A painter's sort ranks a polygon by one depth, so a long surface is overpainted by the small things lying beside it

Fact

Depth sorting without a depth buffer gives each polygon a single number, usually its centroid's distance. A 1400 m runway quad therefore sorts as though all of it were 700 m away. Every terrain cell nearer than that is painted afterwards, straight over the runway's near half.

Cutting the surface into strips fixes it, because each strip's centroid is then close to the geometry it competes with. The strip length has to be comparable to the neighbouring polygons, not merely smaller than the whole.

Coplanar surfaces need a second fix: paint on tarmac, tarmac on terrain, and a level-of-detail ring overlapping its neighbour all sit at the same depth, and no subdivision separates them. Bias the sort key instead — multiply the depth of the layer that must win by slightly less than one.

Why it matters

The symptom is that a large object is simply absent: it is transformed, clipped, projected, coloured and queued, and every one of those steps is correct. Nothing is logged, the polygon count is right, and the natural suspicion falls on the projection or on culling.

How to apply

• Emit large flat surfaces as strips sized like the terrain around them, not as one quad.
• Give every layer that is coplanar with another an explicit depth scale (0.98 for the surface, 0.97 for the markings on it) rather than relying on insertion order — Array.prototype.sort is stable, but the order that reaches it is not meaningful.
• Assert the invariant in a test: after sorting, every item's depth is no greater than its predecessor's.