On XP you don’t paint into ‘pixel buffers’, you just paint onto the screen. What you paint however is clipped by a mask, defined by clipping regions. I don’t k

On XP you don’t paint into ‘pixel buffers’, you just paint onto the screen. What you paint however is clipped by a mask, defined by clipping regions. I don’t know for sure what Microsoft used for their themes but it is far more likely they used the mechanism that already existed for arbitrarily shaped windows, the clipping regions, which happen to nicely match what they tried to do with these rounded windows, instead of using bitmaps, which is less efficient and new.