feat(window-switcher): the expose scatter layout

layout() seeds windows on a golden-angle spiral, most recent at the centre,
pushes overlapping pairs apart along the axis that costs less screen, and
fits the result with one scale so sizes stay relative. The spec's first
seed, the windows' real positions, was prototyped and dropped: every window
on this desk fills its monitor, so they started in one pile, and pushing a
pile apart made a line that still overlapped after 300 passes and filled
8 to 15% of the screen. The spiral converged in 1 to 55 passes. Comparing
overlaps in raw pixels stacked wide windows into a column, which is why the
axis choice divides by the screen's width and height.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 79 insertions, 0 deletions

diff --git a/window-switcher/Expose.js b/window-switcher/Expose.js
new file mode 100644
index 0000000..2b14e4e
--- /dev/null
+++ b/window-switcher/Expose.js
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+.pragma library
+
+// Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License version 2 as
+// published by the Free Software Foundation.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// The expose scatter, kept pure so it runs under node (test_expose.js).
+// Input is [{w, h}] in real pixels, most recently used first; output is
+// [{x, y, w, h}] inside a W by H screen.
+//
+// Windows are seeded on a golden-angle spiral, the most recent at the centre,
+// then pushed apart until nothing overlaps, then fitted with one scale, so
+// their sizes stay relative to each other. Seeding from the windows' real
+// positions was tried first and degenerates here: every window fills its
+// monitor, so they all start in one pile, and pushing a pile apart makes a
+// line that still overlapped after 300 passes and filled under 15% of the
+// screen.
+
+const GAP = 60;          // real pixels kept between two windows
+const PASSES = 300;
+const FILL = 0.92;       // of the screen, each way
+const MAX_SCALE = 0.5;   // a lone window is not a full-screen mirror
+const SPREAD = 0.45;     // spiral step, as a fraction of the tallest window
+const GOLDEN = 137.5 * Math.PI / 180;
+
+function layout(rects, W, H) {
+    if (rects.length === 0) return [];
+    const aspect = W / H;
+    const step = SPREAD * Math.max(...rects.map(o => o.h));
+
+    // The spiral is stretched by the screen's aspect, so the cluster comes
+    // out the shape of the screen rather than round.
+    const r = rects.map((o, k) => {
+        const rad = step * Math.sqrt(k), t = k * GOLDEN;
+        return { x: rad * Math.cos(t) * aspect - o.w / 2,
+                 y: rad * Math.sin(t) - o.h / 2, w: o.w, h: o.h };
+    });
+
+    // ponytail: all pairs every pass, O(n^2); fine for this desk's ~20
+    // windows, a spatial grid if it ever is not.
+    for (let pass = 0; pass < PASSES; pass++) {
+        let moved = false;
+        for (let i = 0; i < r.length; i++) for (let j = i + 1; j < r.length; j++) {
+            const a = r[i], b = r[j];
+            const ox = Math.min(a.x + a.w, b.x + b.w) - Math.max(a.x, b.x) + GAP;
+            const oy = Math.min(a.y + a.h, b.y + b.h) - Math.max(a.y, b.y) + GAP;
+            if (ox <= 0 || oy <= 0) continue;
+            moved = true;
+            // Push along whichever axis costs less screen, measured against
+            // the screen's own width and height: compared in raw pixels, wide
+            // windows always separate vertically and stack into a column.
+            if (ox / W < oy / H) {
+                const s = (b.x + b.w / 2) >= (a.x + a.w / 2) ? 1 : -1;
+                a.x -= s * ox / 2; b.x += s * ox / 2;
+            } else {
+                const s = (b.y + b.h / 2) >= (a.y + a.h / 2) ? 1 : -1;
+                a.y -= s * oy / 2; b.y += s * oy / 2;
+            }
+        }
+        if (!moved) break;
+    }
+
+    let x0 = Infinity, y0 = Infinity, x1 = -Infinity, y1 = -Infinity;
+    for (const o of r) {
+        x0 = Math.min(x0, o.x); y0 = Math.min(y0, o.y);
+        x1 = Math.max(x1, o.x + o.w); y1 = Math.max(y1, o.y + o.h);
+    }
+    const k = Math.min(FILL * W / (x1 - x0), FILL * H / (y1 - y0), MAX_SCALE);
+    const dx = (W - (x1 - x0) * k) / 2, dy = (H - (y1 - y0) * k) / 2;
+    return r.map(o => ({ x: dx + (o.x - x0) * k, y: dy + (o.y - y0) * k,
+                         w: o.w * k, h: o.h * k }));
+}