Sylpheed/crates/sylpheed-formats/examples/tie_break_pixel_cost.rs

//! What does the unknown paint-order TIE-BREAK actually cost, in pixels?
//!
//! `ui-paint-order-derived-check.md` bounds *where* a wrong tie-break could
//! show — 24 overlapping tied pairs across `GP_TITLE` — and says outright that
//! nobody has measured how many of them change a pixel. Overlap is an upper
//! bound: two elements can overlap and still composite identically in either
//! order, if either is transparent where they meet.
//!
//! This renders each screen twice — once in the order `compose` derives, once
//! with one tied pair swapped — and counts the pixels that differ. Same-key
//! elements are contiguous in the derived order (a stable sort by `(key, i)`),
//! so swapping two of them paints nothing else in between: the diff is the
//! tie-break's cost and nothing else.
//!
//! Every entry also runs a CONTROL: a swap of two OVERLAPPING elements with
//! DIFFERENT keys, i.e. a pair whose order the game is known to care about. If
//! the control diff is zero the instrument cannot see a reorder on this screen
//! and its zeros mean nothing.
//!
//!     cargo run -p sylpheed-formats --example tie_break_pixel_cost -- <GP_TITLE.pak>
use sylpheed_formats::{pak, ui_layout};
use ui_layout::{ComposeOptions, UiBuild};

/// Pixels that differ, and the largest per-channel difference.
fn diff(a: &[u8], b: &[u8]) -> (usize, u8) {
    let (mut n, mut worst) = (0usize, 0u8);
    for (pa, pb) in a.chunks_exact(4).zip(b.chunks_exact(4)) {
        if pa != pb {
            n += 1;
            for k in 0..4 {
                worst = worst.max(pa[k].abs_diff(pb[k]));
            }
        }
    }
    (n, worst)
}

/// Where does element `ei` actually put ink? Render with it and without it;
/// the pixels that move are the ones it paints. This is what turns a bare
/// "0 px differ" into an explained one: bounding boxes can overlap while the
/// sprites inside them never touch the same pixel.
fn ink_mask(
    build: &UiBuild,
    bundle: &[u8],
    opts: ComposeOptions,
    order: &[usize],
    base: &[u8],
    ei: usize,
) -> Vec<bool> {
    let n_el = build.elements.iter().map(|e| e.index).max().unwrap_or(0) + 1;
    let mut vis = vec![true; n_el.max(build.elements.len())];
    vis[build.elements[ei].index] = false;
    let without = ui_layout::compose_with_order(build, bundle, opts, Some(&vis), Some(order));
    base.chunks_exact(4)
        .zip(without.rgba.chunks_exact(4))
        .map(|(x, y)| x != y)
        .collect()
}

fn swapped(order: &[usize], a: usize, b: usize) -> Vec<usize> {
    let mut o = order.to_vec();
    let (pa, pb) = (
        o.iter().position(|&e| e == a).unwrap(),
        o.iter().position(|&e| e == b).unwrap(),
    );
    o.swap(pa, pb);
    o
}

/// The element's on-screen rect, the same approximation the tie census uses:
/// the declared pivot doubled, placed at the keyframe. `at` selects the pose —
/// `None` is `rest()`, which is where the original census was computed.
///
/// 🔴 An element that is TRANSPARENT at the chosen pose gets no rect at all. A
/// tie involving something invisible cannot cost a pixel, and counting it as an
/// overlap is what made the original census an upper bound rather than a cost.
fn rect(e: &ui_layout::Element, at: Option<u32>) -> Option<(i32, i32, i32, i32)> {
    let kf = match at {
        Some(t) => e.pose_at(t)?,
        None => e.rest()?.clone(),
    };
    if kf.fade >> 24 == 0 || kf.scale_x == 0 || kf.scale_y == 0 {
        return None;
    }
    let (w, h) = ((e.pivot_x * 2) as i32, (e.pivot_y * 2) as i32);
    if w == 0 || h == 0 {
        return None;
    }
    Some((kf.x, kf.y, w, h))
}

fn overlaps(a: &ui_layout::Element, b: &ui_layout::Element, at: Option<u32>) -> bool {
    let (Some(ra), Some(rb)) = (rect(a, at), rect(b, at)) else {
        return false;
    };
    (ra.0 + ra.2).min(rb.0 + rb.2) - ra.0.max(rb.0) > 0
        && (ra.1 + ra.3).min(rb.1 + rb.3) - ra.1.max(rb.1) > 0
}

struct Case {
    name: &'static str,
    opts: ComposeOptions,
}

fn cases() -> Vec<Case> {
    vec![
        Case {
            name: "default (what `screen render` draws)",
            opts: ComposeOptions {
                backdrop: [0, 0, 0, 255],
                ..Default::default()
            },
        },
        Case {
            name: "everything on (focus+animated+primitives)",
            opts: ComposeOptions {
                include_focus: true,
                include_animated: true,
                include_primitives: true,
                backdrop: [0, 0, 0, 255],
                ..Default::default()
            },
        },
        // 🔴 The two cases above pose at `rest()`, which is each element's last
        // hold picked independently — so they draw transients that the settled
        // screen does not have (`docs/re/structures/ui-settle-time.md`). A tie
        // between two elements that are transparent at the settle time cannot
        // cost a pixel on the screen the player sees, however much their rects
        // overlap at rest. `at` is filled in per entry.
        Case {
            name: "AT THE SETTLE TIME (what the player sees)",
            opts: ComposeOptions {
                backdrop: [0, 0, 0, 255],
                at: Some(0), // replaced per entry
                ..Default::default()
            },
        },
    ]
}

fn tied_overlapping_pairs(build: &UiBuild, bytes: &[u8], at: Option<u32>) -> Vec<(usize, usize, u32)> {
    let keys: Vec<u32> = build
        .elements
        .iter()
        .map(|e| ui_layout::sprite_layer_key(build, bytes, e).unwrap_or(u32::MAX))
        .collect();
    let mut out = Vec::new();
    for a in 0..keys.len() {
        for b in (a + 1)..keys.len() {
            if keys[a] != keys[b] || keys[a] == u32::MAX {
                continue;
            }
            if overlaps(&build.elements[a], &build.elements[b], at) {
                out.push((a, b, keys[a]));
            }
        }
    }
    out
}

/// A pair the game's own order DOES separate: overlapping, different keys.
/// Used as the control — swapping it must move pixels.
fn control_pair(build: &UiBuild, bytes: &[u8], at: Option<u32>) -> Option<(usize, usize)> {
    let keys: Vec<u32> = build
        .elements
        .iter()
        .map(|e| ui_layout::sprite_layer_key(build, bytes, e).unwrap_or(u32::MAX))
        .collect();
    let mut best: Option<(i64, usize, usize)> = None;
    for a in 0..keys.len() {
        for b in (a + 1)..keys.len() {
            if keys[a] == keys[b] || keys[a] == u32::MAX || keys[b] == u32::MAX {
                continue;
            }
            if !overlaps(&build.elements[a], &build.elements[b], at) {
                continue;
            }
            let (ra, rb) = (rect(&build.elements[a], at)?, rect(&build.elements[b], at)?);
            let ox = ((ra.0 + ra.2).min(rb.0 + rb.2) - ra.0.max(rb.0)) as i64;
            let oy = ((ra.1 + ra.3).min(rb.1 + rb.3) - ra.1.max(rb.1)) as i64;
            let area = ox * oy;
            if best.map_or(true, |(x, _, _)| area > x) {
                best = Some((area, a, b));
            }
        }
    }
    best.map(|(_, a, b)| (a, b))
}

fn main() {
    let path = std::env::args()
        .nth(1)
        .expect("usage: tie_break_pixel_cost <pak>");
    let ar = pak::PakArchive::open(&path).expect("open pak");
    let entries: Vec<_> = ar.entries().to_vec();
    println!("# tie-break pixel cost — {path}\n");
    let mut totals = (0usize, 0usize, 0usize); // pairs, changed-a-pixel, controls-dead
    for (i, e) in entries.iter().enumerate() {
        let Ok(bytes) = ar.read(e) else { continue };
        let Some(build) = ui_layout::parse_build(&bytes) else {
            continue;
        };
        // The census pairs are still computed at rest, so the report can say
        // how many of THOSE survive posing at the settle time.
        let pairs_at_rest = tied_overlapping_pairs(&build, &bytes, None);
        if pairs_at_rest.is_empty() {
            continue;
        }
        let settle = build.settle_time();
        println!(
            "entry {i:2}  {} elements  {} overlapping tied pair(s) at rest{}",
            build.elements.len(),
            pairs_at_rest.len(),
            match (settle, build.settle_window()) {
                (Some(t), Some((lo, hi))) => format!("  settle t={t} (window {} units)", hi - lo),
                _ => "  NO SETTLE WINDOW".to_string(),
            }
        );
        let derived = ui_layout::derived_paint_order(&build, &bytes);
        for mut c in cases() {
            // The settle case is a no-op on a bundle that never settles.
            if c.opts.at.is_some() {
                match settle {
                    Some(t) => c.opts.at = Some(t),
                    None => {
                        println!("  [{}] SKIPPED: no settle window", c.name);
                        continue;
                    }
                }
            }
            let pairs = tied_overlapping_pairs(&build, &bytes, c.opts.at);
            if pairs.len() != pairs_at_rest.len() {
                println!(
                    "  [{}] 🔴 {} of the {} tied pairs are GONE at this pose (an element is \
transparent or collapsed there) — they cannot cost a pixel",
                    c.name,
                    pairs_at_rest.len() - pairs.len(),
                    pairs_at_rest.len()
                );
            }
            let base = ui_layout::compose_with_order(&build, &bytes, c.opts, None, Some(&derived));
            let drawn: std::collections::HashSet<usize> = base.drawn.iter().copied().collect();
            // Control first. An instrument that cannot see a reorder it is
            // supposed to see makes every zero below meaningless.
            let ctrl = match control_pair(&build, &bytes, c.opts.at) {
                Some((a, b)) if drawn.contains(&a) && drawn.contains(&b) => {
                    let alt = ui_layout::compose_with_order(
                        &build,
                        &bytes,
                        c.opts,
                        None,
                        Some(&swapped(&derived, a, b)),
                    );
                    let (n, w) = diff(&base.rgba, &alt.rgba);
                    Some((a, b, n, w))
                }
                _ => None,
            };
            match ctrl {
                Some((a, b, n, w)) if n > 0 => println!(
                    "  [{}] CONTROL ok: swapping [{a}] {} x [{b}] {} moves {n} px (max Δ {w})",
                    c.name, build.elements[a].name, build.elements[b].name
                ),
                Some((a, b, _, _)) => {
                    totals.2 += 1;
                    println!(
                        "  [{}] CONTROL DEAD: swapping [{a}] {} x [{b}] {} changes NOTHING — \
zeros below are uninterpretable",
                        c.name, build.elements[a].name, build.elements[b].name
                    )
                }
                None => {
                    totals.2 += 1;
                    println!(
                        "  [{}] CONTROL UNAVAILABLE: no overlapping different-key pair is drawn",
                        c.name
                    )
                }
            }
            for &(a, b, key) in &pairs {
                let both_drawn = drawn.contains(&a) && drawn.contains(&b);
                if !both_drawn {
                    println!(
                        "  [{}] [{a}] {} x [{b}] {} (key {key}): NOT BOTH DRAWN — unreachable here",
                        c.name, build.elements[a].name, build.elements[b].name
                    );
                    continue;
                }
                let alt = ui_layout::compose_with_order(
                    &build,
                    &bytes,
                    c.opts,
                    None,
                    Some(&swapped(&derived, a, b)),
                );
                let (n, w) = diff(&base.rgba, &alt.rgba);
                let total = (base.width as usize) * (base.height as usize);
                // Explain the number: how many pixels do the two BOTH paint on?
                // A zero with a large shared-ink count is a real "order does
                // not matter here"; a zero with no shared ink means the
                // bounding boxes overlapped and the sprites did not.
                let ma = ink_mask(&build, &bytes, c.opts, &derived, &base.rgba, a);
                let mb = ink_mask(&build, &bytes, c.opts, &derived, &base.rgba, b);
                let shared = ma.iter().zip(&mb).filter(|(x, y)| **x && **y).count();
                let (ia, ib) = (
                    ma.iter().filter(|x| **x).count(),
                    mb.iter().filter(|x| **x).count(),
                );
                println!(
                    "  [{}] [{a}] {} x [{b}] {} (key {key}): {n} px differ ({:.4}% of frame), \
max Δ {w}  | ink {ia} / {ib} px, shared {shared} px",
                    c.name,
                    build.elements[a].name,
                    build.elements[b].name,
                    100.0 * n as f64 / total as f64
                );
                if c.name.starts_with("default") {
                    totals.0 += 1;
                    if n > 0 {
                        totals.1 += 1;
                    }
                }
            }
        }
        println!();
    }
    println!(
        "default-options summary: {} of {} overlapping tied pairs change at least one pixel; \
{} dead/unavailable controls",
        totals.1, totals.0, totals.2
    );
}