iter: Add write() method

write() allows callers to directly write pixels to an output stream
(aka Iterator). The parameter P2 allows for direct conversion from
one pixel format to another.

Signed-off-by: Christopher N. Hesse <[email protected]>

ffimage/src/iter.rs

@@ -1,19 +1,19 @@
-use core::marker::PhantomData;
+use core::{marker::PhantomData, ops::Deref};
 
 /// Adapter which converts a bytestream into a typed pixel stream.
 ///
 /// The trait is automatically implemented for all pixel types which implement the `From<[T; C]>`
 /// trait where T: Copy and C means the number of channels (e.g. 3 for RGB).
-pub trait PixelsExt: Iterator {
- fn pixels<P, const C: usize>(self) -> Pixels<Self::Item, Self, P, C>
+pub trait PixelsExt<const C: usize>: Iterator {
+ fn pixels<P>(self) -> Pixels<Self::Item, Self, P, C>
  where
  Self: Sized,
  {
  Pixels::new(self)
  }
 }
 
-impl<I> PixelsExt for I where I: Iterator {}
+impl<I, const C: usize> PixelsExt<C> for I where I: Iterator {}
 
 pub struct Pixels<T, I, P, const C: usize> {
  _marker: PhantomData<(T, P)>,
@@ -29,6 +29,26 @@ impl<T, I, P, const C: usize> Pixels<T, I, P, C> {
  }
 }
 
+impl<'a, T, I, P, const C: usize> Pixels<T, I, P, C>
+where
+ T: Copy + 'a,
+ I: Iterator<Item = T>,
+ P: From<[T; C]>,
+{
+ pub fn write<P2>(self, mut out: impl Iterator<Item = &'a mut T>)
+ where
+ P2: From<P> + Deref,
+ <P2 as Deref>::Target: AsRef<[T]>,
+ {
+ self.map(|p| P2::from(p)).for_each(|p2| {
+ p2.as_ref().iter().for_each(|t| {
+ let _out = out.next().unwrap();
+ *_out = *t;
+ });
+ });
+ }
+}
+
 impl<T, I, P, const C: usize> Iterator for Pixels<T, I, P, C>
 where
  T: Copy,
@@ -49,7 +69,7 @@ where
 #[cfg(test)]
 mod tests {
  use super::*;
- use crate::color::Rgb;
+ use crate::color::{Bgr, Rgb};
 
  #[test]
  fn pixels() {
@@ -61,4 +81,15 @@ mod tests {
  assert_eq!(pixels.next(), Some(Rgb::<u8>([7, 8, 9])));
  assert_eq!(pixels.next(), None);
  }
+
+ #[test]
+ fn write() {
+ let buf = [1, 2, 3, 4, 5, 6, 7, 8, 9];
+ let mut out = [0; 9];
+ buf.iter()
+ .copied()
+ .pixels::<Rgb<u8>>()
+ .write::<Bgr<u8>>(out.iter_mut());
+ assert_eq!(out, [3, 2, 1, 6, 5, 4, 9, 8, 7]);
+ }
 }