Immutable interlace reductions

benches/interlacing.rs

@@ -14,7 +14,7 @@ fn interlacing_16_bits(b: &mut Bencher) {
 
     b.iter(|| {
         let mut safe_png = png.clone();
-        safe_png.change_interlacing(1);
+        safe_png.change_interlacing(1)
     });
 }
 
@@ -25,7 +25,7 @@ fn interlacing_8_bits(b: &mut Bencher) {
 
     b.iter(|| {
         let mut safe_png = png.clone();
-        safe_png.change_interlacing(1);
+        safe_png.change_interlacing(1)
     });
 }
 
@@ -38,7 +38,7 @@ fn interlacing_4_bits(b: &mut Bencher) {
 
     b.iter(|| {
         let mut safe_png = png.clone();
-        safe_png.change_interlacing(1);
+        safe_png.change_interlacing(1)
     });
 }
 
@@ -51,7 +51,7 @@ fn interlacing_2_bits(b: &mut Bencher) {
 
     b.iter(|| {
         let mut safe_png = png.clone();
-        safe_png.change_interlacing(1);
+        safe_png.change_interlacing(1)
     });
 }
 
@@ -64,7 +64,7 @@ fn interlacing_1_bits(b: &mut Bencher) {
 
     b.iter(|| {
         let mut safe_png = png.clone();
-        safe_png.change_interlacing(1);
+        safe_png.change_interlacing(1)
     });
 }
 
@@ -77,7 +77,7 @@ fn deinterlacing_16_bits(b: &mut Bencher) {
 
     b.iter(|| {
         let mut safe_png = png.clone();
-        safe_png.change_interlacing(0);
+        safe_png.change_interlacing(0)
     });
 }
 
@@ -90,7 +90,7 @@ fn deinterlacing_8_bits(b: &mut Bencher) {
 
     b.iter(|| {
         let mut safe_png = png.clone();
-        safe_png.change_interlacing(0);
+        safe_png.change_interlacing(0)
     });
 }
 
@@ -103,7 +103,7 @@ fn deinterlacing_4_bits(b: &mut Bencher) {
 
     b.iter(|| {
         let mut safe_png = png.clone();
-        safe_png.change_interlacing(0);
+        safe_png.change_interlacing(0)
     });
 }
 
@@ -116,7 +116,7 @@ fn deinterlacing_2_bits(b: &mut Bencher) {
 
     b.iter(|| {
         let mut safe_png = png.clone();
-        safe_png.change_interlacing(0);
+        safe_png.change_interlacing(0)
     });
 }
 
@@ -129,6 +129,6 @@ fn deinterlacing_1_bits(b: &mut Bencher) {
 
     b.iter(|| {
         let mut safe_png = png.clone();
-        safe_png.change_interlacing(0);
+        safe_png.change_interlacing(0)
     });
 }

src/interlace.rs

@@ -1,7 +1,9 @@
+use reduction::ReducedPng;
 use bit_vec::BitVec;
 use png::PngData;
 
-pub fn interlace_image(png: &mut PngData) {
+#[must_use]
+pub fn interlace_image(png: &PngData) -> ReducedPng {
     let mut passes: Vec<BitVec> = vec![BitVec::new(); 7];
     let bits_per_pixel = png.ihdr_data.bit_depth.as_u8() * png.channels_per_pixel();
     for (index, line) in png.scan_lines().enumerate() {
@@ -74,14 +76,24 @@ pub fn interlace_image(png: &mut PngData) {
             }
         }
     }
-    let mut output = Vec::new();
+
+    let mut output = Vec::with_capacity(png.raw_data.len());
     for pass in &passes {
         output.extend(pass.to_bytes());
     }
-    png.raw_data = output;
+
+    ReducedPng {
+        raw_data: output,
+        interlaced: 1,
+        color_type: png.ihdr_data.color_type,
+        bit_depth: png.ihdr_data.bit_depth,
+        aux_headers: Default::default(),
+        palette: None,
+        transparency_pixel: None,
+    }
 }
 
-pub fn deinterlace_image(png: &mut PngData) {
+pub fn deinterlace_image(png: &PngData) -> ReducedPng {
     let bits_per_pixel = png.ihdr_data.bit_depth.as_u8() * png.channels_per_pixel();
     let bits_per_line = 8 + bits_per_pixel as usize * png.ihdr_data.width as usize;
     // Initialize each output line with a starting filter byte of 0
@@ -126,14 +138,22 @@ pub fn deinterlace_image(png: &mut PngData) {
             current_y = pass_constants.y_shift as usize;
         }
     }
-    let mut output = Vec::new();
+    let mut output = Vec::with_capacity(png.raw_data.len());
     for line in &mut lines {
         while line.len() % 8 != 0 {
             line.push(false);
         }
         output.extend(line.to_bytes());
     }
-    png.raw_data = output;
+    ReducedPng {
+        raw_data: output,
+        interlaced: 0,
+        color_type: png.ihdr_data.color_type,
+        bit_depth: png.ihdr_data.bit_depth,
+        aux_headers: Default::default(),
+        palette: None,
+        transparency_pixel: None,
+    }
 }
 
 #[derive(Clone, Copy)]

src/lib.rs

@@ -766,8 +766,8 @@ fn perform_reductions(png: &mut PngData, opts: &Options, deadline: &Deadline) ->
     }
 
     if let Some(interlacing) = opts.interlace {
-        if png.change_interlacing(interlacing) {
-            png.ihdr_data.interlaced = interlacing;
+        if let Some(reduced) = png.change_interlacing(interlacing) {
+            png.apply_reduction(reduced);
             reduction_occurred = true;
         }
     }

src/png/mod.rs

@@ -365,6 +365,7 @@ impl PngData {
 
         Some(ReducedPng {
             color_type: self.ihdr_data.color_type,
+            interlaced: self.ihdr_data.interlaced,
             bit_depth: BitDepth::Eight,
             raw_data: reduced,
             palette: self.palette.clone(),
@@ -419,9 +420,10 @@ impl PngData {
         changed
     }
 
-    pub(crate) fn apply_reduction(&mut self, ReducedPng {color_type, bit_depth, raw_data, palette, transparency_pixel, aux_headers}: ReducedPng) {
+    pub(crate) fn apply_reduction(&mut self, ReducedPng {color_type, bit_depth, raw_data, interlaced, palette, transparency_pixel, aux_headers}: ReducedPng) {
         self.ihdr_data.color_type = color_type;
         self.ihdr_data.bit_depth = bit_depth;
+        self.ihdr_data.interlaced = interlaced;
         self.raw_data = raw_data;
         if palette.is_some() {
             self.transparency_pixel = None;
@@ -652,19 +654,19 @@ impl PngData {
     /// The `interlace` parameter specifies the *new* interlacing mode
     /// Assumes that the data has already been de-filtered
     #[inline]
-    pub fn change_interlacing(&mut self, interlace: u8) -> bool {
+    #[must_use]
+    pub fn change_interlacing(&mut self, interlace: u8) -> Option<ReducedPng> {
         if interlace == self.ihdr_data.interlaced {
-            return false;
+            return None;
         }
 
-        if interlace == 1 {
+        Some(if interlace == 1 {
             // Convert progressive to interlaced data
-            interlace_image(self);
+            interlace_image(self)
         } else {
             // Convert interlaced to progressive data
-            deinterlace_image(self);
-        }
-        true
+            deinterlace_image(self)
+        })
     }
 }
 

src/reduction/alpha.rs

@@ -47,6 +47,7 @@ pub fn reduced_alpha_channel(png: &PngData) -> Option<ReducedPng> {
     Some(ReducedPng {
         raw_data,
         bit_depth: png.ihdr_data.bit_depth,
+        interlaced: png.ihdr_data.interlaced,
         color_type: target_color_type,
         aux_headers,
         transparency_pixel: None,

src/reduction/bit_depth.rs

@@ -82,6 +82,7 @@ pub fn reduce_bit_depth_8_or_less(png: &PngData) -> Option<ReducedPng> {
 
     Some(ReducedPng {
         color_type: png.ihdr_data.color_type,
+        interlaced: png.ihdr_data.interlaced,
         raw_data: reduced.to_bytes(),
         bit_depth: BitDepth::from_u8(allowed_bits as u8),
         aux_headers: Default::default(),

src/reduction/color.rs

@@ -61,6 +61,7 @@ pub fn reduce_rgba_to_grayscale_alpha(png: &PngData) -> Option<ReducedPng> {
     Some(ReducedPng {
         raw_data: reduced,
         bit_depth: png.ihdr_data.bit_depth,
+        interlaced: png.ihdr_data.interlaced,
         color_type: ColorType::GrayscaleAlpha,
         palette: None,
         transparency_pixel: None,
@@ -178,6 +179,7 @@ pub fn reduced_color_to_palette(png: &PngData) -> Option<ReducedPng> {
     Some(ReducedPng {
         color_type: ColorType::Indexed,
         bit_depth: png.ihdr_data.bit_depth,
+        interlaced: png.ihdr_data.interlaced,
         aux_headers,
         raw_data,
         transparency_pixel: None,
@@ -242,6 +244,7 @@ pub fn reduce_rgb_to_grayscale(png: &PngData) -> Option<ReducedPng> {
         raw_data: reduced,
         color_type: ColorType::Grayscale,
         bit_depth: png.ihdr_data.bit_depth,
+        interlaced: png.ihdr_data.interlaced,
         palette: None,
         transparency_pixel,
         aux_headers,

src/reduction/mod.rs

@@ -19,6 +19,7 @@ pub struct ReducedPng {
     pub transparency_pixel: Option<Vec<u8>>,
     /// replace if Some, delete if None
     pub aux_headers: HashMap<[u8; 4], Option<Vec<u8>>>,
+    pub interlaced: u8,
 }
 
 /// Attempt to reduce the number of colors in the palette
@@ -109,6 +110,7 @@ fn do_palette_reduction(png: &PngData, palette_map: &[Option<u8>; 256]) -> Optio
     Some(ReducedPng {
         color_type: ColorType::Indexed,
         bit_depth: png.ihdr_data.bit_depth,
+        interlaced: png.ihdr_data.interlaced,
         raw_data,
         transparency_pixel: None,
         palette: Some(reordered_palette(png.palette.as_ref()?, palette_map)),