node_modules/@jimp/plugin-mask/src/index.ts

import { JimpClass, JimpClassSchema } from "@jimp/types";
import { z } from "zod";

const MaskOptionsObjectSchema = z.object({
  src: JimpClassSchema,
  /** the x position to draw the image */
  x: z.number().optional(),
  /** the y position to draw the image */
  y: z.number().optional(),
});

const MaskOptionsSchema = z.union([JimpClassSchema, MaskOptionsObjectSchema]);

export type MaskOptions = z.infer<typeof MaskOptionsSchema>;

export const methods = {
  /**
   * Masks a source image on to this image using average pixel colour. A completely black pixel on the mask will turn a pixel in the image completely transparent.
   * @param src the source Jimp instance
   * @param x the horizontal position to blit the image
   * @param y the vertical position to blit the image
   * @example
   * ```ts
   * import { Jimp } from "jimp";
   *
   * const image = await Jimp.read("test/image.png");
   * const mask = await Jimp.read("test/mask.png");
   *
   * image.mask(mask);
   * ```
   */
  mask<I extends JimpClass>(image: I, options: MaskOptions) {
    MaskOptionsSchema.parse(options);

    let src: JimpClass;
    let x: number;
    let y: number;

    if ("bitmap" in options) {
      src = options as unknown as JimpClass;
      x = 0;
      y = 0;
    } else {
      src = options.src as unknown as JimpClass;
      x = options.x ?? 0;
      y = options.y ?? 0;
    }

    // round input
    x = Math.round(x);
    y = Math.round(y);

    const w = image.bitmap.width;
    const h = image.bitmap.height;

    src.scan(function (sx, sy, idx) {
      const destX = x + sx;
      const destY = y + sy;

      if (destX >= 0 && destY >= 0 && destX < w && destY < h) {
        const dstIdx = image.getPixelIndex(destX, destY);
        const { data } = src.bitmap;
        const avg = (data[idx + 0]! + data[idx + 1]! + data[idx + 2]!) / 3;

        image.bitmap.data[dstIdx + 3] *= avg / 255;
      }
    });

    return image;
  },
};