From f8c62de6c04d3cae30c6b6e308689131b57b5284 Mon Sep 17 00:00:00 2001
From: Josh Holmer <joshua.holmer@nextgearcapital.com>
Date: Sat, 23 Dec 2017 00:36:41 -0500
Subject: [PATCH] Fix unfiltering of first scan line in each pass of an
 interlaced input file

Closes #92
---
 CHANGELOG.md             |   1 +
 src/png.rs               |   7 +++++++
 tests/files/issue-92.png | Bin 0 -> 1909 bytes
 tests/regression.rs      |  38 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 46 insertions(+)
 create mode 100644 tests/files/issue-92.png

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4b46e357..8ead3f13 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 ### Version 0.18.2 (unreleased)
  - Bump `image` to 0.18
+ - Fix unfiltering of scan lines in interlaced images ([#92](https://github.com/shssoichiro/oxipng/issues/92))
 
 ### Version 0.18.1
  - Bump `rayon` to 0.9
diff --git a/src/png.rs b/src/png.rs
index dd35046f..a6b8a6d2 100644
--- a/src/png.rs
+++ b/src/png.rs
@@ -377,7 +377,14 @@ impl PngData {
             8f32)
             .ceil() as usize;
         let mut last_line: Vec<u8> = Vec::new();
+        let mut last_pass = 1;
         for line in self.scan_lines() {
+            if let Some(pass) = line.pass {
+                if pass != last_pass {
+                    last_line = Vec::new();
+                    last_pass = pass;
+                }
+            }
             let unfiltered_line = unfilter_line(line.filter, bpp, &line.data, &last_line);
             unfiltered.push(0);
             unfiltered.extend_from_slice(&unfiltered_line);
diff --git a/tests/files/issue-92.png b/tests/files/issue-92.png
new file mode 100644
index 0000000000000000000000000000000000000000..e1b5f96cdb06dcbbfacab5d87a473d2b5b54f062
GIT binary patch
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diff --git a/tests/regression.rs b/tests/regression.rs
index 02b5498c..77d91496 100644
--- a/tests/regression.rs
+++ b/tests/regression.rs
@@ -325,3 +325,41 @@ fn issue_89() {
         BitDepth::Eight,
     );
 }
+
+#[test]
+fn issue_92_filter_0() {
+    let input = PathBuf::from("tests/files/issue-92.png");
+    let opts = get_opts(&input);
+    let output = opts.out_file.clone();
+
+    test_it_converts(
+        &input,
+        &output,
+        &opts,
+        ColorType::Grayscale,
+        BitDepth::Eight,
+        ColorType::Grayscale,
+        BitDepth::Eight,
+    );
+}
+
+#[test]
+fn issue_92_filter_5() {
+    let input = PathBuf::from("tests/files/issue-92.png");
+    let mut opts = get_opts(&input);
+    let mut filter = HashSet::new();
+    filter.insert(5);
+    opts.filter = filter;
+    opts.out_file = input.with_extension("-f5-out.png").to_owned();
+    let output = opts.out_file.clone();
+
+    test_it_converts(
+        &input,
+        &output,
+        &opts,
+        ColorType::Grayscale,
+        BitDepth::Eight,
+        ColorType::Grayscale,
+        BitDepth::Eight,
+    );
+}