Alpha masking

Alpha masking refers to a special case of alpha blending where all pixels are rendered as either fully opaque (100% alpha) or fully transparent (0% alpha) with no partial transparency. This can be treated as a special case because it does not require alpha sorting in order to produce visually correct results. This provides a significant performance win over an equivalent alpha sorted material.

When an alpha masked texture is recognized, Trainz will also compress texture files using DXT1a compression rather than the DXT3 required for normal alpha blending. This provides a 50% reduction in texture memory usage.

TBD: Materials which support alpha masking.

TBD: Control of alpha masking via texture.txt file

TBD: Image of alpha mask and the in-game result, versus alpha blending.

TBD: Discussion of using alpha testing without a b&w texture.