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///|
/// HEIF (High Efficiency Image File Format) 解码器
///
/// HEIF 基于 HEVC (H.265) 编码，使用 ISOBMFF 容器格式。
/// 本模块提供格式检测和基本头部解析，完整解码需 HEVC 解码器支持。
///
/// Magic bytes: 0x00 0x00 0x00 0x?? 0x66 0x74 0x79 0x70 0x68 0x65 0x69 0x63
/// (ftyp box with brand "heic", "heix", "hevc", or "mif1")
///|
/// HEIF 图像信息
pub struct HeifInfo {
width : Int
height : Int
bit_depth : Int
num_channels : Int
has_alpha : Bool
}
///|
/// 检测数据是否为 HEIF 格式
///
/// HEIF 文件以 ftyp box 开头，brand 为 "heic", "heix", "hevc", "hevm", "heim", "heis", "mif1" 等
pub fn is_heif_format(data : Bytes) -> Bool {
let len = data.length()
if len < 12 {
return false
}
// 检查 ftyp box: bytes 4-7 = "ftyp"
if data[4] != b'f' || data[5] != b't' || data[6] != b'y' || data[7] != b'p' {
return false
}
let b8 = data[8]
let b9 = data[9]
let b10 = data[10]
let b11 = data[11]
// "heic" = 0x68 0x65 0x69 0x63
if b8 == b'h' && b9 == b'e' && b10 == b'i' && b11 == b'c' {
return true
}
// "heix" = 0x68 0x65 0x69 0x78
if b8 == b'h' && b9 == b'e' && b10 == b'i' && b11 == b'x' {
return true
}
// "hevc" = 0x68 0x65 0x76 0x63
if b8 == b'h' && b9 == b'e' && b10 == b'v' && b11 == b'c' {
return true
}
// "mif1" = 0x6D 0x69 0x66 0x31
if b8 == b'm' && b9 == b'i' && b10 == b'f' && b11 == b'1' {
return true
}
false
}
///|
/// 解析 HEIF 头部信息
///
/// 解析 ISOBMFF box 结构，提取图像尺寸和位深信息。
pub fn heif_info(data : Bytes) -> HeifInfo raise @types.LoadError {
if !is_heif_format(data) {
raise @types.LoadError::UnsupportedFormat("Not a HEIF file")
}
let len = data.length()
let mut offset = 0
let mut width = 0
let mut height = 0
let mut bit_depth = 8
let mut has_alpha = false
// 遍历 ISOBMFF boxes
while offset + 8 <= len {
let box_size = (data[offset].to_int() << 24) |
(data[offset + 1].to_int() << 16) |
(data[offset + 2].to_int() << 8) |
data[offset + 3].to_int()
if box_size < 8 || offset + box_size > len {
break
}
let box_type_0 = data[offset + 4]
let box_type_1 = data[offset + 5]
let box_type_2 = data[offset + 6]
let box_type_3 = data[offset + 7]
// 检查 ispe box (ImageSpatialExtentsProperty)
if box_type_0 == b'i' &&
box_type_1 == b's' &&
box_type_2 == b'p' &&
box_type_3 == b'e' {
if offset + 20 <= len {
width = (data[offset + 12].to_int() << 24) |
(data[offset + 13].to_int() << 16) |
(data[offset + 14].to_int() << 8) |
data[offset + 15].to_int()
height = (data[offset + 16].to_int() << 24) |
(data[offset + 17].to_int() << 16) |
(data[offset + 18].to_int() << 8) |
data[offset + 19].to_int()
}
}
// 检查 auxC box for alpha
if box_type_0 == b'a' &&
box_type_1 == b'u' &&
box_type_2 == b'x' &&
box_type_3 == b'C' {
has_alpha = true
}
// 检查 pixi box for bit depth
if box_type_0 == b'p' &&
box_type_1 == b'i' &&
box_type_2 == b'x' &&
box_type_3 == b'i' {
if offset + 13 <= len {
let num_ch = data[offset + 12].to_int()
if num_ch > 0 && offset + 13 + num_ch <= len {
bit_depth = data[offset + 13].to_int()
}
}
}
offset += box_size
}
if width == 0 || height == 0 {
raise @types.LoadError::DecodeFailed(
"HEIF: could not determine image dimensions",
)
}
let num_channels = if has_alpha { 4 } else { 3 }
HeifInfo::{ width, height, bit_depth, num_channels, has_alpha }
}
///|
/// 解码 HEIF 图像
///
/// 注意：完整 HEIF 解码需要 HEVC 解码器，当前返回 UnsupportedFormat。
/// 使用 heif_info 获取元数据。
pub fn heif_decode(data : Bytes) -> @types.Image raise @types.LoadError {
let info = heif_info(data)
raise @types.LoadError::UnsupportedFormat(
"HEIF decode not yet implemented (HEVC decoder required). Image is \{info.width}x\{info.height} \{info.bit_depth}-bit",
)
}