opengl - MSAA の GL_SAMPLE_ALPHA_TO_COVERAGE

Question

MSAA FBO にレンダリングするときにGL_SAMPLE_ALPHA_TO_COVERAGE_ARBを使用するのは理にかなっていますか? それとも、アルファブレンディングが処理されるときのマルチサンプリングの代替ですか?

Answer 1

Alpha to coverage is actually only useful (and thus only used at all) with multisampling, since it transforms a fragment's alpha value into an appropriate coverage value used for determining the contribution of the fragment to its respective samples. Without multisampling this doesn't make any sense at all. Alpha to coverage on its own doesn't do any antialiasing. It is used to improve the multisampling behaviour of highly alpha-tested things (like wire fence or alpha-tested tree leaves and grass), which otherwise don't really profit from multisampling (since it only really works on polygon-edges while those things just consist of a single large polygon) leaving quite jaggy boundaries.