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Filtering microoptimizations

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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
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14
src/png/mod.rs
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@ -254,7 +254,7 @@ impl PngData {
pub fn filter_image(&self, filter: u8) -> Vec<u8> { pub fn filter_image(&self, filter: u8) -> Vec<u8> {
let mut filtered = Vec::with_capacity(self.raw_data.len()); 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 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; let mut last_pass: Option<u8> = None;
for line in self.scan_lines() { for line in self.scan_lines() {
match filter { match filter {
@ -265,21 +265,21 @@ impl PngData {
0 0
}; };
filtered.push(filter); 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 => { 5 => {
// Heuristically guess best filter per line // Heuristically guess best filter per line
// Uses MSAD algorithm mentioned in libpng reference docs // Uses MSAD algorithm mentioned in libpng reference docs
// http://www.libpng.org/pub/png/book/chapter09.html // 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 // Avoid vertical filtering on first line of each interlacing pass
for filter in if last_pass == line.pass { 0..5 } else { 0..2 } { 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 let (best_filter, best_line) = trials
.iter() .iter()
.min_by_key(|x| { .min_by_key(|(_, line)| {
x.1.iter().fold(0u64, |acc, &x| { line.iter().fold(0u64, |acc, &x| {
let signed = x as i8; let signed = x as i8;
acc + i16::from(signed).abs() as u64 acc + i16::from(signed).abs() as u64
}) })
@ -289,7 +289,7 @@ impl PngData {
} }
_ => unreachable!(), _ => unreachable!(),
} }
last_line = line.data.to_vec(); last_line = line.data;
last_pass = line.pass; last_pass = line.pass;
} }
filtered filtered