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";
export class Teletext {
constructor() {
this.prevCol = 0;
this.col = 7;
this.bg = 0;
this.sep = false;
this.dbl = this.oldDbl = this.secondHalfOfDouble = this.wasDbl = false;
this.gfx = false;
this.conceal = false;
this.flash = false;
this.flashTime = 0;
this.heldChar = 0;
this.holdChar = false;
this.cellGlyphIndex = 0;
this.cellFlash = false;
this.cellConceal = false;
this.cellPalette = 0;
this.dataQueue = new Uint8Array(4);
this.scanlineCounter = 0;
this.levelDEW = false;
this.levelDISPTMG = false;
this.levelRA0 = false;
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.nextGlyphs = this.normalGlyphs;
this.curGlyphs = this.normalGlyphs;
this.heldGlyphs = 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() {
// 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.nextGlyphs === table) nextGlyphsName = name;
if (this.curGlyphs === table) curGlyphsName = name;
if (this.heldGlyphs === table) heldGlyphsName = name;
}
return {
prevCol: this.prevCol,
col: this.col,
bg: this.bg,
sep: this.sep,
dbl: this.dbl,
oldDbl: this.oldDbl,
secondHalfOfDouble: this.secondHalfOfDouble,
wasDbl: this.wasDbl,
gfx: this.gfx,
conceal: this.conceal,
flash: this.flash,
flashTime: this.flashTime,
heldChar: this.heldChar,
holdChar: this.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.col = state.col;
this.bg = state.bg;
this.sep = state.sep;
this.dbl = state.dbl;
this.oldDbl = state.oldDbl;
this.secondHalfOfDouble = state.secondHalfOfDouble;
this.wasDbl = state.wasDbl;
this.gfx = state.gfx;
this.conceal = state.conceal ?? false;
this.flash = state.flash;
this.flashTime = state.flashTime;
this.heldChar = state.heldChar;
this.holdChar = state.holdChar;
this.dataQueue.set(state.dataQueue);
this.scanlineCounter = state.scanlineCounter;
this.levelDEW = state.levelDEW;
this.levelDISPTMG = state.levelDISPTMG;
this.levelRA0 = state.levelRA0;
const glyphMap = {
normal: this.normalGlyphs,
graphics: this.graphicsGlyphs,
separated: this.separatedGlyphs,
};
this.nextGlyphs = glyphMap[state.nextGlyphs] || this.normalGlyphs;
this.curGlyphs = glyphMap[state.curGlyphs] || this.normalGlyphs;
this.heldGlyphs = glyphMap[state.heldGlyphs] || this.normalGlyphs;
}
setNextChars() {
if (this.gfx) {
if (this.sep) {
this.nextGlyphs = this.separatedGlyphs;
} else {
this.nextGlyphs = this.graphicsGlyphs;
}
} else {
this.nextGlyphs = this.normalGlyphs;
}
}
handleControlCode(data) {
const wasGfx = this.gfx;
const wasHoldChar = this.holdChar;
switch (data) {
case 1:
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
this.gfx = false;
this.col = data;
this.conceal = false;
this.setNextChars();
break;
case 8:
this.flash = true;
break;
case 9:
this.flash = false;
break;
case 12:
case 13:
this.dbl = !!(data & 1);
Eif (this.dbl) this.wasDbl = true;
break;
case 17:
case 18:
case 19:
case 20:
case 21:
case 22:
case 23:
this.gfx = true;
this.col = data & 7;
this.conceal = false;
this.setNextChars();
break;
case 24:
this.conceal = true;
break;
case 25:
this.sep = false;
this.setNextChars();
break;
case 26:
this.sep = true;
this.setNextChars();
break;
case 28:
this.bg = 0;
break;
case 29:
this.bg = this.col;
break;
case 30:
this.holdChar = true;
break;
case 31:
this.holdChar = false;
break;
}
if (wasGfx && (wasHoldChar || this.holdChar) && this.dbl === this.oldDbl) {
data = this.heldChar;
this.curGlyphs = this.heldGlyphs;
} else {
this.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 & 0x7f;
}
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.scanlineCounter = 0;
this.secondHalfOfDouble = false;
// 3:1 flash ratio.
if (++this.flashTime === 64) this.flashTime = 0;
}
// Flashing text starts off in sync with a slow cursor, extinguished together. Multiple MODE
// changes gradually desynchronise the frame counters.
// TODO(#1057) setDEW is reached a MOS-dependent number of times before Video.frameCount rises, so
// the initial sync here holds under MOS 1.20 only.
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;
}
this.col = 7;
this.bg = 0;
this.holdChar = false;
this.heldChar = 0x20;
this.nextGlyphs = this.heldGlyphs = this.normalGlyphs;
this.flash = false;
this.sep = false;
this.gfx = false;
this.conceal = false;
this.dbl = false;
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.wasDbl;
}
}
this.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.levelRA0 = level;
}
/**
* Clock one character through the chip: take the oldest byte in the pipeline, apply it
* to the character state, and latch how the resulting cell should look.
*/
advance() {
let data = this.dataQueue[0];
this.oldDbl = this.dbl;
this.prevCol = this.col;
this.curGlyphs = this.nextGlyphs;
let flashThisCell = this.flash;
let concealThisCell = this.conceal;
if (data < 0x20) {
data = this.handleControlCode(data);
} else if (this.gfx) {
if (data & 0x20) {
this.heldChar = data;
this.heldGlyphs = this.curGlyphs;
}
} else {
this.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 && !this.flash) flashThisCell = false;
// Conceal (code 24) is "Set At", and a colour code only reveals from the cell after itself.
if (this.conceal) concealThisCell = true;
this.cellGlyphIndex = (data - 32) * 20;
this.cellFlash = flashThisCell;
this.cellConceal = concealThisCell;
this.cellPalette = ((this.bg & 7) << 5) | ((this.prevCol & 7) << 2);
}
glyphScanline() {
let scanline = this.scanlineCounter << 1;
if (this.levelRA0) {
scanline++;
}
if (this.oldDbl) {
scanline = scanline >>> 1;
if (this.secondHalfOfDouble) {
scanline += 10;
}
}
return scanline;
}
/**
* Paint the cell most recently latched by `advance`. Everything else read here changes
* per scanline or per field, not per character.
*/
emit(buf, offset) {
const scanline = this.glyphScanline();
if (this.cellConceal || (this.cellFlash && this.hideFlashing) || (this.secondHalfOfDouble && !this.dbl)) {
const backgroundColour = this.colour[this.cellPalette & 0xe0];
for (let i = 0; i < 16; ++i) {
buf[offset++] = backgroundColour;
}
} else {
let chardef = this.curGlyphs[this.cellGlyphIndex + scanline];
const paletteIndex = this.cellPalette;
for (let pixel = 0; pixel < 16; ++pixel) {
buf[offset + pixel] = this.colour[paletteIndex + (chardef & 3)];
chardef >>>= 2;
}
}
}
// The second half of the cell `emit` last painted, for the ULA's 1MHz repaint.
emitSecondHalf(buf, offset) {
const scanline = this.glyphScanline();
Iif (this.cellConceal || (this.cellFlash && this.hideFlashing) || (this.secondHalfOfDouble && !this.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;
}
}
}
render(buf, offset) {
this.advance();
this.emit(buf, offset);
}
}
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