Alpha to coverage
Alpha to coverage is a multisampling computer graphics technique useful for situations where dense foliage or grass must be rendered in a video game.
This technique uses the alpha channel of textures as a coverage mask for anti-aliasing.
Alpha to coverage multisampling is based on regular multisampling, except that the alpha coverage mask is ANDed with the multisample mask. Alpha-to-coverage converts the alpha component output from the pixel shader to a coverage mask. When the multisampling is applied each output fragment gets a transparency of 0 or 1 depending on alpha coverage and the multisampling result.