这是一个独立的、纯 Rust 实现的 PNG 图像写入函数。
它基于我的 Python 答案here。
注意事项：
- 由于 Rust 没有公开 zlib，这比原始 Python 代码要大很多。
- 这通过写入未压缩的图像来避免使用 zlib。
-
crc32 和 adler32 校验和实现作为模块包含在内。
- 要检查的关键函数是
write，它采用任何可写类型（通常是文件）。
例子：
mod crc32 {
// https://github.com/ledbettj/crc32/blob/master/rust/src/crc32.rs
pub struct Crc32 {
table: [u32; 256],
value: u32,
}
const CRC32_INITIAL: u32 = 0xedb88320;
impl Crc32 {
pub fn new() -> Crc32 {
let mut c = Crc32 {
table: [0; 256],
value: 0xffffffff,
};
for i in 0..256 {
let mut v = i as u32;
for _ in 0..8 {
v = if v & 1 != 0 {
CRC32_INITIAL ^ (v >> 1)
} else {
v >> 1
}
}
c.table[i] = v;
}
return c;
}
pub fn start(&mut self) {
self.value = 0xffffffff;
}
pub fn update(&mut self, buf: &[u8]) {
for &i in buf {
self.value = self.table[((self.value ^ (i as u32)) & 0xff) as usize] ^
(self.value >> 8);
}
}
pub fn finalize(&mut self) -> u32 {
self.value ^ 0xffffffff_u32
}
#[allow(dead_code)]
pub fn crc(&mut self, buf: &[u8]) -> u32 {
self.start();
self.update(buf);
self.finalize()
}
}
}
mod adler32 {
// https://en.wikipedia.org/wiki/Adler-32
pub struct Adler32 {
a: u32,
b: u32,
}
const MOD_ADLER: u32 = 65521;
impl Adler32 {
pub fn new() -> Adler32 {
Adler32 { a: 1, b: 0 }
}
pub fn start(&mut self) {
self.a = 1;
self.b = 0;
}
pub fn update(&mut self, buf: &[u8]) {
for &i in buf {
self.a = (self.a + i as u32) % MOD_ADLER;
self.b = (self.a + self.b) % MOD_ADLER;
}
}
pub fn finalize(&self) -> u32 {
return (self.b << 16) | self.a;
}
#[allow(dead_code)]
pub fn crc(&mut self, buf: &[u8]) -> u32 {
self.start();
self.update(buf);
self.finalize()
}
}
}
// big endian
#[inline]
fn u32_to_u8_be(v: u32) -> [u8; 4] {
[(v >> 24) as u8, (v >> 16) as u8, (v >> 8) as u8, v as u8]
}
mod fake_zlib {
use super::adler32;
use super::u32_to_u8_be;
// Use 'none' compression
pub fn compress(data: &[u8]) -> Vec<u8> {
const CHUNK_SIZE: usize = 65530;
let final_len =
// header
2 +
// every chunk adds 5 bytes [1:type, 4:size].
(5 * {
let n = data.len() / CHUNK_SIZE;
// include an extra chunk when we don't fit exactly into CHUNK_SIZE
(n + {if data.len() == n * CHUNK_SIZE && data.len() != 0 { 0 } else { 1 }})
}) +
// data
data.len() +
// crc
4
;
let mut raw_data = Vec::with_capacity(final_len);
// header
raw_data.extend(&[120, 1]);
let mut pos_curr = 0_usize;
let mut crc = adler32::Adler32::new();
loop {
let pos_next = ::std::cmp::min(data.len(), pos_curr + CHUNK_SIZE);
let chunk_len = (pos_next - pos_curr) as u32;
let is_last = pos_next == data.len();
raw_data.extend(&[
// type
if is_last { 1 } else { 0 },
// size
(chunk_len & 0xff) as u8,
((chunk_len >> 8) & 0xff) as u8,
(0xff - (chunk_len & 0xff)) as u8,
(0xff - ((chunk_len >> 8) & 0xff)) as u8,
]);
raw_data.extend(&data[pos_curr..pos_next]);
crc.update(&data[pos_curr..pos_next]);
if is_last {
break;
}
pos_curr = pos_next;
}
raw_data.extend(&u32_to_u8_be(crc.finalize()));
assert_eq!(final_len, raw_data.len());
return raw_data;
}
}
///
/// Write RGBA pixels to uncompressed PNG.
///
pub fn write<W: ::std::io::Write>(
file: &mut W,
image: &[u8],
w: u32,
h: u32,
) -> Result<(), ::std::io::Error> {
assert!(w as usize * h as usize * 4 == image.len());
fn png_pack<W: ::std::io::Write>(
file: &mut W,
png_tag: &[u8; 4],
data: &[u8],
) -> Result<(), ::std::io::Error> {
file.write(&u32_to_u8_be(data.len() as u32))?;
file.write(png_tag)?;
file.write(data)?;
{
let mut crc = crc32::Crc32::new();
crc.start();
crc.update(png_tag);
crc.update(data);
file.write(&u32_to_u8_be(crc.finalize()))?;
}
Ok(())
}
file.write(b"\x89PNG\r\n\x1a\n")?;
{
let wb = u32_to_u8_be(w);
let hb = u32_to_u8_be(h);
let data = [wb[0], wb[1], wb[2], wb[3],
hb[0], hb[1], hb[2], hb[3],
8, 6, 0, 0, 0];
png_pack(file, b"IHDR", &data)?;
}
{
let width_byte_4 = w * 4;
let final_len = (width_byte_4 + 1) * h;
let mut raw_data = Vec::with_capacity(final_len as usize);
let mut span: u32 = (h - 1) * width_byte_4;
loop {
raw_data.push(0);
raw_data.extend(&image[(span as usize)..(span + width_byte_4) as usize]);
if span == 0 {
break;
}
span -= width_byte_4;
}
assert!(final_len == (raw_data.len() as u32));
png_pack(file, b"IDAT", &fake_zlib::compress(&raw_data))?;
}
png_pack(file, b"IEND", &[])?;
Ok(())
}
fn main() {
let mut f = std::fs::File::create("test.png").unwrap();
// image from bottom to top 3x2
let image_width = 3;
let image_height = 2;
let image = vec!(
// R G B A
0xff, 0x00, 0x00, 0xff,
0x00, 0xff, 0x00, 0xff,
0x00, 0x00, 0xff, 0xff,
0x80, 0x00, 0x00, 0xff,
0x00, 0x80, 0x00, 0xff,
0x00, 0x00, 0x80, 0xff,
);
match write(&mut f, &image, image_width, image_height) {
Ok(_) => println!("Written image!"),
Err(e) => println!("Error {:?}", e),
}
}
这个后来做成了png_encode_mini crate，和这个sn-p基本一样。