From 39a0c6aa547d6bad87bc22cc0824f45ee54ce0b1 Mon Sep 17 00:00:00 2001
From: Vikram Bhaskaran <vikram.bhaskaran@outlook.com>
Date: Sat, 10 Oct 2026 21:42:03 +1100
Subject: [PATCH] Move a layer when Position is edited and its dimensions are
 separated.

The renderer follows X, Y and Z Position once those channels exist. The Position command was writing only the combined property, so the layer stayed where it was.
---
 crates/engine/src/commands/layer_menu.rs | 26 ++++++++++++
 crates/engine/src/tests_menu_cmds.rs     | 53 ++++++++++++++++++++++++
 2 files changed, 79 insertions(+)

diff --git a/crates/engine/src/commands/layer_menu.rs b/crates/engine/src/commands/layer_menu.rs
index 5ad0c1fc..ba00db38 100644
--- a/crates/engine/src/commands/layer_menu.rs
+++ b/crates/engine/src/commands/layer_menu.rs
@@ -192,6 +192,32 @@ fn set_transform(s: &mut Session, p: &Value) -> Result<Value> {
         for lid in &ids {
             let l = layer_mut(proj, cid, *lid)?;
             let lt = l.layer_time(t);
+            // Separate Dimensions: the picture follows X/Y/Z Position, not the combined property.
+            if m == "position" && l.transform().is_some_and(|tr| tr.get("positionX").is_some()) {
+                let cur = l
+                    .transform()
+                    .map(|tr| {
+                        [
+                            tr.get("positionX").map(|p| p.value_at(lt).as_f64()).unwrap_or(0.0),
+                            tr.get("positionY").map(|p| p.value_at(lt).as_f64()).unwrap_or(0.0),
+                            tr.get("positionZ").map(|p| p.value_at(lt).as_f64()).unwrap_or(0.0),
+                        ]
+                    })
+                    .unwrap_or([0.0; 3]);
+                // Two numbers keep the current z.
+                let j = match &v {
+                    Value::Array(a) if a.len() == 2 => json!([a[0], a[1], cur[2]]),
+                    _ => v.clone(),
+                };
+                let nv = KV::Vec3(cur).coerce_json(&j).ok_or_else(|| bad("layer.setTransform", format!("can't use {v} for {label}")))?;
+                let xyz = nv.as_vec3();
+                let Some(tr) = l.transform_mut() else { continue };
+                super::layer::update_position(tr, lt, |_| xyz);
+                if let Some(pr) = tr.get_mut("position") {
+                    pr.set_value_at(lt, KV::Vec3(xyz));
+                }
+                continue;
+            }
             let Some(pr) = l.transform_mut().and_then(|tr| tr.get_mut(m)) else { continue };
             let cur = pr.value_at(lt);
             // Two numbers for a 3D value keep the current z.
diff --git a/crates/engine/src/tests_menu_cmds.rs b/crates/engine/src/tests_menu_cmds.rs
index c342f72f..0d626dd8 100644
--- a/crates/engine/src/tests_menu_cmds.rs
+++ b/crates/engine/src/tests_menu_cmds.rs
@@ -3,6 +3,7 @@
 
 use effectcraft_keyframe::Value as KV;
 use effectcraft_project::{FrameBlend, ItemKind, MatteKind, Quality, Sampling};
+use effectcraft_time::Tick;
 use serde_json::{Value, json};
 
 use crate::{EngineError, Event, Session};
@@ -103,6 +104,58 @@ fn transform_dialog_values_and_center_anchor() {
     assert_eq!(layer(&s, a).auto_orient, effectcraft_project::AutoOrient::AlongPath);
 }
 
+/// Pixel-centre of the opaque samples, so a 10×10 solid centred on (11, 22) reports (11, 22).
+fn opaque_centroid(s: &Session) -> (f64, f64, u32) {
+    let img = s.render(s.active_comp_id().unwrap(), Tick::ZERO, Default::default());
+    let mut n = 0u32;
+    let mut sx = 0.0;
+    let mut sy = 0.0;
+    for y in 0..img.height {
+        for x in 0..img.width {
+            if img.get(x as i64, y as i64)[3] > 0.5 {
+                n += 1;
+                sx += x as f64 + 0.5;
+                sy += y as f64 + 0.5;
+            }
+        }
+    }
+    assert!(n > 0, "the layer rendered nothing");
+    (sx / n as f64, sy / n as f64, n)
+}
+
+#[test]
+fn separated_position_set_transform_moves_the_layer() {
+    let mut s = Session::default();
+    s.execute("comp.new", json!({"name": "Scene", "width": 100, "height": 100, "frameRate": 30, "duration": 2})).unwrap();
+    let a = s.execute("layer.newSolid", json!({"name": "Square", "color": "#ff0000", "width": 10, "height": 10})).unwrap()["layer"].as_u64().unwrap();
+    let (x, y, n) = opaque_centroid(&s);
+    assert_eq!(n, 100);
+    assert!((x - 50.0).abs() < 0.6 && (y - 50.0).abs() < 0.6, "starts centred, centroid ({x}, {y})");
+
+    s.execute("prop.separateDimensions", json!({"layer": a, "value": true})).unwrap();
+    s.execute("layer.setTransform", json!({"layers": [a], "prop": "position", "value": [11, 22]})).unwrap();
+    let l = layer(&s, a);
+    let tr = l.transform().unwrap();
+    assert!((tr.get("positionX").unwrap().value.as_f64() - 11.0).abs() < 1e-6);
+    assert!((tr.get("positionY").unwrap().value.as_f64() - 22.0).abs() < 1e-6);
+    assert_eq!(tr.get("position").unwrap().value, KV::Vec3([11.0, 22.0, 0.0]));
+    let (x, y, n) = opaque_centroid(&s);
+    assert_eq!(n, 100);
+    assert!((x - 11.0).abs() < 0.6 && (y - 22.0).abs() < 0.6, "separated position renders at ({x}, {y})");
+
+    s.execute("edit.undo", json!({})).unwrap();
+    let (x, y, _) = opaque_centroid(&s);
+    assert!((x - 50.0).abs() < 0.6 && (y - 50.0).abs() < 0.6, "undo puts it back at ({x}, {y})");
+
+    // Combined Position, the control, still moves.
+    s.execute("edit.undo", json!({})).unwrap();
+    assert!(layer(&s, a).transform().unwrap().get("positionX").is_none());
+    s.execute("layer.setTransform", json!({"prop": "position", "value": [11, 22]})).unwrap();
+    let (x, y, n) = opaque_centroid(&s);
+    assert_eq!(n, 100);
+    assert!((x - 11.0).abs() < 0.6 && (y - 22.0).abs() < 0.6, "combined position renders at ({x}, {y})");
+}
+
 #[test]
 fn mask_menu_on_existing_masks() {
     let mut s = comp();