Press n or j to go to the next uncovered block, b, p or k for the previous block.
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import { BbcDefaultPalette as BbcDefaultCollook } from "./bbc-palette.js";
import { makeFast32 } from "./binary.js";
import {
TeletextBlack,
TeletextCellCapacity,
TeletextDoubled,
TeletextOffsetShift,
TeletextPaletteMask,
} from "./video-drain.js";
// A line that ends logs at most 256 entries, one per character clock; this bounds the log when no DISPTMG
// falling edge ends a line, as while R8 disables the display. Every entry can be a cell to paint.
const LogCapacity = TeletextCellCapacity;
const DataBits = 0x7f;
const ClockedEntry = 0x80;
const ShownEntry = 0x100;
const DoubleHeight = 13;
export const PipelineLength = 4;
export const PipelineLag = PipelineLength - 1;
// What `clockCharacter` reads or changes besides the pipeline and the cell it latches.
class LineState {
constructor(glyphs) {
this.wasDbl = false;
this.reset(glyphs);
}
// A DISPTMG falling edge; `setDISPTMG` clears `wasDbl` itself, once the row end has read it.
reset(glyphs) {
this.col = 7;
this.bg = 0;
this.holdChar = false;
this.heldChar = 0x20;
this.nextGlyphs = this.heldGlyphs = glyphs;
this.flash = false;
this.sep = false;
this.gfx = false;
this.conceal = false;
this.dbl = false;
}
}
export class Teletext {
constructor() {
this.prevCol = 0;
this.oldDbl = this.secondHalfOfDouble = false;
this.flashTime = 0;
this.cellGlyphIndex = 0;
this.cellFlash = false;
this.cellConceal = false;
this.cellPalette = 0;
this.dataQueue = new Uint8Array(PipelineLength);
this.scanlineCounter = 0;
this.levelDEW = false;
this.levelDISPTMG = false;
this.levelRA0 = false;
// Bytes on the chip's input that it has not run yet, bit 7 set where it was clocked, and the cells to paint
// where the clocked byte is shown.
this.log = new Int32Array(LogCapacity);
this.logLength = 0;
this.logShows = false;
this.output = null;
// The cell `clockCharacter` latches outlives the line reset, and a snapshot saves part of it. So the last
// line skipped by `skipLine` is kept with the state it started from, until a clocked byte replaces
// that cell.
this.skippedLog = new Int32Array(LogCapacity);
this.skippedLogLength = 0;
this.skippedQueue = new Uint8Array(PipelineLength);
this.normalGlyphs = makeFast32(new Uint32Array(96 * 20));
this.graphicsGlyphs = makeFast32(new Uint32Array(96 * 20));
this.separatedGlyphs = makeFast32(new Uint32Array(96 * 20));
this.colour = makeFast32(new Uint32Array(256));
this.curGlyphs = this.normalGlyphs;
this.line = new LineState(this.normalGlyphs);
this.skippedLine = new LineState(this.normalGlyphs);
this.init();
}
init() {
const charData = makeChars();
// Build palette from BBC default colours.
this.rebuildColours(BbcDefaultCollook);
function getLoResGlyphRow(c, row) {
if (row < 0 || row >= 20) {
return 0;
} else {
let index = c * 60 + (row >>> 1) * 6;
let result = 0;
for (let x = 0; x < 6; ++x) {
result |= (charData[index++] * 3) << (x * 2);
}
return result;
}
}
function combineRows(a, b) {
return a | ((a >>> 1) & b & ~(b >>> 1)) | ((a << 1) & b & ~(b << 1));
}
function makeHiResGlyphs(dest, graphicsGlyphs) {
let index = 0;
for (let c = 0; c < 96; ++c) {
for (let row = 0; row < 20; ++row) {
let data;
if (!graphicsGlyphs || !!(c & 32)) {
data = combineRows(getLoResGlyphRow(c, row), getLoResGlyphRow(c, row + (row & 1 ? 1 : -1)));
} else {
data = getLoResGlyphRow(c, row);
}
dest[index++] =
(data & 0x1) * 0x7 +
(data & 0x2) * 0x14 +
(data & 0x4) * 0x34 +
(data & 0x8) * 0xe0 +
(data & 0x10) * 0x280 +
(data & 0x20) * 0x680 +
(data & 0x40) * 0x1c00 +
(data & 0x80) * 0x5000 +
(data & 0x100) * 0xd000 +
(data & 0x200) * 0x38000 +
(data & 0x400) * 0xa0000 +
(data & 0x800) * 0x1a0000;
}
}
}
makeHiResGlyphs(this.normalGlyphs, false);
function setGraphicsBlock(c, x, y, w, h, sep, n) {
for (let yy = 0; yy < h; ++yy) {
for (let xx = 0; xx < w; ++xx) {
charData[c * 60 + (y + yy) * 6 + (x + xx)] = sep && (xx === 0 || yy === h - 1) ? 0 : n;
}
}
}
// Build graphics character set
for (let c = 0; c < 96; ++c) {
if (!(c & 32)) {
setGraphicsBlock(c, 0, 0, 3, 3, false, !!(c & 1));
setGraphicsBlock(c, 3, 0, 3, 3, false, !!(c & 2));
setGraphicsBlock(c, 0, 3, 3, 4, false, !!(c & 4));
setGraphicsBlock(c, 3, 3, 3, 4, false, !!(c & 8));
setGraphicsBlock(c, 0, 7, 3, 3, false, !!(c & 16));
setGraphicsBlock(c, 3, 7, 3, 3, false, !!(c & 64));
}
}
makeHiResGlyphs(this.graphicsGlyphs, true);
// Build separated graphics character set
for (let c = 0; c < 96; ++c) {
if (!(c & 32)) {
setGraphicsBlock(c, 0, 0, 3, 3, true, !!(c & 1));
setGraphicsBlock(c, 3, 0, 3, 3, true, !!(c & 2));
setGraphicsBlock(c, 0, 3, 3, 4, true, !!(c & 4));
setGraphicsBlock(c, 3, 3, 3, 4, true, !!(c & 8));
setGraphicsBlock(c, 0, 7, 3, 3, true, !!(c & 16));
setGraphicsBlock(c, 3, 7, 3, 3, true, !!(c & 64));
}
}
makeHiResGlyphs(this.separatedGlyphs, true);
}
/**
* Rebuild the 256-entry colour lookup from a 16-entry ABGR collook palette.
* Each entry encodes: bits 7-5 = background colour index (0-7),
* bits 4-2 = foreground colour index (0-7), bits 1-0 = blend weight.
* Reference: b-em mode7_gen_nula_lookup().
* @param {Uint32Array} collook - 16-entry palette in ABGR format (0xffBBGGRR).
*/
rebuildColours(collook) {
const gamma = 1.0 / 2.2;
for (let i = 0; i < 256; ++i) {
const weight = (i & 3) / 3.0;
const fgIndex = (i >> 2) & 7;
const bgIndex = (i >> 5) & 7;
const fgColour = collook[fgIndex];
const bgColour = collook[bgIndex];
const fgR = (fgColour & 0xff) / 255;
const fgG = ((fgColour >> 8) & 0xff) / 255;
const fgB = ((fgColour >> 16) & 0xff) / 255;
const bgR = (bgColour & 0xff) / 255;
const bgG = ((bgColour >> 8) & 0xff) / 255;
const bgB = ((bgColour >> 16) & 0xff) / 255;
const blendedR = Math.pow(fgR * weight + bgR * (1.0 - weight), gamma) * 240;
const blendedG = Math.pow(fgG * weight + bgG * (1.0 - weight), gamma) * 240;
const blendedB = Math.pow(fgB * weight + bgB * (1.0 - weight), gamma) * 240;
this.colour[i] = blendedR | 0 | ((blendedG | 0) << 8) | ((blendedB | 0) << 16) | (0xff << 24);
}
}
snapshotState() {
this.catchUp();
// Encode glyph table references as strings for serialization
let nextGlyphsName, curGlyphsName, heldGlyphsName;
for (const [name, table] of [
["normal", this.normalGlyphs],
["graphics", this.graphicsGlyphs],
["separated", this.separatedGlyphs],
]) {
if (this.line.nextGlyphs === table) nextGlyphsName = name;
if (this.curGlyphs === table) curGlyphsName = name;
if (this.line.heldGlyphs === table) heldGlyphsName = name;
}
return {
prevCol: this.prevCol,
col: this.line.col,
bg: this.line.bg,
sep: this.line.sep,
dbl: this.line.dbl,
oldDbl: this.oldDbl,
secondHalfOfDouble: this.secondHalfOfDouble,
wasDbl: this.line.wasDbl,
gfx: this.line.gfx,
conceal: this.line.conceal,
flash: this.line.flash,
flashTime: this.flashTime,
heldChar: this.line.heldChar,
holdChar: this.line.holdChar,
dataQueue: [...this.dataQueue],
scanlineCounter: this.scanlineCounter,
levelDEW: this.levelDEW,
levelDISPTMG: this.levelDISPTMG,
levelRA0: this.levelRA0,
nextGlyphs: nextGlyphsName,
curGlyphs: curGlyphsName,
heldGlyphs: heldGlyphsName,
};
}
restoreState(state) {
this.prevCol = state.prevCol;
this.line.col = state.col;
this.line.bg = state.bg;
this.line.sep = state.sep;
this.line.dbl = state.dbl;
this.oldDbl = state.oldDbl;
this.secondHalfOfDouble = state.secondHalfOfDouble;
this.line.wasDbl = state.wasDbl;
this.line.gfx = state.gfx;
this.line.conceal = state.conceal ?? false;
this.line.flash = state.flash;
this.flashTime = state.flashTime;
this.line.heldChar = state.heldChar;
this.line.holdChar = state.holdChar;
this.dataQueue.set(state.dataQueue);
this.scanlineCounter = state.scanlineCounter;
this.levelDEW = state.levelDEW;
this.levelDISPTMG = state.levelDISPTMG;
this.levelRA0 = state.levelRA0;
this.logLength = 0;
this.logShows = false;
this.skippedLogLength = 0;
const glyphMap = {
normal: this.normalGlyphs,
graphics: this.graphicsGlyphs,
separated: this.separatedGlyphs,
};
this.line.nextGlyphs = glyphMap[state.nextGlyphs] || this.normalGlyphs;
this.curGlyphs = glyphMap[state.curGlyphs] || this.normalGlyphs;
this.line.heldGlyphs = glyphMap[state.heldGlyphs] || this.normalGlyphs;
}
setNextChars() {
const line = this.line;
if (line.gfx) {
if (line.sep) {
line.nextGlyphs = this.separatedGlyphs;
} else {
line.nextGlyphs = this.graphicsGlyphs;
}
} else {
line.nextGlyphs = this.normalGlyphs;
}
}
handleControlCode(data) {
const line = this.line;
const wasGfx = line.gfx;
const wasHoldChar = line.holdChar;
switch (data) {
case 1:
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
line.gfx = false;
line.col = data;
line.conceal = false;
this.setNextChars();
break;
case 8:
line.flash = true;
break;
case 9:
line.flash = false;
break;
case 12:
case 13:
line.dbl = !!(data & 1);
if (line.dbl) line.wasDbl = true;
break;
case 17:
case 18:
case 19:
case 20:
case 21:
case 22:
case 23:
line.gfx = true;
line.col = data & 7;
line.conceal = false;
this.setNextChars();
break;
case 24:
line.conceal = true;
break;
case 25:
line.sep = false;
this.setNextChars();
break;
case 26:
line.sep = true;
this.setNextChars();
break;
case 28:
line.bg = 0;
break;
case 29:
line.bg = line.col;
break;
case 30:
line.holdChar = true;
break;
case 31:
line.holdChar = false;
break;
}
if (wasGfx && (wasHoldChar || line.holdChar) && line.dbl === this.oldDbl) {
data = line.heldChar;
this.curGlyphs = line.heldGlyphs;
} else {
line.heldChar = 0x20;
data = 0x20;
}
return data;
}
fetchData(data) {
// `copyWithin` over four bytes costs more than the moves it saves.
this.dataQueue[0] = this.dataQueue[1];
this.dataQueue[1] = this.dataQueue[2];
this.dataQueue[2] = this.dataQueue[3];
this.dataQueue[3] = data & DataBits;
}
/** Feeds `data` and clocks the chip with the byte leaving the pipeline, by the time anything reads the chip. */
logClocked(data) {
if (this.logLength === LogCapacity) this.catchUp();
this.log[this.logLength++] = data | ClockedEntry;
}
/** Feeds `data` without clocking the chip, as `fetchData` does, by the time anything reads the chip. */
logFed(data) {
Iif (this.logLength === LogCapacity) this.catchUp();
this.log[this.logLength++] = data & DataBits;
}
/**
* Paints shown cells with `drain`, from now on in its teletextColour, which takes on the colours so far.
* @param {import("./video-drain.js").VideoDrain} drain
*/
setOutput(drain) {
drain.teletextColour.set(this.colour);
this.colour = drain.teletextColour;
this.output = drain;
}
/**
* Shows the cell the byte logged last clocks at `offset` in the framebuffer, painted when the log runs.
* @param {number} offset
* @param {boolean} doubledLines also paint the row below
* @param {boolean} black show black, as the "TTX trick" does, rather than the chip's output
*/
showLatest(offset, doubledLines, black) {
this.log[this.logLength - 1] |=
(offset << TeletextOffsetShift) |
ShownEntry |
(doubledLines ? TeletextDoubled : 0) |
(black ? TeletextBlack : 0);
this.logShows = true;
}
/**
* Runs everything logged, so the chip is as if each byte had been run as it arrived, and paints the cells it
* shows. Painting the chip, or feeding it directly with `fetchData`, must come after this once anything has been
* logged.
*/
catchUp() {
const length = this.logLength;
this.logLength = 0;
this.logShows = false;
if (this.replayLog(this.log, length)) this.skippedLogLength = 0;
this.replaySkippedLine();
}
/** Runs the log if it holds a cell to paint: before anything that changes how one paints, or reads the picture. */
catchUpShown() {
if (this.logShows) this.catchUp();
}
// Returns whether any entry clocked the chip.
replayLog(log, length) {
const queue = this.dataQueue;
// Everything a shown cell reads besides the cell catches the log up before it changes.
const glyphRow = this.glyphRow();
const doubleHeightGlyphRow = this.doubleHeightGlyphRow();
const hideFlashing = this.hideFlashing;
const cells = this.output?.teletextCells;
let cellWords = 0;
let clocked = false;
// The first few clocked entries run bytes still in the pipeline; see skipLine.
for (let i = 0; i < length; ++i) {
const entry = log[i];
if (!(entry & ClockedEntry)) continue;
clocked = true;
this.clockCharacter(i < PipelineLag ? queue[i + 1] : log[i - PipelineLag] & DataBits);
if (!(entry & ShownEntry)) continue;
// Two bits a pixel, indexing the cell's palette; none set shows only the background.
let pixels = 0;
if (!(
entry & TeletextBlack ||
this.cellConceal ||
(this.cellFlash && hideFlashing) ||
(this.secondHalfOfDouble && !this.line.dbl)
)) {
pixels = this.curGlyphs[this.cellGlyphIndex + (this.oldDbl ? doubleHeightGlyphRow : glyphRow)];
}
cells[cellWords++] = pixels;
// A shown entry is a painted cell's second word (see video-drain.js) once its low byte holds the palette.
cells[cellWords++] = (entry & ~TeletextPaletteMask) | this.cellPalette;
}
if (cellWords) this.output.paintTeletext(cellWords >> 1);
this.feedLast(log, length);
return clocked;
}
// Leaves the pipeline as feeding the log's entries would.
feedLast(log, length) {
if (length < PipelineLength) {
for (let i = 0; i < length; ++i) this.fetchData(log[i]);
} else {
for (let i = 0; i < PipelineLength; ++i) this.dataQueue[i] = log[length - PipelineLength + i] & DataBits;
}
}
/**
* Brings the log to the end of a line without running it, for the DISPTMG reset that follows: that
* reset leaves the pipeline, whether a double height code reached its head, and the latched cell.
*/
skipLine() {
const length = this.logLength;
if (length === 0) return;
this.logLength = 0;
const log = this.log;
const queue = this.dataQueue;
let anyClocked = false;
for (let i = length - 1; i >= 0 && !anyClocked; --i) anyClocked = !!(log[i] & ClockedEntry);
if (anyClocked) {
this.skippedQueue.set(queue);
Object.assign(this.skippedLine, this.line);
this.log = this.skippedLog;
this.skippedLog = log;
this.skippedLogLength = length;
}
// Each clocked entry runs the byte fed PipelineLag entries before it.
for (let i = 0; i < Math.min(PipelineLag, length); ++i) {
if (log[i] & ClockedEntry && queue[i + 1] === DoubleHeight) this.line.wasDbl = true;
}
for (let i = 0; i + PipelineLag < length; ++i) {
if ((log[i] & DataBits) === DoubleHeight && log[i + PipelineLag] & ClockedEntry) {
this.line.wasDbl = true;
break;
}
}
this.feedLast(log, length);
}
// Recovers the cell latched by the last line `skipLine` passed over, leaving everything else as it is.
replaySkippedLine() {
if (this.skippedLogLength === 0) return;
const line = this.line;
this.line = this.skippedLine;
const queue = this.dataQueue.slice();
this.dataQueue.set(this.skippedQueue);
this.replayLog(this.skippedLog, this.skippedLogLength);
this.skippedLine = this.line;
this.line = line;
this.dataQueue.set(queue);
this.skippedLogLength = 0;
}
setDEW(level) {
// The SAA5050 input pin "DEW" is connected to the 6845 output pin
// "VSYNC" and it is used to track frames.
const oldLevel = this.levelDEW;
this.levelDEW = level;
// Trigger on high -> low. This appears to be what the hardware does.
// It needs to be this way for the scanline counter to stay in sync
// if you set R6>R4.
if (!oldLevel || level) {
return;
}
this.catchUpShown();
this.scanlineCounter = 0;
this.secondHalfOfDouble = false;
// 3:1 flash ratio.
if (++this.flashTime === 64) this.flashTime = 0;
}
// This counts DEW (VSYNC) pulses while the cursor blink counts R6 hits, so their phase starts at
// the MOS-dependent number of pulses before the first R6 hit and moves whenever a field has one
// without the other. The SAA5050 has no reset, so hardware presumably has no fixed phase either.
get hideFlashing() {
return this.flashTime < 16;
}
setDISPTMG(level) {
// The SAA5050 input pin "LOSE" is connected to the 6845 output pin
// "DISPTMG" and it is used to track scanlines.
const oldLevel = this.levelDISPTMG;
this.levelDISPTMG = level;
// Trigger on high -> low. This is probably what the hardware does as
// we need to increment scanline at the end of the scanline, not the
// beginning.
if (!oldLevel || level) {
return;
}
if (this.logShows) {
this.catchUp();
} else {
this.skipLine();
}
this.line.reset(this.normalGlyphs);
this.scanlineCounter++;
// Check for end of character row.
if (this.scanlineCounter === 10) {
this.scanlineCounter = 0;
if (this.secondHalfOfDouble) {
this.secondHalfOfDouble = false;
} else {
this.secondHalfOfDouble = this.line.wasDbl;
}
}
this.line.wasDbl = false;
}
setRA0(level) {
// The SAA5050 input pin "CRS" is connected to the 6845 output pin
// "RA0", via a signal inverter, and it is used to select between a
// normal scanline and a calculated smoothing scanline.
this.catchUpShown();
this.levelRA0 = level;
}
/** Applies `data`, as the byte leaving the pipeline, to the character state and latches the cell it shows. */
clockCharacter(data) {
const line = this.line;
this.oldDbl = line.dbl;
this.prevCol = line.col;
this.curGlyphs = line.nextGlyphs;
let flashThisCell = line.flash;
let concealThisCell = line.conceal;
if (data < 0x20) {
data = this.handleControlCode(data);
} else if (line.gfx) {
if (data & 0x20) {
line.heldChar = data;
line.heldGlyphs = this.curGlyphs;
}
} else {
line.heldChar = 32;
}
// Flash (code 8) is "Set After" — flashThisCell retains the pre-control-code state.
// Steady (code 9) is "Set At" — update so this cell stops flashing immediately.
if (flashThisCell && !line.flash) flashThisCell = false;
// Conceal (code 24) is "Set At", and a colour code only reveals from the cell after itself.
if (line.conceal) concealThisCell = true;
this.cellGlyphIndex = (data - 32) * 20;
this.cellFlash = flashThisCell;
this.cellConceal = concealThisCell;
this.cellPalette = ((line.bg & 7) << 5) | ((this.prevCol & 7) << 2);
}
glyphScanline() {
return this.oldDbl ? this.doubleHeightGlyphRow() : this.glyphRow();
}
glyphRow() {
return (this.scanlineCounter << 1) | (this.levelRA0 ? 1 : 0);
}
doubleHeightGlyphRow() {
return (this.glyphRow() >>> 1) + (this.secondHalfOfDouble ? 10 : 0);
}
// The second half of the latched cell, for the ULA's 1MHz repaint.
emitSecondHalf(buf, offset) {
const scanline = this.glyphScanline();
if (this.cellConceal || (this.cellFlash && this.hideFlashing) || (this.secondHalfOfDouble && !this.line.dbl)) {
const backgroundColour = this.colour[this.cellPalette & 0xe0];
for (let pixel = 8; pixel < 16; ++pixel) {
buf[offset + pixel] = backgroundColour;
}
} else {
let chardef = this.curGlyphs[this.cellGlyphIndex + scanline] >>> 16;
const paletteIndex = this.cellPalette;
for (let pixel = 8; pixel < 16; ++pixel) {
buf[offset + pixel] = this.colour[paletteIndex + (chardef & 3)];
chardef >>>= 2;
}
}
}
}
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