It was just form of 2D acceleration. We even see it now, sometimes called "hardware cursor" in various games settings, althought pipeline is much longer. Just

It was just form of 2D acceleration. We even see it now, sometimes called "hardware cursor" in various games settings, althought pipeline is much longer. Just that old small hardware had little to no memory protection and very tight integration so stuff like that could be done directly instead of going thru many layers of abstraction