From 6688e05c5548ed079085821090552b667d1ea02a Mon Sep 17 00:00:00 2001
From: midasmatterhorn <248507632+midasmatterhorn@users.noreply.github.com>
Date: Thu, 15 Oct 2026 17:51:42 +0300
Subject: [PATCH] cms: write_cube keeps a non-default input domain
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The parser reads and validates DOMAIN_MIN/DOMAIN_MAX and the type
documents them as meaningful ('the input domain the table expects'), but
the writer never emitted them: a custom-domain .cube re-saved through
parse → write_cube came back with the default domain, passed the
domain_is_default gate that used to reject it, and every row silently
mapped colours over the wrong input range.

Emit DOMAIN_MIN/DOMAIN_MAX when the domain is not the default (parse_cube
matches keywords line by line and accepts them anywhere; {} on f32 prints
the shortest roundtripping form). Regression test:
cube_domain_survives_a_write — fails today (the written table loses the
domain), round-trips exactly with the emission.
---
 crates/cms/src/lutfile.rs | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/crates/cms/src/lutfile.rs b/crates/cms/src/lutfile.rs
index 880d9a64..1bd0e6e3 100644
--- a/crates/cms/src/lutfile.rs
+++ b/crates/cms/src/lutfile.rs
@@ -230,6 +230,12 @@ pub fn write_cube(l: &LutFile) -> String {
     if !l.title.is_empty() {
         s.push_str(&format!("TITLE \"{}\"\n", l.title.replace('"', "'")));
     }
+    // The domain is what every row means: a table read with a non-default one must not be
+    // written back as if it expected inputs in 0..1. `parse_cube` accepts these anywhere.
+    if !l.domain_is_default() {
+        s.push_str(&format!("DOMAIN_MIN {} {} {}\n", l.domain_min[0], l.domain_min[1], l.domain_min[2]));
+        s.push_str(&format!("DOMAIN_MAX {} {} {}\n", l.domain_max[0], l.domain_max[1], l.domain_max[2]));
+    }
     s.push_str(&format!("LUT_3D_SIZE {}\n", l.size));
     for c in l.data.as_chunks::<3>().0 {
         s.push_str(&format!("{:.6} {:.6} {:.6}\n", c[0], c[1], c[2]));
@@ -444,4 +450,25 @@ DOMAIN_MAX 0.5 1 1
         }
         assert!(builtin("nope").is_none());
     }
+
+    #[test]
+    fn cube_domain_survives_a_write() {
+        let cube = "DOMAIN_MIN 0.25 0.25 0.25
+DOMAIN_MAX 0.75 0.75 0.75
+LUT_3D_SIZE 2
+0 0 0
+0 0 1
+0 1 0
+0 1 1
+1 0 0
+1 0 1
+1 1 0
+1 1 1
+";
+        let l = parse_cube(cube).expect("a cube with a non-default domain");
+        assert!(!l.domain_is_default());
+        let back = parse_cube(&write_cube(&l)).expect("roundtrip");
+        assert_eq!(back.domain_min, l.domain_min, "the written table must mean the same");
+        assert_eq!(back.domain_max, l.domain_max);
+    }
 }