Tile buffers in a graphics processing system are managed use
"copy-on-write" semantics, in which tile data stored in a memory location
is not transferred to another location until the tile data for one of the
buffers is modified. Two memory spaces store tile data, and two logical
buffers are used to access the memory spaces. For each tile, a tile
association is maintained, indicating which of the two memory spaces is
associated with each of the two logical buffers. To copy a tile of the
first logical buffer to the second logical buffer, the tile association
for the tile being copied is modified. Data for a tile is written to the
memory space associated with a target logical buffer after ensuring that
the tile association for the tile associates the target logical buffer
with a different one of the two memory spaces from the other logical
buffer.
