cosmic::cctk::sctk::reexports::protocols::wp::linux_dmabuf::zv1::server::zwp_linux_dmabuf_feedback_v1

Struct ZwpLinuxDmabufFeedbackV1

pub struct ZwpLinuxDmabufFeedbackV1 { /* private fields */ }

Available on crate feature wayland and Linux only.

Expand description

dmabuf feedback

This object advertises dmabuf parameters feedback. This includes the preferred devices and the supported formats/modifiers.

The parameters are sent once when this object is created and whenever they change. The done event is always sent once after all parameters have been sent. When a single parameter changes, all parameters are re-sent by the compositor.

Compositors can re-send the parameters when the current client buffer allocations are sub-optimal. Compositors should not re-send the parameters if re-allocating the buffers would not result in a more optimal configuration. In particular, compositors should avoid sending the exact same parameters multiple times in a row.

The tranche_target_device and tranche_formats events are grouped by tranches of preference. For each tranche, a tranche_target_device, one tranche_flags and one or more tranche_formats events are sent, followed by a tranche_done event finishing the list. The tranches are sent in descending order of preference. All formats and modifiers in the same tranche have the same preference.

To send parameters, the compositor sends one main_device event, tranches (each consisting of one tranche_target_device event, one tranche_flags event, tranche_formats events and then a tranche_done event), then one done event.

See also the Request enum for this interface.

Implementations§

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impl ZwpLinuxDmabufFeedbackV1

pub fn done(&self)

all feedback has been sent

This event is sent after all parameters of a wp_linux_dmabuf_feedback object have been sent.

This allows changes to the wp_linux_dmabuf_feedback parameters to be seen as atomic, even if they happen via multiple events.

pub fn format_table(&self, fd: BorrowedFd<'_>, size: u32)

format and modifier table

This event provides a file descriptor which can be memory-mapped to access the format and modifier table.

The table contains a tightly packed array of consecutive format + modifier pairs. Each pair is 16 bytes wide. It contains a format as a 32-bit unsigned integer, followed by 4 bytes of unused padding, and a modifier as a 64-bit unsigned integer. The native endianness is used.

The client must map the file descriptor in read-only private mode.

Compositors are not allowed to mutate the table file contents once this event has been sent. Instead, compositors must create a new, separate table file and re-send feedback parameters. Compositors are allowed to store duplicate format + modifier pairs in the table.

pub fn main_device(&self, device: Vec<u8>)

preferred main device

This event advertises the main device that the server prefers to use when direct scan-out to the target device isn’t possible. The advertised main device may be different for each wp_linux_dmabuf_feedback object, and may change over time.

There is exactly one main device. The compositor must send at least one preference tranche with tranche_target_device equal to main_device.

Clients need to create buffers that the main device can import and read from, otherwise creating the dmabuf wl_buffer will fail (see the wp_linux_buffer_params.create and create_immed requests for details). The main device will also likely be kept active by the compositor, so clients can use it instead of waking up another device for power savings.

In general the device is a DRM node. The DRM node type (primary vs. render) is unspecified. Clients must not rely on the compositor sending a particular node type. Clients cannot check two devices for equality by comparing the dev_t value.

If explicit modifiers are not supported and the client performs buffer allocations on a different device than the main device, then the client must force the buffer to have a linear layout.

pub fn tranche_done(&self)

a preference tranche has been sent

This event splits tranche_target_device and tranche_formats events in preference tranches. It is sent after a set of tranche_target_device and tranche_formats events; it represents the end of a tranche. The next tranche will have a lower preference.

pub fn tranche_target_device(&self, device: Vec<u8>)

target device

This event advertises the target device that the server prefers to use for a buffer created given this tranche. The advertised target device may be different for each preference tranche, and may change over time.

There is exactly one target device per tranche.

The target device may be a scan-out device, for example if the compositor prefers to directly scan-out a buffer created given this tranche. The target device may be a rendering device, for example if the compositor prefers to texture from said buffer.

The client can use this hint to allocate the buffer in a way that makes it accessible from the target device, ideally directly. The buffer must still be accessible from the main device, either through direct import or through a potentially more expensive fallback path. If the buffer can’t be directly imported from the main device then clients must be prepared for the compositor changing the tranche priority or making wl_buffer creation fail (see the wp_linux_buffer_params.create and create_immed requests for details).

If the device is a DRM node, the DRM node type (primary vs. render) is unspecified. Clients must not rely on the compositor sending a particular node type. Clients cannot check two devices for equality by comparing the dev_t value.

This event is tied to a preference tranche, see the tranche_done event.

pub fn tranche_formats(&self, indices: Vec<u8>)

supported buffer format modifier

This event advertises the format + modifier combinations that the compositor supports.

It carries an array of indices, each referring to a format + modifier pair in the last received format table (see the format_table event). Each index is a 16-bit unsigned integer in native endianness.

For legacy support, DRM_FORMAT_MOD_INVALID is an allowed modifier. It indicates that the server can support the format with an implicit modifier. When a buffer has DRM_FORMAT_MOD_INVALID as its modifier, it is as if no explicit modifier is specified. The effective modifier will be derived from the dmabuf.

A compositor that sends valid modifiers and DRM_FORMAT_MOD_INVALID for a given format supports both explicit modifiers and implicit modifiers.

Compositors must not send duplicate format + modifier pairs within the same tranche or across two different tranches with the same target device and flags.

This event is tied to a preference tranche, see the tranche_done event.

For the definition of the format and modifier codes, see the wp_linux_buffer_params.create request.

pub fn tranche_flags(&self, flags: TrancheFlags)

tranche flags

This event sets tranche-specific flags.

The scanout flag is a hint that direct scan-out may be attempted by the compositor on the target device if the client appropriately allocates a buffer. How to allocate a buffer that can be scanned out on the target device is implementation-defined.

This event is tied to a preference tranche, see the tranche_done event.