Avoid cloning every frame metadata

Author: kornelski

src/common.rs

@@ -338,6 +338,24 @@ impl Frame<'static> {
         }
         Frame::from_rgba_speed(width, height, &mut vec, speed)
     }
+
+    /// Leaves empty buffer and empty palette behind
+    #[inline]
+    pub(crate) fn take(&mut self) -> Self {
+        Frame {
+            delay: self.delay,
+            dispose: self.dispose,
+            transparent: self.transparent,
+            needs_user_input: self.needs_user_input,
+            top: self.top,
+            left: self.left,
+            width: self.width,
+            height: self.height,
+            interlaced: self.interlaced,
+            palette: std::mem::take(&mut self.palette),
+            buffer: std::mem::replace(&mut self.buffer, Cow::Borrowed(&[])),
+        }
+    }
 }
 
 #[test]

src/reader/decoder.rs

@@ -141,7 +141,7 @@ pub enum Decoded<'a> {
     /// Decoded all information of the next frame, except the image data.
     ///
     /// The returned frame does **not** contain any owned image data.
-    FrameMetadata(&'a Frame<'static>, FrameDataType),
+    FrameMetadata(&'a mut Frame<'static>, FrameDataType),
     /// Decoded some data of the current frame.
     BytesDecoded(usize),
     /// Copied (or consumed and discarded) compressed data of the current frame. In bytes.

src/reader/mod.rs

@@ -308,9 +308,9 @@ impl<R> Decoder<R> where R: Read {
         loop {
             match self.decoder.decode_next(&mut OutputBuffer::None)? {
                 Some(Decoded::FrameMetadata(frame, frame_data_type)) => {
-                    self.current_frame = frame.clone();
+                    self.current_frame = frame.take();
                     self.current_frame_data_type = frame_data_type;
-                    if frame.palette.is_none() && self.global_palette.is_none() {
+                    if self.current_frame.palette.is_none() && self.global_palette.is_none() {
                         return Err(DecodingError::format(
                             "no color table available for current frame",
                         ));

tests/decode.rs

@@ -107,8 +107,13 @@ fn check_skip_frame_data_decode_frame_error() {
     let mut skipping_decoder = options.read_info(image).unwrap();
     let mut normal_decoder = DecodeOptions::new().read_info(image).unwrap();
 
-    while let Ok(Some(_normal_frame)) = normal_decoder.read_next_frame() {
-        let _compressed_frame = skipping_decoder.read_next_frame().unwrap().unwrap();
+    while let Ok(Some(normal_frame)) = normal_decoder.read_next_frame() {
+        let compressed_frame = skipping_decoder.read_next_frame().unwrap().unwrap();
+        assert_eq!(normal_frame.width, compressed_frame.width);
+        assert_eq!(normal_frame.height, compressed_frame.height);
+        assert_eq!(normal_frame.delay, compressed_frame.delay);
+        assert!(!normal_frame.buffer.is_empty());
+        assert!(!compressed_frame.buffer.is_empty());
     }
     assert!(skipping_decoder.read_next_frame().unwrap().is_none());