export function generateStaticCharAtlasTexture()

in src/shared/atlas/CharAtlasGenerator.ts [26:118]
70 lines of code
11 McCabe index (conditional complexity)

export function generateStaticCharAtlasTexture(context: Window, canvasFactory: (width: number, height: number) => HTMLCanvasElement | IOffscreenCanvas, config: ICharAtlasConfig): HTMLCanvasElement | Promise<ImageBitmap> {
  const cellWidth = config.scaledCharWidth + CHAR_ATLAS_CELL_SPACING;
  const cellHeight = config.scaledCharHeight + CHAR_ATLAS_CELL_SPACING;
  const canvas = canvasFactory(
    /*255 ascii chars*/255 * cellWidth,
    (/*default+default bold*/2 + /*0-15*/16 + /*0-15 bold*/16) * cellHeight
  );
  const ctx = canvas.getContext('2d', {alpha: config.allowTransparency});

  ctx.fillStyle = config.colors.background.css;
  ctx.fillRect(0, 0, canvas.width, canvas.height);

  ctx.save();
  ctx.fillStyle = config.colors.foreground.css;
  ctx.font = getFont(config.fontWeight, config);
  ctx.textBaseline = 'top';

  // Default color
  for (let i = 0; i < 256; i++) {
    ctx.save();
    ctx.beginPath();
    ctx.rect(i * cellWidth, 0, cellWidth, cellHeight);
    ctx.clip();
    ctx.fillText(String.fromCharCode(i), i * cellWidth, 0);
    ctx.restore();
  }
  // Default color bold
  ctx.save();
  ctx.font = getFont(config.fontWeightBold, config);
  for (let i = 0; i < 256; i++) {
    ctx.save();
    ctx.beginPath();
    ctx.rect(i * cellWidth, cellHeight, cellWidth, cellHeight);
    ctx.clip();
    ctx.fillText(String.fromCharCode(i), i * cellWidth, cellHeight);
    ctx.restore();
  }
  ctx.restore();

  // Colors 0-15
  ctx.font = getFont(config.fontWeight, config);
  for (let colorIndex = 0; colorIndex < 16; colorIndex++) {
    const y = (colorIndex + 2) * cellHeight;
    // Draw ascii characters
    for (let i = 0; i < 256; i++) {
      ctx.save();
      ctx.beginPath();
      ctx.rect(i * cellWidth, y, cellWidth, cellHeight);
      ctx.clip();
      ctx.fillStyle = config.colors.ansi[colorIndex].css;
      ctx.fillText(String.fromCharCode(i), i * cellWidth, y);
      ctx.restore();
    }
  }

  // Colors 0-15 bold
  ctx.font = getFont(config.fontWeightBold, config);
  for (let colorIndex = 0; colorIndex < 16; colorIndex++) {
    const y = (colorIndex + 2 + 16) * cellHeight;
    // Draw ascii characters
    for (let i = 0; i < 256; i++) {
      ctx.save();
      ctx.beginPath();
      ctx.rect(i * cellWidth, y, cellWidth, cellHeight);
      ctx.clip();
      ctx.fillStyle = config.colors.ansi[colorIndex].css;
      ctx.fillText(String.fromCharCode(i), i * cellWidth, y);
      ctx.restore();
    }
  }
  ctx.restore();

  // Support is patchy for createImageBitmap at the moment, pass a canvas back
  // if support is lacking as drawImage works there too. Firefox is also
  // included here as ImageBitmap appears both buggy and has horrible
  // performance (tested on v55).
  if (!('createImageBitmap' in context) || isFirefox || isSafari) {
    // Don't attempt to clear background colors if createImageBitmap is not supported
    if (canvas instanceof HTMLCanvasElement) {
      // Just return the HTMLCanvas if it's a HTMLCanvasElement
      return canvas;
    }
    // Transfer to an ImageBitmap is this is an OffscreenCanvas
    return new Promise((r: (bitmap: ImageBitmap) => void) => r(canvas.transferToImageBitmap()));
  }

  const charAtlasImageData = ctx.getImageData(0, 0, canvas.width, canvas.height);

  // Remove the background color from the image so characters may overlap
  clearColor(charAtlasImageData, config.colors.background);

  return context.createImageBitmap(charAtlasImageData);
}