wlr export DMA-BUF

A protocol for low overhead screen content capturing

An interface to capture surfaces in an efficient way by exporting DMA-BUFs.

Warning! The protocol described in this file is experimental and backward incompatible changes may be made. Backward compatible changes may be added together with the corresponding interface version bump. Backward incompatible changes are done by bumping the version number in the protocol and interface names and resetting the interface version. Once the protocol is to be declared stable, the 'z' prefix and the version number in the protocol and interface names are removed and the interface version number is reset.

Manager to inform clients and begin capturing

This object is a manager with which to start capturing from sources.

capture_output(frame: new_id<zwlr_export_dmabuf_frame_v1>, overlay_cursor: int, output: object<wl_output>)
Argument
Type
Description
framenew_id<zwlr_export_dmabuf_frame_v1>
overlay_cursorint
include custom client hardware cursor on top of the frame
outputobject<wl_output>
Capture a frame from an output

Capture the next frame of an entire output.

destroy()
Destroy the manager

All objects created by the manager will still remain valid, until their appropriate destroy request has been called.


A DMA-BUF frame

This object represents a single DMA-BUF frame.

If the capture is successful, the compositor will first send a "frame" event, followed by one or several "object". When the frame is available for readout, the "ready" event is sent.

If the capture failed, the "cancel" event is sent. This can happen anytime before the "ready" event.

Once either a "ready" or a "cancel" event is received, the client should destroy the frame. Once an "object" event is received, the client is responsible for closing the associated file descriptor.

All frames are read-only and may not be written into or altered.

destroy()
Delete this object, used or not

Unreferences the frame. This request must be called as soon as its no longer used.

It can be called at any time by the client. The client will still have to close any FDs it has been given.

frame(width: uint, height: uint, offset_x: uint, offset_y: uint, buffer_flags: uint, flags: uint<zwlr_export_dmabuf_frame_v1.flags>, format: uint, mod_high: uint, mod_low: uint, num_objects: uint)
Argument
Type
Description
widthuint
frame width in pixels
heightuint
frame height in pixels
offset_xuint
crop offset for the x axis
offset_yuint
crop offset for the y axis
buffer_flagsuint
flags which indicate properties (invert, interlacing), has the same values as zwp_linux_buffer_params_v1:flags
flagsuint<zwlr_export_dmabuf_frame_v1.flags>
indicates special frame features
formatuint
format of the frame (DRM_FORMAT_*)
mod_highuint
drm format modifier, high
mod_lowuint
drm format modifier, low
num_objectsuint
indicates how many objects (FDs) the frame has (max 4)
A frame description

Main event supplying the client with information about the frame. If the capture didn't fail, this event is always emitted first before any other events.

This event is followed by a number of "object" as specified by the "num_objects" argument.

object(index: uint, fd: fd, size: uint, offset: uint, stride: uint, plane_index: uint)
Argument
Type
Description
indexuint
index of the current object
fdfd
fd of the current object
sizeuint
size in bytes for the current object
offsetuint
starting point for the data in the object's fd
strideuint
line size in bytes
plane_indexuint
index of the plane the data in the object applies to
An object description

Event which serves to supply the client with the file descriptors containing the data for each object.

After receiving this event, the client must always close the file descriptor as soon as they're done with it and even if the frame fails.

ready(tv_sec_hi: uint, tv_sec_lo: uint, tv_nsec: uint)
Argument
Type
Description
tv_sec_hiuint
high 32 bits of the seconds part of the timestamp
tv_sec_louint
low 32 bits of the seconds part of the timestamp
tv_nsecuint
nanoseconds part of the timestamp
Indicates frame is available for reading

This event is sent as soon as the frame is presented, indicating it is available for reading. This event includes the time at which presentation happened at.

The timestamp is expressed as tv_sec_hi, tv_sec_lo, tv_nsec triples, each component being an unsigned 32-bit value. Whole seconds are in tv_sec which is a 64-bit value combined from tv_sec_hi and tv_sec_lo, and the additional fractional part in tv_nsec as nanoseconds. Hence, for valid timestamps tv_nsec must be in [0, 999999999]. The seconds part may have an arbitrary offset at start.

After receiving this event, the client should destroy this object.

Argument
Type
Description
reasonuint<zwlr_export_dmabuf_frame_v1.cancel_reason>
indicates a reason for cancelling this frame capture
Indicates the frame is no longer valid

If the capture failed or if the frame is no longer valid after the "frame" event has been emitted, this event will be used to inform the client to scrap the frame.

If the failure is temporary, the client may capture again the same source. If the failure is permanent, any further attempts to capture the same source will fail again.

After receiving this event, the client should destroy this object.

flags { transient } 
Argument
Value
Description
transient0x1
clients should copy frame before processing
Frame flags

Special flags that should be respected by the client.

cancel_reason { temporary, permanent, resizing } 
Argument
Value
Description
temporary0
temporary error, source will produce more frames
permanent1
fatal error, source will not produce frames
resizing2
temporary error, source will produce more frames
Cancel reason

Indicates reason for cancelling the frame.


Copyright © 2018 Rostislav Pehlivanov

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