Merge PR #137 from alexanderalber: Morph: a picture cropped differently on the next slide morphs its crop (#118)

# Conflicts:
#	crates/anim/src/lib.rs
#	crates/anim/src/tests.rs

crates/anim/src/lib.rs

@@ -38,7 +38,7 @@ use serde::{Deserialize, Serialize};
 pub use easing::ease;
 pub use interact::{Click, HitShape, Target};
 pub use mesh::{MeshVertex, layer_mesh};
-pub use morph::{MorphFrame, MorphPath, MorphText, morph_frame, morph_pairs, morph_xfrm};
+pub use morph::{MorphFrame, MorphPath, MorphText, morph_crop, morph_frame, morph_pairs, morph_xfrm};
 pub use path::{MotionPath, default_path};
 pub use show::{LinkJump, ShowAction, ShowState, safe_url, show_order};
 pub use timeline::{EffectTiming, Sequence, StepStamp, Timeline, TriggerPlay};

crates/anim/src/morph.rs

@@ -176,9 +176,58 @@ fn reshaped(a: &Shape, b: &Shape) -> bool {
     a.geom != b.geom && outlined(a) && outlined(b) && Shape { geom: Geom::default(), ..content(a) } == Shape { geom: Geom::default(), ..content(b) }
 }
 
+/// The content of a shape apart from what Morph interpolates, with a picture's crop left out.
+fn uncropped(s: &Shape) -> Shape {
+    let mut c = content(s);
+    if let ShapeKind::Picture { fill } = &mut c.kind {
+        fill.crop = [0.0; 4];
+    }
+    c
+}
+
+fn crop_of(s: &Shape) -> [f64; 4] {
+    match &s.kind {
+        ShapeKind::Picture { fill } => fill.crop,
+        _ => [0.0; 4],
+    }
+}
+
+/// Whether two pictures differ in their crop only (apart from box and fill), so the crop can morph.
+fn recropped(a: &Shape, b: &Shape) -> bool {
+    matches!(a.kind, ShapeKind::Picture { .. }) && crop_of(a) != crop_of(b) && uncropped(a) == uncropped(b)
+}
+
+/// The crop (left, top, right, bottom) of a picture morphing from box `xa` cropped by `ca` to box
+/// `xb` cropped by `cb`, when its box is `x` at progress `t`: the whole image moves and scales
+/// linearly between where it lies on either slide, and the crop is what of it `x` shows. Falls back
+/// to blending the crops when a crop leaves nothing visible.
+pub fn morph_crop(ca: [f64; 4], xa: Xfrm, cb: [f64; 4], xb: Xfrm, x: Xfrm, t: f64) -> [f64; 4] {
+    // Along one axis: (box start, box size, crop before, crop after) → the crops at `t`.
+    let axis = |(pa, sa, la, ha): (f64, f64, f64, f64), (pb, sb, lb, hb): (f64, f64, f64, f64), (p, s): (f64, f64)| {
+        let (va, vb) = (1.0 - la - ha, 1.0 - lb - hb);
+        if va <= 1e-6 || vb <= 1e-6 {
+            return (lerp(la, lb, t), lerp(ha, hb, t));
+        }
+        // The whole image: its extent and start on either slide.
+        let (ea, eb) = (sa / va, sb / vb);
+        let e = lerp(ea, eb, t);
+        if !e.is_finite() || e.abs() <= 1e-9 {
+            return (lerp(la, lb, t), lerp(ha, hb, t));
+        }
+        let o = lerp(pa - la * ea, pb - lb * eb, t);
+        let lo = (p - o) / e;
+        (lo, 1.0 - lo - s / e)
+    };
+    let (l, r) = axis((xa.x, xa.w, ca[0], ca[2]), (xb.x, xb.w, cb[0], cb[2]), (x.x, x.w));
+    let (tp, bt) = axis((xa.y, xa.h, ca[1], ca[3]), (xb.y, xb.h, cb[1], cb[3]), (x.y, x.h));
+    let c = [l, tp, r, bt];
+    if c.iter().all(|v| v.is_finite()) { c } else { cb }
+}
+
 /// Morph frame from slide `a` to slide `b` at progress `t` (0..1, eased here). Paired shapes
 /// ([`morph_pairs`]) move along [`morph_xfrm`]; when they differ only in solid fill colour the
-/// colour blends, when only in geometry (and fill colour) the outline morphs ([`MorphFrame::paths`]),
+/// colour blends, when pictures differ only in crop the crop morphs ([`morph_crop`]), when only
+/// in geometry (and fill colour) the outline morphs ([`MorphFrame::paths`]),
 /// otherwise the new shape fades in under the fading old one on the same moving
 /// box; with the transition option `words` or `characters` their texts are listed in
 /// [`MorphFrame::text`] to morph word by word or character by character. Unpaired shapes of `a` fade out, unpaired shapes of `b` fade in, and shapes of `b` for
@@ -226,8 +275,18 @@ pub fn morph_frame(pres: &Presentation, a: &Slide, b: &Slide, t: f64, hidden_b:
             (_, xb) => xb,
         };
         let reshape = reshaped(sa, sb);
-        if reshape || content(sa) == content(sb) {
+        let recrop = recropped(sa, sb);
+        if reshape || recrop || content(sa) == content(sb) {
             let mut m = Shape { xfrm: x, ..sb.clone() };
+            if recrop && let ShapeKind::Picture { fill } = &mut m.kind {
+                fill.crop = match (xa, xb, x) {
+                    (Some(xa), Some(xb), Some(x)) => morph_crop(crop_of(sa), xa, crop_of(sb), xb, x, s),
+                    _ => {
+                        let (ca, cb) = (crop_of(sa), crop_of(sb));
+                        [lerp(ca[0], cb[0], s), lerp(ca[1], cb[1], s), lerp(ca[2], cb[2], s), lerp(ca[3], cb[3], s)]
+                    }
+                };
+            }
             if let (Some(fa), Some(fb)) = (solid_color(ca.as_ref(), sa), solid_color(cb.as_ref(), sb))
                 && fa != fb
             {

crates/anim/src/tests.rs

@@ -549,6 +549,41 @@ fn morph_pairs_leaves_unrelated_text_boxes_alone() {
     assert_eq!(morph_pairs(&a, &b), [(ShapeId(1), ShapeId(2)), (ShapeId(3), ShapeId(4))]);
 }
 
+#[test]
+fn morph_crop_moves_the_image_linearly() {
+    let bx = |x, w| Xfrm::new(x, 0.0, w, 100.0);
+    // Same box, the crop pans from the left half to the right half of a 200-wide image.
+    let c = morph_crop([0.0, 0.0, 0.5, 0.0], bx(0.0, 100.0), [0.5, 0.0, 0.0, 0.0], bx(0.0, 100.0), bx(0.0, 100.0), 0.5);
+    assert!(c.iter().zip([0.25, 0.0, 0.25, 0.0]).all(|(a, b)| (a - b).abs() < 1e-9), "{c:?}");
+    // The box shrinks over an image that stays put: only the right crop grows.
+    let c = morph_crop([0.0; 4], bx(0.0, 100.0), [0.0, 0.0, 0.5, 0.0], bx(0.0, 50.0), bx(0.0, 75.0), 0.5);
+    assert!(c.iter().zip([0.0, 0.0, 0.25, 0.0]).all(|(a, b)| (a - b).abs() < 1e-9), "{c:?}");
+    // Nothing visible on one side: the crops blend.
+    let c = morph_crop([0.5, 0.0, 0.5, 0.0], bx(0.0, 100.0), [0.0; 4], bx(0.0, 100.0), bx(0.0, 100.0), 0.5);
+    assert!(c.iter().all(|v| v.is_finite()) && (c[0] - 0.25).abs() < 1e-9, "{c:?}");
+}
+
+#[test]
+fn morph_frame_morphs_a_picture_crop() {
+    // A picture recropped on the next slide stays one picture whose crop morphs (#118).
+    let p = deckcraft_model::defaults::new_presentation(None);
+    let pic = |id, crop| Shape {
+        kind: deckcraft_model::ShapeKind::Picture { fill: deckcraft_model::style::PictureFill { crop, ..Default::default() } },
+        ..shape(id, "Picture 1")
+    };
+    let mut a = Slide::default();
+    let mut b = Slide::default();
+    a.shapes = vec![pic(1, [0.0, 0.0, 0.5, 0.0])];
+    b.shapes = vec![pic(2, [0.5, 0.0, 0.0, 0.0])];
+    let f = morph_frame(&p, &a, &b, 0.5, &|_| false);
+    assert_eq!(f.shapes.len(), 1);
+    assert!(f.opacity.is_empty());
+    let deckcraft_model::ShapeKind::Picture { fill } = &f.shapes[0].0.kind else { panic!("not a picture") };
+    let want = 0.5 * f.mix;
+    assert!((fill.crop[0] - want).abs() < 1e-9 && (fill.crop[2] - (0.5 - want)).abs() < 1e-9, "{:?}", fill.crop);
+    assert_eq!(morph_frame(&p, &a, &b, 1.0, &|_| false).shapes[0].0.kind, b.shapes[0].kind);
+}
+
 #[test]
 fn morph_xfrm_interpolates() {
     let a = Xfrm { rot: 350.0, ..Xfrm::new(0.0, 0.0, 100.0, 100.0) };

docs/animation-parity.md

@@ -42,7 +42,7 @@ perspective-correct subdivided meshes.
 | Duration, advance on click / after time, Apply To All | yes | yes |
 | Transition sounds | yes | yes: Transitions › Sound offers six built-in sounds (synthesised, no sound files shipped), Other Sound…, [Stop Previous Sound] and Loop Until Next Sound; they play in the show and round-trip |
 | Preview in the editor | yes | yes |
-| Morph: objects move, resize, recolour; unmatched text boxes fade in place | yes | yes (#119) |
+| Morph: objects move, resize, recolour; unmatched text boxes fade in place; a picture's crop morphs | yes | yes (#119, #118) |
 | Morph: Words and Characters | yes | yes (#5) |
 | Morph: geometry (circle to star) | yes | yes (#27) |
 | Morph: `!!` name forcing, pictures, 3-D models, ink | yes | names partly; no 3-D or ink |
@@ -100,4 +100,5 @@ In, Wipe, Zoom, Float In, Grow/Shrink, Pulse, Spin, motion lines): weighted, ~85
 | 2026-10-13 | major | Transitions measured frame by frame against PowerPoint's video export and retuned (mean diff 35.7 → 15.0); PowerPoint's XML defaults and option meanings; new options |
 | 2026-10-13 | minor | Triggers now play in the slide show (they were read and written but never started), effects of different triggers apply in the order they were clicked |
 | 2026-10-11 | minor | Morph leaves unrelated text boxes unpaired: they fade in place (#119) |
+| 2026-10-11 | minor | Morph animates a changed picture crop (#118) |
 | 2026-10-10 | major | Created: 48/48 transitions, 64 of ~190 animation effects, pane and option depth, estimates |