memo.md

zigimg

• zigimg's README says:

  This project assume current Zig master (0.10.0+)

  but accutually it only works with 0.11.0+, not 0.10.0+.

  • Mainly due to incompatibilities of std.buildin.Type.StructField.

• Images of any format can be read using Image.fromFilePath/fromFile/fromMemory, as value of the Image type.

• In addition to pixel data, we can get width and height of the image from struct Image.

• An iterator that iterates over pixels of the image can be obtained from Image by iterator method.

I/O in zig

• Via io.FixedBufferStream([]u8), we can use []u8 as io.Writer and io.Reader.

var buf = [100]u8 = undefined;
var stream = std.io.fixedBufferStream(buf); // convenient constructor is available

stream.writer();    // convert to `io.Writer`
stream.reader();    // convert to `io.Reader`

• io.StreamSource abstracts over File(.file), FixedBuffer([]u8)(.buffer) and FixedBuffer([]const u8)(.const_buffer) and offers generic I/O interface w/ seeking.

  • if it is .const_buffer variant, writing to it will always return error.

• io.Writer and io.Reader has useful methods for serializing to/deserializing from binary data.

  • reader.readIntBig(u32) reads big-endian binary data from the reader as u32 value.
  • writer.writeIntBig(u32, n) writes u32 value to the writer as big-endian binary data.

Testing

• To test functions that have comptime parameter (e.g. type) in Table Driven Testing style, use inline for instead of bare for to iterate over a test table.

  • It makes the for loop unrolled, and the value in the loop variable compile-time known as an additional effect.
  • If you use bare for loop, compiler complains with the error like: error: values of type '[N]SomeType' must be comptime-known, but index value is runtime-known

• We can skip tests according to some runtime conditions by returning error.SkipZigTest.