const { themes, buildColorTable, SELECTION_FG, SELECTION_BG } = require('./themes') // Some non-bold Fraktur symbols are outside the contiguous block const frakturExceptions = { 'C': '\u212d', 'H': '\u210c', 'I': '\u2111', 'R': '\u211c', 'Z': '\u2128' } // TODO do not repeat - this is also defined in screen_parser ... /* eslint-disable no-multi-spaces */ const ATTR_FG = (1 << 0) // 1 if not using default background color (ignore cell bg) - color extension bit const ATTR_BG = (1 << 1) // 1 if not using default foreground color (ignore cell fg) - color extension bit const ATTR_BOLD = (1 << 2) // Bold font const ATTR_UNDERLINE = (1 << 3) // Underline decoration const ATTR_INVERSE = (1 << 4) // Invert colors - this is useful so we can clear then with SGR manipulation commands const ATTR_BLINK = (1 << 5) // Blinking const ATTR_ITALIC = (1 << 6) // Italic font const ATTR_STRIKE = (1 << 7) // Strike-through decoration const ATTR_OVERLINE = (1 << 8) // Over-line decoration const ATTR_FAINT = (1 << 9) // Faint foreground color (reduced alpha) const ATTR_FRAKTUR = (1 << 10) // Fraktur font (unicode substitution) /* eslint-enable no-multi-spaces */ module.exports = class ScreenRenderer { constructor (screen) { this.screen = screen this.ctx = screen.ctx this._palette = null // colors 0-15 this.defaultBgNum = 0 this.defaultFgNum = 7 // 256color lookup table // should not be used to look up 0-15 (will return transparent) this.colorTable256 = buildColorTable() this.resetDrawn() this.blinkStyleOn = false this.blinkInterval = null this.cursorBlinkOn = false this.cursorBlinkInterval = null // start blink timers this.resetBlink() this.resetCursorBlink() } resetDrawn () { // used to determine if a cell should be redrawn; storing the current state // as it is on screen if (this.screen.window && this.screen.window.debug) { console.log('Resetting drawn screen') } this.drawnScreen = [] this.drawnScreenFG = [] this.drawnScreenBG = [] this.drawnScreenAttrs = [] this.drawnCursor = [-1, -1, ''] } /** * The color palette. Should define 16 colors in an array. * @type {string[]} */ get palette () { return this._palette || themes[0] } /** @type {string[]} */ set palette (palette) { if (this._palette !== palette) { this._palette = palette this.resetDrawn() this.scheduleDraw('palette') } } loadTheme (i) { if (i in themes) this.palette = themes[i] } setDefaultColors (fg, bg) { if (fg !== this.defaultFgNum || bg !== this.defaultBgNum) { this.resetDrawn() this.defaultFgNum = fg this.defaultBgNum = bg this.scheduleDraw('default-colors') } } /** * Schedule a draw in the next millisecond * @param {string} why - the reason why the draw occured (for debugging) * @param {number} [aggregateTime] - time to wait for more scheduleDraw calls * to occur. 1 ms by default. */ scheduleDraw (why, aggregateTime = 1) { clearTimeout(this._scheduledDraw) this._scheduledDraw = setTimeout(() => this.draw(why), aggregateTime) } /** * Returns the specified color. If `i` is in the palette, it will return the * palette color. If `i` is between 16 and 255, it will return the 256color * value. If `i` is larger than 255, it will return an RGB color value. If `i` * is -1 (foreground) or -2 (background), it will return the selection colors. * @param {number} i - the color * @returns {string} the CSS color */ getColor (i) { // return palette color if it exists if (i < 16 && i in this.palette) return this.palette[i] // -1 for selection foreground, -2 for selection background if (i === -1) return SELECTION_FG if (i === -2) return SELECTION_BG // 256 color if (i > 15 && i < 256) return this.colorTable256[i] // true color, encoded as (hex) + 256 (such that #000 == 256) if (i > 255) { i -= 256 let red = (i >> 16) & 0xFF let green = (i >> 8) & 0xFF let blue = i & 0xFF return `rgb(${red}, ${green}, ${blue})` } // return error color return (Date.now() / 1000) % 2 === 0 ? '#f0f' : '#0f0' } /** * Resets the cursor blink to on and restarts the timer */ resetCursorBlink () { this.cursorBlinkOn = true clearInterval(this.cursorBlinkInterval) this.cursorBlinkInterval = setInterval(() => { this.cursorBlinkOn = this.screen.cursor.blinking ? !this.cursorBlinkOn : true if (this.screen.cursor.blinking) this.scheduleDraw('cursor-blink') }, 500) } /** * Resets the blink style to on and restarts the timer */ resetBlink () { this.blinkStyleOn = true clearInterval(this.blinkInterval) let intervals = 0 this.blinkInterval = setInterval(() => { if (this.screen.blinkingCellCount <= 0) return intervals++ if (intervals >= 4 && this.blinkStyleOn) { this.blinkStyleOn = false intervals = 0 this.scheduleDraw('blink-style') } else if (intervals >= 1 && !this.blinkStyleOn) { this.blinkStyleOn = true intervals = 0 this.scheduleDraw('blink-style') } }, 200) } /** * Draws a cell's background with the given parameters. * @param {Object} options * @param {number} options.x - x in cells * @param {number} options.y - y in cells * @param {number} options.cellWidth - cell width in pixels * @param {number} options.cellHeight - cell height in pixels * @param {number} options.bg - the background color */ drawBackground ({ x, y, cellWidth, cellHeight, bg }) { const ctx = this.ctx const { width, height } = this.screen.window const padding = Math.round(this.screen._padding) ctx.fillStyle = this.getColor(bg) let screenX = x * cellWidth + padding let screenY = y * cellHeight + padding let isBorderCell = x === 0 || y === 0 || x === width - 1 || y === height - 1 if (isBorderCell) { let left = screenX let top = screenY let right = screenX + cellWidth let bottom = screenY + cellHeight if (x === 0) left -= padding else if (x === width - 1) right += padding if (y === 0) top -= padding else if (y === height - 1) bottom += padding ctx.clearRect(left, top, right - left, bottom - top) ctx.fillRect(left, top, right - left, bottom - top) } else { ctx.clearRect(screenX, screenY, cellWidth, cellHeight) ctx.fillRect(screenX, screenY, cellWidth, cellHeight) } } /** * Draws a cell's character with the given parameters. Won't do anything if * text is an empty string. * @param {Object} options * @param {number} options.x - x in cells * @param {number} options.y - y in cells * @param {Object} options.charSize - the character size, an object with * `width` and `height` in pixels * @param {number} options.cellWidth - cell width in pixels * @param {number} options.cellHeight - cell height in pixels * @param {string} options.text - the cell content * @param {number} options.fg - the foreground color * @param {number} options.attrs - the cell's attributes */ drawCharacter ({ x, y, charSize, cellWidth, cellHeight, text, fg, attrs }) { if (!text) return const ctx = this.ctx const padding = Math.round(this.screen._padding) let underline = false let strike = false let overline = false if (attrs & ATTR_FAINT) ctx.globalAlpha = 0.5 if (attrs & ATTR_UNDERLINE) underline = true if (attrs & ATTR_FRAKTUR) text = ScreenRenderer.alphaToFraktur(text) if (attrs & ATTR_STRIKE) strike = true if (attrs & ATTR_OVERLINE) overline = true ctx.fillStyle = this.getColor(fg) let screenX = x * cellWidth + padding let screenY = y * cellHeight + padding let codePoint = text.codePointAt(0) if (codePoint >= 0x2580 && codePoint <= 0x259F) { // block elements ctx.beginPath() const left = screenX const top = screenY const cw = cellWidth const ch = cellHeight const c2w = cellWidth / 2 const c2h = cellHeight / 2 // http://www.fileformat.info/info/unicode/block/block_elements/utf8test.htm // 0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0A 0x0B 0x0C 0x0D 0x0E 0x0F // 0x2580 ▀ ▁ ▂ ▃ ▄ ▅ ▆ ▇ █ ▉ ▊ ▋ ▌ ▍ ▎ ▏ // 0x2590 ▐ ░ ▒ ▓ ▔ ▕ ▖ ▗ ▘ ▙ ▚ ▛ ▜ ▝ ▞ ▟ if (codePoint === 0x2580) { // upper half block >▀< ctx.rect(left, top, cw, c2h) } else if (codePoint <= 0x2588) { // lower n eighth block (increasing) >▁< to >█< let offset = (1 - (codePoint - 0x2580) / 8) * ch ctx.rect(left, top + offset, cw, ch - offset) } else if (codePoint <= 0x258F) { // left n eighth block (decreasing) >▉< to >▏< let offset = (codePoint - 0x2588) / 8 * cw ctx.rect(left, top, cw - offset, ch) } else if (codePoint === 0x2590) { // right half block >▐< ctx.rect(left + c2w, top, c2w, ch) } else if (codePoint <= 0x2593) { // shading >░< >▒< >▓< // dot spacing by dividing cell size by a constant. This could be // reworked to always return a whole number, but that would require // prime factorization, and doing that without a loop would let you // take over the world, which is not within the scope of this project. let dotSpacingX, dotSpacingY, dotSize if (codePoint === 0x2591) { dotSpacingX = cw / 4 dotSpacingY = ch / 10 dotSize = 1 } else if (codePoint === 0x2592) { dotSpacingX = cw / 6 dotSpacingY = cw / 10 dotSize = 1 } else if (codePoint === 0x2593) { dotSpacingX = cw / 4 dotSpacingY = cw / 7 dotSize = 2 } let alignRight = false for (let dy = 0; dy < ch; dy += dotSpacingY) { for (let dx = 0; dx < cw; dx += dotSpacingX) { // prevent overflow let dotSizeY = Math.min(dotSize, ch - dy) ctx.rect(left + (alignRight ? cw - dx - dotSize : dx), top + dy, dotSize, dotSizeY) } alignRight = !alignRight } } else if (codePoint === 0x2594) { // upper one eighth block >▔< ctx.rect(left, top, cw, ch / 8) } else if (codePoint === 0x2595) { // right one eighth block >▕< ctx.rect(left + (7 / 8) * cw, top, cw / 8, ch) } else if (codePoint === 0x2596) { // left bottom quadrant >▖< ctx.rect(left, top + c2h, c2w, c2h) } else if (codePoint === 0x2597) { // right bottom quadrant >▗< ctx.rect(left + c2w, top + c2h, c2w, c2h) } else if (codePoint === 0x2598) { // left top quadrant >▘< ctx.rect(left, top, c2w, c2h) } else if (codePoint === 0x2599) { // left chair >▙< ctx.rect(left, top, c2w, ch) ctx.rect(left + c2w, top + c2h, c2w, c2h) } else if (codePoint === 0x259A) { // quadrants lt rb >▚< ctx.rect(left, top, c2w, c2h) ctx.rect(left + c2w, top + c2h, c2w, c2h) } else if (codePoint === 0x259B) { // left chair upside down >▛< ctx.rect(left, top, c2w, ch) ctx.rect(left + c2w, top, c2w, c2h) } else if (codePoint === 0x259C) { // right chair upside down >▜< ctx.rect(left, top, cw, c2h) ctx.rect(left + c2w, top + c2h, c2w, c2h) } else if (codePoint === 0x259D) { // right top quadrant >▝< ctx.rect(left + c2w, top, c2w, c2h) } else if (codePoint === 0x259E) { // quadrants lb rt >▞< ctx.rect(left, top + c2h, c2w, c2h) ctx.rect(left + c2w, top, c2w, c2h) } else if (codePoint === 0x259F) { // right chair upside down >▟< ctx.rect(left, top + c2h, c2w, c2h) ctx.rect(left + c2w, top, c2w, ch) } ctx.fill() } else if (codePoint >= 0xE0B0 && codePoint <= 0xE0B3) { // powerline symbols, except branch, line, and lock. Basically, just the triangles ctx.beginPath() if (codePoint === 0xE0B0 || codePoint === 0xE0B1) { // right-pointing triangle ctx.moveTo(screenX, screenY) ctx.lineTo(screenX + cellWidth, screenY + cellHeight / 2) ctx.lineTo(screenX, screenY + cellHeight) } else if (codePoint === 0xE0B2 || codePoint === 0xE0B3) { // left-pointing triangle ctx.moveTo(screenX + cellWidth, screenY) ctx.lineTo(screenX, screenY + cellHeight / 2) ctx.lineTo(screenX + cellWidth, screenY + cellHeight) } if (codePoint % 2 === 0) { // triangle ctx.fill() } else { // chevron ctx.strokeStyle = ctx.fillStyle ctx.stroke() } } else { // Draw other characters using the text renderer ctx.fillText(text, screenX + 0.5 * cellWidth, screenY + 0.5 * cellHeight) } // -- line drawing - a reference for a possible future rect/line implementation --- // http://www.fileformat.info/info/unicode/block/box_drawing/utf8test.htm // 0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0A 0x0B 0x0C 0x0D 0x0E 0x0F // 0x2500 ─ ━ │ ┃ ┄ ┅ ┆ ┇ ┈ ┉ ┊ ┋ ┌ ┍ ┎ ┏ // 0x2510 ┐ ┑ ┒ ┓ └ ┕ ┖ ┗ ┘ ┙ ┚ ┛ ├ ┝ ┞ ┟ // 0x2520 ┠ ┡ ┢ ┣ ┤ ┥ ┦ ┧ ┨ ┩ ┪ ┫ ┬ ┭ ┮ ┯ // 0x2530 ┰ ┱ ┲ ┳ ┴ ┵ ┶ ┷ ┸ ┹ ┺ ┻ ┼ ┽ ┾ ┿ // 0x2540 ╀ ╁ ╂ ╃ ╄ ╅ ╆ ╇ ╈ ╉ ╊ ╋ ╌ ╍ ╎ ╏ // 0x2550 ═ ║ ╒ ╓ ╔ ╕ ╖ ╗ ╘ ╙ ╚ ╛ ╜ ╝ ╞ ╟ // 0x2560 ╠ ╡ ╢ ╣ ╤ ╥ ╦ ╧ ╨ ╩ ╪ ╫ ╬ ╭ ╮ ╯ // 0x2570 ╰ ╱ ╲ ╳ ╴ ╵ ╶ ╷ ╸ ╹ ╺ ╻ ╼ ╽ ╾ ╿ if (underline || strike || overline) { ctx.strokeStyle = this.getColor(fg) ctx.lineWidth = 1 ctx.lineCap = 'round' ctx.beginPath() if (underline) { let lineY = Math.round(screenY + charSize.height) + 0.5 ctx.moveTo(screenX, lineY) ctx.lineTo(screenX + cellWidth, lineY) } if (strike) { let lineY = Math.round(screenY + 0.5 * cellHeight) + 0.5 ctx.moveTo(screenX, lineY) ctx.lineTo(screenX + cellWidth, lineY) } if (overline) { let lineY = Math.round(screenY) + 0.5 ctx.moveTo(screenX, lineY) ctx.lineTo(screenX + cellWidth, lineY) } ctx.stroke() } ctx.globalAlpha = 1 } /** * Returns all adjacent cell indices given a radius. * @param {number} cell - the center cell index * @param {number} [radius] - the radius. 1 by default * @returns {number[]} an array of cell indices */ getAdjacentCells (cell, radius = 1) { const { width, height } = this.screen.window const screenLength = width * height let cells = [] for (let x = -radius; x <= radius; x++) { for (let y = -radius; y <= radius; y++) { if (x === 0 && y === 0) continue cells.push(cell + x + y * width) } } return cells.filter(cell => cell >= 0 && cell < screenLength) } /** * Updates the screen. * @param {string} why - the draw reason (for debugging) */ draw (why) { const ctx = this.ctx const { width, height, devicePixelRatio, statusScreen } = this.screen.window if (statusScreen) { // draw status screen instead this.drawStatus(statusScreen) this.startDrawLoop() return } else this.stopDrawLoop() const charSize = this.screen.getCharSize() const { width: cellWidth, height: cellHeight } = this.screen.getCellSize() const screenLength = width * height ctx.setTransform(devicePixelRatio, 0, 0, devicePixelRatio, 0, 0) if (this.screen.window.debug && this.screen._debug) this.screen._debug.drawStart(why) ctx.font = this.screen.getFont() ctx.textAlign = 'center' ctx.textBaseline = 'middle' // bits in the attr value that affect the font const FONT_MASK = ATTR_BOLD | ATTR_ITALIC // Map of (attrs & FONT_MASK) -> Array of cell indices let fontGroups = new Map() // Map of (cell index) -> boolean, whether or not a cell has updated let updateMap = new Map() for (let cell = 0; cell < screenLength; cell++) { let x = cell % width let y = Math.floor(cell / width) let isCursor = this.cursorBlinkOn && this.screen.cursor.x === x && this.screen.cursor.y === y && this.screen.cursor.visible let wasCursor = x === this.drawnCursor[0] && y === this.drawnCursor[1] let inSelection = this.screen.isInSelection(x, y) let text = this.screen.screen[cell] let fg = this.screen.screenFG[cell] | 0 let bg = this.screen.screenBG[cell] | 0 let attrs = this.screen.screenAttrs[cell] | 0 if (!(attrs & ATTR_FG)) fg = this.defaultFgNum if (!(attrs & ATTR_BG)) bg = this.defaultBgNum if (attrs & ATTR_INVERSE) [fg, bg] = [bg, fg] // swap - reversed character colors if (this.screen.reverseVideo) [fg, bg] = [bg, fg] // swap - reversed all screen if (attrs & ATTR_BLINK && !this.blinkStyleOn) { // blinking is enabled and blink style is off // set text to nothing so drawCharacter doesn't draw anything text = '' } if (inSelection) { fg = -1 bg = -2 } let didUpdate = text !== this.drawnScreen[cell] || // text updated fg !== this.drawnScreenFG[cell] || // foreground updated, and this cell has text bg !== this.drawnScreenBG[cell] || // background updated attrs !== this.drawnScreenAttrs[cell] || // attributes updated isCursor !== wasCursor || // cursor blink/position updated (isCursor && this.screen.cursor.style !== this.drawnCursor[2]) || // cursor style updated (isCursor && this.screen.cursor.hanging !== this.drawnCursor[3]) // cursor hanging updated let font = attrs & FONT_MASK if (!fontGroups.has(font)) fontGroups.set(font, []) fontGroups.get(font).push({ cell, x, y, text, fg, bg, attrs, isCursor, inSelection }) updateMap.set(cell, didUpdate) } // Map of (cell index) -> boolean, whether or not a cell should be redrawn const redrawMap = new Map() let isTextWide = text => text !== ' ' && ctx.measureText(text).width >= (cellWidth + 0.05) // decide for each cell if it should be redrawn let updateRedrawMapAt = cell => { let shouldUpdate = updateMap.get(cell) || redrawMap.get(cell) || false // TODO: fonts (necessary?) let text = this.screen.screen[cell] let isWideCell = isTextWide(text) let checkRadius = isWideCell ? 2 : 1 if (!shouldUpdate) { // check adjacent cells let adjacentDidUpdate = false for (let adjacentCell of this.getAdjacentCells(cell, checkRadius)) { // update this cell if: // - the adjacent cell updated (For now, this'll always be true because characters can be slightly larger than they say they are) // - the adjacent cell updated and this cell or the adjacent cell is wide if (updateMap.get(adjacentCell) && (this.screen.window.graphics < 2 || isWideCell || isTextWide(this.screen.screen[adjacentCell]))) { adjacentDidUpdate = true break } } if (adjacentDidUpdate) shouldUpdate = true } redrawMap.set(cell, shouldUpdate) } for (let cell of updateMap.keys()) updateRedrawMapAt(cell) // mask to redrawing regions only if (this.screen.window.graphics >= 1) { let debug = this.screen.window.debug && this.screen._debug let padding = Math.round(this.screen._padding) ctx.save() ctx.beginPath() for (let y = 0; y < height; y++) { let regionStart = null for (let x = 0; x < width; x++) { let cell = y * width + x let redrawing = redrawMap.get(cell) if (redrawing && regionStart === null) regionStart = x if (!redrawing && regionStart !== null) { ctx.rect(padding + regionStart * cellWidth, padding + y * cellHeight, (x - regionStart) * cellWidth, cellHeight) if (debug) this.screen._debug.clipRect(regionStart * cellWidth, y * cellHeight, (x - regionStart) * cellWidth, cellHeight) regionStart = null } } if (regionStart !== null) { ctx.rect(padding + regionStart * cellWidth, padding + y * cellHeight, (width - regionStart) * cellWidth, cellHeight) if (debug) this.screen._debug.clipRect(regionStart * cellWidth, y * cellHeight, (width - regionStart) * cellWidth, cellHeight) } } ctx.clip() } // pass 1: backgrounds for (let font of fontGroups.keys()) { for (let data of fontGroups.get(font)) { let { cell, x, y, text, bg } = data if (redrawMap.get(cell)) { this.drawBackground({ x, y, cellWidth, cellHeight, bg }) if (this.screen.window.debug && this.screen._debug) { // set cell flags let flags = (+redrawMap.get(cell)) flags |= (+updateMap.get(cell)) << 1 flags |= (+isTextWide(text)) << 2 this.screen._debug.setCell(cell, flags) } } } } // reset drawn cursor this.drawnCursor = [-1, -1, -1] // pass 2: characters for (let font of fontGroups.keys()) { // set font once because in Firefox, this is a really slow action for some // reason let modifiers = {} if (font & ATTR_BOLD) modifiers.weight = 'bold' if (font & ATTR_ITALIC) modifiers.style = 'italic' ctx.font = this.screen.getFont(modifiers) for (let data of fontGroups.get(font)) { let { cell, x, y, text, fg, bg, attrs, isCursor, inSelection } = data if (redrawMap.get(cell)) { this.drawCharacter({ x, y, charSize, cellWidth, cellHeight, text, fg, attrs }) this.drawnScreen[cell] = text this.drawnScreenFG[cell] = fg this.drawnScreenBG[cell] = bg this.drawnScreenAttrs[cell] = attrs if (isCursor) this.drawnCursor = [x, y, this.screen.cursor.style, this.screen.cursor.hanging] // draw cursor if (isCursor && !inSelection) { ctx.save() ctx.beginPath() let cursorX = x let cursorY = y if (this.screen.cursor.hanging) { // draw hanging cursor in the margin cursorX += 1 } let screenX = cursorX * cellWidth + this.screen._padding let screenY = cursorY * cellHeight + this.screen._padding if (this.screen.cursor.style === 'block') { // block ctx.rect(screenX, screenY, cellWidth, cellHeight) } else if (this.screen.cursor.style === 'bar') { // vertical bar let barWidth = 2 ctx.rect(screenX, screenY, barWidth, cellHeight) } else if (this.screen.cursor.style === 'line') { // underline let lineHeight = 2 ctx.rect(screenX, screenY + charSize.height, cellWidth, lineHeight) } ctx.clip() // swap foreground/background ;[fg, bg] = [bg, fg] // HACK: ensure cursor is visible if (fg === bg) bg = fg === 0 ? 7 : 0 this.drawBackground({ x: cursorX, y: cursorY, cellWidth, cellHeight, bg }) this.drawCharacter({ x: cursorX, y: cursorY, charSize, cellWidth, cellHeight, text, fg, attrs }) ctx.restore() } } } } if (this.screen.window.graphics >= 1) ctx.restore() if (this.screen.window.debug && this.screen._debug) this.screen._debug.drawEnd() this.screen.emit('draw', why) } drawStatus (statusScreen) { const ctx = this.ctx const { fontFamily, width, height, devicePixelRatio } = this.screen.window // reset drawnScreen to force redraw when statusScreen is disabled this.drawnScreen = [] const cellSize = this.screen.getCellSize() const screenWidth = width * cellSize.width + 2 * this.screen._padding const screenHeight = height * cellSize.height + 2 * this.screen._padding ctx.setTransform(devicePixelRatio, 0, 0, devicePixelRatio, 0, 0) ctx.fillStyle = this.getColor(this.defaultBgNum) ctx.fillRect(0, 0, screenWidth, screenHeight) ctx.font = `24px ${fontFamily}` ctx.fillStyle = this.getColor(this.defaultFgNum) ctx.textAlign = 'center' ctx.textBaseline = 'middle' ctx.fillText(statusScreen.title || '', screenWidth / 2, screenHeight / 2 - 50) if (statusScreen.loading) { // show loading spinner ctx.save() ctx.translate(screenWidth / 2, screenHeight / 2 + 20) ctx.strokeStyle = this.getColor(this.defaultFgNum) ctx.lineWidth = 5 ctx.lineCap = 'round' let t = Date.now() / 1000 for (let i = 0; i < 12; i++) { ctx.rotate(Math.PI / 6) let offset = ((t * 12) - i) % 12 ctx.globalAlpha = Math.max(0.2, 1 - offset / 3) ctx.beginPath() ctx.moveTo(0, 15) ctx.lineTo(0, 30) ctx.stroke() } ctx.restore() } } startDrawLoop () { if (this._drawTimerThread) return let threadID = Math.random().toString(36) this._drawTimerThread = threadID this.drawTimerLoop(threadID) } stopDrawLoop () { this._drawTimerThread = null } drawTimerLoop (threadID) { if (!threadID || threadID !== this._drawTimerThread) return window.requestAnimationFrame(() => this.drawTimerLoop(threadID)) this.draw('draw-loop') } /** * Converts an alphabetic character to its fraktur variant. * @param {string} character - the character * @returns {string} the converted character */ static alphaToFraktur (character) { if (character >= 'a' && character <= 'z') { character = String.fromCodePoint(0x1d51e - 0x61 + character.charCodeAt(0)) } else if (character >= 'A' && character <= 'Z') { character = frakturExceptions[character] || String.fromCodePoint(0x1d504 - 0x41 + character.charCodeAt(0)) } return character } }