macintosh.js/src/renderer/screen.js

const { videoModeBufferView } = require('./video');
const { audioContext } = require('./audio');

const SCREEN_WIDTH = 800;
const SCREEN_HEIGHT = 600;
const SCREEN_BUFFER_SIZE = SCREEN_WIDTH * SCREEN_HEIGHT * 4; // 32bpp;

const screenBuffer = new SharedArrayBuffer(SCREEN_BUFFER_SIZE);
const screenBufferView = new Uint8Array(screenBuffer);

canvas.width = SCREEN_WIDTH;
canvas.height = SCREEN_HEIGHT;

const canvasCtx = canvas.getContext('2d');
const imageData = canvasCtx.createImageData(SCREEN_WIDTH, SCREEN_HEIGHT);

function drawScreen() {
  const pixelsRGBA = imageData.data;
  const numPixels = SCREEN_WIDTH * SCREEN_HEIGHT;
  const expandedFromPalettedMode = videoModeBufferView[3];
  const start = audioContext.currentTime;

  if (expandedFromPalettedMode) {
    for (var i = 0; i < numPixels; i++) {
      // palette
      pixelsRGBA[i * 4 + 0] = screenBufferView[i * 4 + 0];
      pixelsRGBA[i * 4 + 1] = screenBufferView[i * 4 + 1];
      pixelsRGBA[i * 4 + 2] = screenBufferView[i * 4 + 2];
      pixelsRGBA[i * 4 + 3] = 255; // full opacity
    }
  } else {
    for (var i = 0; i < numPixels; i++) {
      // ARGB
      pixelsRGBA[i * 4 + 0] = screenBufferView[i * 4 + 1];
      pixelsRGBA[i * 4 + 1] = screenBufferView[i * 4 + 2];
      pixelsRGBA[i * 4 + 2] = screenBufferView[i * 4 + 3];
      pixelsRGBA[i * 4 + 3] = 255; // full opacity
    }
  }


  canvasCtx.putImageData(imageData, 0, 0);
}

module.exports = {
  screenBuffer,
  screenBufferView,
  SCREEN_BUFFER_SIZE,
  drawScreen,
  SCREEN_WIDTH,
  SCREEN_HEIGHT
}