To start painting, call:
gui$get_window_backing_store()
Then finish up with:
gui$release_window_backing_store()
Process will retain the underlying GraphicsBitmap behind the scenes.
This fixes racing between the WindowServer and GUI clients.
This patch also adds a WSWindowLocker that is exactly what it sounds like.
Previously we'd blit every pixel in every window that intersected any dirty
rect to the back buffer. With this patch, we limit ourselves to blitting the
pixels inside the actual dirty rects.
There's still a lot of optimizations to make in this code.
Only booleans are supported at first. More types can be added easily.
Use this to add /proc/sys/wm_flash_flush which when enabled flashes pending
screen flush rects in yellow before they happen.
Windows that don't intersect any of the dirty rects don't need to be copied
into the back buffer since they won't be affected by the subsequent flushes.
It's a bit confusing that the "current" process is not actually running
while we're inside the scheduler. Perhaps the scheduler should redirect
"current" to its own dummy Process. I'm not sure.
Regardless, this patch improves responsiveness by allowing the scheduler
to unblock a process right after it calls select() in case it already has
a pending wakeup request.
