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The DRI3 Extension
Version 1.0
2013-6-4
Keith Packard
keithp@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@anholt.net>
Dave Airlie <airlied@redhat.com>
Kristian Høgsberg <krh@bitplanet.net>
James Jones <janomes@nvidia.com>
Arthur Huillet <arthur.huillet@free.fr>
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2. Data Types
The DRI3 extension 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.
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4. Errors
DRI3 defines no errors.
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5. Events
DRI3 defines no events.
❄ ❄ ❄ ❄ ❄ ❄ ❄
6. Protocol Types
DRI3 defines no new protocol types.
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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.
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8. Extension Requests
┌───
DRI3Open
drawable: DRAWABLE
provider: PROVIDER
▶
nfd: CARD8
device: FD
└───
Errors: Drawable, Value, Match
This requests that the X server open the direct rendering
device associated with drawable and RandR provider. The
provider must support SourceOutput or SourceOffload.
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 are not required to
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 are not required to
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.
┌───
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.
┌───
DRI3FDFromFence
drawable: DRAWABLE
fence: FENCE
▶
fd: FD
└───
Errors: IDchoice, Drawable, Match
Given a Sync extension Fence that provides the regular Sync
extension semantics, returns 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. 'drawable' must be
associated with a direct rendering device that 'fence' can
work with, otherwise a Match error results.
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9. Extension Events
DRI3 defines no events.
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10. Extension Versioning
The DRI3 extension is adapted from the DRI2 extension.
1.0: First published version
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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 is both an application interface and an X extension. OpenGL
applications using the GLX API will use the GLX extension, DRI3 and
Present when doing direct rendering.
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.
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Appendix A. Protocol Encoding
Syntactic Conventions
This document uses the same syntactic conventions as the core X
protocol encoding document.
A.1 Common Types
None.
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
└───
┌───
DRI3FenceFromFD
1 CARD8 major opcode
1 4 DRI3 opcode
2 4 length
4 Drawable drawable
4 Fence fence
1 BOOL initially triggered
3 unused
0 FD fence fd
└───
┌───
DRI3FDFromFence
1 CARD8 major opcode
1 5 DRI3 opcode
2 3 length
4 Drawable drawable
4 Fence fence
▶
1 1 Reply
1 1 nfd
2 CARD16 sequence number
4 0 reply length
24 unused
0 FD fence fd
└───
A.3 Protocol Events
The DRI3 extension defines no events.
A.4 Protocol Errors
The DRI3 extension defines no errors.
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