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// 纯 MoonBit PNG 16-bit 解码（全目标可用：native/wasm/js）
// 支持 8-bit PNG 上采样为 16-bit，以及原生 16-bit PNG
// 输出 Image16（little-endian uint16 per sample）
///|
/// PNG 16-bit 解码（纯 MoonBit，全目标可用）。
/// 支持 bit depth 8（上采样为 16-bit）和 16（原生）。
/// color type 0/2/3/4/6，不支持 interlace。
/// req_channels: 0/None=原色, 1=灰度, 2=灰度+alpha, 3=RGB, 4=RGBA
pub fn decode_png_16_pure(
data : Bytes,
req_channels? : Int? = None,
) -> @types.Image16 raise @types.LoadError {
match req_channels {
Some(n) =>
if n < 1 || n > 4 {
raise @types.LoadError::DecodeFailed("req_channels 必须为 1-4")
}
None => ()
}
let len = data.length()
if len < 8 || !is_png_signature(data, 0) {
raise @types.LoadError::DecodeFailed("PNG signature 错误")
}
let mut pos = 8
let mut width = 0
let mut height = 0
let mut bit_depth = 0
let mut color_type = 0
let mut interlace = 0
let palette : Array[(Int, Int, Int)] = []
let idat_data : Array[Byte] = []
let mut found_ihdr = false
let mut found_iend = false
while pos < len && !found_iend {
if pos + 8 > len {
raise @types.LoadError::DecodeFailed("PNG chunk 头部过短")
}
let chunk_len = read_u32_be(data, pos)
let chunk_key = read_u32_be(data, pos + 4)
pos += 8
if pos + chunk_len > len {
raise @types.LoadError::DecodeFailed("PNG chunk 数据越界")
}
match chunk_key {
0x49484452 => {
if chunk_len < 13 {
raise @types.LoadError::DecodeFailed("PNG IHDR 过短")
}
width = read_u32_be(data, pos)
height = read_u32_be(data, pos + 4)
bit_depth = data[pos + 8].to_int()
color_type = data[pos + 9].to_int()
interlace = data[pos + 12].to_int()
found_ihdr = true
}
0x504C5445 => {
let num_colors = chunk_len / 3
for i in 0..<num_colors {
palette.push(
(
data[pos + i * 3].to_int(),
data[pos + i * 3 + 1].to_int(),
data[pos + i * 3 + 2].to_int(),
),
)
}
}
0x49444154 =>
for i in 0..<chunk_len {
idat_data.push(data[pos + i])
}
0x49454E44 => found_iend = true
_ => ()
}
pos += chunk_len + 4
}
if !found_ihdr {
raise @types.LoadError::DecodeFailed("PNG 无 IHDR chunk")
}
if width <= 0 || height <= 0 {
raise @types.LoadError::DecodeFailed("PNG 尺寸无效")
}
if interlace != 0 {
raise @types.LoadError::DecodeFailed("PNG interlace 不支持")
}
if bit_depth != 8 && bit_depth != 16 {
raise @types.LoadError::DecodeFailed(
"PNG 16-bit 解码仅支持 bit depth 8 或 16",
)
}
let ch = match png_channels(color_type) {
Some(c) => c
None => raise @types.LoadError::DecodeFailed("PNG 无效 color type")
}
let raw = @util.zlib_inflate(Bytes::from_array(idat_data))
// bytes per pixel for filtering
let bpp = ch * (bit_depth / 8)
let stride = width * bpp
let unfiltered : Array[Byte] = Array::make(height * stride, b'\x00')
let mut raw_pos = 0
for y in 0..<height {
if raw_pos >= raw.length() {
raise @types.LoadError::DecodeFailed("PNG 解压数据过短")
}
let filter_type = raw[raw_pos].to_int()
raw_pos += 1
for x in 0..<stride {
if raw_pos >= raw.length() {
raise @types.LoadError::DecodeFailed("PNG 解压数据过短")
}
let raw_byte = raw[raw_pos].to_int()
raw_pos += 1
let a = if x >= bpp {
unfiltered[y * stride + x - bpp].to_int()
} else {
0
}
let b = if y > 0 { unfiltered[(y - 1) * stride + x].to_int() } else { 0 }
let c = if x >= bpp && y > 0 {
unfiltered[(y - 1) * stride + x - bpp].to_int()
} else {
0
}
let val = match filter_type {
0 => raw_byte
1 => (raw_byte + a) & 0xFF
2 => (raw_byte + b) & 0xFF
3 => (raw_byte + (a + b) / 2) & 0xFF
4 => (raw_byte + paeth_predict(a, b, c)) & 0xFF
_ => raise @types.LoadError::DecodeFailed("PNG 无效 filter type")
}
unfiltered[y * stride + x] = val.to_byte()
}
}
// 转换为 16-bit samples (little-endian)
let pixel_count = width * height
let out_ch = match req_channels {
Some(n) => n
None => ch
}
// 先提取原生 16-bit samples
let samples16 : Array[Int] = Array::make(pixel_count * ch, 0)
if bit_depth == 16 {
// big-endian → native int
for i in 0..<(pixel_count * ch) {
let hi = unfiltered[i * 2].to_int()
let lo = unfiltered[i * 2 + 1].to_int()
samples16[i] = hi * 256 + lo
}
} else {
// 8-bit → upscale: v * 257
for i in 0..<(pixel_count * ch) {
samples16[i] = unfiltered[i].to_int() * 257
}
}
// 通道转换
let out_data : Array[Byte] = Array::make(pixel_count * out_ch * 2, b'\x00')
for i in 0..<pixel_count {
let (r16, g16, b16, a16) = if ch == 1 {
let v = samples16[i]
(v, v, v, 65535)
} else if ch == 2 {
let v = samples16[i * 2]
let a = samples16[i * 2 + 1]
(v, v, v, a)
} else if ch == 3 {
(samples16[i * 3], samples16[i * 3 + 1], samples16[i * 3 + 2], 65535)
} else {
(
samples16[i * 4],
samples16[i * 4 + 1],
samples16[i * 4 + 2],
samples16[i * 4 + 3],
)
}
let (or16, og16, ob16, oa16) = match out_ch {
1 => {
let gray = (r16 * 299 + g16 * 587 + b16 * 114) / 1000
(gray, gray, gray, 65535)
}
2 => {
let gray = (r16 * 299 + g16 * 587 + b16 * 114) / 1000
(gray, gray, gray, a16)
}
3 => (r16, g16, b16, 65535)
_ => (r16, g16, b16, a16)
}
// little-endian uint16
out_data[i * out_ch * 2] = (or16 & 0xFF).to_byte()
out_data[i * out_ch * 2 + 1] = ((or16 >> 8) & 0xFF).to_byte()
if out_ch >= 2 {
out_data[i * out_ch * 2 + 2] = (og16 & 0xFF).to_byte()
out_data[i * out_ch * 2 + 3] = ((og16 >> 8) & 0xFF).to_byte()
}
if out_ch >= 3 {
out_data[i * out_ch * 2 + 4] = (ob16 & 0xFF).to_byte()
out_data[i * out_ch * 2 + 5] = ((ob16 >> 8) & 0xFF).to_byte()
}
if out_ch >= 4 {
out_data[i * out_ch * 2 + 6] = (oa16 & 0xFF).to_byte()
out_data[i * out_ch * 2 + 7] = ((oa16 >> 8) & 0xFF).to_byte()
}
}
@types.Image16::{
width,
height,
channels: out_ch,
data: Bytes::from_array(out_data),
}
}