Alpha to coverage
Translates a fragment's alpha into an MSAA coverage mask, approximating transparency without sorting or blending.
Rather than blending semi-transparent fragments — which demands sorting them back to front — the technique lets the alpha value decide how many of a pixel's MSAA subsamples are written. The result is order-independent and made for alpha-tested geometry: foliage, grass, hair, chain-link, where the hard cutout edge otherwise looks jagged.
The price is that opacity is quantised to the subsample count — four-sample MSAA gives only four levels — so edges can look dithery, which is often softened with a noise pattern. It requires MSAA to be on and is switched on with a single state flag in both OpenGL and Direct3D.