Refactor allowing multiple pixel formats

src/image/farbfeld.rs

@@ -2,59 +2,8 @@ use super::*;
 
 pub struct Farbfeld;
 
-fn read_header<I>(input: &mut I) -> Result<Extent, Error>
-where
-    I: std::io::Read,
-{
-    let mut bytes: [u8; 16] = [0; 16];
-    if input.read(&mut bytes)? < 16 || &bytes[0..8] != b"farbfeld" {
-        Err(Error::Invalid)
-    } else {
-        Ok(Extent {
-            x: u32::from_be_bytes(bytes[8..12].try_into().unwrap()),
-            y: u32::from_be_bytes(bytes[12..16].try_into().unwrap()),
-        })
-    }
-}
-
-fn read_pixels<I>(input: &mut I, extent: Extent) -> Result<Vec<Pixel>, Error>
-where
-    I: std::io::Read,
-{
-    let mut pixels = Vec::with_capacity(extent.size() as usize);
-    for _ in 0..extent.size() {
-        pixels.push(read_pixel(input)?);
-    }
-    Ok(pixels)
-}
-
-fn read_pixel<I>(input: &mut I) -> Result<Pixel, Error>
-where
-    I: std::io::Read,
-{
-    let mut bytes: [u8; 8] = [0; 8];
-    if input.read(&mut bytes)? < 8 {
-        Err(Error::Invalid)
-    } else {
-        Ok(Pixel {
-            r: to_channel(bytes[0..2].try_into().unwrap()),
-            g: to_channel(bytes[2..4].try_into().unwrap()),
-            b: to_channel(bytes[4..6].try_into().unwrap()),
-            a: to_channel(bytes[6..8].try_into().unwrap()),
-        })
-    }
-}
-
-fn to_channel(bytes: [u8; 2]) -> f32 {
-    u16::from_be_bytes(bytes) as f32 / u16::MAX as f32
-}
-
-fn from_channel(channel: f32) -> [u8; 2] {
-    ((channel * u16::MAX as f32) as u16).to_be_bytes()
-}
-
-impl Format for Farbfeld {
-    fn read<I>(input: &mut I) -> Result<Image, Error>
+impl Format<SRGBA> for Farbfeld {
+    fn read<I>(input: &mut I) -> Result<Image<SRGBA>, Error>
     where
         I: std::io::Read,
     {
@@ -65,13 +14,13 @@ impl Format for Farbfeld {
         })
     }
 
-    fn write<O>(output: &mut O, img: &Image) -> std::io::Result<()>
+    fn write<O>(output: &mut O, img: &Image<SRGBA>) -> std::io::Result<()>
     where
         O: std::io::Write,
     {
         output.write_all(b"farbfeld")?;
-        output.write_all(&img.extent.x.to_be_bytes())?;
-        output.write_all(&img.extent.y.to_be_bytes())?;
+        output.write_all(&(img.extent.x as u32).to_be_bytes())?;
+        output.write_all(&(img.extent.y as u32).to_be_bytes())?;
         for pixel in &img.pixels {
             output.write_all(&from_channel(pixel.r))?;
             output.write_all(&from_channel(pixel.g))?;
@@ -82,6 +31,62 @@ impl Format for Farbfeld {
     }
 }
 
+fn read_header<I>(input: &mut I) -> Result<Extent, Error>
+where
+    I: std::io::Read,
+{
+    let mut bytes: [u8; 16] = [0; 16];
+    if input.read(&mut bytes)? < 16 || &bytes[0..8] != b"farbfeld" {
+        Err(Error::Invalid)
+    } else {
+        Ok(Extent {
+            x: be_u32_at(&bytes, 8) as usize,
+            y: be_u32_at(&bytes, 12) as usize,
+        })
+    }
+}
+
+fn read_pixels<I>(input: &mut I, extent: Extent) -> Result<Vec<SRGBA>, Error>
+where
+    I: std::io::Read,
+{
+    let mut pixels = Vec::with_capacity(extent.size() as usize);
+    for _ in 0..extent.size() {
+        pixels.push(read_pixel(input)?);
+    }
+    Ok(pixels)
+}
+
+fn read_pixel<I>(input: &mut I) -> Result<SRGBA, Error>
+where
+    I: std::io::Read,
+{
+    let mut bytes: [u8; 8] = [0; 8];
+    if input.read(&mut bytes)? < 8 {
+        Err(Error::Invalid)
+    } else {
+        Ok(SRGBA {
+            r: to_channel(bytes[0..2].try_into().unwrap()),
+            g: to_channel(bytes[2..4].try_into().unwrap()),
+            b: to_channel(bytes[4..6].try_into().unwrap()),
+            a: to_channel(bytes[6..8].try_into().unwrap()),
+        })
+    }
+}
+
+fn be_u32_at(bytes: &[u8], start: usize) -> u32 {
+    let end = start + std::mem::size_of::<u32>();
+    u32::from_be_bytes(bytes[start..end].try_into().unwrap())
+}
+
+fn to_channel(bytes: [u8; 2]) -> f32 {
+    u16::from_be_bytes(bytes) as f32 / u16::MAX as f32
+}
+
+fn from_channel(channel: f32) -> [u8; 2] {
+    ((channel * u16::MAX as f32) as u16).to_be_bytes()
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -177,7 +182,7 @@ mod tests {
     fn write_magic() {
         let img = Image {
             extent: Extent { x: 1, y: 1 },
-            pixels: vec![Pixel {
+            pixels: vec![SRGBA {
                 r: 0.0,
                 g: 0.0,
                 b: 0.0,
@@ -193,7 +198,7 @@ mod tests {
     fn write_extent() {
         let img = Image {
             extent: Extent { x: 1, y: 2 },
-            pixels: vec![Pixel {
+            pixels: vec![SRGBA {
                 r: 0.0,
                 g: 0.0,
                 b: 0.0,
@@ -210,7 +215,7 @@ mod tests {
     fn write_pixel() {
         let img = Image {
             extent: Extent { x: 1, y: 1 },
-            pixels: vec![Pixel {
+            pixels: vec![SRGBA {
                 r: 0.0,
                 g: 0.25,
                 b: 0.5,