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// ---------------------------------------------------------------------
// gifImage (B/W)
// ---------------------------------------------------------------------
/**
*
* @param {number} width - image width
* @param {number} height - image height
* @returns {BlackWhiteGIFImage} Black and white GIF image
*/
export function gifImage (width, height) {
const _width = width
const _height = height
const _data = new Array(width * height).fill(1)
return {
setPixel: (x, y, pixel) => { _data[y * _width + x] = pixel },
write (out) {
// ---------------------------------
// GIF Signature
out.writeString('GIF87a')
// ---------------------------------
// Screen Descriptor
out.writeShort(_width)
out.writeShort(_height)
out.writeByte(0x80) // 2bit
out.writeByte(0)
out.writeByte(0)
// ---------------------------------
// Global Color Map
// black
out.writeByte(0x00)
out.writeByte(0x00)
out.writeByte(0x00)
// white
out.writeByte(0xff)
out.writeByte(0xff)
out.writeByte(0xff)
// ---------------------------------
// Image Descriptor
out.writeString(',')
out.writeShort(0)
out.writeShort(0)
out.writeShort(_width)
out.writeShort(_height)
out.writeByte(0)
// ---------------------------------
// Local Color Map
// ---------------------------------
// Raster Data
const lzwMinCodeSize = 2
const raster = getLZWRaster(_data, lzwMinCodeSize)
out.writeByte(lzwMinCodeSize)
let offset = 0
while (raster.length - offset > 255) {
out.writeByte(255)
out.writeBytes(raster, offset, 255)
offset += 255
}
out.writeByte(raster.length - offset)
out.writeBytes(raster, offset, raster.length - offset)
out.writeByte(0x00)
// ---------------------------------
// GIF Terminator
out.writeString(';')
},
}
};
/**
* @param {number[]} data - gif pixel data
* @param {number} lzwMinCodeSize - lzw minimum code size
*/
function getLZWRaster (data, lzwMinCodeSize) {
const clearCode = 1 << lzwMinCodeSize
const endCode = (1 << lzwMinCodeSize) + 1
let bitLength = lzwMinCodeSize + 1
// Setup LZWTable
const table = lzwTable()
for (let i = 0; i < clearCode; i += 1) {
table.add(String.fromCodePoint(i))
}
table.add(String.fromCodePoint(clearCode))
table.add(String.fromCodePoint(endCode))
const byteOut = new ByteArrayOutputStream()
const bitOut = bitOutputStream(byteOut)
// clear code
bitOut.write(clearCode, bitLength)
let dataIndex = 0
let s = String.fromCodePoint(data[dataIndex])
dataIndex += 1
while (dataIndex < data.length) {
const c = String.fromCodePoint(data[dataIndex])
dataIndex += 1
if (table.contains(s + c)) {
s = s + c
} else {
bitOut.write(table.indexOf(s), bitLength)
if (table.size < 0xfff) {
if (table.size === (1 << bitLength)) {
bitLength += 1
}
table.add(s + c)
}
s = c
}
}
bitOut.write(table.indexOf(s), bitLength)
// end code
bitOut.write(endCode, bitLength)
bitOut.flush()
return byteOut.toByteArray()
}
/** @param {import('../utils/bite-array-output-stream').ByteArrayOutputStream} out - output stream */
function bitOutputStream (out) {
const _out = out
let _bitLength = 0
let _bitBuffer = 0
return {
/**
* @param {number} data - numeric data
* @param {number} length - data bit length
*/
write (data, length) {
if ((data >>> length) !== 0) {
throw Error('length over')
}
while (_bitLength + length >= 8) {
_out.writeByte(0xff & ((data << _bitLength) | _bitBuffer))
length -= (8 - _bitLength)
data >>>= (8 - _bitLength)
_bitBuffer = 0
_bitLength = 0
}
_bitBuffer = (data << _bitLength) | _bitBuffer
_bitLength = _bitLength + length
},
flush: () => { _bitLength > 0 && _out.writeByte(_bitBuffer) },
}
}
/**
* @returns {LzwTable} created LZW table
*/
function lzwTable () {
/** @type {Record<string,number>} */
const _map = {}
let _size = 0
const _this = /** @type {LzwTable} */ ({
add: (key) => {
if (_this.contains(key)) {
throw Error(`dup key: ${key}`)
}
_map[key] = _size
_size += 1
},
get size () { return _size },
indexOf: (key) => _map[key],
contains: (key) => _map[key] != null,
})
return _this
}
/**
* @typedef {object} LzwTable
* @property {(key: string) => void} add - add key to table
* @property {number} size - table size
* @property {(key: string) => number} indexOf - get index of key
* @property {(key: string) => boolean} contains - check if key is already in table
*/
/**
* @typedef {object} BlackWhiteGIFImage
* Black and white GIF image
* @property {(x: number, y: number, pixel: number) => void} setPixel - set pixel in position
* @property {(out: import('../utils/bite-array-output-stream').ByteArrayOutputStream) => void} write - write to output stream
*/
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