Fix issue with alpha optim on interlaced images

Closes #113

CHANGELOG.md

@@ -1,3 +1,6 @@
+### Version 2.0.2
+ - Fix an issue in alpha optimization on interlaced images ([#113](https://github.com/shssoichiro/oxipng/issues/113))
+
 ### Version 2.0.1
  - Revert making Cloudflare zlib the default, as it introduced a major memory leak. It will be put back behind a feature flag, and reenabled when the issue is fixed.
 

src/png/mod.rs

@@ -713,10 +713,14 @@ impl PngData {
 
     fn reduce_alpha_to_up(&self, bpc: usize, bpp: usize) -> Vec<u8> {
         let mut lines = Vec::new();
-        let scan_lines = self.scan_lines().collect::<Vec<ScanLine>>();
+        let scan_lines = self.scan_lines()
+            .collect::<Vec<ScanLine>>()
+            .into_iter()
+            .rev()
+            .collect::<Vec<ScanLine>>();
         let mut last_line = vec![0; scan_lines[0].data.len()];
         let mut current_line = Vec::with_capacity(last_line.len());
-        for line in scan_lines.into_iter().rev() {
+        for line in scan_lines.into_iter() {
             current_line.push(line.filter);
             for (pixel, last_pixel) in line.data.chunks(bpp).zip(last_line.chunks(bpp)) {
                 if pixel.iter().skip(bpp - bpc).fold(0, |sum, i| sum | i) == 0 {

tests/regression.rs

@@ -289,3 +289,23 @@ fn issue_92_filter_5() {
         BitDepth::Eight,
     );
 }
+
+#[test]
+fn issue_113() {
+    let input = "tests/files/issue-113.png";
+    let (_, mut opts) = get_opts(Path::new(input));
+    opts.interlace = Some(1);
+    opts.alphas = HashSet::new();
+    opts.alphas.insert(AlphaOptim::Up);
+    let output = OutFile::Path(Some(
+        Path::new(input).with_extension("-f5-out.png").to_owned(),
+    ));
+    test_it_converts(
+        input,
+        Some((output, opts)),
+        ColorType::RGBA,
+        BitDepth::Eight,
+        ColorType::GrayscaleAlpha,
+        BitDepth::Eight,
+    );
+}