---
name: "wayland_zwp_linux_dmabuf_feedback_v1_t"
section: "3"
platform: "linux"
package: "waylandpp-dev"
version: "1.0.0-6+b2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/wayland_zwp_linux_dmabuf_feedback_v1_t"
---

# wayland\_zwp\_linux\_dmabuf\_feedback\_v1\_t(3)

dmabuf feedback

## NAME

wayland::zwp\_linux\_dmabuf\_feedback\_v1\_t - dmabuf feedback

## SYNOPSIS

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

Inherits **wayland::proxy\_t**.

### Public Types

enum class **wrapper\_type** { **standard**, **display**, **foreign**, **proxy\_wrapper** }\

### Public Member Functions

std::function\< void()\> & **on\_done** ()\
 all feedback has been sent  std::function\< void(int, uint32\_t)\> & **on\_format\_table** ()\
 format and modifier table  std::function\< void(array\_t)\> & **on\_main\_device** ()\
 preferred main device  std::function\< void()\> & **on\_tranche\_done** ()\
 a preference tranche has been sent  std::function\< void(array\_t)\> & **on\_tranche\_target\_device** ()\
 target device  std::function\< void(array\_t)\> & **on\_tranche\_formats** ()\
 supported buffer format modifier  std::function\< void(zwp\_linux\_dmabuf\_feedback\_v1\_tranche\_flags)\> & **on\_tranche\_flags** ()\
 tranche flags  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.  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

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\_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. 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\_modifier events and then a tranche\_done event), then one done event.

Definition at line **1938** of file **wayland-client-protocol-unstable.hpp**.

## Member Enumeration Documentation

### enum class wayland::proxy\_t::wrapper\_type` [strong]`, ` [inherited]`

Underlying wl\_proxy type and properties of a **proxy\_t** that affect construction, destruction, and event handling

**Enumerator**

- *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.*

- *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.*

- *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***. Lifetime of such wrappers should preferably be short to minimize the chance that the owning library decides to destroy the wl\_proxy.*

- *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.*

*Definition at line* **116** *of file* **wayland-client.hpp***.*

## Member Function Documentation

### wl\_proxy \* wayland::proxy\_t::c\_ptr () const` [inherited]`

*Get a pointer to the underlying C struct.*

**Returns**

*The underlying wl\_proxy wrapped by this* **proxy\_t** *if it exists, otherwise an exception is thrown*

### std::string wayland::proxy\_t::get\_class () const` [inherited]`

*Get the interface name (class) of a proxy object.*

**Returns**

*The interface name of the object associated with the proxy*

### uint32\_t wayland::proxy\_t::get\_id () const` [inherited]`

*Get the id of a proxy object.*

**Returns**

*The id the object associated with the proxy*

### uint32\_t wayland::proxy\_t::get\_version () const` [inherited]`

*Get the protocol object version of a proxy object. Gets the protocol object version of a proxy object, or 0 if the proxy was created with unversioned API.*

*A returned value of 0 means that no version information is available, so the caller must make safe assumptions about the object's real version.*

**display\_t** *will always return version 0.*

**Returns**

*The protocol object version of the proxy or 0*

### wrapper\_type wayland::proxy\_t::get\_wrapper\_type () const` [inline]`, ` [inherited]`

*Get the type of a proxy object.*

*Definition at line* **302** *of file* **wayland-client.hpp***.*

### std::function\< void()\> & zwp\_linux\_dmabuf\_feedback\_v1\_t::on\_done ()

*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.*

*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 ()

*format and modifier table*

**Parameters**

*fd table file descriptor* \
 *size table size, in bytes*

*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.*

*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 ()

*preferred main device*

**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.*

*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.*

*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 This event splits tranche\_target\_device and tranche\_modifier events in preference tranches. It is sent after a set of tranche\_target\_device and tranche\_modifier events; it represents the end of a tranche. The next tranche will have a lower preference.*

*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*

**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.*

*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*

**Parameters**

*indices array of 16-bit indexes*

*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.*

*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*

**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.*

*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.*

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

### wayland::proxy\_t::operator bool () const` [inherited]`

*Check whether this wrapper actually wraps an object.*

**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]`

*Check whether two wrappers refer to different objects.*

### bool wayland::proxy\_t::operator== (const proxy\_t & right) const` [inherited]`

*Check whether two wrappers refer to the same object.*

### bool wayland::proxy\_t::proxy\_has\_object () const` [inherited]`

*Check whether this wrapper actually wraps an object.*

**Returns**

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

### void wayland::proxy\_t::proxy\_release ()` [inherited]`

*Release the wrapped object (if any), making this an empty wrapper. Note that* **display\_t** *instances cannot be released this way. Attempts to do so are ignored.*

**Examples** **foreign\_display.cpp***.*

### void wayland::proxy\_t::set\_queue (event\_queue\_t queue)` [inherited]`

*Assign a proxy to an event queue.*

**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.*

*See also:* **display\_t::dispatch\_queue()***.*

**Examples** **proxy\_wrapper.cpp***.*

## Author

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