Alpha-tested foliage thins out and vanishes with distance unless its texture covers more than the cutoff

Fact

Mipmapping averages alpha, and an alpha test compares that average against its cutoff. A leaf card whose texture is under half opaque (with a 0.5 cutoff) drops below it in the smaller mip levels, so far away the whole card is discarded: crowns of trees and tufts of grass thin out with distance, then disappear.

Why it matters

Up close everything looks right, so the bug shows only on a distant view and reads as a culling or level-of-detail problem. Sparse, delicate leaf pictures, the ones that look best up close, fail first.

How to apply

• Paint each card so that more of it is opaque than the cutoff (about 55-70% for a 0.5 cutoff): bigger, overlapping leaves rather than a few small ones.
• Or keep coverage per mip level: rescale each mip's alpha so the share of texels past the cutoff matches the base level, or use alpha-to-coverage with MSAA.
• Check foliage from far away, not only up close.