feat: add asset import services

src/lib/services/imager/png-decode.ts

@@ -0,0 +1,136 @@
+import { inflateSync } from 'node:zlib'
+
+export interface DecodedPng {
+  width: number
+  height: number
+  /** RGBA8888, row-major, length = width * height * 4 */
+  rgba: Buffer
+}
+
+function paeth(a: number, b: number, c: number): number {
+  const p = a + b - c
+  const pa = Math.abs(p - a)
+  const pb = Math.abs(p - b)
+  const pc = Math.abs(p - c)
+  if (pa <= pb && pa <= pc) return a
+  if (pb <= pc) return b
+  return c
+}
+
+function unfilter(filter: number, cur: Buffer, prev: Buffer, bpp: number): void {
+  const n = cur.length
+  switch (filter) {
+    case 0:
+      break
+    case 1:
+      for (let i = 0; i < n; i++) cur[i] = (cur[i] + (i >= bpp ? cur[i - bpp] : 0)) & 0xff
+      break
+    case 2:
+      for (let i = 0; i < n; i++) cur[i] = (cur[i] + prev[i]) & 0xff
+      break
+    case 3:
+      for (let i = 0; i < n; i++) {
+        const a = i >= bpp ? cur[i - bpp] : 0
+        cur[i] = (cur[i] + ((a + prev[i]) >> 1)) & 0xff
+      }
+      break
+    case 4:
+      for (let i = 0; i < n; i++) {
+        const a = i >= bpp ? cur[i - bpp] : 0
+        const c = i >= bpp ? prev[i - bpp] : 0
+        cur[i] = (cur[i] + paeth(a, prev[i], c)) & 0xff
+      }
+      break
+    default:
+      throw new Error(`unknown PNG filter ${filter}`)
+  }
+}
+
+/**
+ * Minimal PNG decoder for 8-bit non-interlaced images (color type 6/RGBA,
+ * 2/RGB, 0/grayscale). Enough to read Nitro spritesheet PNGs (RGBA8888).
+ * Returns RGBA pixels. Throws on unsupported formats.
+ */
+export function decodePng(buf: Buffer): DecodedPng {
+  if (buf.length < 8 || buf[0] !== 0x89 || buf[1] !== 0x50 || buf[2] !== 0x4e || buf[3] !== 0x47) {
+    throw new Error('not a PNG')
+  }
+  let off = 8
+  let width = 0
+  let height = 0
+  let bitDepth = 0
+  let colorType = 0
+  let interlace = 0
+  const idat: Buffer[] = []
+  while (off + 8 <= buf.length) {
+    const len = buf.readUInt32BE(off)
+    const type = buf.toString('ascii', off + 4, off + 8)
+    const data = buf.subarray(off + 8, off + 8 + len)
+    off += 12 + len // length(4) + type(4) + data + crc(4)
+    if (type === 'IHDR') {
+      width = data.readUInt32BE(0)
+      height = data.readUInt32BE(4)
+      bitDepth = data[8]
+      colorType = data[9]
+      interlace = data[12]
+    } else if (type === 'IDAT') {
+      idat.push(data)
+    } else if (type === 'IEND') {
+      break
+    }
+  }
+  if (bitDepth !== 8) throw new Error(`unsupported PNG bit depth ${bitDepth}`)
+  if (interlace !== 0) throw new Error('interlaced PNG not supported')
+  const channels = colorType === 6 ? 4 : colorType === 2 ? 3 : colorType === 0 ? 1 : -1
+  if (channels === -1) throw new Error(`unsupported PNG color type ${colorType}`)
+
+  const raw = inflateSync(Buffer.concat(idat))
+  const stride = width * channels
+  const planar = Buffer.alloc(height * stride)
+  let prev = Buffer.alloc(stride)
+  let rp = 0
+  for (let y = 0; y < height; y++) {
+    const filter = raw[rp++]
+    const cur = planar.subarray(y * stride, y * stride + stride)
+    raw.copy(cur, 0, rp, rp + stride)
+    rp += stride
+    unfilter(filter, cur, prev, channels)
+    prev = cur
+  }
+
+  if (channels === 4) return { width, height, rgba: planar }
+
+  const rgba = Buffer.alloc(width * height * 4)
+  for (let i = 0, j = 0; i < width * height; i++) {
+    if (channels === 3) {
+      rgba[j++] = planar[i * 3]
+      rgba[j++] = planar[i * 3 + 1]
+      rgba[j++] = planar[i * 3 + 2]
+    } else {
+      const g = planar[i]
+      rgba[j++] = g
+      rgba[j++] = g
+      rgba[j++] = g
+    }
+    rgba[j++] = 255
+  }
+  return { width, height, rgba }
+}
+
+/** Crop a w×h RGBA region at (x,y) out of a sheetW-wide RGBA buffer. */
+export function cropRgba(
+  rgba: Buffer,
+  sheetW: number,
+  x: number,
+  y: number,
+  w: number,
+  h: number,
+): Buffer {
+  const out = Buffer.alloc(w * h * 4)
+  for (let row = 0; row < h; row++) {
+    const src = ((y + row) * sheetW + x) * 4
+    rgba.copy(out, row * w * 4, src, src + w * 4)
+  }
+  return out
+}
+