Count the camera ground estimate within the surface sample budget

A pass checked its budget of 16 tile samples before each point, but a
point that needed the estimate of the ground under the camera took two
samples, so a pass could reach 17. The point is now left for the next
pass when the estimate used the last sample.

src/globe/surfacePlacement.js

@@ -176,6 +176,11 @@ export function createSurfacePoints(
     for (const { set, points, exclude = [set] } of groups()) {
       if (!set) continue;
       let changed = false;
+      const yieldPass = () => {
+        if (changed) set.commit();
+        if (changed || moved) request();
+        timer = setTimeout(place, 0);
+      };
       for (let index = 0; index < points.length; index++) {
         const point = points[index];
         if (point.surfaceRevision === revision) continue;
@@ -183,12 +188,11 @@ export function createSurfacePoints(
           samples >= SAMPLES_PER_PASS ||
           (visited > 0 && performance.now() - started >= SAMPLE_BUDGET_MS)
         ) {
-          if (changed) set.commit();
+          yieldPass();
-          if (changed || moved) request();
-          timer = setTimeout(place, 0);
           return;
         }
         visited++;
+        const previousRevision = point.surfaceRevision;
         point.surfaceRevision = revision;
         if (point.show === false) continue;
         const offset =
@@ -215,6 +219,13 @@ export function createSurfacePoints(
             )
           : point.position;
         if (!onScreen(position, size)) continue;
+        // The camera estimate above counts too: leave this point for the
+        // next pass rather than go over the budget.
+        if (samples >= SAMPLES_PER_PASS) {
+          point.surfaceRevision = previousRevision;
+          yieldPass();
+          return;
+        }
         samples++;
         const height = readSurface(engine, point.cartographic, {
           exclude,

src/globe/surfacePlacement.test.mjs

@@ -211,6 +211,22 @@ test('initial placement projects high ground before testing the screen and retai
   assert.ok(Math.abs(heights()[0] - 2502) < 0.01);
 });
 
+test('the camera ground estimate counts against the per-pass sample budget', async (t) => {
+  const { engine, surface } = setup(t, 20, { estimateGround: true });
+  await engine.maps.setPhotorealTiles({});
+  // Fifteen points find plausible terrain; the sixteenth needs the camera
+  // estimate, which is a tile sample of its own.
+  let terrainReads = 0;
+  engine.fake.script('terrainHeight', () => (++terrainReads <= 15 ? 10 : 20000));
+  engine.fake.script('sampleHeight', 50);
+  const sampled = t.mock.method(engine.surface, 'sampleHeight');
+  surface.place();
+  assert.ok(
+    sampled.mock.callCount() <= 16,
+    `${sampled.mock.callCount()} samples in one pass`,
+  );
+});
+
 test('a consumer with its own visibility gate can place a ground vertical whose base does not project', (t) => {
   const { engine, surface, heights } = setup(t, 1, { screenMargin: Infinity });
   engine.fake.script('terrainHeight', 2500);