feat(globe3d=11): latf/lngf/zy/zx land plate zoom URL params

Default latf=1.25; linear multiply on lon/lat plus optional non-linear
bias via zy/zx toward equator and prime meridian.

Co-authored-by: Cursor <cursoragent@cursor.com>

assets/hub-globe.js

@@ -12,7 +12,7 @@
  * globe3d=9: v4 sphere grid only (thin E–W + N–S) — proper rotation baseline.
  * globe3d=10: v4 visible-arc → screen ellipse (hub ry), disk-clipped.
  * globe3d=11: v10 grid + geographic mercator-flat land (360° U-wrap).
- *   ?f=0.66 — N–S latitude factor (default 0.66; lower = more squeeze).
+ *   ?latf=1.25&lngf=1&zy=0&zx=0 — land plate zoom (linear + non-linear).
  */
 export const GLOBE_VIEW = { imgW: 1920, imgH: 1080, cx: 720, cy: 560, r: 322, rim: 330 };
 
@@ -30,14 +30,39 @@ const CONTINENT_INNER_SX = 1.2408477842003853;
 const CONTINENT_INNER_SY = 1.2408477842003853;
 /** Map plate center longitude (extract_red_polygons.py CENTER_LON). */
 const MERCATOR_LON_CENTER = (12 * Math.PI) / 180;
-/** Default N–S latitude factor (override with ?f= on globe3d=11). */
-const CONTINENT_LAT_FACTOR_DEFAULT = 0.66;
+/** Default land-plate zoom (?latf / ?lngf / ?zy / ?zx on globe3d=11). */
+const LAND_ZOOM_DEFAULT = { latf: 1.25, lngf: 1, zy: 0, zx: 0 };
 
-function resolveContinentLatFactor(raw) {
-  if (typeof raw !== 'number' || !isFinite(raw)) {
-    return CONTINENT_LAT_FACTOR_DEFAULT;
+function clampZoomNum(v, min, max, fallback) {
+  if (typeof v !== 'number' || !isFinite(v)) {
+    return fallback;
   }
-  return Math.max(0.05, Math.min(2, raw));
+  return Math.max(min, Math.min(max, v));
+}
+
+function resolveLandZoom(raw) {
+  const r = raw && typeof raw === 'object' ? raw : {};
+  return {
+    latf: clampZoomNum(r.latf, 0.05, 4, LAND_ZOOM_DEFAULT.latf),
+    lngf: clampZoomNum(r.lngf, 0.05, 4, LAND_ZOOM_DEFAULT.lngf),
+    zy: clampZoomNum(r.zy, -4, 4, LAND_ZOOM_DEFAULT.zy),
+    zx: clampZoomNum(r.zx, -4, 4, LAND_ZOOM_DEFAULT.zx),
+  };
+}
+
+/**
+ * Linear latf/lngf on sphere lon/lat; zy/zx bias zoom toward equator/ prime meridian:
+ * mul = factor × (1 + z×(1−t²)), t = |coord|/pole (1 at pole, 0 at center line).
+ */
+function landZoomLonLat(lon, lat, zoom) {
+  const latT = Math.min(1, Math.abs(lat) / (Math.PI / 2));
+  const lonT = Math.min(1, Math.abs(lon) / Math.PI);
+  const latMul = zoom.latf * (1 + zoom.zy * (1 - latT * latT));
+  const lonMul = zoom.lngf * (1 + zoom.zx * (1 - lonT * lonT));
+  return {
+    lon: wrapLon(lon * lonMul + MERCATOR_LON_CENTER),
+    lat: Math.max(-1.52, Math.min(1.52, lat * latMul)),
+  };
 }
 const RASTER_SCALE = 2;
 const AXIS_STEPS = 160;
@@ -961,11 +986,10 @@ function sampleFlatPlateFromHub(mercFlat, hpX, hpY) {
 }
 
 /** Sphere tex → mercator-flat plate (lon center + inverse Mercator Y). */
-function sampleMercFlatFromTex(mercFlat, tex, latFactor) {
+function sampleMercFlatFromTex(mercFlat, tex, landZoom) {
   const ll = texLonLat(tex);
-  const lon = wrapLon(ll.lon + MERCATOR_LON_CENTER);
-  const lat = Math.max(-1.52, Math.min(1.52, ll.lat * latFactor));
-  return sampleMercFlat(mercFlat, lon, lat);
+  const mapped = landZoomLonLat(ll.lon, ll.lat, landZoom);
+  return sampleMercFlat(mercFlat, mapped.lon, mapped.lat);
 }
 
 function isLandPixel(r, g, b, a) {
@@ -1077,11 +1101,11 @@ function sampleLandRgbaMercator(mercFlat, tex) {
 }
 
 /** globe3d=11 — geographic mercator wrap (360°); z > LIMB_Z only. */
-function sampleLandVisibleHemisphere(mercFlat, tex, latFactor) {
+function sampleLandVisibleHemisphere(mercFlat, tex, landZoom) {
   if (tex.z <= LIMB_Z) {
     return null;
   }
-  const flat = sampleMercFlatFromTex(mercFlat, tex, latFactor);
+  const flat = sampleMercFlatFromTex(mercFlat, tex, landZoom);
   if (isHubContinentPixel(flat[0], flat[1], flat[2], flat[3])) {
     return hubContinentRgba(flat);
   }
@@ -1187,7 +1211,7 @@ export async function mountHubGlobe(stage, opts) {
   const build = opts.build || 'earth3d';
   const reducedMotion = !!opts.reducedMotion;
   const renderVersion = Math.max(1, parseInt(opts.renderVersion, 10) || 1);
-  const continentLatFactor = resolveContinentLatFactor(opts.continentLatFactor);
+  const landZoom = resolveLandZoom(opts.landZoom);
 
   const canvas = document.createElement('canvas');
   canvas.className = 'hub-globe-canvas';
@@ -1299,7 +1323,7 @@ export async function mountHubGlobe(stage, opts) {
         cy,
         r,
         fillDiskRegion(ctx, cx, cy, r, rotation, function (tex) {
-          const l = sampleLandVisibleHemisphere(mercFlat, tex, continentLatFactor);
+          const l = sampleLandVisibleHemisphere(mercFlat, tex, landZoom);
           return l || [0, 0, 0, 0];
         })
       );
@@ -1375,7 +1399,10 @@ export async function mountHubGlobe(stage, opts) {
   raf = requestAnimationFrame(tick);
   stage.dataset.globe3d = String(renderVersion);
   if (renderVersion >= 11) {
-    stage.dataset.globeLatFactor = String(continentLatFactor);
+    stage.dataset.globeLatf = String(landZoom.latf);
+    stage.dataset.globeLngf = String(landZoom.lngf);
+    stage.dataset.globeZy = String(landZoom.zy);
+    stage.dataset.globeZx = String(landZoom.zx);
   }
   stage.dataset.globeAxis =
     renderVersion === 11
@@ -1405,7 +1432,10 @@ export async function mountHubGlobe(stage, opts) {
       canvas.remove();
       delete stage.dataset.globe3d;
       delete stage.dataset.globeAxis;
-      delete stage.dataset.globeLatFactor;
+      delete stage.dataset.globeLatf;
+      delete stage.dataset.globeLngf;
+      delete stage.dataset.globeZy;
+      delete stage.dataset.globeZx;
     },
   };
 }