Press n or j to go to the next uncovered block, b, p or k for the previous block.
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import { encodeLineGrid } from "./video-filters/pixel-grid.js";
import { makeFast32 } from "./binary.js";
const VDISPENABLE = 1 << 0,
HDISPENABLE = 1 << 1,
FRAMESKIPENABLE = 1 << 5;
// , EVERYTHINGENABLED = VDISPENABLE | HDISPENABLE | FRAMESKIPENABLE
/*
http://mdfs.net/Docs/Comp/Acorn/Atom/atap25.htm
25.5 Input/Output Port Allocations
The 8255 Programmable Peripheral Interface Adapter contains three 8-bit ports, and all but one of these lines is used by the ATOM.
Port A - #B000
Output bits: Function:
0 - 3 Keyboard row
4 - 7 Graphics mode
Hardware: PPIA 8255
output b000 0 - 3 keyboard row, 4 - 7 graphics mode
b002 0 cas output, 1 enable 2.4kHz, 2 buzzer, 3 colour set
input b001 0 - 5 keyboard column, 6 CTRL key, 7 SHIFT key
b002 4 2.4kHz input, 5 cas input, 6 REPT key, 7 60 Hz input
AG AS INTEXT INV GM2 GM1 GM0
-- -- ------ --- --- --- ---
0 0 0 0 X X X Internal Alphanumerics
0 0 0 1 X X X Internal Alphanumerics Inverted
0 0 1 0 X X X External Alphanumerics
0 0 1 1 X X X External Alphanumerics Inverted
0 1 0 X X X X Semigraphics 4
0 1 1 X X X X Semigraphics 6
1 X X X 0 0 0 Graphics CG1 (64x64x4) (16 bpr) #10
1 X X X 0 0 1 Graphics RG1 (128x64x2) (16 bpr) #30
1 X X X 0 1 0 Graphics CG2 (128x64x4) (32 bpr) #50
1 X X X 0 1 1 Graphics RG2 (128x96x2) (16 bpr) #70
1 X X X 1 0 0 Graphics CG3 (128x96x4) (32 bpr) #90
1 X X X 1 0 1 Graphics RG3 (128x192x2) (16 bpr) #b0
1 X X X 1 1 0 Graphics CG6 (128x192x4) (32 bpr) #d0
1 X X X 1 1 1 Graphics RG6 (256x192x2) (32 bpr) #f0
http://members.casema.nl/hhaydn/howel/logic/6847_clone.htm
256 = 256/8 = 32 32x1bpp = reg1:32 0x20
128 = 128/8 = 16 16x2bpp = reg1:32 0x20
128 = 128/8 = 16 16x1bpp = reg1:16 (xscale*2) 0x10
64 = 64/8 = 8 8x2bpp = reg1:16 (xscale*2) 0x10
# Data on PORTA used to set the screen mode; 0x10 means graphics mode, and then 0x20, 0x40, 0x80 are used to set the graphics mode.
# Data on PORTC used to set the colour select bit, which is used in conjunction with the graphics mode bits to select the colour of the screen.
# css = 0 means Black/Green
# css = 1 means Black/Orange
# PORTA is #b000 and PORTC is #b002
# bits 4-7 on #b000 are used to set the graphics mode, )
# and bit 3 on #b002 is used to set the colour select bit. (CSS connected to PC3 on 8255 via)
# eight bits 0-7
// video mode constants
//ppia PORTA
MODE_GM2 = 0x80; // only used if AG is 1 (bit 7)
MODE_GM1 = 0x40; // only used if AG is 1 (bit 6)
MODE_GM0 = 0x20; // only used if AG is 1 (bit 5)
MODE_AG = 0x10; // alpha or graphics (bit 4)
//ppia PORTC
MODE_CSS = 0x08; // colour select (bit 3)
when reading a byte from the VDG, looking at
// WITHIN THE VIDEO MEMORY (bit 6, 6, 7) (AS, INTEXT, INV resp.)
(INT/EXT & A/S connected to D6, and INV connected to D7 from CPU
This means D6 switches between internal alphanumeric, and semigraphics 6 (SG6)
// A/S-INT/EXT, INV can be changed character by character, and CSS on interrupt from CPU
// these not used if AG is 1, GM not used if AG is 0
for bits
CG1, CG2, CG3, CG6, RG6 are 2bpp
RG1, RG2, RG3 are 1bpp
?#B002=8
F.I=0TO255;I?#8000=I;N.
text colours are black/green (css=0) and black/orange (css=1); border black always
css not used for semigraphics 4 : THIS IS NOT AVAILABLE ON ATOM?
css is used for semigraphics 6,
they use 4 bits and 6 bits for luminance (0 off, 1 on)
and the last 2 or 3 bits are used for colour
(UNAVAILABLE) SG4 : 3 bits : 8 colours + black: green, yellow, blue, red , buff, cyan, magenta, orange
(PARTIALLY AVAILABLE) SG6 : 2 bits : 4 colours + black: css = 0, green, yellow, blue, red, css=1, buff, cyan, magenta, orange
only 1 bit is used of SG6 - to get yellow/red, cyan/orange
*/
// const MODE_AG = 0x80,
// MODE_GM2 = 0x40,
// MODE_GM1 = 0x20,
// MODE_GM0 = 0x10;
// constant for the graphics mode
const MODE_AG = 0x10; // graphics mode
// The MC6847 datasheet specifies 3.579545 MHz, but 3.638004 is used here as an
// empirical correction to align VSync/interrupt timing with the CPU clock.
// TODO(#1067) revisit once full integration is testable.
const VdgClockMhz = 3.638004;
export class Video6847 {
constructor(video) {
this.video = video;
this.ppia = null; // set during reset
this.levelDEW = false;
this.levelDISPTMG = false;
// 8 colours (alpha on MSB)
//
this.collook = makeFast32(
new Uint32Array([
0xff000000, // #00000000, // black
0xff03b91e, // #00ff00, // green
0xff00ffff, // #ffff00, // yellow
0xffff083b, // #3b08ff, // blue
0xff0516b9, // #b91605, // red
0xff018eb4, // #b48e01, // buff
0xffeb9200, // #0092eb, // cyan
0xffff1cff, // #ff1cff, // magenta
0xff005bbd, // #bd5b00, // orange
0xff000600, // dark green (char background) #000600
0xff000d1c, // dark orange (char background) #1c0d00
]),
);
// { 0, 0, 0 }, /*Black 0*/
// { 0, 63, 0 }, /*Green 1*/
// { 63, 63, 0 }, /*Yellow 2*/
// { 0, 0, 63 }, /*Blue 3 */
// { 63, 0, 0 }, /*Red 4 */
// { 63, 63, 63 }, /*Buff 5*/
// { 0, 63, 63 }, /*Cyan 6*/
// { 63, 0, 63 }, /*Magenta 7*/
// { 63, 32, 0 }, /*Orange 8 - can be red on the Atom*/
// /* dark green 9 */
// /* dark orange 10 */
this.interlacedSyncAndVideo = false;
// The 6847 blitters always write two framebuffer lines per pixel row,
// so Video.clearPaintBuffer() must clear both lines.
this.doubledScanlines = true;
this.regs = new Uint8Array(32);
this.bitmapX = 0;
this.bitmapY = 0;
this.frameCount = 0;
this.inHSync = false;
this.inVSync = false;
this.horizCounter = 0;
this.vertCounter = 0;
this.scanlineCounter = 0;
this.addr = 0;
this.lineStartAddr = 0;
this.nextLineStartAddr = 0;
this.pixelsPerChar = 8;
this.bitmapPxPerPixel = 2; // each pixel is 2 bitmap pixels wide and high
this.pixelsPerBit = this.bitmapPxPerPixel;
this.bpp = 1;
this.updateLineGrid();
this.cpuAddr = 0;
this.dispEnabled = 0;
//PAL based = 312 lines
//NTSC based = 262 lines
// initialiser is outside the function to improve performance
this.modes = {
//perchar , pixpb,lines, bpp
0xf0: [8, 1, 1, 1], //clear4 256x192x2, pixels 1w1h MAIN MENU
0xb0: [16, 2, 1, 1], //clear3 128x192x2, pixels 2w1h BABIES
0x70: [16, 2, 2, 1], //clear2 128x96x2, pixels 2w2h 3D ASTEROIDS
0x30: [16, 2, 3, 1], //clear1 128x64x2 , pixels 3w4h (2w4h) 3D MAZE
0xd0: [8, 2, 1, 2], //?#B000=#D0 128x192x4,pixels 2w1h CHUCKIE EGG
0x90: [8, 2, 2, 2], //?#B000=#90 128x96x4, pixels 2w2h FLAPPY BIRD
0x50: [8, 2, 3, 2], //?#B000=#50 128x64x4 , pixels 3w3h (4w3h) BREAKOUT (maingame)
0x10: [16, 4, 3, 2], //?#B000=#10 64x64x4 , pixels 4w3h FIZZLE BRICKS
0x00: [8, -1, 12, 1], // clear0 //0,0 not used on Mode 0 (uses blitChar), pixelsPerBit, bpp
};
// THESE MIDDLE THREE NUMBERS - THE SECOND AND THIRD ONE AFFECT THE VSYNC TIMING
// first is end of frame - i.e. full lines to display
// second is vsync start based on vertcounter
// third is total lines in a full frame
// vpulsewidth is how far through the individual scanline to end the vsync - i.e. sub scanline tine
this.lastmode = 0xff;
this.lastseconds = 0;
this.vdg_cycles = 0;
this.charTime = 0;
this.bordercolour = 0x00; // 0x00 black 0x01 // green or orange depending on CSS
this.init();
this.reset(null, null); // bit daft but it creates the members.
this.clearPaintBuffer();
this.paint();
}
init() {
this.curGlyphs = fontData.makeCharsAtom();
}
reset(cpu, ppia) {
this.cpu = cpu;
this.ppia = ppia;
// polltime() is handed CPU cycles, so how far the VDG advances per
// cycle depends on how fast the CPU it's attached to runs.
this.vdgCyclesPerCpuCycle = cpu ? VdgClockMhz / cpu.model.clockMhz : 0;
}
// USE PAINT from VIDEO
paint() {
this.video.paint();
}
clearPaintBuffer() {
this.video.interlacedSyncAndVideo = this.interlacedSyncAndVideo;
this.video.doubledScanlines = this.doubledScanlines;
this.video.frameCount = this.frameCount;
this.video.bitmapX = this.bitmapX;
this.video.bitmapY = this.bitmapY;
this.video.clearPaintBuffer();
}
// END
paintAndClear() {
// skip 5 frames
if (this.dispEnabled & FRAMESKIPENABLE) {
this.paint();
this.clearPaintBuffer();
}
this.dispEnabled &= ~FRAMESKIPENABLE;
let enable = FRAMESKIPENABLE;
if (this.frameCount % 5) enable = 0;
this.dispEnabled |= enable;
this.frameCount++;
this.bitmapY = 0;
}
/*
Snow is caused by the CPU changing the address bus for 500ns at the
same time as the VDG is expecting to get data from the address it has
requested, which takes 1100ns (1.1us). This only occurs if the cpu is
access graphics memory. So while the VDG is generating a scanline, the address
will change for 500ns based on the CPU memory accesses (read or write) and
the VDG will read 'noise' from the CPU addressed memory location instead.
*/
cpuAddrAccess(addr) {
// CPU has read from memory here
// VDG can read from this address for a cycle if it was video memory
// to generate snow
this.cpuAddr = addr;
}
// atom video memory is 0x8000->0x9fff (8k but only bottom 6k used)
// effecively goes up to 0x9800
readVideoMem() {
let cpuaddr = this.cpuAddr;
this.cpuAddr = 0; // reset the memory access by cpu but if it tries again it'll be set again
// during a vdg cycle, cpu might be active
if (this.vdg_cycles >= 0 && this.vdg_cycles < 1) {
if (cpuaddr >= 0x8000 && cpuaddr <= 0x9800) {
return this.cpu.videoRead(cpuaddr);
}
}
let memAddr = this.addr & 0x1fff;
memAddr |= 0x8000;
return this.cpu.videoRead(memAddr);
}
dispEnableSet(flag) {
this.dispEnabled |= flag;
}
dispEnableClear(flag) {
this.dispEnabled &= ~flag;
}
setValuesFromMode(mode) {
mode = mode & 0xf0;
// In text mode (AG=0), the GM bits are ignored per MC6847 datasheet.
// Force mode to 0x00 so we don't index into undefined modes table entries.
if (!(mode & MODE_AG)) mode = 0x00;
// if no change in mode then do nothing
if (this.lastmode === mode) return;
this.lastmode = mode;
this.pixelsPerChar = this.modes[mode][0]; // 8 pixels per element
this.pixelsPerBit = this.bitmapPxPerPixel * this.modes[mode][1];
let linesPerRow = this.modes[mode][2]; // move to reg9
this.bpp = this.modes[mode][3];
this.updateLineGrid();
this.charLinesreg9 = linesPerRow - 1; //2 - scanlines per char
//NEED TO RESET THE LINE IF
//MODE SWITCH MID FRAME
this.scanlineCounter = 0;
this.lineStartAddr = this.nextLineStartAddr;
}
// this is usually called from 'video' so 'this'
// is a reference to 'video'
polltimeFacade(clocks) {
if (this.video6847 != undefined) {
this.video6847.polltime(clocks);
return;
}
throw new Error("Video6847 not attached — polltimeFacade called before video.video6847 was initialised");
}
// ATOM uses 6847 chip
polltime(clocks) {
const mode = this.ppia.portapins & 0xf0;
const css = (this.ppia.portcpins & 0x08) >>> 2;
this.setValuesFromMode(mode);
// Note: Polltime is called from the CPU many times during a frame. Once the VDG has drawn a bit of a frame
// it returns, and then comes back here later to continue the same frame. That's how the snow is able to work
// it doesn't draw the whole frame. It regularly gives control back to the CPU.
const vdgcharclock = this.pixelsPerChar / 2; // 4 or 8
this.vdg_cycles += clocks * this.vdgCyclesPerCpuCycle;
const vdgframelines = 262; // 312 PAL (but no pal on standard atom) 262; // NTSC
const vdglinetime = 228; // vdg cycles to do a line; not 227.5
// full bordered width is 185.5 cycles
// (185.5+42 = 227.5)
const HBNK = 42; // left border start (16.5+25.5)
const leftborder = 29; // 29.5
const displayH = 128; //cycles - 186 cycles including borders - 228 for full horizontal
const rightborder = 29; //28.5
// total = 29+29+128+42 = 228
const vertblank = 13; //13
const topborder = 25; //25
const displayV = 192;
// let bottomborder = 26; // 26 + 6 = 32 = time in vsync
// let vertretrace = 6;
// ALL ADDS UP TO 262
// in vsync for 32 lines = bottomborder+vertretrace
// out vsync for 230 lines = vertblank+topborder+displayV
while (this.vdg_cycles >= 1) {
this.vdg_cycles -= 1;
this.charTime -= 1;
let nextChar = this.charTime <= 0;
if (nextChar) {
this.charTime += vdgcharclock;
this.bitmapX += this.pixelsPerChar * this.bitmapPxPerPixel;
}
if (this.inHSync) {
// Start at -ve pos because new character is added before the pixel render
this.bitmapX = -this.pixelsPerChar * this.bitmapPxPerPixel;
this.bitmapY += this.bitmapPxPerPixel;
if (this.bitmapY >= 768) {
// Arbitrary moment when TV will give up and start flyback in the absence of an explicit VSync signal
this.paintAndClear();
}
this.inHSync = false;
}
// right border - record addr for next FULL line
if (this.horizCounter === HBNK + leftborder + displayH) this.nextLineStartAddr = this.addr;
// Stop drawing outside the right border
if (this.horizCounter === HBNK + leftborder + displayH) {
this.dispEnableClear(HDISPENABLE);
}
// left border - start the next line (not necessarily the FULL line)
if (this.horizCounter === HBNK + leftborder) {
this.dispEnableSet(HDISPENABLE);
this.addr = this.lineStartAddr;
this.charTime = 0;
}
// vertcounter runs from 0 to 262
// got to the end, start again
if (this.vertCounter === vertblank + topborder) {
this.scanlineCounter = 0;
this.nextLineStartAddr = 0;
this.lineStartAddr = this.nextLineStartAddr;
this.dispEnableSet(VDISPENABLE);
}
if (this.vertCounter === vertblank + topborder + displayV) {
this.dispEnableClear(VDISPENABLE);
}
// reached end of the vdgline - start the hsync
if (this.horizCounter === HBNK + leftborder + displayH + rightborder && !this.inHSync) {
this.inHSync = true;
}
// image between 0 and 191 inc.
// vsync start (1) at line 192
// vsync end (0) at line 224
// 32 lines between inVSync and !inVSync
let vSyncEnding = false;
let vSyncStarting = false;
if (this.vertCounter === vertblank + topborder + displayV && !this.inVSync) {
vSyncStarting = true;
this.inVSync = true;
// Frame Sync is high normally and
// goes low when in VSync
// in VSync for 32 lines, and
// out of VSync for 262-32 lines
}
if (this.vertCounter === 0 && this.inVSync) {
vSyncEnding = true;
this.inVSync = false;
}
if (!vSyncStarting && vSyncEnding) {
this.paintAndClear();
}
if (vSyncStarting || vSyncEnding) {
this.ppia.setVBlankInt(this.inVSync);
// if (vSyncEnding)
// {
// let seconds = this.cpu.cycleSeconds+this.cpu.currentCycles/1000000.0;
// let diff = seconds - this.lastseconds;
// $("#vdg_text").html(
// "FPS "+(1/diff).toFixed(5)+" ("+diff.toFixed(5)+")<br>"
// );
// this.lastseconds = seconds ?? 0;
// }
// fix the border colour at the end/start of a frame
// it won't change within a frame
let AGM = (mode & MODE_AG) === 0;
if (AGM)
this.bordercolour = 0x00; // black
else this.bordercolour = 0x01; // green orange
}
if (nextChar) {
// once the whole of the Vertical and Horizontal is complete then do this
let insideBorder = (this.dispEnabled & (HDISPENABLE | VDISPENABLE)) === (HDISPENABLE | VDISPENABLE);
if (insideBorder) {
// read from video memory - uses this.addr
let dat = this.readVideoMem();
let offset = this.bitmapY;
offset = offset * 1024 + this.bitmapX;
// Render data depending on display enable state.
if (this.bitmapX >= 0 && this.bitmapX < 1024 && this.bitmapY < 625) {
{
// TODO(#1067) Add in the INTEXT modifiers to mode (if necessary)
// blit into the fb32 buffer which is painted by VIDEO
const textMode = (mode & MODE_AG) === 0; // 0x10 is the AG bit
this.recordLineGrid(textMode);
if (textMode) this.blitChar(this.video.fb32, dat, offset, this.pixelsPerChar, css);
else this.blitPixels(this.video.fb32, dat, offset, css);
}
}
} else {
// draw border (black, or green/buff depending on bordercolour and CSS)
if (this.bitmapX >= 0 && this.bitmapX < 1024 && this.bitmapY >= 0 && this.bitmapY < 625) {
const offset = this.bitmapY * 1024 + this.bitmapX;
this.blitBorder(this.video.fb32, this.bordercolour, offset, css);
}
}
this.addr = (this.addr + 1) & 0x1fff;
}
// end of horizontal line
if (this.horizCounter === vdglinetime) {
let completedCharVertical = this.scanlineCounter === this.charLinesreg9; // regs9 - scanlines per char // 9 Maximum Raster Address
//keep drawing same memory addresses until end of scanlines
if (completedCharVertical) {
this.lineStartAddr = this.nextLineStartAddr;
}
this.scanlineCounter += 1;
if (completedCharVertical) {
// this.hadVSyncThisRow = false;
this.scanlineCounter = 0;
}
// end of vertical frame was detected
if (this.vertCounter >= vdgframelines) {
this.vertCounter = 0;
} else {
this.vertCounter = (this.vertCounter + 1) & 0x1ff;
}
// start new horizontal line
this.horizCounter = 0;
} else {
this.horizCounter = (this.horizCounter + 1) & 0xff;
}
// // dump some data to CSV
// let a = this.cpu.cycleSeconds*1000000.0+this.cpu.currentCycles;
// let b = this.horizCounter;
// let c = this.vertCounter;
// let d = this.inVSync;
// let e = css;
// //using template literals for strings substitution
// if (this.cpu.cycleSeconds==10 && this.cpu.currentCycles<60000 && this.horizCounter == 0)
// {
// $("#csv_output").append(
// `<br>${a},${b},${c},${d},${e}`);
// }
} // matches while
}
blitBorder(buf, data, destOffset, css) {
const bpp = this.bpp;
const pixelsPerBit = this.pixelsPerBit / bpp;
const numPixels = 8 * pixelsPerBit; //per char
const fb32 = buf;
const colour = data === 0x00 ? this.collook[0] : this.collook[css ? 5 : 1];
for (let i = 0; i < numPixels; ++i) {
const n = numPixels - 1 - i; // pixels in reverse order
fb32[destOffset + n] = fb32[destOffset + n + 1024] = colour;
}
}
blitPixels(buf, data, destOffset, css) {
// let scanline = this.scanlineCounterT;
// bitpattern from data is either 4 or 8 pixels in raw graphics
// either white and black
// or 3 colours and black (in pairs of bits)
// that is: all graphics modes are 1bpp or 2bpp giving 2 colours or 4 colours
const bitdef = data;
const bpp = this.bpp;
const pixelsPerBit = this.pixelsPerBit / bpp;
let colour; // see 'collook' // alpha, blue, green, red
// MODE NEED TO CHANGE THE RASTER SCAN
// currently 32 x 16 - 256 x 192 (with 12 lines per row)
// can get wide with 16 pixels
destOffset |= 0;
let fb32 = buf;
const numPixels = 8 * pixelsPerBit; //per char
// draw two,four pixels for each bit in the data to fill the width.
for (let i = 0; i < numPixels; i++) {
const n = numPixels - 1 - i; // pixels in reverse order
// get bits in pairs or singles
const j = Math.floor(i / pixelsPerBit);
// get just one bit
// RG modes
if (bpp === 1) {
// get a bit
const cval = (bitdef >>> j) & 0x1;
// CSS=0: green foreground, CSS=1: buff foreground
colour = cval !== 0 ? this.collook[css ? 5 : 1] : this.collook[0];
// two bitmap lines per 1 pixel
fb32[destOffset + n + 1024] = fb32[destOffset + n] = colour;
} // CG modes
else {
//let cval = (bitdef>>>(j&0xe))&0x3;
const cval = (bitdef >>> (j & 0xe)) & 0x3;
// 2 or 4 - green/yellow/blue/red
let colindex = 1 + (cval | (css << 1));
colour = this.collook[colindex];
// two bitmap lines per 1 pixel
fb32[destOffset + n + 1024] = fb32[destOffset + n] = colour;
}
}
}
/**
* Precompute this mode's grid descriptors, one per blitter.
*
* The two blitters derive their widths differently and cannot be unified:
* `blitChar` splits the character's texels across eight glyph bits, while
* `blitPixels` takes the bit width from the mode table — which for text
* mode holds -1, since it does not blit pixels at all.
*
* `pixelsPerBit` is right for graphics at 2bpp as well as 1bpp: the blitter
* steps its bit groups by `pixelsPerBit / bpp`, but reads the colour with
* `j & 0xe`, so pairs of groups share one and each pixel is twice as wide.
*/
updateLineGrid() {
// Every 6847 blitter writes each pixel row into two framebuffer lines.
// Text mode's entry is only reachable through blitChar, which is just
// as well: the mode table holds -1 for it and would not encode.
this.lineGridText = encodeLineGrid((this.pixelsPerChar * this.bitmapPxPerPixel) / 8, true);
this.lineGridGraphics = this.pixelsPerBit > 0 ? encodeLineGrid(this.pixelsPerBit, true) : this.lineGridText;
}
/**
* Note the logical pixel size of the two rows about to be written, so
* display filters can see the picture as pixels rather than as raster
* samples (see video-filters/pixel-grid.js). Only the picture records a
* grid: the border is a solid colour, and letting it write here would
* leave the row describing the border rather than the picture on it.
*
* @param {boolean} textMode whether the character blitter is about to run
*/
recordLineGrid(textMode) {
const grid = textMode ? this.lineGridText : this.lineGridGraphics;
this.video.lineGrid[this.bitmapY] = grid;
this.video.lineGrid[this.bitmapY + 1] = grid;
}
blitChar(buf, data, destOffset, numPixels, css) {
const scanline = this.scanlineCounter;
const chr = data & 0x7f;
// character set is just the pixel data
// 0 - 63 is alphachars green (0x00-0x3f) bits 0-5 for character
// 64-127 is 16 alphagraphics in 4 colours green/yellow/blue/red (0x40-0x7f) bit 6,7 (0xC0)
// bit 7 set is inverted and the alphagraphics again
// 128 - 191 is alphachars inverted green (0x80-0xbf)
// 192-255 is alphagraphics in different colours buff/cyan/magenta/orange (0xc0-0xff) bit 6,7 set (0xC0)
// in the data; bits 0-5 are the pixels
// bit 7 and CSS give the colour
// bit 6 indicates TEXT or GRAPHICS
// thus green and blue (css=0) alphagraphics cannot be accessed
// and buff and magenta (css=1) alphagraphics cannot be accessed
// bits 7,6
// [00] green text (or orange)
// [01] yellow graphics (or cyan)
// [10] inv green text (or inv orange)
// [11] red graphics (or orange)
// invert the char if bit 7 is set
const inv = !!(data & 0x80);
// graphics if bit 6 is set
const agmode = !!(data & 0x40);
//bitpattern for chars is in rows; each char is 12 rows deep
let chardef = this.curGlyphs[chr * 12 + scanline];
Iif (inv && !agmode) chardef = ~chardef;
numPixels |= 0;
numPixels *= this.bitmapPxPerPixel;
// can get wide with 16 pixels
const pixelsPerBit = numPixels / 8;
destOffset |= 0;
let fb32 = buf;
for (let i = 0; i < numPixels; ++i) {
const n = numPixels - 1 - i; // pixels in reverse order
const j = i / pixelsPerBit;
// text is either green/black or buff/black - nothing else
// css is 2 or 0 on input
let fgcol = this.collook[css ? 5 : 1];
Iif (agmode) {
// alphagraphics 6
// inv css | colour
// 0 0 | yellow (2) 10 + 0000
// 1 0 | red (4) 10 + 0010
// 0 2 | cyan (6) 10 + 0100
// 1 2 | orange (8) 10 + 0110
// css is 2 or 0 on input
fgcol = this.collook[2 + ((inv | css) << 1)];
}
const luminance = (chardef >>> j) & 0x1;
const colour = luminance ? fgcol : this.collook[css ? 10 : 9]; //dark orange or green
fb32[destOffset + n] = fb32[destOffset + n + 1024] = // two lines
colour;
}
}
}
/* Video modes:
Alpha internal
Alpha external
SemiGraphics Four 0011 CLEAR 1
SemiGraphics Six 0111 CLEAR 2
0001 ?#B000=#10 1a
Colour Graphics 1 - 8 colours (CSS/C1/C0) - 64x64
1024 bytes - 2bpp (4x3) - 4 pixels x 3 rows
0011 clear 1
Resolution Graphics 1 - 4 colours (Lx) - 128x64
1024 bytes - 1bpp (3x3)
0101 ?#B000=#50 2a
Colour Graphics 2 - 8 colours (CSS/C1/C0) - 128x64
2048 bytes - 2bpp (3x3)
1011 CLEAR 2
Resolution Graphics 2 - 4 colours (Lx) - 128x96
1536 bytes - 1bpp (2x2)
1001 ?#B000=#90 3a
Colour Graphics 3 - 8 colours (CSS/C1/C0) - 128x96
3072 bytes - 2bpp (2x2)
1011 clear 3
Resolution Graphics 3 - 4 colours (Lx)- 128x192
3072 bytes - 1bpp (2x1)
110 ?#B000=#d0 4a
Colour Graphics 6 - 8 colours (CSS/C1/C0) - 128x192
6144 bytes - 2bpp (4x1)
1111 clear 4
Resolution Graphics 6 - 4 colours (Lx) 256x192
6144 bytes - 1bpp (8x1)
*/
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