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Extract a separate
unfiltered_rows_buffer module.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,112 @@ | ||
| use super::stream::{DecodingError, FormatErrorInner}; | ||
| use crate::common::BytesPerPixel; | ||
| use crate::filter::{unfilter, FilterType}; | ||
|
|
||
| // Buffer for temporarily holding decompressed, not-yet-`unfilter`-ed rows. | ||
| pub(crate) struct UnfilteredRowsBuffer { | ||
| /// Vec containing the uncompressed image data currently being processed. | ||
| data_stream: Vec<u8>, | ||
| /// Index in `data_stream` where the previous row starts. | ||
| /// This excludes the filter type byte - it points at the first byte of actual pixel data. | ||
| /// The pixel data is already-`unfilter`-ed. | ||
| /// If `prev_start == current_start` then it means that there is no previous row. | ||
| prev_start: usize, | ||
| /// Index in `data_stream` where the current row starts. | ||
| /// This points at the filter type byte of the current row (i.e. the actual pixel data starts at `current_start + 1`) | ||
| /// The pixel data is not-yet-`unfilter`-ed. | ||
| current_start: usize, | ||
| } | ||
|
|
||
| impl UnfilteredRowsBuffer { | ||
| /// Asserts in debug builds that all the invariants hold. No-op in release | ||
| /// builds. Intended to be called after creating or mutating `self` to | ||
| /// ensure that the final state preserves the invariants. | ||
| fn debug_assert_invariants(&self) { | ||
| debug_assert!(self.prev_start <= self.current_start); | ||
| debug_assert!(self.prev_start <= self.data_stream.len()); | ||
| debug_assert!(self.current_start <= self.data_stream.len()); | ||
| } | ||
|
|
||
| pub fn new() -> Self { | ||
| let result = Self { | ||
| data_stream: Vec::new(), | ||
| prev_start: 0, | ||
| current_start: 0, | ||
| }; | ||
| result.debug_assert_invariants(); | ||
| result | ||
| } | ||
|
|
||
| /// Called to indicate that there is no previous row (e.g. when the current | ||
| /// row is the first scanline of a given Adam7 pass). | ||
| pub fn reset_prev_row(&mut self) { | ||
| self.prev_start = self.current_start; | ||
| self.debug_assert_invariants(); | ||
| } | ||
|
|
||
| /// Returns the previous (already `unfilter`-ed) row. | ||
| pub fn prev_row(&self) -> &[u8] { | ||
| // No point calling this if there is no previous row. | ||
| debug_assert!(self.prev_start < self.current_start); | ||
|
|
||
| &self.data_stream[self.prev_start..self.current_start] | ||
| } | ||
|
|
||
| /// Returns how many bytes of the current row are present in the buffer. | ||
| pub fn curr_row_len(&self) -> usize { | ||
| self.data_stream.len() - self.current_start | ||
| } | ||
|
|
||
| /// Returns a `&mut Vec<u8>` suitable for passing to | ||
| /// `ReadDecoder.decode_image_data` or `StreamingDecoder.update`. | ||
| /// | ||
| /// Invariants of `self` depend on the assumption that the caller will only | ||
| /// append new bytes to the returned vector (which is indeed the behavior of | ||
| /// `ReadDecoder` and `StreamingDecoder`). TODO: Consider protecting the | ||
| /// invariants by returning an append-only view of the vector | ||
| /// (`FnMut(&[u8])`??? or maybe `std::io::Write`???). | ||
| pub fn as_mut_vec(&mut self) -> &mut Vec<u8> { | ||
| // Opportunistically compact the current buffer by discarding bytes | ||
| // before `prev_start`. | ||
| if self.prev_start > 0 { | ||
| self.data_stream.copy_within(self.prev_start.., 0); | ||
| self.data_stream | ||
| .truncate(self.data_stream.len() - self.prev_start); | ||
| self.current_start -= self.prev_start; | ||
| self.prev_start = 0; | ||
| self.debug_assert_invariants(); | ||
| } | ||
|
|
||
| &mut self.data_stream | ||
| } | ||
|
|
||
| /// Runs `unfilter` on the current row, and then shifts rows so that the current row becomes the previous row. | ||
| /// | ||
| /// Will panic if `self.curr_row_len() < rowlen`. | ||
| pub fn unfilter_curr_row( | ||
| &mut self, | ||
| rowlen: usize, | ||
| bpp: BytesPerPixel, | ||
| ) -> Result<(), DecodingError> { | ||
| debug_assert!(rowlen >= 2); // 1 byte for `FilterType` and at least 1 byte of pixel data. | ||
|
|
||
| let (prev, row) = self.data_stream.split_at_mut(self.current_start); | ||
| let prev: &[u8] = prev; // `prev` is immutable | ||
| let prev = &prev[self.prev_start..]; | ||
| debug_assert!(prev.is_empty() || prev.len() == (rowlen - 1)); | ||
|
|
||
| // Get the filter type. | ||
| let filter = FilterType::from_u8(row[0]).ok_or(DecodingError::Format( | ||
| FormatErrorInner::UnknownFilterMethod(row[0]).into(), | ||
| ))?; | ||
| let row = &mut row[1..rowlen]; | ||
|
|
||
| unfilter(filter, bpp, prev, row); | ||
|
|
||
| self.prev_start = self.current_start + 1; | ||
| self.current_start += rowlen; | ||
| self.debug_assert_invariants(); | ||
|
|
||
| Ok(()) | ||
| } | ||
| } |