The DRI2 Extension
Version 2.0
2008-09-04
Kristian Høgsberg
krh@redhat.com
Red Hat, Inc
1. Introduction
The DRI2 extension is designed to associate and access auxiliary
rendering buffers with an X drawable.
DRI2 is a essentially a helper extension to support implementation of
direct rendering drivers/libraries/technologies.
The main consumer of this extension will be a direct rendering OpenGL
driver, but the DRI2 extension is not designed to be OpenGL specific.
Direct rendering implementations of OpenVG, Xv, cairo and other
graphics APIs should find the functionality exposed by this extension
helpful and hopefully sufficient.
Relation to XF86DRI
1.1. Acknowledgements
Kevin E. Martin <kem@redhat.com>
Keith Packard <keithp@keithp.com>
Eric Anholt <eric@anholt.net>
Keith Whitwell <keith@tungstengraphics.com>
Jerome Glisse <glisse@freedesktop.org>
Ian Romanick <ian.d.romanick@intel.com>
Michel Dänzer <michel@tungstengraphics.com>
Jesse Barnes <jbarnes@virtuousgeek.org>
⚙ ⚙ ⚙ ⚙ ⚙ ⚙
2. DRI2 Concepts
2.1. Attachment points
Stolen from OpenGL FBOs, I guess.
2.2. Kernel rendering manager
This specification assumes a rendering architecture, where an
underlying kernel rendering manager that can provide 32 bit integer
handles to video memory buffers. These handles can be passed between
processes, which, through a direct rendering driver, submit rendering
to the kernel rendering manager, targeting and/or sourcing from these
buffers. This extension provides a means to communicate about such
buffers as associated with an X drawable.
The details of how the direct rendering driver use the buffer names
and submit the rendering requests is outside the scope of this
specification. However, Appendix B does discuss implementation of
this specification on the Graphics Execution Manager (GEM).
2.3. Request ordering
No ordering between swap buffers and X rendering. X rendering to src
buffers will block if they have a vblank pending.
2.4 Authentication model
The purpose of the DRM authentication scheme is to grant access to the
kernel rendering manager buffers created by the X server if, and only
if, the client has access to the X server. This is achieved in a
three-step protocol:
1) The client gets a token from the kernel rendering manager
that uniquely identifies it. The token is a 32 bit integer.
2) The client passes the token to the X server in the
DRI2Authenticate request. This request is a round trip to
make sure the X server has received and processed the
authentication before the client starts accessing the DRM.
3) The X server authorizes the client by passing the token to
the kernel rendering manager.
A kernel rendering manager can choose not to implement any
authentication and just allow access to all buffers.
2.5 Rendering to the X front buffer
OpenGL allows the client to render to the front buffer, either by
using a single-buffered configuration or but explicitly setting the
draw buffer to GL_FRONT_LEFT. Not allowed!
The client must ask for a fake front buffer, render to that and then
use DRI2CopyRegion to copy contents back and forth between the fake
front buffer and the real front buffer. When X and direct rendering
to a front buffer is interleaved, it is the responsibility of the
application to synchronize access using glXWaitGL and glXWaitX. A
DRI2 implementation of direct rendering GLX, should use these entry
points to copy contents back and forth to as necessary to ensure
consistent rendering.
The client may also use the DRI2SwapBuffers function to request a swap
of the front and back buffers. If the display server supports it, this
operation may be preferred, since it may be easier and/or more performant
for the server to perform a simple buffer swap rather than a blit.
2.6 Synchronizing rendering
DRI2 provides several methods for synchronizing drawing with various events.
The protocol for these methods is based on the SGI_video_sync and
OML_sync_control GLX extensions. Using the DRI2WaitMSC request, a client
can wait for a specific frame count or divisor/remainder before continuing
its processing. With the DRI2WaitSBC request, clients can block until a given
swap count is reached (as incremented by DRI2SwapBuffers). Finally, using
DRI2SwapBuffers, clients can limit their frame rate by specifying a swap
interval using the swap interval call (currently only available through GLX)
or by using the OML swap buffers routine.
2.7 Events
DRI2 provides an event to indicate when a DRI2SwapBuffers request has
been completed. This can be used to throttle drawing on the client
side and tie into application main loops.
Another event is generated when the validity of the requested buffers
changes.
⚙ ⚙ ⚙ ⚙ ⚙ ⚙
3. Data Types
The server side region support specified in the Xfixes extension
version 2 is used in the CopyRegion request.
⚙ ⚙ ⚙ ⚙ ⚙ ⚙
4. Errors
No errors are defined by the DRI2 extension.
⚙ ⚙ ⚙ ⚙ ⚙ ⚙
5. Events
The only events provided by DRI2 are DRI2_BufferSwapComplete
and DRI2InvalidateBuffers.
⚙ ⚙ ⚙ ⚙ ⚙ ⚙
6. Protocol Types
DRI2DRIVER { DRI2DriverDRI
DRI2DriverVDPAU }
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.
DRI2ATTACHMENT { DRI2BufferFrontLeft
DRI2BufferBackLeft
DRI2BufferFrontRight
DRI2BufferBackRight
DRI2BufferDepth
DRI2BufferStencil
DRI2BufferAccum
DRI2BufferFakeFrontLeft
DRI2BufferFakeFrontRight
DRI2BufferDepthStencil
DRI2BufferHiz }
These values describe various attachment points for DRI2
buffers.
DRI2BUFFER { attachment: CARD32
name: CARD32
pitch: CARD32
cpp: CARD32
flags: CARD32 }
The DRI2BUFFER describes an auxiliary rendering buffer
associated with an X drawable. 'attachment' describes the
attachment point for the buffer, 'name' is the name of the
underlying kernel buffer,
DRI2ATTACH_FORMAT { attachment: CARD32
format: CARD32 }
The DRI2ATTACH_FORMAT describes an attachment and the associated
format. 'attachment' describes the attachment point for the buffer,
'format' describes an opaque, device-dependent format for the buffer.
⚙ ⚙ ⚙ ⚙ ⚙ ⚙
7. Extension Initialization
The name of this extension is "DRI2".
┌───
DRI2QueryVersion
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, but also new value types in the DRI2CopyRegion
request. When new values are introduced, the minor version
will be increased so the client can know which values the X
server understands from the version number.
⚙ ⚙ ⚙ ⚙ ⚙ ⚙
8. Extension Requests
┌───
DRI2Connect
window: WINDOW
driverType: DRI2DRIVER
▶
driver: STRING
device: STRING
└───
Returns the driver name and device file to use for the
specified driver type for the screen associated with 'window'.
'type' identifies the type of driver to query for.
'driver' is the name of the driver to load. The client is
assumed to know where to look for the drivers and what to do
with it.
'device' is the filename of the DRM device file.
If the client is not local, or the request driver type is
unknown or not available, 'driver' and 'device' will be empty
strings. We are not using an regular X
error here to indicate failure, which will allow the client
fall back to other options more easily.
ISSUE: We could add the list of supported attachments and the
supported DRI2CopyRegion values here (just the bitmask of all
supported values).
┌───
DRI2Authenticate
window: WINDOW
token: CARD32
▶
authenticated: CARD32
└───
Errors: Window
Request that the X server authenticates 'token', allowing the
client to access the DRM buffers created by the X server on
the screen associated with 'window'.
Authentication shouldn't fail at this point, except if an
invalid token is passed, in which case authenticated is False.
┌───
DRI2GetBuffers
drawable: DRAWABLE
attachments: LISTofDRI2ATTACHMENTS
▶
width, height: CARD32
buffers: LISTofDRI2BUFFER
└───
Errors: Window
Get buffers for the provided attachment points for the given
drawable.
If the DDX driver does not support one or more of the
specified attachment points, a Value error is generated, with
the first unsupported attachment point as the error value.
'width' and 'height' describes the dimensions of the drawable.
'buffers' is a list of DRI2BUFFER for the given DRI2
attachment points.
┌───
DRI2CopyRegion
drawable: DRAWABLE
region: REGION
source: DRI2ATTACHMENT
destination: DRI2ATTACHMENT
▶
└───
Errors: Window, Value
Schedule a copy from one DRI2 buffer to another.
The DRICopyRegion request has a reply but it is empty. The
reply is there to let the direct rendering client wait until
the server has seen the request before proceeding with
rendering the next frame.
┌───
DRI2SwapBuffers
drawable: DRAWABLE
target_msc: two CARD32s
divisor: two CARD32s
remainder: two CARD32s
▶
swap: two CARD32s
└───
Errors: Window
Schedule a swap of the front and back buffers with the display
server.
Returns the swap count value when the swap will actually occur (e.g.
the last queued swap count + (pending swap count * swap interval)).
This request is only available with protocol version 1.2 or
later.
┌───
DRI2GetBuffersWithFormat
drawable: DRAWABLE
attachments: LISTofDRI2ATTACH_FORMAT
▶
width, height: CARD32
buffers: LISTofDRI2BUFFER
└───
Errors: Window
Get buffers for the provided attachment points with the specified
formats for the given drawable.
If the DDX driver does not support one or more of the
specified attachment points or formats, a Value error is generated,
with the first unsupported attachment point as the error value.
'width' and 'height' describes the dimensions of the drawable.
'buffers' is a list of DRI2BUFFER for the given DRI2
attachment points.
This request is only available with protocol version 1.1 or
later.
┌───
DRI2GetMSC
drawable: DRAWABLE
▶
ust, msc, sbc: CARD64
└───
Errors: Window
Get the current media stamp counter (MSC) and swap buffer count (SBC)
along with the unadjusted system time (UST) when the MSC was last
incremented.
This request is only available with protocol version 1.2 or
later.
┌───
DRI2WaitMSC
drawable: DRAWABLE
target_msc: two CARD32s
divisor: two CARD32s
remainder: two CARD32s
▶
ust, msc, sbc: CARD64
└───
Errors: Window
Blocks the client until either the frame count reaches target_msc or,
if the frame count is already greater than target_msc when the request
is received, until the frame count % divisor = remainder. If divisor
is 0, the client will be unblocked if the frame count is greater than
or equal to the target_msc.
Returns the current media stamp counter (MSC) and swap buffer count
(SBC) along with the unadjusted system time (UST) when the MSC was last
incremented.
This request is only available with protocol version 1.2 or
later.
┌───
DRI2WaitSBC
drawable: DRAWABLE
target_sbc: two CARD32s
▶
ust, msc, sbc: CARD64
└───
Errors: Window
Blocks the client until the swap buffer count reaches target_sbc. If
the swap buffer count is already greater than or equal to target_sbc
when the request is received, this request will return immediately.
If target_sbc is 0, this request will block the client until all
previous DRI2SwapBuffers requests have completed.
Returns the current media stamp counter (MSC) and swap buffer count
(SBC) along with the unadjusted system time (UST) when the MSC was last
incremented.
This request is only available with protocol version 1.2 or
later.
┌───
DRI2SwapInterval
drawable: DRAWABLE
interval: CARD32
▶
└───
Errors: Window
Sets the swap interval for DRAWABLE. This will throttle
DRI2SwapBuffers requests to swap at most once per interval frames,
which is useful useful for limiting the frame rate.
┌───
DRI2GetParam
drawable: DRAWABLE
param: CARD32
▶
is_param_recognized: BOOL
value: CARD64
└───
Errors: Drawable
Get the value of a parameter. The parameter's value is looked up on
the screen associated with 'drawable'.
Parameter names in which the value of the most significant byte is
0 are reserved for the X server. Currently, no such parameter names
are defined. (When any such names are defined, they will be defined in
this extension specification and its associated headers).
Parameter names in which the byte's value is 1 are reserved for the
DDX. Such names are private to each driver and shall be defined in the
respective driver's headers.
Parameter names in which the byte's value is neither 0 nor 1 are
reserved for future use.
Possible values of 'is_param_recognized' are true (1) and false (0).
If false, then 'value' is undefined.
This request is only available with protocol version 1.4 or later.
⚙ ⚙ ⚙ ⚙ ⚙ ⚙
9. Extension Events
┌───
DRI2BufferSwapComplete
▶
event_type: CARD16
drawable: CARD32
ust: CARD64
msc: CARD64
sbc: CARD64
└───
This event reports the status of the last DRI2SwapBuffers event to
the client. The event type should be one of DRI2_EXCHANGE_COMPLETE,
indicating a successful buffer exchange, DRI2_BLIT_COMPLETE, indicating
the swap was performed with a blit, and DRI2_FLIP_COMPLETE, indicating
a full page flip was completed.
┌───
DRI2InvalidateBuffers
▶
drawable: CARD32
└───
This event is generated when the buffers the client had
requested for 'drawable' (with DRI2GetBuffers or
DRI2GetBuffersWithFormat) become inappropriate because they
don't match the drawable dimensions anymore, or a buffer swap
has been performed.
Note that the server is only required to warn the client once
about this condition, until the client takes care of bringing
them back up-to-date with another GetBuffers request.
⚙ ⚙ ⚙ ⚙ ⚙ ⚙
10. Extension Versioning
The DRI2 extension has undergone a number of revisions before
1.0: Released, but never used. Relied on a number of
constructs from the XF86DRI extension, such as a
shared memory area (SAREA) to communicate changes in
cliprects and window sizes, and
1.99.1: Move the swap buffer functionality into the X server,
introduce SwapBuffer request to copy back buffer
contents to the X drawable.
1.99.2: Rethink the SwapBuffer request as an asynchronous
request to copy a region between DRI2 buffers. Drop
CreateDrawable and DestroyDrawable, update Connect to
support different driver types and to send the
authentication group.
1.99.3: Drop the bitmask argument intended to indicate
presence of optional arguments for CopyRegion.
2.0: Awesomeness!
2.1: True excellence. Added DRI2GetBuffersWithFormat to allow
more flexible object creation.
2.2: Approaching perfection. Added requests for swapbuffers,
MSC and SBC related requests, and events.
2.3: Added the DRI2InvalidateBuffers event.
2.6: Enlightenment attained. Added the DRI2BufferHiz attachment.
2.7: Added the DRI2GetParam request.
Compatibility up to 2.0 is not preserved, but was also never released.
⚙ ⚙ ⚙ ⚙ ⚙ ⚙
11. Relationship with other extensions
As an extension designed to support other extensions, there is
naturally some interactions with other extensions.
11.1 GLX
The GL auxiliary buffers map directly to the DRI2 buffers... eh
11.2 DBE
The DBE back buffer must correspond to the DRI2_BUFFER_FRONT_LEFT
DRI2 buffer for servers that support both DBE and DRI2.
11.3 XvMC / Xv
We might add a DRI2_BUFFER_YUV to do vsynced colorspace conversion
blits. Maybe... not really sure.
⚙ ⚙ ⚙ ⚙ ⚙ ⚙
Appendix A. Protocol Encoding
Syntactic Conventions
This document uses the same syntactic conventions as the core X
protocol encoding document.
A.1 Common Types
┌───
DRI2DRIVER
0x0 DRI2DriverDRI
0x1 DRI2DriverVDPAU
└───
┌───
DRI2ATTACHMENT
0x0 DRI2BufferFrontLeft
0x1 DRI2BufferBackLeft
0x2 DRI2BufferFrontRight
0x3 DRI2BufferBackRight
0x4 DRI2BufferDepth
0x5 DRI2BufferStencil
0x6 DRI2BufferAccum
0x7 DRI2BufferFakeFrontLeft
0x8 DRI2BufferFakeFrontRight
0x9 DRI2BufferDepthStencil
0xa DRI2BufferHiz
└───
Used to encode the possible attachment points. The attachment
DRI2BufferDepthStencil is only available with protocol version 1.1 or
later.
┌───
DRI2BUFFER
4 CARD32 attachment
4 CARD32 name
4 CARD32 pitch
4 CARD32 cpp
4 CARD32 flags
└───
A DRI2 buffer specifies the attachment, the kernel memory
manager name, the pitch and chars per pixel for a buffer
attached to a given drawable.
┌───
DRI2ATTACH_FORMAT
4 CARD32 attachment
4 CARD32 format
└───
Used to describe the attachment and format requested from the server.
This data type is only available with protocol version 1.1 or
later.
A.2 Protocol Requests
┌───
DRI2QueryVersion
1 CARD8 major opcode
1 0 DRI2 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
└───
┌───
DRI2Connect
1 CARD8 major opcode
1 1 DRI2 opcode
2 3 length
4 WINDOW window
4 CARD32 driver type
▶
1 1 Reply
1 unused
2 CARD16 sequence number
4 (n+m+p+q)/4 reply length
4 n driver name length
4 m device name length
16 unused
n CARD8 driver name
p unused, p=pad(n)
m CARD8 device name
q unused, q=pad(m)
└───
┌───
DRI2Authenticate
1 CARD8 major opcode
1 2 DRI2 opcode
2 3 length
4 WINDOW window
4 CARD32 authentication token
▶
1 1 Reply
1 unused
2 CARD16 sequence number
4 0 reply length
4 CARD32 authenticated
20 unused
└───
┌───
DRI2GetBuffers
1 CARD8 major opcode
1 5 DRI2 opcode
2 3 length
4 DRAWABLE drawable
4 n number of attachments
4n LISTofDRI2ATTACHMENTS attachments
▶
1 1 Reply
1 unused
2 CARD16 sequence number
4 0 reply length
4 CARD32 width of drawable
4 CARD32 height of drawable
4 CARD32 buffer count
12 unused
5n LISTofDRI2BUFFER buffers
└───
┌───
DRI2CopyRegion
1 CARD8 major opcode
1 6 DRI2 opcode
2 3 length
4 DRAWABLE drawable
4 REGION region
4 DRI2ATTACHMENT source
4 DRI2ATTACHMENT destination
▶
1 1 Reply
1 unused
2 CARD16 sequence number
4 0 reply length
24 unused
└───
┌───
DRI2GetBuffersWithFormat
1 CARD8 major opcode
1 7 DRI2 opcode
2 3 length
4 DRAWABLE drawable
4 n number of attachments
8n LISTofDRI2ATTACH_FORMAT attachments and formats
▶
1 1 Reply
1 unused
2 CARD16 sequence number
4 0 reply length
4 CARD32 width of drawable
4 CARD32 height of drawable
4 CARD32 buffer count
12 unused
5n LISTofDRI2BUFFER buffers
└───
┌───
DRI2SwapBuffers
1 CARD8 major opcode
1 8 DRI2 opcode
2 8 length
4 DRAWABLE drawable
4 CARD32 target_msc_hi
4 CARD32 target_msc_lo
4 CARD32 divisor_hi
4 CARD32 divisor_lo
4 CARD32 remainder_hi
4 CARD32 remainder_lo
▶
1 1 Reply
1 unused
2 CARD16 sequence number
4 0 reply length
4 CARD32 swap_hi
4 CARD32 swap_lo
20 unused
└───
┌───
DRI2GetMSC
1 CARD8 major opcode
1 9 DRI2 opcode
2 8 length
4 DRAWABLE drawable
▶
1 1 Reply
1 unused
2 CARD16 sequence number
4 0 reply length
4 CARD32 ust_hi
4 CARD32 ust_lo
4 CARD32 msc_hi
4 CARD32 msc_lo
4 CARD32 sbc_hi
4 CARD32 sbc_lo
└───
┌───
DRI2WaitMSC
1 CARD8 major opcode
1 10 DRI2 opcode
2 8 length
4 DRAWABLE drawable
4 CARD32 target_msc_hi
4 CARD32 target_msc_lo
4 CARD32 divisor_hi
4 CARD32 divisor_lo
4 CARD32 remainder_hi
4 CARD32 remainder_lo
▶
1 1 Reply
1 unused
2 CARD16 sequence number
4 0 reply length
4 CARD32 ust_hi
4 CARD32 ust_lo
4 CARD32 msc_hi
4 CARD32 msc_lo
4 CARD32 sbc_hi
4 CARD32 sbc_lo
└───
┌───
DRI2WaitSBC
1 CARD8 major opcode
1 11 DRI2 opcode
2 8 length
4 DRAWABLE drawable
4 CARD32 swap_hi
4 CARD32 swap_lo
▶
1 1 Reply
1 unused
2 CARD16 sequence number
4 0 reply length
4 CARD32 ust_hi
4 CARD32 ust_lo
4 CARD32 msc_hi
4 CARD32 msc_lo
4 CARD32 sbc_hi
4 CARD32 sbc_lo
└───
┌───
DRI2SwapInterval
1 CARD8 major opcode
1 12 DRI2 opcode
2 8 length
4 DRAWABLE drawable
4 CARD32 interval
▶
└───
┌───
DRI2GetParam
1 CARD8 major opcode
1 13 DRI2 opcode
2 8 length
4 DRAWABLE drawable
4 CARD32 param
▶
1 1 Reply
1 BOOL is_param_recognized
2 CARD16 sequence number
4 0 reply length
4 CARD32 value_hi
4 CARD32 value_lo
16 unused
└───
A.3 Protocol Events
The DRI2 extension specifies DRI2_BufferSwapComplete and
DRI2_InvalidateBuffers events.
┌───
DRI2_BufferSwapComplete
1 CARD8 type
1 CARD8 extension
2 CARD16 sequenceNumber
2 CARD16 event_type
4 DRAWABLE drawable
4 CARD32 ust_hi
4 CARD32 ust_lo
4 CARD32 msc_hi
4 CARD32 msc_lo
4 CARD32 sbc_hi
4 CARD32 sbc_lo
└───
┌───
DRI2_InvalidateBuffers
1 CARD8 type
1 CARD8 extension
2 CARD16 sequenceNumber
4 DRAWABLE drawable
4 CARD32 unused
4 CARD32 unused
4 CARD32 unused
4 CARD32 unused
4 CARD32 unused
4 CARD32 unused
└───
A.4 Protocol Errors
The DRI2 extension specifies no errors.
⚙ ⚙ ⚙ ⚙ ⚙ ⚙
Appendix B. Implementation on GEM
Where to begin...
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