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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 auxillary 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> ⚙ ⚙ ⚙ ⚙ ⚙ ⚙ 2. DRI2 Concepts 2.1. Attachment points Stolen from OpenGL FBOs, I guess. 2.2. Kernel rendering manager This specification assumes a rendering architechture, 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 a 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 enty points to copy contents back and forth to as necessary to ensure consistent rendering. ⚙ ⚙ ⚙ ⚙ ⚙ ⚙ 3. Data Types The server side region support specified in the Xfixes extension version 2 is used in the CopyRegion request. ⚙ ⚙ ⚙ ⚙ ⚙ ⚙ 4. Errors No errrors defined by the DRI2 extension. ⚙ ⚙ ⚙ ⚙ ⚙ ⚙ 5. Protocol Types DRI2DRIVER { DRI2DriverDRI } 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 } These values describe various attachment points for DRI2 buffers. DRI2BUFFER { attachment: CARD32 name: CARD32 pitch: CARD32 cpp: CARD32 flags: CARD32 } The DRI2BUFFER describes an auxillary 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. ⚙ ⚙ ⚙ ⚙ ⚙ ⚙ 6. 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. ⚙ ⚙ ⚙ ⚙ ⚙ ⚙ 7. 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, 'group' will be '0'. 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. ┌─── 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. ⚙ ⚙ ⚙ ⚙ ⚙ ⚙ 8. 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! Compatibility up to 2.0 is not preserved, but was also never released. ⚙ ⚙ ⚙ ⚙ ⚙ ⚙ 10. Relationship with other extensions As an extension designed to support other extensions, there is naturally some interactions with other extensions. 10.1 GLX The GL auxilary buffers map directly to the DRI2 buffers... eh 10.2 DBE The DBE back buffer must correspond to the DRI2_BUFFER_FRONT_LEFT DRI2 buffer for servers that support both DBE and DRI2. 10.3 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 └─── ┌─── DRI2ATTACHMENT 0x0 DRI2BufferFrontLeft 0x1 DRI2BufferBackLeft 0x2 DRI2BufferFrontRight 0x3 DRI2BufferBackRight 0x4 DRI2BufferDepth 0x5 DRI2BufferStencil 0x6 DRI2BufferAccum 0x7 DRI2BufferFakeFrontLeft 0x8 DRI2BufferFakeFrontRight 0x9 DRI2BufferDepthStencil └─── 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+(n+p)/4 length 4 WINDOW window 4 CARD32 driver type ▶ 1 1 Reply 1 unused 2 CARD16 sequence number 4 (n+m+p)/4 reply length 4 n driver name length 4 m device name length 16 unused n CARD8 driver name m CARD8 device name p unused, p=pad(n+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 3 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 4 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 3 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 └─── A.3 Protocol Events The DRI2 extension specifies no events. A.4 Protocol Errors The DRI2 extension specifies no errors. ⚙ ⚙ ⚙ ⚙ ⚙ ⚙ Appendix B. Implementation on GEM Where to begin...