UHD_Media_Tool/packages/adapters/src/browser/image.ts

/**
 * 截图的解码、缩放与编码(VIS-1):交给视觉模型的截图缩放到不超过 maxWidth(缺省 1280)像素宽,
 * 证据缩略图更小。PNG 自己解码 / 编码(node:zlib),JPEG 用 jpeg-js(纯 JS,无原生依赖,deno compile 可嵌入)。
 * 只支持浏览器截图实际会出现的格式:8 位 PNG(灰度 / RGB / 调色板 / 带 alpha,非隔行)与基线 JPEG。
 */
import { deflateSync, inflateSync } from "node:zlib";
import { decode as decodeJpeg, encode as encodeJpeg } from "jpeg-js";

export interface RgbaImage {
  width: number;
  height: number;
  /** RGBA,每像素 4 字节 */
  data: Uint8Array;
}

export interface EncodedImage {
  mimeType: "image/png" | "image/jpeg";
  data: Uint8Array;
  width: number;
  height: number;
}

export interface PrepareImageOptions {
  /** 最大宽度(像素);原图更窄时不放大 */
  maxWidth?: number;
  /** 输出格式;缺省 jpeg */
  format?: "png" | "jpeg";
  /** JPEG 质量 1–100,缺省 70 */
  quality?: number;
}

/** PNG IHDR / JPEG SOF 里的像素尺寸;不认识的格式返回 null */
export function imageDimensions(data: Uint8Array): { width: number; height: number } | null {
  if (data.length > 24 && data[0] === 0x89 && data[1] === 0x50 && data[2] === 0x4e && data[3] === 0x47) {
    const v = new DataView(data.buffer, data.byteOffset, data.byteLength);
    return { width: v.getUint32(16), height: v.getUint32(20) };
  }
  if (data[0] === 0xff && data[1] === 0xd8) {
    let i = 2;
    while (i + 9 < data.length) {
      if (data[i] !== 0xff) break;
      const marker = data[i + 1]!;
      const len = (data[i + 2]! << 8) | data[i + 3]!;
      if (marker >= 0xc0 && marker <= 0xc3)
        return { width: (data[i + 7]! << 8) | data[i + 8]!, height: (data[i + 5]! << 8) | data[i + 6]! };
      i += 2 + len;
    }
  }
  return null;
}

export function decodeImage(data: Uint8Array): RgbaImage {
  if (data[0] === 0x89 && data[1] === 0x50) return decodePng(data);
  if (data[0] === 0xff && data[1] === 0xd8) {
    const img = decodeJpeg(data, { useTArray: true, formatAsRGBA: true, maxMemoryUsageInMB: 256 });
    return { width: img.width, height: img.height, data: img.data };
  }
  throw new Error("不支持的图片格式");
}

/** 解码 8 位、非隔行 PNG(颜色类型 0/2/3/4/6) */
export function decodePng(bytes: Uint8Array): RgbaImage {
  const v = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
  let pos = 8;
  let width = 0;
  let height = 0;
  let depth = 0;
  let color = 0;
  let interlace = 0;
  let palette: Uint8Array | null = null;
  let trns: Uint8Array | null = null;
  const idat: Uint8Array[] = [];
  while (pos + 8 <= bytes.length) {
    const len = v.getUint32(pos);
    const type = String.fromCharCode(bytes[pos + 4]!, bytes[pos + 5]!, bytes[pos + 6]!, bytes[pos + 7]!);
    const body = bytes.subarray(pos + 8, pos + 8 + len);
    if (type === "IHDR") {
      width = v.getUint32(pos + 8);
      height = v.getUint32(pos + 12);
      depth = bytes[pos + 16]!;
      color = bytes[pos + 17]!;
      interlace = bytes[pos + 20]!;
    } else if (type === "PLTE") palette = body;
    else if (type === "tRNS") trns = body;
    else if (type === "IDAT") idat.push(body);
    else if (type === "IEND") break;
    pos += 12 + len;
  }
  if (depth !== 8 || interlace !== 0) throw new Error(`不支持的 PNG(位深 ${depth},隔行 ${interlace})`);
  const channels = ({ 0: 1, 2: 3, 3: 1, 4: 2, 6: 4 } as Record<number, number>)[color];
  if (!channels) throw new Error(`不支持的 PNG 颜色类型 ${color}`);
  if (width <= 0 || height <= 0 || width * height > 40_000_000) throw new Error("PNG 尺寸异常");
  const raw = new Uint8Array(inflateSync(concat(idat)));
  const stride = width * channels;
  const out = new Uint8Array(width * height * 4);
  let prev = new Uint8Array(stride);
  let cur = new Uint8Array(stride);
  for (let y = 0; y < height; y++) {
    const off = y * (stride + 1);
    const filter = raw[off]!;
    for (let i = 0; i < stride; i++) {
      const x = raw[off + 1 + i]!;
      const a = i >= channels ? cur[i - channels]! : 0;
      const b = prev[i]!;
      const c = i >= channels ? prev[i - channels]! : 0;
      let val: number;
      switch (filter) {
        case 0:
          val = x;
          break;
        case 1:
          val = x + a;
          break;
        case 2:
          val = x + b;
          break;
        case 3:
          val = x + ((a + b) >> 1);
          break;
        case 4: {
          const p = a + b - c;
          const pa = Math.abs(p - a);
          const pb = Math.abs(p - b);
          const pc = Math.abs(p - c);
          val = x + (pa <= pb && pa <= pc ? a : pb <= pc ? b : c);
          break;
        }
        default:
          throw new Error(`PNG 过滤类型 ${filter} 非法`);
      }
      cur[i] = val & 0xff;
    }
    for (let px = 0; px < width; px++) {
      const o = (y * width + px) * 4;
      const s = px * channels;
      if (color === 6) {
        out[o] = cur[s]!;
        out[o + 1] = cur[s + 1]!;
        out[o + 2] = cur[s + 2]!;
        out[o + 3] = cur[s + 3]!;
      } else if (color === 2) {
        out[o] = cur[s]!;
        out[o + 1] = cur[s + 1]!;
        out[o + 2] = cur[s + 2]!;
        out[o + 3] = 255;
      } else if (color === 0 || color === 4) {
        out[o] = out[o + 1] = out[o + 2] = cur[s]!;
        out[o + 3] = color === 4 ? cur[s + 1]! : 255;
      } else {
        const idx = cur[s]!;
        out[o] = palette?.[idx * 3] ?? 0;
        out[o + 1] = palette?.[idx * 3 + 1] ?? 0;
        out[o + 2] = palette?.[idx * 3 + 2] ?? 0;
        out[o + 3] = trns?.[idx] ?? 255;
      }
    }
    [prev, cur] = [cur, prev];
  }
  return { width, height, data: out };
}

/** 编码为 8 位 RGBA PNG(每行 filter 0,deflate 压缩) */
export function encodePng(img: RgbaImage): Uint8Array {
  const stride = img.width * 4;
  const raw = new Uint8Array((stride + 1) * img.height);
  for (let y = 0; y < img.height; y++) raw.set(img.data.subarray(y * stride, (y + 1) * stride), y * (stride + 1) + 1);
  const ihdr = new Uint8Array(13);
  const hv = new DataView(ihdr.buffer);
  hv.setUint32(0, img.width);
  hv.setUint32(4, img.height);
  ihdr[8] = 8;
  ihdr[9] = 6;
  return concat([
    new Uint8Array([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]),
    chunk("IHDR", ihdr),
    chunk("IDAT", new Uint8Array(deflateSync(raw))),
    chunk("IEND", new Uint8Array()),
  ]);
}

/** 按面积平均缩小到 maxWidth(等比);不放大 */
export function downscale(img: RgbaImage, maxWidth: number): RgbaImage {
  if (img.width <= maxWidth) return img;
  const w = Math.max(1, Math.round(maxWidth));
  const h = Math.max(1, Math.round((img.height * w) / img.width));
  const sx = img.width / w;
  const sy = img.height / h;
  const out = new Uint8Array(w * h * 4);
  for (let y = 0; y < h; y++) {
    const y0 = Math.floor(y * sy);
    const y1 = Math.max(y0 + 1, Math.min(img.height, Math.floor((y + 1) * sy)));
    for (let x = 0; x < w; x++) {
      const x0 = Math.floor(x * sx);
      const x1 = Math.max(x0 + 1, Math.min(img.width, Math.floor((x + 1) * sx)));
      let r = 0;
      let g = 0;
      let b = 0;
      let a = 0;
      for (let yy = y0; yy < y1; yy++) {
        let i = (yy * img.width + x0) * 4;
        for (let xx = x0; xx < x1; xx++, i += 4) {
          r += img.data[i]!;
          g += img.data[i + 1]!;
          b += img.data[i + 2]!;
          a += img.data[i + 3]!;
        }
      }
      const n = (y1 - y0) * (x1 - x0);
      const o = (y * w + x) * 4;
      out[o] = r / n;
      out[o + 1] = g / n;
      out[o + 2] = b / n;
      out[o + 3] = a / n;
    }
  }
  return { width: w, height: h, data: out };
}

/** 截图 → 交给模型 / 证据用的图片:缩放到 maxWidth 以内,按 format 编码 */
export function prepareImage(data: Uint8Array, opts: PrepareImageOptions = {}): EncodedImage {
  const maxWidth = opts.maxWidth ?? 1280;
  const format = opts.format ?? "jpeg";
  const dim = imageDimensions(data);
  const isPng = data[0] === 0x89 && data[1] === 0x50;
  // 已经够小且格式一致:原样返回,不重新编码
  if (dim && dim.width <= maxWidth && ((format === "png" && isPng) || (format === "jpeg" && !isPng)))
    return { mimeType: format === "png" ? "image/png" : "image/jpeg", data, ...dim };
  const img = downscale(decodeImage(data), maxWidth);
  if (format === "png") return { mimeType: "image/png", data: encodePng(img), width: img.width, height: img.height };
  const quality = Math.min(100, Math.max(1, Math.round(opts.quality ?? 70)));
  const jpeg = encodeJpeg({ width: img.width, height: img.height, data: img.data }, quality);
  return { mimeType: "image/jpeg", data: new Uint8Array(jpeg.data), width: img.width, height: img.height };
}

export function toBase64(data: Uint8Array): string {
  let s = "";
  for (let i = 0; i < data.length; i += 0x8000) s += String.fromCharCode(...data.subarray(i, i + 0x8000));
  return btoa(s);
}

function concat(parts: Uint8Array[]): Uint8Array {
  const out = new Uint8Array(parts.reduce((n, p) => n + p.length, 0));
  let o = 0;
  for (const p of parts) {
    out.set(p, o);
    o += p.length;
  }
  return out;
}

const CRC_TABLE = (() => {
  const t = new Uint32Array(256);
  for (let n = 0; n < 256; n++) {
    let c = n;
    for (let k = 0; k < 8; k++) c = c & 1 ? 0xedb88320 ^ (c >>> 1) : c >>> 1;
    t[n] = c >>> 0;
  }
  return t;
})();

function crc32(buf: Uint8Array): number {
  let c = 0xffffffff;
  for (const b of buf) c = CRC_TABLE[(c ^ b) & 0xff]! ^ (c >>> 8);
  return (c ^ 0xffffffff) >>> 0;
}

function chunk(type: string, data: Uint8Array): Uint8Array {
  const out = new Uint8Array(12 + data.length);
  const v = new DataView(out.buffer);
  v.setUint32(0, data.length);
  for (let i = 0; i < 4; i++) out[4 + i] = type.charCodeAt(i);
  out.set(data, 8);
  v.setUint32(8 + data.length, crc32(out.subarray(4, 8 + data.length)));
  return out;
}