If there are several software fallbacks affecting the system memory copy of the
same pixmap, only copy the results back to the driver pixmap when it's used for
acceleration again, or in the BlockHandler, whichever happens first.
If the PrepareAccess hook fails, use the DownloadFromScreen hook to retrieve
driver pixmap contents to a system RAM copy, perform software rendering on that
and copy the results back using the UploadToScreen hook. Use the classic
migration logic to minimize transfers (which as a bonus allows slightly
cleaning up some of the existing mixed pixmap code).
This enables things that weren't possible before with driver-allocated pixmap
storage: If some (or all) GPU pixmap storage can't be mapped directly by the
CPU, this can be handled between the PrepareAccess and
DownloadFrom/UploadToScreen hooks, e.g.:
* Radeon KMS on big endian machines can fail PrepareAccess if the pixmap
requires byte-swapping and swap bytes in DownloadFrom/UploadToScreen.
* Environments where GPU and CPU don't have a shared address space at all.
Here the driver PrepareAccess hook will always fail and leave all transfers
between GPU / CPU storage to the Download/From/UploadToScreen hooks.
Drivers which can handle all pixmaps in the PrepareAccess hook should notice
little if any difference.
- Based on driver pixmaps with some changes (completely transparent to driver).
- It helps with the problem of known software fallbacks, such as trapezoids.
- exaDoMigration is now called for all cases that provide a do_migration hook.
- exa_migration.c is renamed to exa_migration_classic.c
