apply that permission:

• For MacOS “xattr -cr bitty_stage.app”, then “chmod 777 bitty_stage.app/Contents/MacOS/bitty_stage”
• For Linux “chmod 777 x64/bitty”

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Building for HTML

Click “Project”, “Build”, then “HTML” to make an executable for browser with the current opened project. It requires a WebAssembly capable browser.

You can upload it to cloud or host it on your own server for others to play.

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