Vendor things

third-party/vendor/png/src/test_utils.rs

@@ -0,0 +1,118 @@
+//! A set of test utilities.
+//!
+//! There is some overlap between this module and `src/encoder.rs` module, but:
+//!
+//! * This module (unlike `src/encoder.rs`) performs no validation of the data being written - this
+//!   allows building testcases that use arbitrary, potentially invalid PNGs as input.
+//! * This module can be reused from `benches/decoder.rs` (a separate crate).
+
+use byteorder::WriteBytesExt;
+use std::io::Write;
+
+/// Generates a store-only, non-compressed image:
+///
+/// * `00` compression mode (i.e.`BTYPE` = `00` = no compression) is used
+/// * No filter is applied to the image rows
+///
+/// Currently the image always has the following properties:
+///
+/// * Single `IDAT` chunk
+/// * Zlib chunks of maximum possible size
+/// * 8-bit RGBA
+///
+/// These images are somewhat artificial, but may be useful for benchmarking performance of parts
+/// outside of `fdeflate` crate and/or the `unfilter` function (e.g. these images were originally
+/// used to evaluate changes to minimize copying of image pixels between various buffers - see
+/// [this
+/// discussion](https://github.com/image-rs/image-png/discussions/416#discussioncomment-7436871)
+/// for more details).
+#[allow(dead_code)] // Used from `benches/decoder.rs`
+pub fn write_noncompressed_png(w: &mut impl Write, size: u32, idat_bytes: usize) {
+    write_png_sig(w);
+    write_rgba8_ihdr_with_width(w, size);
+    write_rgba8_idats(w, size, idat_bytes);
+    write_iend(w);
+}
+
+/// Writes PNG signature.
+/// See http://www.libpng.org/pub/png/spec/1.2/PNG-Structure.html#PNG-file-signature
+pub fn write_png_sig(w: &mut impl Write) {
+    const SIG: [u8; 8] = [137, 80, 78, 71, 13, 10, 26, 10];
+    w.write_all(&SIG).unwrap();
+}
+
+/// Writes an arbitrary PNG chunk.
+pub fn write_chunk(w: &mut impl Write, chunk_type: &[u8], data: &[u8]) {
+    assert_eq!(chunk_type.len(), 4);
+    let crc = {
+        let input = chunk_type
+            .iter()
+            .copied()
+            .chain(data.iter().copied())
+            .collect::<Vec<_>>();
+        crc32fast::hash(input.as_slice())
+    };
+    w.write_u32::<byteorder::BigEndian>(data.len() as u32)
+        .unwrap();
+    w.write_all(chunk_type).unwrap();
+    w.write_all(data).unwrap();
+    w.write_u32::<byteorder::BigEndian>(crc).unwrap();
+}
+
+/// Writes an IHDR chunk that indicates a non-interlaced RGBA8 that uses the same height and
+/// `width`.  See http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html#C.IHDR
+pub fn write_rgba8_ihdr_with_width(w: &mut impl Write, width: u32) {
+    let mut data = Vec::new();
+    data.write_u32::<byteorder::BigEndian>(width).unwrap();
+    data.write_u32::<byteorder::BigEndian>(width).unwrap(); // height
+    data.write_u8(8).unwrap(); // bit depth = always 8-bits per channel
+    data.write_u8(6).unwrap(); // color type = color + alpha
+    data.write_u8(0).unwrap(); // compression method (0 is the only allowed value)
+    data.write_u8(0).unwrap(); // filter method (0 is the only allowed value)
+    data.write_u8(0).unwrap(); // interlace method = no interlacing
+    write_chunk(w, b"IHDR", &data);
+}
+
+/// Generates RGBA8 `width` x `height` image and wraps it in a store-only zlib container.
+pub fn generate_rgba8_with_width_and_height(width: u32, height: u32) -> Vec<u8> {
+    // Generate arbitrary test pixels.
+    let image_pixels = {
+        let mut row = Vec::new();
+        row.write_u8(0).unwrap(); // filter = no filter
+
+        let row_pixels = (0..width).flat_map(|i| {
+            let color: u8 = (i * 255 / width) as u8;
+            let alpha: u8 = 0xff;
+            [color, 255 - color, color / 2, alpha]
+        });
+        row.extend(row_pixels);
+
+        std::iter::repeat(row)
+            .take(height as usize)
+            .flatten()
+            .collect::<Vec<_>>()
+    };
+
+    let mut zlib_data = Vec::new();
+    let mut store_only_compressor =
+        fdeflate::StoredOnlyCompressor::new(std::io::Cursor::new(&mut zlib_data)).unwrap();
+    store_only_compressor.write_data(&image_pixels).unwrap();
+    store_only_compressor.finish().unwrap();
+
+    zlib_data
+}
+
+/// Writes an IDAT chunk.
+pub fn write_rgba8_idats(w: &mut impl Write, size: u32, idat_bytes: usize) {
+    let data = generate_rgba8_with_width_and_height(size, size);
+
+    for chunk in data.chunks(idat_bytes) {
+        write_chunk(w, b"IDAT", chunk);
+    }
+}
+
+/// Writes an IEND chunk.
+/// See http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html#C.IEND
+pub fn write_iend(w: &mut impl Write) {
+    write_chunk(w, b"IEND", &[]);
+}