fix (i hope) all bugs

src/icons.js

@@ -120,6 +120,36 @@ function pngSize(img) {
   return null
 }
 
+// Raw RT_ICON payloads are BITMAPINFOHEADER-based bitmaps: biSize, biWidth,
+// biHeight (2x the visible height - XOR + AND mask), biPlanes, biBitCount,
+// ..., biClrUsed. Read the real dimensions from there instead of treating the
+// first bytes as an ICONDIRENTRY (which yielded garbage like h=0, planes=48
+// and made Chromium decode an empty image).
+function bmpDims(img) {
+  if (img.length < 12) return null
+  const biSize = img.readUInt32LE(0)
+  if (biSize === 12) {
+    // BITMAPCOREHEADER (Win 2.x/3.x era icons): DWORD size, then WORD width,
+    // height, planes, bitcount
+    const w = img.readUInt16LE(4)
+    const h = Math.floor(img.readUInt16LE(6) / 2)
+    const planes = img.readUInt16LE(8) || 1
+    const bpp = img.readUInt16LE(10) || 32
+    const colors = bpp <= 8 ? 1 << bpp : 0
+    if (w > 0 && h > 0 && w <= 1024 && h <= 1024) return { w, h, planes, bpp, colors }
+    return null
+  }
+  if (biSize >= 40 && biSize <= 124 && img.length > 40) {
+    const w = img.readUInt32LE(4)
+    const h = Math.floor(img.readUInt32LE(8) / 2)
+    const planes = img.readUInt16LE(12) || 1
+    const bpp = img.readUInt16LE(14) || 32
+    const colors = img.readUInt32LE(32) || (bpp <= 8 ? 1 << bpp : 0)
+    if (w > 0 && h > 0 && w <= 1024 && h <= 1024) return { w, h, planes, bpp, colors }
+  }
+  return null
+}
+
 function buildIco(images) {
   const header = Buffer.alloc(6)
   header.writeUInt16LE(0, 0)
@@ -135,16 +165,27 @@ function buildIco(images) {
       w = dim.w
       h = dim.h
     } else {
-      w = img.readUInt8(0) || 256
-      h = img.readUInt8(1) || 256
-      colors = img.readUInt8(2)
-      planes = img.length > 4 ? img.readUInt16LE(4) || 1 : 1
-      bpp = img.length > 6 ? img.readUInt16LE(6) || 32 : 32
+      const dims = bmpDims(img)
+      if (dims) {
+        w = dims.w
+        h = dims.h
+        colors = dims.colors
+        planes = dims.planes
+        bpp = dims.bpp
+      } else {
+        // legacy fallback: ICONDIRENTRY-style first bytes (PNG-era heuristic)
+        w = img.readUInt8(0) || 256
+        h = img.readUInt8(1) || 256
+        colors = img.readUInt8(2)
+        planes = img.length > 4 ? img.readUInt16LE(4) || 1 : 1
+        bpp = img.length > 6 ? img.readUInt16LE(6) || 32 : 32
+      }
     }
     const meta = Buffer.alloc(16)
     meta.writeUInt8(w >= 256 ? 0 : w, 0)
     meta.writeUInt8(h >= 256 ? 0 : h, 1)
-    meta.writeUInt8(colors, 2)
+    // 0 in the ICO dir entry means "256+ colors" (palette implied by bpp)
+    meta.writeUInt8(colors >= 256 ? 0 : colors, 2)
     meta.writeUInt8(0, 3)
     meta.writeUInt16LE(planes, 4)
     meta.writeUInt16LE(bpp, 6)