wayland::zwp_..._feedback_v1_t(3)

📦
version 1.0.1 · 10 versions
, in ubuntu stonking

💖 NAME 💖

okay so this is wayland::zwp_linux_dmabuf_feedback_v1_t — it's literally the dmabuf feedback object, bestie. that's the whole vibe. it's a class in the Wayland++ manual, section 3. no cap.

🦋 SYNOPSIS 🦋

pull it in like this, periodt:

#include <wayland-client-protocol-unstable.hpp>

and know that it inherits wayland::proxy_t — yes, that's its parent, it's giving nepo baby but make it protocol 💅

✨ Public Types ✨

  • enum class wrapper_type { standard, display, foreign, proxy_wrapper } — the enum that tells you what kind of underlying pointer this wrapper is holding. full breakdown further down, iykyk.

🎀 Public Member Functions 🎀

these are the callbacks and helpers you get. all of them, in order, no skipping:

  • std::function< void()> & on_done () — fires when all feedback has been sent. the grand finale event 🎉
  • std::function< void(int, uint32_t)> & on_format_table () — the format and modifier table callback.
  • std::function< void(array_t)> & on_main_device () — the preferred main device callback. main character device energy 👑
  • std::function< void()> & on_tranche_done () — fires when a preference tranche has been sent — i.e. one full chunk of prefs is wrapped up.
  • std::function< void(array_t)> & on_tranche_target_device () — the target device callback for a tranche.
  • std::function< void(array_t)> & on_tranche_formats () — the supported buffer format modifier callback for a tranche.
  • std::function< void(zwp_linux_dmabuf_feedback_v1_tranche_flags)> & on_tranche_flags () — the tranche flags callback.
  • uint32_t get_id () const — Get the id of a proxy object.
  • std::string get_class () const — Get the interface name (class) of a proxy object.
  • uint32_t get_version () const — Get the protocol object version of a proxy object.
  • wrapper_type get_wrapper_type () const — Get the type of a proxy object.
  • void set_queue (event_queue_t queue) — Assign a proxy to an event queue.
  • wl_proxy * c_ptr () const — Get a pointer to the underlying C struct.
  • bool proxy_has_object () const — Check whether this wrapper actually wraps an object.
  • operator bool () const — Check whether this wrapper actually wraps an object. (same check, operator flavor 🫶)
  • bool operator== (const proxy_t &right) const — Check whether two wrappers refer to the same object.
  • bool operator!= (const proxy_t &right) const — Check whether two wrappers refer to different objects.
  • void proxy_release () — Release the wrapped object (if any), making this an empty wrapper.

🌈 Detailed Description 🌈

dmabuf feedback. (that's the whole name-and-address, honestly)

okay so here's the tea ☕ — this object advertises dmabuf parameters feedback. and what's in that feedback? the preferred devices and the supported formats/modifiers. that's it, that's the whole job 🫡

the parameters get sent once when this object is created, and again whenever they change. the done event is always sent once after all parameters have been sent. and heads up — when a single parameter changes, all parameters are re-sent by the compositor. so it's all-or-nothing, no picking and choosing 💀

compositors can re-send the parameters when the current client buffer allocations are sub-optimal. but — and this is important — compositors should not re-send the parameters if re-allocating the buffers would not result in a more optimal configuration. and in particular 👀 compositors should avoid sending the exact same parameters multiple times in a row. like, don't spam the group chat with the same message, it's giving desperate.

the tranche_target_device and tranche_modifier events are grouped by tranches of preference. for each tranche: a tranche_target_device, one tranche_flags, and one or more tranche_modifier events are sent, followed by a tranche_done event finishing the list. and the tranches are sent in descending order of preference — best one first, icon behavior ✨. all formats and modifiers in the same tranche have the same preference.

to send parameters, the compositor sends one main_device event, then tranches (each consisting of one tranche_target_device event, one tranche_flags event, tranche_modifier events, and then a tranche_done event), then one done event. that's the whole sequence, in that exact order, don't shuffle it 🔥

for real, this is defined at line 1939 of file wayland-client-protocol-unstable.hpp. go look, it's there 💅

🌸 Member Enumeration Documentation 🌸

🧚 enum class wayland::proxy_t::wrapper_type [strong], [inherited] 🧚

so this enum describes the underlying wl_proxy type and the properties of a proxy_t that affect construction, destruction, and event handling. basically it's the vibe check for what kind of wrapper you're holding.

Enumerators, one by one 💜

  • standard — C pointer is a standard type compatible with wl_proxy*. Events are dispatched and it is destructed when the proxy_t is destructed. User data is set. the normal one, the default kid.
  • display — C pointer is a wl_display*. No events are dispatched, wl_display_disconnect is called when the proxy_t is destructed. User data is set. special display treatment, okurrr 💅
  • foreign — C pointer is a standard type compatible with wl_proxy*, but another library owns it and it should not be touched in a way that could affect the operation of the other library. No events are dispatched, wl_proxy_destroy is not called when the proxy_t is destructed, user data is not touched. consequently, there is no reference counting for the proxy_t. and the lifetime of such wrappers should preferably be short to minimize the chance that the owning library decides to destroy the wl_proxy. so like… don't get attached 🥲
  • proxy_wrapper — C pointer is a wl_proxy* that was constructed with wl_proxy_create_wrapper. No events are dispatched, wl_proxy_wrapper_destroy is called when the proxy_t is destroyed. Reference counting is active. a reference to the proxy_t creating this proxy wrapper is held to extend its lifetime until after the proxy wrapper is destroyed. mutual support, we love to see it 🫶
this one's defined at line 117 of file wayland-client.hpp. noted. saved. screenshotted. 📌

✨ okay that's part 1 bestie, part 2 is right behind it — don't go anywhere 💖

std::function< void()> & zwp_linux_dmabuf_feedback_v1_t::on_done ()

okay so this one is the "that's a wrap" event 🎬 — all feedback has been sent. It fires after every single parameter of a wp_linux_dmabuf_feedback object has been sent.

Why does this matter? Because it lets changes to the wp_linux_dmabuf_feedback parameters be seen as atomic ✨ — even when they arrive across multiple events. So you don't get caught mid-update looking goofy. Slay.

Definition at line 5429 of file wayland-client-protocol-unstable.cpp.

std::function< void(int, uint32_t)> & zwp_linux_dmabuf_feedback_v1_t::on_format_table ()

the format and modifier table 📊 bestie this is the good stuff.

Parameters:

  • fd — table file descriptor
  • size — table size, in bytes

This event gifts you a file descriptor that can be memory-mapped to access the format and modifier table. Love that for us.

So what's actually in the table? A tightly packed array of consecutive format + modifier pairs, no padding between entries beyond what's described. Each pair is 16 bytes wide. Each one 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 — no byte-swapping drama.

The client must map the file descriptor in read-only private mode. No exceptions, no cap 🫶

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. That said, compositors are allowed to store duplicate format + modifier pairs in the table. So duplicates? Fine. Mutation? Jail. 💀

Definition at line 5434 of file wayland-client-protocol-unstable.cpp.

std::function< void(array_t)> & zwp_linux_dmabuf_feedback_v1_t::on_main_device ()

the preferred main device 👑 the main character of devices, literally.

Parameters:

  • device — device dev_t value

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. So don't get attached 💅

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. Efficiency queen 🌸

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 — nope, not a valid vibe check 🙈

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. That part is mandatory, not a suggestion.

Definition at line 5439 of file wayland-client-protocol-unstable.cpp.

std::function< void()> & zwp_linux_dmabuf_feedback_v1_t::on_tranche_done ()

a preference tranche has been sent — tranche: complete ✅

This event splits tranche_target_device and tranche_modifier events in preference tranches. It's sent after a set of tranche_target_device and tranche_modifier events; it represents the end of a tranche. And heads up: the next tranche will have a lower preference. Ranking's real, it's giving leaderboard energy 📉

Definition at line 5444 of file wayland-client-protocol-unstable.cpp.

std::function< void(zwp_linux_dmabuf_feedback_v1_tranche_flags)> & zwp_linux_dmabuf_feedback_v1_t::on_tranche_flags ()

tranche flags 🚩 the little extras.

Parameters:

  • flags — 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 — so that's an "ask your compositor" situation, iykyk.

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

Definition at line 5459 of file wayland-client-protocol-unstable.cpp.

std::function< void(array_t)> & zwp_linux_dmabuf_feedback_v1_t::on_tranche_formats ()

supported buffer format modifier 🎀 the actual menu of what works.

Parameters:

  • indices — array of 16-bit indexes

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

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. Both flavors, no gatekeeping 🫶

Compositors must not send duplicate format + modifier pairs within the same tranche or across two different tranches with the same target device and flags. (Different rules than the format table — yes, we noticed 💀)

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.

Definition at line 5454 of file wayland-client-protocol-unstable.cpp.

std::function< void(array_t)> & zwp_linux_dmabuf_feedback_v1_t::on_tranche_target_device ()

target device 🎯 the one this tranche is rooting for.

Parameters:

  • device — device dev_t value

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. Very "don't text back" of it.

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. Either way, valid 💅

The client can use this hint to allocate the buffer in a way that makes it accessible from the target device, ideally directly. But — and this is the important part — 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). So be ready for the plot twist 😭

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. Same rule as before, fr fr.

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

Definition at line 5449 of file wayland-client-protocol-unstable.cpp.

wayland::proxy_t::operator bool () const [inherited]

The vibe check operator ✨ Does this wrapper actually wrap an object or is it just standing there?

Returns: true if there is an underlying object, false if this wrapper is empty

bool wayland::proxy_t::operator!= (const proxy_t & right) const [inherited]

Checks whether two wrappers refer to different objects. Not the same thing, bestie 💀

bool wayland::proxy_t::operator== (const proxy_t & right) const [inherited]

Checks whether two wrappers refer to the same object. Matching outfits energy 🎀

bool wayland::proxy_t::proxy_has_object () const [inherited]

Same question as operator bool, just spelled out for clarity: does this wrapper actually wrap an object?

Returns: true if there is an underlying object, false if this wrapper is empty

void wayland::proxy_t::proxy_release () [inherited]

Releases the wrapped object (if any), making this an empty wrapper. Like clearing the group chat and starting fresh 🌸

Careful though: display_t instances cannot be released this way. Attempts to do so are ignored. So don't try it, it's literally not going to work 🙈

Examples: foreign_display.cpp.

void wayland::proxy_t::set_queue (event_queue_t queue) [inherited]

Assigns a proxy to an event queue. Sorting your mail into the right inbox 📬

Parameters:

  • queue — The event queue that will handle this proxy

Assign proxy to event queue. Events coming from proxy will be queued in queue instead of the display's main queue. Custom routing, we love to see it.

See also: display_t::dispatch_queue().

Examples: proxy_wrapper.cpp.

👑 Author

Generated automatically by Doxygen for Wayland++ from the source code.

aaaand that's the whole page, bestie 🫶💖 This was Wayland++ Version 1.0.1, dated Fri Mar 27 2026 — go forth and allocate those dmabufs responsibly 🌈✨

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