1 files changed, 33 insertions, 0 deletions
diff --git a/util/png.py b/util/png.py
new file mode 100644
index 0000000..0936cf0
--- /dev/null
+++ b/util/png.py
@@ -0,0 +1,33 @@
+import struct
+import zlib
+
+def encode(buf, width, height):
+  """ buf: must be bytes or a bytearray in py3, a regular string in py2. formatted RGBRGB... """
+  assert (width * height * 3 == len(buf))
+  bpp = 3
+
+  def raw_data():
+    # reverse the vertical line order and add null bytes at the start
+    row_bytes = width * bpp
+    for row_start in range((height - 1) * width * bpp, -1, -row_bytes):
+      yield b'\x00'
+      yield buf[row_start:row_start + row_bytes]
+
+  def chunk(tag, data):
+    return [
+        struct.pack("!I", len(data)),
+        tag,
+        data,
+        struct.pack("!I", 0xFFFFFFFF & zlib.crc32(data, zlib.crc32(tag)))
+      ]
+
+  SIGNATURE = b'\x89PNG\r\n\x1a\n'
+  COLOR_TYPE_RGB = 2
+  COLOR_TYPE_RGBA = 6
+  bit_depth = 8
+  return b''.join(
+      [ SIGNATURE ] +
+      chunk(b'IHDR', struct.pack("!2I5B", width, height, bit_depth, COLOR_TYPE_RGB, 0, 0, 0)) +
+      chunk(b'IDAT', zlib.compress(b''.join(raw_data()), 9)) +
+      chunk(b'IEND', b'')
+    )