Foo

src/main.rs

@@ -1,6 +1,6 @@
 use clap::Parser;
-use eyre::{Context, ContextCompat, bail, eyre};
-use image::{DynamicImage, GrayImage, ImageReader, imageops::overlay};
+use eyre::{Context, ContextCompat, bail, ensure, eyre};
+use image::{DynamicImage, GrayAlphaImage, ImageReader, imageops::overlay};
 use nix::ioctl_write_ptr;
 use std::{
     fs::File,
@@ -49,23 +49,19 @@ ioctl_write_ptr!(
     DrmRockchipEbcOffScreen
 );
 
-fn to_grayscale(path: &Path, image: DynamicImage) -> GrayImage {
-    if let DynamicImage::ImageLuma8(image) = image {
+/// Convert [DynamicImage] into a [GrayAlphaImage].
+/// Note that we use [GrayAlphaImage] instead of `GrayImage` because we need the alpha channel to
+/// be able to add stamps.
+fn to_grayscale(path: &Path, image: DynamicImage) -> GrayAlphaImage {
+    if let DynamicImage::ImageLumaA8(image) = image {
         return image;
     }
 
-    eprintln!("Image {path:?} is not 8-bit grayscale. Converting...");
-    image.to_luma8()
+    eprintln!("Image {path:?} is not 16-bit grayscale+alpha. Converting...");
+    image.to_luma_alpha8()
 }
 
-fn load_image(path: &Path) -> eyre::Result<GrayImage> {
-    eprintln!("Opening image at {path:?}");
-
-    let image = ImageReader::open(path)?.decode()?;
-    Ok(to_grayscale(path, image))
-}
-
-fn load_wallpaper(path: &Path) -> eyre::Result<GrayImage> {
+fn load_wallpaper(path: &Path) -> eyre::Result<GrayAlphaImage> {
     eprintln!("Opening image at {path:?}");
 
     let mut image = ImageReader::open(path)?.decode()?;
@@ -91,7 +87,7 @@ fn main() -> eyre::Result<()> {
         apply_stamp(stamp, &mut image)?;
     }
 
-    let pixels = image_to_offimage_buffer(image);
+    let pixels = image_to_offimage_buffer(image)?;
 
     let set_off_screen_data = DrmRockchipEbcOffScreen {
         info1: 0, // TODO: what is this?
@@ -109,23 +105,41 @@ fn main() -> eyre::Result<()> {
     Ok(())
 }
 
-fn image_to_offimage_buffer(image: image::ImageBuffer<image::Luma<u8>, Vec<u8>>) -> Vec<u8> {
-    let mut pixels = image.into_vec();
+fn image_to_offimage_buffer(image: GrayAlphaImage) -> eyre::Result<Box<[u8; IOCTL_BUFFER_SIZE]>> {
+    let mut buf: Box<[u8; IOCTL_BUFFER_SIZE]> = vec![0u8; IOCTL_BUFFER_SIZE]
+        .into_boxed_slice()
+        .try_into()
+        .expect("Buffer is the correct size");
 
-    // Convert 8-bit colorspace to 4-bits by truncating the 4 least significant bits.
-    // Yes, this means that the most-significant 4 bits of each byte are unused.
-    // Not idea why they designed it this way. Maybe it's faster?
-    for pixel in &mut pixels {
-        *pixel >>= 4;
+    let image = image.into_vec();
+
+    ensure!(
+        image.len() / 2 + 1 == IOCTL_BUFFER_SIZE,
+        "Invalid size of image backing buffer. Bug?",
+    );
+
+    // Iterate over pixels and copy them into `buf`.
+    for (i, pixel) in image.chunks_exact(2).enumerate() {
+        let &[gray, alpha] = pixel else {
+            unreachable!()
+        };
+
+        // ignore the alpha channel.
+        let _ = alpha;
+
+        // Convert 8-bit colorspace to 4-bits by truncating the 4 least significant bits.
+        // Yes, this means that the most-significant 4 bits of each byte are unused.
+        // Not idea why they designed it this way. Maybe it's faster?
+        buf[i] = gray >> 4;
     }
 
-    // Add a null-terminator. No idea why this is necessary, but it is.
-    pixels.push(0u8);
-
     // Sanity check buffer length
-    assert!(pixels.len() == IOCTL_BUFFER_SIZE);
+    assert_eq!(buf.len(), IOCTL_BUFFER_SIZE);
 
-    pixels
+    // Sanity-check that last byte is null.
+    assert_eq!(buf.last(), Some(&0u8));
+
+    Ok(buf)
 }
 
 fn parse_stamp(stamp: &str) -> Option<(i64, i64, &Path)> {
@@ -138,13 +152,21 @@ fn parse_stamp(stamp: &str) -> Option<(i64, i64, &Path)> {
     Some((x, y, path))
 }
 
-fn apply_stamp(stamp: &str, onto: &mut GrayImage) -> eyre::Result<()> {
+fn apply_stamp(stamp: &str, onto: &mut GrayAlphaImage) -> eyre::Result<()> {
     let (x, y, path) =
         parse_stamp(stamp).wrap_err_with(|| eyre!("Invalid stamp format: {stamp:?}"))?;
 
-    let image = load_image(path)?;
+    let image = load_stamp(path)?;
 
     overlay(onto, &image, x, y);
 
     Ok(())
 }
+
+fn load_stamp(path: &Path) -> eyre::Result<GrayAlphaImage> {
+    eprintln!("Opening image at {path:?}");
+
+    let image = ImageReader::open(path)?.decode()?;
+
+    Ok(to_grayscale(path, image))
+}