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 use the alpha channel of textures as a coverage mask for anti_aliasing.
Alpha-to-coverage multisampling is essentially the same as regular multisampling except that the alpha coverage mask is generated and 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 pixel gets a transparency of 0 or 1 depending on alpha coverage and the multisampling result.
This method do not work if the alpha value of the texture is used, for example when simulating looking through a window.