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framebuffer_session: atomic blitting and panning

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By enhancing the Framebuffer::Session interface by the new RPC functions
'blit' and 'panning', GUI clients become able to attain tearing-free
output. Two modes of operations are supported.

1. Atomic back-to-front blitting

   GUI clients that partially update their user interface like regular
   application dialogs, can now implement double buffering by placing
   both the back buffer and front buffer within the GUI session's
   framebuffer and configuring a view that shows only the front buffer.
   The 'blit' operation allows the client to atomically flush pixels
   from the back buffer to the front buffer.

2. Atomic buffer flipping

   GUI clients that always update all pixels like a media player or
   a game can now use the 'panning' feature to atomically redirect the
   displayed pixels to a different portion of the GUI session's virtual
   frame buffer. The virtual framebuffer always contains two frames,
   the displayed one and the next one. Once the next frame is complete,
   the client changes the panning position to the portion containing
   the next frame.

Issue #5350
This commit is contained in:
Norman Feske
2024-09-23 16:54:05 +02:00
committed by Christian Helmuth
parent 0e33830d1f
commit 8082aa980e
13 changed files with 308 additions and 52 deletions
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75
repos/os/include/framebuffer_session/framebuffer_session.h
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@ -22,7 +22,6 @@
namespace Framebuffer {
struct Mode;
struct Session;
struct Session_client;
@ -31,22 +30,49 @@ namespace Framebuffer {
using Area = Surface_base::Area;
using Point = Surface_base::Point;
using Rect = Surface_base::Rect;
struct Mode
{
Area area;
size_t bytes_per_pixel() const { return 4; }
void print(Output &out) const { Genode::print(out, area); }
};
struct Transfer
{
Rect from; /* source rectangle */
Point to; /* destination position */
/**
* Return true if transfer is applicable to 'mode'
*
* Pixels are transferred only if the source rectangle lies within
* the bounds of the framebuffer, and source does not overlap the
* destination.
*/
bool valid(Mode const &mode) const
{
Rect const fb { { }, mode.area };
Rect const dest { to, from.area };
return from.area.valid()
&& fb.contains(from.p1()) && fb.contains(from.p2())
&& fb.contains(dest.p1()) && fb.contains(dest.p2())
&& !Rect::intersect(from, dest).valid();
}
};
struct Blit_batch
{
static constexpr unsigned N = 4;
Transfer transfer[N];
};
}
/**
* Framebuffer mode info as returned by 'Framebuffer::Session::mode()'
*/
struct Framebuffer::Mode
{
Area area;
size_t bytes_per_pixel() const { return 4; }
void print(Output &out) const { Genode::print(out, area); }
};
struct Framebuffer::Session : Genode::Session
{
/**
@ -102,6 +128,23 @@ struct Framebuffer::Session : Genode::Session
*/
virtual void refresh(Rect rect) = 0;
enum class Blit_result { OK, OVERLOADED };
/**
* Transfer pixel regions within the framebuffer
*/
virtual Blit_result blit(Blit_batch const &) = 0;
/**
* Define panning position of the framebuffer
*
* The panning position is the point within the framebuffer that
* corresponds to the top-left corner of the output. It is designated
* for implementing buffer flipping of double-buffered output, and for
* scrolling.
*/
virtual void panning(Point pos) = 0;
/**
* Register signal handler for refresh synchronization
*/
@ -115,11 +158,13 @@ struct Framebuffer::Session : Genode::Session
GENODE_RPC(Rpc_dataspace, Dataspace_capability, dataspace);
GENODE_RPC(Rpc_mode, Mode, mode);
GENODE_RPC(Rpc_refresh, void, refresh, Rect);
GENODE_RPC(Rpc_blit, Blit_result, blit, Blit_batch const &);
GENODE_RPC(Rpc_panning, void, panning, Point);
GENODE_RPC(Rpc_mode_sigh, void, mode_sigh, Signal_context_capability);
GENODE_RPC(Rpc_sync_sigh, void, sync_sigh, Signal_context_capability);
GENODE_RPC_INTERFACE(Rpc_dataspace, Rpc_mode, Rpc_mode_sigh, Rpc_refresh,
Rpc_sync_sigh);
Rpc_blit, Rpc_panning, Rpc_sync_sigh);
};
#endif /* _INCLUDE__FRAMEBUFFER_SESSION__FRAMEBUFFER_SESSION_H_ */