Why is AA in video games so damanding?
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The ways to do it right essentially all require looking at a given pixel multiple times. This might not sound like much, but it’s computationally similar to running a game at a higher resolution. 4x MSAA (or Multi Sample Anti Aliasing) will look at each pixel 4 times, once in each corner and take the average color of that pixel and display that to the screen. At 1080p resolution this bumps it up from 2,073,600 “real pixels” to 8,294,400 “sampled pixels”.
Even if you have a buffer to say where the harsh edges on the screen are and use that to apply your anti-aliasing algorithm, you’re still having to look at a single pixel multiple times each frame.
On top of all of that, blurring operations are always slow, because division on computers is slow. To get the average pixel color you have to take the Red, Green and Blue values all, add them up and divide them. This has to happen every single frame.
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