Current DRI3 specification
Keith Packard
keithp at keithp.com
Tue Jun 4 16:51:33 PDT 2013
I've gotten DRI3 working and posted an article about it here:
http://keithp.com/blogs/dri3_extension/
I thought now might be a great time to post the current DRI3 protocol
specification and let people take a look (and comment!)
The DRI3 Extension
Version 1.0
2013-6-4
Keith Packard
keithp at keithp.com
Intel Corporation
1. Introduction
The DRI3 extension provides mechanisms to translate between direct
rendered buffers and X pixmaps. When combined with the Present extension,
a complete direct rendering solution for OpenGL is provided.
The direct rendered buffers are passed across the protocol via
standard POSIX file descriptor passing mechanisms. On Linux, these
buffers are DMA-BUF objects.
DRI3 also includes a mechanism to translate between Linux Futexes
and X Sync extension Fences. This provides a synchronization mechanism
which can be used to serialize access to shared render buffers.
1.1. Acknowledgments
Eric Anholt <eric at anholt.net>
Dave Airlie <airlied at redhat.com>
Kristian Høgsberg <krh at bitplanet.net>
James Jones <janomes at nvidia.com>
❄ ❄ ❄ ❄ ❄ ❄ ❄
2. Data Types
DRI3EVENTID { XID }
Defines a unique event delivery target for DRI3
events. Multiple event IDs can be allocated to provide
multiple distinct event delivery contexts.
DRI3EVENTMASK { DRI3ConfigureNotifyMask }
The DRI3 extension also uses the RandR extension Provider data type to
select among multiple GPUs on a single screen and the Sync extension
fence object to provide graphics object synchronization.
❄ ❄ ❄ ❄ ❄ ❄ ❄
4. Errors
No errors are defined by the DRI3 extension.
❄ ❄ ❄ ❄ ❄ ❄ ❄
5. Events
DRI3 adds a ConfigureNotify event to inform clients about window
configuration changes which can affect the allocation of
window-related direct rendered buffers.
❄ ❄ ❄ ❄ ❄ ❄ ❄
6. Protocol Types
DRI3DRIVER { DRI3DriverDRI
DRI3DriverVDPAU }
These values describe the type of driver the client will want
to load. The server sends back the name of the driver to use
for the screen in question.
❄ ❄ ❄ ❄ ❄ ❄ ❄
7. Extension Initialization
The name of this extension is "DRI3"
┌───
DRI3QueryVersion
client-major-version: CARD32
client-minor-version: CARD32
▶
major-version: CARD32
minor-version: CARD32
└───
The client sends the highest supported version to the server
and the server sends the highest version it supports, but no
higher than the requested version. Major versions changes can
introduce incompatibilities in existing functionality, minor
version changes introduce only backward compatible changes.
It is the clients responsibility to ensure that the server
supports a version which is compatible with its expectations.
Backwards compatible changes included addition of new
requests.
❄ ❄ ❄ ❄ ❄ ❄ ❄
8. Extension Requests
┌───
DRI3Open
drawable: DRAWABLE
driverType: DRI3DRIVER
provider: PROVIDER
▶
nfd: CARD8
driver: STRING
device: FD
└───
Errors: Drawable, Value, Match
This requests that the X server open the direct rendering
device associated with drawable, driverType and RandR
provider. The provider must support SourceOutput or SourceOffload.
The direct rendering library used to implement the specified
'driverType' is returned in 'driver'. The file
descriptor for the device is returned in 'device'. 'nfd' will
be set to one (this is strictly a convenience for XCB which
otherwise would need request-specific information about how
many file descriptors were associated with this reply).
┌───
DRI3PixmapFromBuffer
pixmap: PIXMAP
drawable: DRAWABLE
size: CARD32
width, height, stride: CARD16
depth, bpp: CARD8
buffer: FD
└───
Errors: Alloc, Drawable, IDChoice, Value, Match
Creates a pixmap for the direct rendering object associated
with 'buffer'. Changes to pixmap will be visible in that
direct rendered object and changes to the direct rendered
object will be visible in the pixmap.
'size' specifies the total size of the buffer bytes. 'width',
'height' describe the geometry (in pixels) of the underlying
buffer. 'stride' specifies the number of bytes per scanline in
the buffer. The pixels within the buffer may not be arranged
in a simple linear fashion, but 'size' will be at least
'height' * 'stride'.
Precisely how any additional information about the buffer is
shared is outside the scope of this extension.
If buffer cannot be used with the screen associated with
drawable, a Match error is returned.
If depth or bpp are not supported by the screen, a Value error
is returned.
┌───
DRI3BufferFromPixmap
pixmap: PIXMAP
▶
nfd: CARD8
size: CARD32
width, height, stride: CARD16
depth, bpp: CARD8
buffer: FD
└───
Errors: Pixmap, Match
Pass back a direct rendering object associated with
pixmap. Changes to pixmap will be visible in that
direct rendered object and changes to the direct rendered
object will be visible in the pixmap.
'size' specifies the total size of the buffer bytes. 'width',
'height' describe the geometry (in pixels) of the underlying
buffer. 'stride' specifies the number of bytes per scanline in
the buffer. The pixels within the buffer may not be arranged
in a simple linear fashion, but 'size' will be at least
'height' * 'stride'.
Precisely how any additional information about the buffer is
shared is outside the scope of this extension.
If buffer cannot be used with the screen associated with
drawable, a Match error is returned.
┌───
DRI3SelectInput
eventContext: DRI3EVENTID
window: WINDOW
eventMask: SETofDRI3EVENT
└───
Errors: Window, Value, Match, IDchoice
Selects the set of DRI3 events to be delivered for the
specified window and event context. DRI3SelectInput can
create, modifiy or delete event contexts. An event context is
associated with a specific window; using an existing event
context with a different window generates a Match error.
If eventContext specifies an existing event context, then if
eventMask is empty, DRI3SelectInput deletes the specified
context, otherwise the specified event context is changed to
select a different set of events.
If eventContext is an unused XID, then if eventMask is empty
no operation is performed. Otherwise, a new event context is
created selecting the specified events.
┌───
DRI3FenceFromFD
drawable: DRAWABLE
fence: FENCE
initially-triggered: BOOL
fd: FD
└───
Errors: IDchoice, Drawable
Creates a Sync extension Fence that provides the regular Sync
extension semantics along with a file descriptor that provides
a device-specific mechanism to manipulate the fence directly.
Details about the mechanism used with this file descriptor are
outside the scope of the DRI3 extension.
❄ ❄ ❄ ❄ ❄ ❄ ❄
9. Extension Events
DRI3ConfigureNotify is sent if DRI3SelectInput has requested it.
DRI3ConfigureNotify events are XGE events and so do not have a unique
event ID.
┌───
DRI3ConfigureNotify
type: CARD8 XGE event type (35)
extension: CARD8 DRI3 extension request number
length: CARD16 2
evtype: CARD16 DRI3_ConfigureNotify
eventID: DRI3EVENTID
window: WINDOW
x: INT16
y: INT16
width: CARD16
height: CARD16
off_x: INT16
off_y: INT16
pixmap_width: CARD16
pixmap_height: CARD16
pixmap_flags: CARD32
└───
'x' and 'y' are the parent-relative location of 'window'.
❄ ❄ ❄ ❄ ❄ ❄ ❄
10. Extension Versioning
The DRI3 extension is adapted from the DRI2 extension.
1.0: First published version
❄ ❄ ❄ ❄ ❄ ❄ ❄
11. Relationship with other extensions
As an extension designed to support other extensions, there is
naturally some interactions with other extensions.
11.1 GLX
GLX has no direct relation with DRI3, but a direct rendering OpenGL
application will presumably use both, and target
11.2 Present
The Present extension provides a way to synchronize the display of pixmap
contents to the screen. When used in conjunction with DRI3, they
provide a complete direct rendering solution for OpenGL or other APIs.
11.3 DRI2
DRI3 provides similar functionality to the DRI2Connect and
DRI2GetBuffersWithFormat requests, however DRI3 uses file descriptors
to refer to the direct rendering device and buffers.
Present and DRI3 are designed in conjunction to replace DRI2
11.2 XvMC / Xv
It might be nice to be able to reference YUV formatted direct rendered
objects from the X server.
❄ ❄ ❄ ❄ ❄ ❄ ❄
Appendix A. Protocol Encoding
Syntactic Conventions
This document uses the same syntactic conventions as the core X
protocol encoding document.
A.1 Common Types
┌───
DRI3DRIVER
0x0 DRI3DriverDRI
0x1 DRI3DriverVDPAU
└───
Note that these match the DRI2 values.
A.2 Protocol Requests
┌───
DRI3QueryVersion
1 CARD8 major opcode
1 0 DRI3 opcode
2 3 length
4 CARD32 major version
4 CARD32 minor version
▶
1 1 Reply
1 unused
2 CARD16 sequence number
4 0 reply length
4 CARD32 major version
4 CARD32 minor version
16 unused
└───
┌───
DRI3Open
1 CARD8 major opcode
1 1 DRI3 opcode
2 4 length
4 DRAWABLE drawable
4 CARD32 driver type
4 PROVIDER provider
▶
1 1 Reply
1 1 nfd
2 CARD16 sequence number
4 (n + p) / 4 reply length
4 n driver name length (n)
20 unused
n CARD8 driver name
p unused, p=pad(n)
0 FD device
└───
┌───
DRI3PixmapFromBuffer
1 CARD8 major opcode
1 2 DRI3 opcode
2 6 length
4 Pixmap pixmap
4 Drawable drawable
4 CARD32 size
2 CARD16 width
2 CARD16 height
2 CARD16 stride
1 CARD8 depth
1 CARD8 bpp
0 FD buffer
└───
┌───
DRI3BufferFromPixmap
1 CARD8 major opcode
1 3 DRI3 opcode
2 2 length
4 Pixmap pixmap
▶
1 1 Reply
1 1 nfd
2 CARD16 sequence number
4 0 reply length
4 CARD32 size
2 CARD16 width
2 CARD16 height
2 CARD16 stride
1 CARD8 depth
1 CARD8 bpp
12 unused
0 FD buffer
└───
┌───
DRI3SelectInput
1 CARD8 major opcode
1 4 DRI3 opcode
2 3 length
4 Window window
4 CARD32 eid
4 CARD32 event mask
└───
┌───
DRI3FenceFromFD
1 CARD8 major opcode
1 5 DRI3 opcode
2 4 length
4 Drawable drawable
4 Fence fence
1 BOOL initially triggered
3 unused
0 FD fence fd
└───
A.3 Protocol Events
┌───
RRScreenChangeNotify
1 35 XGE
1 CARD8 DRI3 extension opcode
2 CARD16 sequence number
4 2 length
2 0 DRI3ConfigureNotify
2 unused
4 CARD32 event id
4 Window window
2 INT16 x
2 INT16 y
2 CARD16 width
2 CARD16 height
2 INT16 off x
2 INT16 off y
2 CARD16 pixmap width
2 CARD16 pixmap height
4 CARD32 pixmap flags
└───
A.4 Protocol Errors
The DRI3 extension defines no errors.
❄ ❄ ❄ ❄ ❄ ❄ ❄
--
keith.packard at intel.com
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