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// 纯 MoonBit PNG 编码（全目标可用：native/wasm/js）
// 使用 filter type 0 (None) + zlib stored blocks（无压缩但有效）
///|
/// 简单 zlib deflate（stored blocks，无压缩）
fn zlib_deflate_stored(data : Bytes) -> Bytes {
let out : Array[Byte] = []
// zlib header: CMF=0x78, FLG=0x01 (check: 0x78*256+0x01 = 30721, 30721%31=0)
out.push(b'\x78')
out.push(b'\x01')
// DEFLATE stored blocks
let len = data.length()
let mut pos = 0
while pos < len {
let block_len = if len - pos > 65535 { 65535 } else { len - pos }
let is_final = if pos + block_len >= len { 1 } else { 0 }
// BFINAL + BTYPE = 0b?00, aligned to byte → 0x01 for final, 0x00 for non-final
out.push(is_final.to_byte())
// LEN (little-endian)
out.push((block_len & 0xFF).to_byte())
out.push(((block_len >> 8) & 0xFF).to_byte())
// NLEN (one's complement of LEN)
out.push((block_len & 0xFF).to_byte() ^ b'\xFF')
out.push(((block_len >> 8) & 0xFF).to_byte() ^ b'\xFF')
// Data
for i in 0..<block_len {
out.push(data[pos + i])
}
pos += block_len
}
// ADLER32 (big-endian)
let adler = @util.adler32(data)
out.push(((adler >> 24) & 0xFF).to_byte())
out.push(((adler >> 16) & 0xFF).to_byte())
out.push(((adler >> 8) & 0xFF).to_byte())
out.push((adler & 0xFF).to_byte())
Bytes::from_array(out)
}
///|
/// 写入 PNG chunk
fn write_chunk(out : Array[Byte], chunk_type : String, data : Bytes) -> Unit {
let len = data.length()
// length (big-endian)
out.push(((len >> 24) & 0xFF).to_byte())
out.push(((len >> 16) & 0xFF).to_byte())
out.push(((len >> 8) & 0xFF).to_byte())
out.push((len & 0xFF).to_byte())
// type
let type_bytes = @encoding/utf8.encode(chunk_type)
for i in 0..<4 {
out.push(type_bytes[i])
}
// data
for i in 0..<len {
out.push(data[i])
}
// CRC (over type + data)
let crc_data : Array[Byte] = []
for i in 0..<4 {
crc_data.push(type_bytes[i])
}
for i in 0..<len {
crc_data.push(data[i])
}
let crc = @util.crc32(Bytes::from_array(crc_data))
out.push(((crc >> 24) & 0xFF).to_byte())
out.push(((crc >> 16) & 0xFF).to_byte())
out.push(((crc >> 8) & 0xFF).to_byte())
out.push((crc & 0xFF).to_byte())
}
///|
/// PNG 编码（纯 MoonBit，全目标可用）。
/// 输入 Image（RGB），返回 PNG 格式字节流。
/// 使用 filter type 0 (None) + zlib stored blocks（无压缩）。
pub fn encode_png_pure(img : @types.Image) -> Bytes {
let width = img.width
let height = img.height
let ch = img.channels
// 确定输出通道数
let out_ch = if ch == 4 {
4
} else if ch == 2 {
2
} else if ch == 1 {
1
} else {
3
}
let color_type = if out_ch == 1 {
0
} else if out_ch == 2 {
4
} else if out_ch == 4 {
6
} else {
2
}
let out : Array[Byte] = []
// PNG signature
out.push(b'\x89')
out.push(b'\x50')
out.push(b'\x4E')
out.push(b'\x47')
out.push(b'\x0D')
out.push(b'\x0A')
out.push(b'\x1A')
out.push(b'\x0A')
// IHDR chunk
let ihdr : Array[Byte] = []
// width (big-endian)
ihdr.push(((width >> 24) & 0xFF).to_byte())
ihdr.push(((width >> 16) & 0xFF).to_byte())
ihdr.push(((width >> 8) & 0xFF).to_byte())
ihdr.push((width & 0xFF).to_byte())
// height (big-endian)
ihdr.push(((height >> 24) & 0xFF).to_byte())
ihdr.push(((height >> 16) & 0xFF).to_byte())
ihdr.push(((height >> 8) & 0xFF).to_byte())
ihdr.push((height & 0xFF).to_byte())
ihdr.push(b'\x08') // bit depth = 8
ihdr.push(color_type.to_byte())
ihdr.push(b'\x00') // compression = 0
ihdr.push(b'\x00') // filter = 0
ihdr.push(b'\x00') // interlace = 0
write_chunk(out, "IHDR", Bytes::from_array(ihdr))
// 构建过滤后的图像数据
let filtered : Array[Byte] = []
for y in 0..<height {
filtered.push(b'\x00') // filter type 0 (None)
for x in 0..<width {
let src_off = (y * width + x) * ch
if ch == out_ch {
// 直接拷贝
for c in 0..<ch {
filtered.push(img.data[src_off + c])
}
} else {
// 通道数不匹配时，取前 out_ch 个通道
for c in 0..<out_ch {
if c < ch {
filtered.push(img.data[src_off + c])
} else {
filtered.push(b'\xFF')
}
}
}
}
}
// zlib deflate
let compressed = zlib_deflate_stored(Bytes::from_array(filtered))
// IDAT chunk
write_chunk(out, "IDAT", compressed)
// IEND chunk
write_chunk(out, "IEND", Bytes::from_array([]))
Bytes::from_array(out)
}