deckcraft/crates/anim/src/morph.rs

//! Morph: matching shapes between two slides, interpolating their boxes and building the frames.

use deckcraft_model::resolve::{self, Ctx};
use deckcraft_model::{ColorRef, Fill, Geom, Presentation, Rgba, Shape, ShapeId, ShapeKind, Slide, Xfrm, walk};

use crate::clampf;
use crate::easing::smooth;

fn text_of(s: &Shape) -> String {
    s.text.as_ref().map(|t| t.text()).unwrap_or_default()
}

/// Pairs of (shape on `a`, shape on `b`) that Morph animates from one to the other: first by
/// `!!name` (forced match), then by exact name, then by the same kind and text, then by the same
/// kind and preset geometry. Each shape is used once; top-level shapes only (groups move whole).
pub fn morph_pairs(a: &Slide, b: &Slide) -> Vec<(ShapeId, ShapeId)> {
    let mut pairs: Vec<(ShapeId, ShapeId)> = Vec::new();
    let mut used_a = vec![false; a.shapes.len()];
    let mut used_b = vec![false; b.shapes.len()];
    let passes: [&dyn Fn(&Shape, &Shape) -> bool; 4] = [
        &|x, y| x.name.starts_with("!!") && x.name == y.name,
        &|x, y| !x.name.is_empty() && x.name == y.name,
        &|x, y| {
            if x.kind_name() != y.kind_name() {
                return false;
            }
            let tx = text_of(x);
            !tx.trim().is_empty() && tx == text_of(y)
        },
        &|x, y| {
            x.kind_name() == y.kind_name()
                && x.geom.preset_name().is_some()
                && x.geom.preset_name() == y.geom.preset_name()
                && text_of(x).trim().is_empty() == text_of(y).trim().is_empty()
        },
    ];
    for pass in passes {
        for (i, sa) in a.shapes.iter().enumerate() {
            if used_a.get(i).copied().unwrap_or(true) {
                continue;
            }
            let found = b.shapes.iter().enumerate().find(|(j, sb)| !used_b.get(*j).copied().unwrap_or(true) && pass(sa, sb));
            if let Some((j, sb)) = found {
                if let Some(u) = used_a.get_mut(i) {
                    *u = true;
                }
                if let Some(u) = used_b.get_mut(j) {
                    *u = true;
                }
                pairs.push((sa.id, sb.id));
            }
        }
    }
    pairs
}

fn lerp(a: f64, b: f64, t: f64) -> f64 {
    let v = a + (b - a) * t;
    if v.is_finite() {
        v
    } else if t < 0.5 {
        a
    } else {
        b
    }
}

/// Interpolate a box from `a` to `b` at `t` (0..1): position and size linearly, rotation along the
/// shortest way round; flips switch at the midpoint.
pub fn morph_xfrm(a: Xfrm, b: Xfrm, t: f64) -> Xfrm {
    let t = clampf(t, 0.0, 1.0, 0.0);
    if t >= 1.0 {
        return b;
    }
    if t <= 0.0 {
        return a;
    }
    let ra = if a.rot.is_finite() { a.rot } else { 0.0 };
    let rb = if b.rot.is_finite() { b.rot } else { 0.0 };
    let mut d = (rb - ra).rem_euclid(360.0);
    if d > 180.0 {
        d -= 360.0;
    }
    let rot = (ra + d * t).rem_euclid(360.0);
    let late = t >= 0.5;
    Xfrm {
        x: lerp(a.x, b.x, t),
        y: lerp(a.y, b.y, t),
        w: lerp(a.w, b.w, t),
        h: lerp(a.h, b.h, t),
        rot: if rot.is_finite() { rot } else { 0.0 },
        flip_h: if late { b.flip_h } else { a.flip_h },
        flip_v: if late { b.flip_v } else { a.flip_v },
    }
}

/// One frame of a Morph transition, ready for the renderer's `render_blend`: the backdrops of the
/// two slides cross-fade by [`MorphFrame::mix`], the shapes are drawn in order on top.
#[derive(Clone, Debug, Default)]
pub struct MorphFrame {
    /// Shapes with fresh ids, each flagged `true` when it comes from the old slide (it resolves
    /// its placeholder, theme and style against that slide).
    pub shapes: Vec<(Shape, bool)>,
    /// Opacity of the frame's shapes by id; shapes not listed are opaque.
    pub opacity: Vec<(ShapeId, f64)>,
    pub mix: f64,
    /// With the Words or Characters option: pairs of frame shapes whose texts morph by words or
    /// characters instead of cross-fading (the renderer's `TextMorph`).
    pub text: Vec<MorphText>,
    /// Frame shapes whose outline turns from another geometry into their own (the renderer's
    /// `PathMorph`).
    pub paths: Vec<MorphPath>,
}

/// A frame shape whose outline morphs from `from` (the old shape's geometry) into its own.
#[derive(Clone, Debug, PartialEq)]
pub struct MorphPath {
    pub id: ShapeId,
    pub from: Geom,
    /// The boxes of the old and the new shape on their own slides.
    pub from_box: Xfrm,
    pub to_box: Xfrm,
}

/// Two frame shapes whose texts morph by words or characters.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct MorphText {
    /// Frame shape ids: from the old slide, from the new slide.
    pub old: ShapeId,
    pub new: ShapeId,
    /// The boxes of the two shapes on their own slides.
    pub from: Xfrm,
    pub to: Xfrm,
    pub chars: bool,
}

impl MorphFrame {
    /// Opacity of shape `id` of the frame.
    pub fn opacity_of(&self, id: ShapeId) -> f64 {
        self.opacity.iter().find(|(s, _)| *s == id).map(|(_, o)| *o).unwrap_or(1.0)
    }
}

fn mix_color(a: Rgba, b: Rgba, t: f64) -> Rgba {
    let m = |x: u8, y: u8| clampf(lerp(x as f64, y as f64, t), 0.0, 255.0, 0.0).round() as u8;
    Rgba { r: m(a.r, b.r), g: m(a.g, b.g), b: m(a.b, b.b), a: m(a.a, b.a) }
}

fn solid_color(ctx: Option<&Ctx>, s: &Shape) -> Option<Rgba> {
    let ctx = ctx?;
    match resolve::fill(ctx, s) {
        (Some(Fill::Solid { color }), ph) => Some(ctx.color(&color, ph)),
        _ => None,
    }
}

fn box_of(ctx: Option<&Ctx>, s: &Shape) -> Option<Xfrm> {
    match ctx {
        Some(c) => Some(resolve::xfrm(c, s)),
        None => s.xfrm,
    }
}

/// The content of a shape apart from what Morph interpolates (identity, box and fill).
fn content(s: &Shape) -> Shape {
    Shape { id: ShapeId(0), name: String::new(), xfrm: None, fill: None, ..s.clone() }
}

/// Whether two shapes differ in their geometry only, and it is drawn as an outline (shapes,
/// pictures, connectors), so the outline can morph.
fn reshaped(a: &Shape, b: &Shape) -> bool {
    let outlined = |s: &Shape| matches!(s.kind, ShapeKind::Shape | ShapeKind::Picture { .. } | ShapeKind::Connector { .. });
    a.geom != b.geom && outlined(a) && outlined(b) && Shape { geom: Geom::default(), ..content(a) } == Shape { geom: Geom::default(), ..content(b) }
}

/// 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`]),
/// 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
/// which `hidden_b` is true (entrance animations, hidden media) stay out of the frame.
pub fn morph_frame(pres: &Presentation, a: &Slide, b: &Slide, t: f64, hidden_b: &dyn Fn(ShapeId) -> bool) -> MorphFrame {
    let s = smooth(clampf(t, 0.0, 1.0, 0.0));
    let ca = Ctx::for_slide(pres, a);
    let cb = Ctx::for_slide(pres, b);
    let pairs: Vec<(ShapeId, ShapeId)> = morph_pairs(a, b).into_iter().filter(|(_, ib)| !hidden_b(*ib)).collect();
    let mut next = 1u32;
    walk(&a.shapes, &mut |x, _| next = next.max(x.id.0.saturating_add(1)));
    walk(&b.shapes, &mut |x, _| next = next.max(x.id.0.saturating_add(1)));
    let mut f = MorphFrame { mix: s, ..Default::default() };
    let by = b.transition.as_ref().map(|tr| tr.option.as_str()).unwrap_or("");
    let (by_text, chars) = (by == "words" || by == "characters", by == "characters");
    let has_text = |x: &Shape| x.text.as_ref().is_some_and(|t| !t.is_empty()) && !matches!(x.kind, ShapeKind::Group { .. } | ShapeKind::Table(_));
    let mut text = Vec::new();
    let mut paths = Vec::new();
    let mut push = |mut sh: Shape, old: bool, op: f64| {
        let id = ShapeId(next);
        sh.id = id;
        next = next.saturating_add(1);
        if op < 1.0 {
            f.opacity.push((id, op));
        }
        f.shapes.push((sh, old));
        id
    };
    for sa in &a.shapes {
        if !pairs.iter().any(|(ia, _)| *ia == sa.id) {
            push(sa.clone(), true, 1.0 - s);
        }
    }
    for sb in &b.shapes {
        let pair = pairs.iter().find(|(_, ib)| *ib == sb.id).and_then(|(ia, _)| a.shapes.iter().find(|x| x.id == *ia));
        let Some(sa) = pair else {
            if !hidden_b(sb.id) {
                push(sb.clone(), false, s);
            }
            continue;
        };
        let (xa, xb) = (box_of(ca.as_ref(), sa), box_of(cb.as_ref(), sb));
        let x = match (xa, xb) {
            (Some(xa), Some(xb)) => Some(morph_xfrm(xa, xb, s)),
            (_, xb) => xb,
        };
        let reshape = reshaped(sa, sb);
        if reshape || content(sa) == content(sb) {
            let mut m = Shape { xfrm: x, ..sb.clone() };
            if let (Some(fa), Some(fb)) = (solid_color(ca.as_ref(), sa), solid_color(cb.as_ref(), sb))
                && fa != fb
            {
                m.fill = Some(Fill::solid(ColorRef::rgb(mix_color(fa, fb, s))));
            }
            let id = push(m, false, 1.0);
            if reshape && let (Some(from_box), Some(to_box)) = (xa, xb) {
                paths.push(MorphPath { id, from: sa.geom.clone(), from_box, to_box });
            }
        } else {
            let new = push(Shape { xfrm: x, ..sb.clone() }, false, s);
            let old = push(Shape { xfrm: x, ..sa.clone() }, true, 1.0 - s);
            // The same text in shapes that differ otherwise (a title slide's centred title and a
            // content slide's title: other placeholder, size, alignment) moves and resizes word
            // by word even with the Objects option, as PowerPoint does, instead of cross-fading.
            let same_text = text_of(sa).trim() == text_of(sb).trim();
            if (by_text || same_text)
                && has_text(sa)
                && has_text(sb)
                && let (Some(from), Some(to)) = (box_of(ca.as_ref(), sa), box_of(cb.as_ref(), sb))
            {
                text.push(MorphText { old, new, from, to, chars });
            }
        }
    }
    f.text = text;
    f.paths = paths;
    f
}