[MAPS3D-1467] Fix precision related flickering on far plane (internal…

…-1876) The high resolution of depth buffer is not required for very high zooms (e.g. 19) while the flickering effects are possible on sources with low max zoom. Anyway, when tilting the map to show horizon, a way further far distance is used with no problems so there should be no issues for doing the same in this case.
mapbox · Sep 26, 2024 · 67672bc · 67672bc
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commit 67672bc
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Showing 7 changed files with 13 additions and 2 deletions.
diff --git a/src/geo/projection/far_z.ts b/src/geo/projection/far_z.ts
@@ -19,10 +19,16 @@ export function farthestPixelDistanceOnPlane(tr: Transform, pixelsPerMeter: numb
     const topHalfSurfaceDistance = Math.sin(fovAboveCenter) * cameraToSeaLevelDistance / Math.sin(Math.max(Math.PI / 2.0 - tr._pitch - fovAboveCenter, 0.01));
 
     // Calculate z distance of the farthest fragment that should be rendered.
-    const furthestDistance = Math.sin(tr._pitch) * topHalfSurfaceDistance + cameraToSeaLevelDistance;
+    let furthestDistance = Math.sin(tr._pitch) * topHalfSurfaceDistance + cameraToSeaLevelDistance;
     const horizonDistance = cameraToSeaLevelDistance * (1 / tr._horizonShift);
 
     // Add a bit extra to avoid precision problems when a fragment's distance is exactly `furthestDistance`
+    // Due to precision of sources with low maxZoom, content is prone to flickering on zoom above 18.
+    // Use larger furthest distance also on pitch before the horizon, especially on higher zoom to limit
+    // the performance and depth range resolution impact.
+    if (!tr.elevation || tr.elevation.exaggeration() === 0) {
+        furthestDistance *= (1.0 + Math.max(tr.zoom - 17, 0));
+    }
     return Math.min(furthestDistance * 1.01, horizonDistance);
 }
 

diff --git a/test/integration/render-tests/model-layer/environment-test/expected.png b/test/integration/render-tests/model-layer/environment-test/expected.png
diff --git a/test/integration/render-tests/model-layer/model-rotation/expected.png b/test/integration/render-tests/model-layer/model-rotation/expected.png
diff --git a/test/integration/render-tests/model-layer/model-rts/expected.png b/test/integration/render-tests/model-layer/model-rts/expected.png
diff --git a/test/integration/render-tests/model-layer/model-scale/expected.png b/test/integration/render-tests/model-layer/model-scale/expected.png
diff --git a/...er-tests/text-pitch-alignment/viewport-text-rotation-alignment-map/expected.png b/...er-tests/text-pitch-alignment/viewport-text-rotation-alignment-map/expected.png
diff --git a/test/unit/geo/projection/far_z.test.ts b/test/unit/geo/projection/far_z.test.ts
@@ -27,9 +27,14 @@ describe('FarZ', () => {
         pixelsPerMeter = mercator.pixelsPerMeter(tr.center.lat, tr.worldSize);
         expect(farthestPixelDistanceOnPlane(tr, pixelsPerMeter).toFixed(3)).toBe("151.500");
 
-        tr.zoom = 22.0;
+        tr.zoom = 17.0;
         pixelsPerMeter = mercator.pixelsPerMeter(tr.center.lat, tr.worldSize);
         expect(farthestPixelDistanceOnPlane(tr, pixelsPerMeter).toFixed(3)).toBe("151.500");
+
+        // Expanded furthest distance to prevent flicker on far plane
+        tr.zoom = 22.0;
+        pixelsPerMeter = mercator.pixelsPerMeter(tr.center.lat, tr.worldSize);
+        expect(farthestPixelDistanceOnPlane(tr, pixelsPerMeter).toFixed(3)).toBe("909.000");
     });
 
     test('farthestPixelDistanceOnSphere', () => {