XBox360's GPU supports free 4x AA (multisampling) when alpha blending is off.
What to do you need in order to have 'free' 4x AA?
1) Enough bandwith! edram and buses were designed around free AA. edram supports maximum memory troughput is needed to store 2 quads per clock cycles (8 pixels per clock)
2) Multisampling AA techniques oversample only the z-buffer, not the color buffer.
What does that mean? It means you have just to spend extra transistors to generate 4x 'zixels' per clock, color is replicated for each multisamplex zixel.
Thus when 4x AA is on we're not running shader on a number of pixel 4 times bigger than before, we're shading the SAME number of pixels we shade when AA is off.
Multisampling can reduce aliasing only along primitives edges, that's it.
If your favourite game have tons of alphated textures used to simulate leaves, trees, grass, and so on..you will still get a lot of aliasing on Xbox360 too, sorry guys :lol
So can it be free? Yes..it can!
Obviously designers devoted die area (transistors!!) to support wide buses , edram ,extra z-buffer interpolators and more complex ROPs to achieve such a result.
Nothing is free, never!
What to do you need in order to have 'free' 4x AA?
1) Enough bandwith! edram and buses were designed around free AA. edram supports maximum memory troughput is needed to store 2 quads per clock cycles (8 pixels per clock)
2) Multisampling AA techniques oversample only the z-buffer, not the color buffer.
What does that mean? It means you have just to spend extra transistors to generate 4x 'zixels' per clock, color is replicated for each multisamplex zixel.
Thus when 4x AA is on we're not running shader on a number of pixel 4 times bigger than before, we're shading the SAME number of pixels we shade when AA is off.
Multisampling can reduce aliasing only along primitives edges, that's it.
If your favourite game have tons of alphated textures used to simulate leaves, trees, grass, and so on..you will still get a lot of aliasing on Xbox360 too, sorry guys :lol
So can it be free? Yes..it can!
Obviously designers devoted die area (transistors!!) to support wide buses , edram ,extra z-buffer interpolators and more complex ROPs to achieve such a result.
Nothing is free, never!