correct for both 4 bytes per pixel and 2 bytes

examples/live.rs

@@ -11,6 +11,8 @@ struct Args {
     temperature: bool,
     #[arg(short, long, default_value = "/dev/video0")]
     device: String,
+    #[arg(short, long)]
+    red_cutoff: Option<f64>,
 }
 
 fn pixel_to_celcius(x: u16) -> u16 {
@@ -48,17 +50,25 @@ fn main() -> anyhow::Result<()> {
 
     const WIDTH: usize = 288;
     const HEIGHT: usize = 384;
-    let fourcc_repr = [
+    let greyscale = !args.temperature || args.red_cutoff.is_none();
+    let fourcc_repr = if greyscale {
+        [
             b'Y', // | 0b10000000
             b'1', b'6',
             b' ', // Note: not using b' ' | 0x80, (V4L2_PIX_FMT_Y16_BE)
                   // because VID_S_FMT ioctl returns EINVAL, so just swap the bytes here
-    ];
+        ]
+    } else {
+        // RGB32 is 4 bytes R, G, B, A
+        [b'R', b'G', b'B', b'4']
+    };
+    let bytes_per_pixel = if greyscale { 2 } else { 4 };
     let fourcc = v4l::format::FourCC { repr: fourcc_repr };
     let mut out = v4l::Device::with_path(output)?;
     // To find the fourcc code, use v4l2-ctl --list-formats-out /dev/video0
     // (or read the source :)
-    let format = v4l::Format::new(WIDTH as u32, HEIGHT as u32, fourcc);
+    // flip axes
+    let format = v4l::Format::new(HEIGHT as u32, WIDTH as u32, fourcc);
     Output::set_format(&out, &format)?;
 
     // Setup Capture
@@ -70,9 +80,13 @@ fn main() -> anyhow::Result<()> {
 
     // get a packet and print its bytes
     const PACKET_LEN: usize = 6972;
+    // input is grayscale 16 bits per pixel
     const FRAME_LEN: usize = WIDTH * HEIGHT * 2;
     let mut frame = [0u8; FRAME_LEN];
     let mut len = 0;
+    let output_frame_len = WIDTH * HEIGHT * bytes_per_pixel;
+    let mut swapped_vec = vec![0u8; output_frame_len];
+    let swapped = &mut swapped_vec;
     while let Ok(p) = cap.next_packet() {
         let data = p.data;
         if data.len() != PACKET_LEN {
@@ -91,14 +105,30 @@ fn main() -> anyhow::Result<()> {
             if len == FRAME_LEN {
                 // swap the bytes, we are using LE, not BE, 16 bit grayscale
                 // possibly limitation of current v4l2loopback or v4l rust wrapper or libv4l2
-                let mut swapped = [0u8; FRAME_LEN];
                 for i in 0..FRAME_LEN / 2 {
+                    let x = i % WIDTH;
+                    let y = (i / WIDTH) % HEIGHT;
                     let mut pixel = u16::from_be_bytes([frame[i * 2], frame[i * 2 + 1]]);
+                    if greyscale {
                         if args.temperature {
                             pixel = pixel_to_celcius(pixel);
                         }
                         let pixel_swapped = pixel.to_le_bytes();
-                    swapped[i * 2..i * 2 + 2].copy_from_slice(&pixel_swapped);
+                        let out_i = ((HEIGHT - 1 - y) + (WIDTH - 1 - x) * HEIGHT) * 2;
+                        swapped[out_i..out_i + 2].copy_from_slice(&pixel_swapped);
+                    } else {
+                        pixel = pixel_to_celcius(pixel);
+                        let cutoff = args.red_cutoff.unwrap();
+                        let r = if pixel > (256.0 * cutoff) as u16 {
+                            255
+                        } else {
+                            0
+                        };
+                        let g = frame[i * 2];
+                        let b = frame[i * 2 + 1];
+                        let out_i = ((HEIGHT - 1 - y) + (WIDTH - 1 - x) * HEIGHT) * 4;
+                        swapped[out_i..out_i + 4].copy_from_slice(&[0, r, g, b]);
+                    }
                 }
                 out.write_all(&swapped[..])?;
             }