danvics/oxipng
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Filtering microoptimizations

Browse source
This commit is contained in:
Kornel Lesiński 2018-11-16 16:00:00 +00:00
parent d2f6004482
commit 9a0f0e4e57
1 changed files with 7 additions and 7 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

14
src/png/mod.rs
View file

@ -254,7 +254,7 @@ impl PngData {
pub fn filter_image(&self, filter: u8) -> Vec<u8> {
let mut filtered = Vec::with_capacity(self.raw_data.len());
let bpp = ((self.ihdr_data.bit_depth.as_u8() * self.channels_per_pixel() + 7) / 8) as usize;
let mut last_line: Vec<u8> = Vec::new();
let mut last_line: &[u8] = &[];
let mut last_pass: Option<u8> = None;
for line in self.scan_lines() {
match filter {
@ -265,21 +265,21 @@ impl PngData {
0
};
filtered.push(filter);
filtered.extend_from_slice(&filter_line(filter, bpp, &line.data, &last_line));
filtered.extend_from_slice(&filter_line(filter, bpp, &line.data, last_line));
}
5 => {
// Heuristically guess best filter per line
// Uses MSAD algorithm mentioned in libpng reference docs
// http://www.libpng.org/pub/png/book/chapter09.html
let mut trials: HashMap<u8, Vec<u8>> = HashMap::with_capacity(5);
let mut trials: Vec<(u8, Vec<u8>)> = Vec::with_capacity(5);
// Avoid vertical filtering on first line of each interlacing pass
for filter in if last_pass == line.pass { 0..5 } else { 0..2 } {
trials.insert(filter, filter_line(filter, bpp, &line.data, &last_line));
trials.push((filter, filter_line(filter, bpp, &line.data, last_line)));
}
let (best_filter, best_line) = trials
.iter()
.min_by_key(|x| {
x.1.iter().fold(0u64, |acc, &x| {
.min_by_key(|(_, line)| {
line.iter().fold(0u64, |acc, &x| {
let signed = x as i8;
acc + i16::from(signed).abs() as u64
})
@ -289,7 +289,7 @@ impl PngData {
}
_ => unreachable!(),
}
last_line = line.data.to_vec();
last_line = line.data;
last_pass = line.pass;
}
filtered