FourCC: Improve debug prints

src/format/fourcc.rs

@@ -1,6 +1,6 @@
 use std::{fmt, str};
 
-#[derive(Debug, Default, Copy, Clone, Eq)]
+#[derive(Default, Copy, Clone, Eq)]
 /// Four character code representing a pixelformat
 pub struct FourCC {
     pub repr: [u8; 4],
@@ -38,6 +38,20 @@ impl FourCC {
     }
 }
 
+impl fmt::Debug for FourCC {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let string = str::from_utf8(&self.repr);
+        if let Ok(string) = string {
+            write!(f, "FourCC(")?;
+            string.fmt(f)?;
+            write!(f, ")")?;
+        } else {
+            write!(f, "FourCC({:02x} {:02x} {:02x} {:02x})", self.repr[0], self.repr[1], self.repr[2], self.repr[3])?;
+        }
+        Ok(())
+    }
+}
+
 impl fmt::Display for FourCC {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let string = str::from_utf8(&self.repr);
@@ -65,3 +79,19 @@ impl From<FourCC> for u32 {
         Self::from_le_bytes(fourcc.repr)
     }
 }
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn debug_fourcc_string() {
+        assert_eq!(format!("{:?}", FourCC::new(b"MJPG")), "FourCC(\"MJPG\")");
+    }
+
+    #[test]
+    fn debug_fourcc_nonascii() {
+        assert_eq!(format!("{:?}", FourCC::new(&[0x01, 0xff, 0x20, 0xcd])), "FourCC(01 ff 20 cd)");
+    }
+}