Scale Composition: comp.scale resizes a comp and scales its layers, keys, cameras and guides by one factor

Like After Effects' File > Scripts > Scale Composition.jsx: a factor, or a new width or height that keeps the aspect ratio, in one undo step. Layers whose parent has a Scale follow that parent; nested precomps and expressions are left as they are. No dialog yet. Refs #2208
2026-11-01 14:08:38 -06:00 · 2026-10-30 00:44:58 +01:00
parent a8d83b9717
commit 4aaba7c3bf
4 changed files with 214 additions and 3 deletions
@@ -1,5 +1,5 @@
-//! Composition menu, part two: crop to region of interest / layer bounds, Save Frame As ▸ File,
-//! Copy Frame to Clipboard, Responsive Design — Time.
+//! Composition menu, part two: crop to region of interest / layer bounds, Scale Composition, Save
+//! Frame As ▸ File, Copy Frame to Clipboard, Responsive Design — Time.

 use effectcraft_project::Marker;
 use effectcraft_time::Tick;
@@ -71,6 +71,82 @@ fn crop_to_layers(s: &mut Session, p: &Value) -> Result<Value> {
    crop(s, cid, [x0, y0, b[2].ceil() - x0, b[3].ceil() - y0], "Crop Comp to Selected Layer(s) Bounds")
 }

+/// Multiply a property's value, every key, its spatial tangents and its speeds by `f`.
+fn scale_prop(pr: &mut effectcraft_project::Property, f: f64) {
+    use effectcraft_keyframe::Value as KV;
+    let mul = |v: &KV| match v {
+        KV::Scalar(x) => KV::Scalar(x * f),
+        KV::Vec2(a) => KV::Vec2(a.map(|x| x * f)),
+        KV::Vec3(a) => KV::Vec3(a.map(|x| x * f)),
+        other => other.clone(),
+    };
+    pr.value = mul(&pr.value);
+    for k in &mut pr.keys {
+        k.value = mul(&k.value);
+        k.spatial_in = k.spatial_in.map(|x| x * f);
+        k.spatial_out = k.spatial_out.map(|x| x * f);
+        for e in k.in_ease.iter_mut().chain(&mut k.out_ease) {
+            e.speed *= f;
+        }
+    }
+}
+
+/// Scale Composition (After Effects ships it as File ▸ Scripts ▸ Scale Composition.jsx): the comp
+/// and its contents grow or shrink by one factor, keys included, in one undo step. Layers whose
+/// parent has a Scale follow that parent; everything else scales its Position (and Point of
+/// Interest) and Scale. Anchor Point, masks, shapes and effects live in layer space and follow the
+/// layer's Scale. Cameras scale their Zoom so 3D layers keep their place in the frame.
+fn scale_comp(s: &mut Session, p: &Value) -> Result<Value> {
+    const C: &str = "comp.scale";
+    let cid = comp_id(s, p)?;
+    let comp = s.project.comp(cid).ok_or(EngineError::NoComp)?;
+    let (ow, oh) = (f64::from(comp.width), f64::from(comp.height));
+    let f = match (f_p(p, "factor"), f_p(p, "width"), f_p(p, "height")) {
+        (Some(f), ..) => f,
+        (None, Some(w), _) => w / ow,
+        (None, None, Some(h)) => h / oh,
+        _ => return Err(bad(C, "pass `factor`, `width` or `height`")),
+    };
+    let (w, h) = ((ow * f).round(), (oh * f).round());
+    let max = f64::from(effectcraft_project::limits::MAX_SIZE);
+    if !f.is_finite() || f <= 0.0 || !(4.0..=max).contains(&w) || !(4.0..=max).contains(&h) {
+        return Err(bad(C, format!("the composition would be {w}×{h}: width and height run from 4 to 30,000 px")));
+    }
+    let (w, h) = (w as u32, h as u32);
+    s.edit("Scale Composition", None, |proj, _| {
+        let c = proj.comp_mut(cid).ok_or(EngineError::NoComp)?;
+        // A parent's Scale carries its children; a camera or light parent has none.
+        let scaling_parents: std::collections::HashSet<_> =
+            c.layers.iter().filter(|l| l.transform().is_some_and(|tr| tr.get("scale").is_some())).map(|l| l.id).collect();
+        for l in &mut c.layers {
+            let follows_parent = l.parent.is_some_and(|id| scaling_parents.contains(&id));
+            if !follows_parent && let Some(tr) = l.transform_mut() {
+                for name in ["position", "positionX", "positionY", "positionZ", "poi", "scale"] {
+                    if let Some(pr) = tr.get_mut(name) {
+                        scale_prop(pr, f);
+                    }
+                }
+            }
+            if let Some(cam) = l.props.sub_mut("cameraOptions") {
+                for name in ["zoom", "focusDistance", "aperture"] {
+                    if let Some(pr) = cam.get_mut(name) {
+                        scale_prop(pr, f);
+                    }
+                }
+            }
+        }
+        let (old_w, old_h) = (c.width, c.height);
+        for g in &mut c.guides {
+            let px = g.px(old_w, old_h) * f;
+            g.set_px(px, w, h);
+        }
+        c.width = w;
+        c.height = h;
+        Ok(())
+    })?;
+    Ok(json!({"width": w, "height": h, "factor": f}))
+}
+
 /// Encode straight 8-bit RGBA as PNG.
 pub(crate) fn encode_png(rgba: &[u8], w: u32, h: u32) -> std::result::Result<Vec<u8>, String> {
    use image::ImageEncoder;
@@ -233,6 +309,15 @@ pub fn specs() -> Vec<CommandSpec> {
    vec![
        cmd!("comp.cropToRegionOfInterest", "Crop Comp to Region of Interest", ["Composition"], None, "{comp?}", has_roi, crop_to_roi),
        cmd!("comp.cropToLayerBounds", "Crop Comp to Selected Layer(s) Bounds", ["Composition"], None, "{layers?}", has_layers, crop_to_layers),
+        cmd!(
+            "comp.scale",
+            "Scale Composition",
+            [],
+            None,
+            "{comp?, factor? (2 = twice the size) | width? | height? (the other side keeps the aspect ratio)}",
+            has_comp,
+            scale_comp
+        ),
        cmd!(
            "comp.saveFrameAs",
            "File...",
@@ -38,6 +38,7 @@ mod quick_offset;
 mod replace_source;
 mod rig3d;
 pub(crate) mod roto;
+mod scale_comp;
 mod sequence;
 mod session;
 mod settings;
@@ -0,0 +1,125 @@
+//! Scale Composition (`comp.scale`, #2208): the comp and everything in it grow or shrink by one
+//! factor, so the frame looks the same at the new size.
+
+use effectcraft_project::{Layer, LayerId};
+use effectcraft_time::Tick;
+use serde_json::json;
+
+use crate::Session;
+
+fn comp(w: u32, h: u32) -> Session {
+    let mut s = Session::default();
+    s.execute("comp.new", json!({"name": "Main", "width": w, "height": h, "frameRate": 10, "duration": 2})).unwrap();
+    s
+}
+
+fn solid(s: &mut Session, color: &str, w: u32, h: u32) -> u64 {
+    s.execute("layer.newSolid", json!({"color": color, "width": w, "height": h})).unwrap()["layer"].as_u64().unwrap()
+}
+
+fn layer(s: &Session, id: u64) -> Layer {
+    s.active_comp().unwrap().layer(LayerId(id)).unwrap().clone()
+}
+
+fn v3(s: &Session, id: u64, path: &str, t: f64) -> [f64; 3] {
+    layer(s, id).props.prop(path).unwrap().value_at(Tick::from_seconds_f64(t)).as_vec3()
+}
+
+/// Opaque pixels of `color_channel` (0 = red, 1 = green) at `t`: (x0, y0, x1, y1, count).
+fn bounds(s: &Session, t: f64, channel: usize) -> (i64, i64, i64, i64, u32) {
+    let img = s.render(s.active_comp_id().unwrap(), Tick::from_seconds_f64(t), Default::default());
+    let (mut x0, mut y0, mut x1, mut y1, mut n) = (i64::MAX, i64::MAX, i64::MIN, i64::MIN, 0);
+    for y in 0..img.height as i64 {
+        for x in 0..img.width as i64 {
+            let p = img.get(x, y);
+            if p[3] > 0.5 && p[channel] > 0.5 {
+                n += 1;
+                (x0, y0, x1, y1) = (x0.min(x), y0.min(y), x1.max(x), y1.max(y));
+            }
+        }
+    }
+    (x0, y0, x1, y1, n)
+}
+
+/// Twice as large on every side, from a pixel-exact frame.
+fn doubled(b: (i64, i64, i64, i64, u32)) -> (i64, i64, i64, i64, u32) {
+    (b.0 * 2, b.1 * 2, b.2 * 2 + 1, b.3 * 2 + 1, b.4 * 4)
+}
+
+#[test]
+fn scale_comp_doubles_the_frame_with_keys_and_parented_layers() {
+    let mut s = comp(200, 100);
+    // A red solid moving right (two Position keys), and a green solid parented to a null.
+    let red = solid(&mut s, "#ff0000", 20, 10);
+    s.execute("prop.addKey", json!({"layer": red, "path": "transform/position", "time": 0, "value": [30, 20]})).unwrap();
+    s.execute("prop.addKey", json!({"layer": red, "path": "transform/position", "time": 1, "value": [70, 20]})).unwrap();
+    let green = solid(&mut s, "#00ff00", 10, 10);
+    let rig = s.execute("layer.newNull", json!({})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("prop.set", json!({"layer": rig, "path": "transform/position", "value": [150, 60]})).unwrap();
+    s.execute("layer.setParent", json!({"layers": [green], "parent": rig})).unwrap();
+    s.execute("prop.set", json!({"layer": green, "path": "transform/position", "value": [10, 15]})).unwrap();
+    let before = s.project.clone();
+    let (red0, red1, green0) = (bounds(&s, 0.0, 0), bounds(&s, 1.0, 0), bounds(&s, 0.0, 1));
+    assert_eq!(red0, (20, 15, 39, 24, 200));
+
+    let r = s.execute("comp.scale", json!({"factor": 2})).unwrap();
+    assert_eq!((r["width"].as_u64(), r["height"].as_u64()), (Some(400), Some(200)));
+    let c = s.active_comp().unwrap();
+    assert_eq!((c.width, c.height), (400, 200));
+    // Every key moves, not only the value at the current time.
+    assert_eq!(bounds(&s, 0.0, 0), doubled(red0));
+    assert_eq!(bounds(&s, 1.0, 0), doubled(red1));
+    assert_eq!(v3(&s, red, "transform/scale", 1.0), [200.0; 3]);
+    // The child keeps its own transform: its scaled parent carries it.
+    assert_eq!(bounds(&s, 0.0, 1), doubled(green0));
+    assert_eq!(v3(&s, green, "transform/position", 0.0)[..2], [10.0, 15.0]);
+    assert_eq!(v3(&s, green, "transform/scale", 0.0), [100.0; 3]);
+
+    // One undo step.
+    s.execute("edit.undo", json!({})).unwrap();
+    assert!(s.project == before, "undo restores the comp and every layer");
+}
+
+#[test]
+fn scale_comp_to_a_width_keeps_the_aspect_and_scales_cameras_3d_and_guides() {
+    let mut s = comp(640, 360);
+    let card = solid(&mut s, "#ff0000", 100, 100);
+    s.execute("layer.setSwitch", json!({"layers": [card], "switch": "threeD", "value": true})).unwrap();
+    s.execute("prop.set", json!({"layer": card, "path": "transform/position", "value": [100, 50, 200]})).unwrap();
+    let cam = s.execute("layer.newCamera", json!({})).unwrap()["layer"].as_u64().unwrap();
+    s.execute("view.addGuide", json!({"orientation": "vertical", "position": 160})).unwrap();
+    s.execute("view.addGuide", json!({"orientation": "horizontal", "position": 25, "percent": true})).unwrap();
+    let zoom = |s: &Session| layer(s, cam).props.prop("cameraOptions/zoom").unwrap().value.as_f64();
+    let (zoom0, cam0, poi0) = (zoom(&s), v3(&s, cam, "transform/position", 0.0), v3(&s, cam, "transform/poi", 0.0));
+    let seen0 = bounds(&s, 0.0, 0);
+
+    let r = s.execute("comp.scale", json!({"width": 960})).unwrap();
+    assert_eq!((r["width"].as_u64(), r["height"].as_u64(), r["factor"].as_f64()), (Some(960), Some(540), Some(1.5)));
+    assert_eq!(v3(&s, card, "transform/position", 0.0), [150.0, 75.0, 300.0]);
+    assert_eq!(v3(&s, card, "transform/scale", 0.0), [150.0; 3]);
+    assert!((zoom(&s) - zoom0 * 1.5).abs() < 1e-9, "the camera sees the same frame");
+    assert_eq!(v3(&s, cam, "transform/position", 0.0), cam0.map(|v| v * 1.5));
+    assert_eq!(v3(&s, cam, "transform/poi", 0.0), poi0.map(|v| v * 1.5));
+    // Through the camera the card covers the same part of the frame.
+    let seen = bounds(&s, 0.0, 0);
+    let near = |a: i64, b: i64| (a as f64 - b as f64 * 1.5).abs() <= 2.0;
+    assert!(near(seen.0, seen0.0) && near(seen.1, seen0.1) && near(seen.2, seen0.2) && near(seen.3, seen0.3), "{seen0:?} → {seen:?}");
+    let c = s.active_comp().unwrap();
+    assert_eq!(c.guides[0].px(c.width, c.height), 240.0);
+    assert_eq!(c.guides[1].position, 25.0, "a percentage guide keeps its percent");
+
+    // A height alone works the same way.
+    let r = s.execute("comp.scale", json!({"height": 270})).unwrap();
+    assert_eq!((r["width"].as_u64(), r["height"].as_u64()), (Some(480), Some(270)));
+}
+
+#[test]
+fn scale_comp_refuses_a_bad_factor_and_changes_nothing() {
+    let mut s = comp(640, 360);
+    solid(&mut s, "#ff0000", 100, 100);
+    let before = s.project.clone();
+    for p in [json!({}), json!({"factor": 0}), json!({"factor": -2}), json!({"width": 0}), json!({"factor": 100}), json!({"factor": 0.001})] {
+        assert!(s.execute("comp.scale", p.clone()).is_err(), "{p} is refused");
+        assert!(s.project == before, "{p} leaves the project alone");
+    }
+}