Import Lightroom presets as looks

A Lightroom preset changes the settings it was saved with and leaves every
other one where the photograph had it. Imported as a whole edit, a preset
holding only a grade reset the exposure, white balance and noise reduction
it was put on top of — the opposite of what the photographer had in
Lightroom.

Imported presets now reach only the operations they name
(`Reach::Named`), the rule the shipped presets already follow.

core/dr-preset-xmp/src/lib.rs

@@ -44,7 +44,7 @@
 
 use std::collections::BTreeMap;
 
-use dr_pipeline::Preset;
+use dr_pipeline::{Preset, Reach};
 use quick_xml::events::Event;
 use quick_xml::XmlVersion;
 
@@ -300,7 +300,11 @@ pub fn read_xmp(text: &str) -> Result<Import, ImportError> {
 
     Ok(Import {
         name,
-        preset: Preset::from_params(params),
+        // A look, because that is what a Lightroom preset is: it changes the
+        // settings it was saved with and leaves every other one where the
+        // photograph had it. Applied as a whole edit instead, a preset
+        // holding only a grade would reset the exposure it was put on top of.
+        preset: Preset::from_params(params).with_reach(Reach::Named),
         skipped,
     })
 }
@@ -485,6 +489,26 @@ mod tests {
         );
     }
 
+    /// TRACES: FR-DEV-6
+    /// Lightroom's own rule: a preset changes what it was saved with and
+    /// nothing else, so a grade lands on top of the photograph's correction.
+    #[test]
+    fn an_imported_preset_leaves_what_it_does_not_set_alone() {
+        use dr_pipeline::ops::dehaze;
+
+        let import = read_xmp(ATTRIBUTE_FORM).unwrap();
+        assert_eq!(import.preset.reach(), Reach::Named);
+        assert!(value(&import, "dehaze", "amount").is_none());
+
+        let mut graph = EditGraph::default_chain();
+        graph.set_param(dehaze::ID, dehaze::AMOUNT, 30.0);
+        import
+            .preset
+            .apply(&mut graph, Scope::adjustments())
+            .expect_no_film();
+        assert_eq!(graph.param(dehaze::ID, dehaze::AMOUNT), Some(30.0));
+    }
+
     #[test]
     fn a_value_that_is_not_a_number_costs_that_setting_and_not_the_file() {
         let text =