Protocol color_representation_v1 — color representation protocol extension

This protocol extension delivers the metadata required to define alpha mode, the color model, sub-sampling and quantization range used when interpreting buffer contents. The main use case is defining how the YCbCr family of pixel formats convert to RGB.

Note that this protocol does not define the colorimetry of the resulting RGB channels / tristimulus values. Without the help of other extensions the resulting colorimetry is therefore implementation defined.

If this extension is not used, the color representation used is compositor implementation defined.

Recommendation ITU-T H.273 "Coding-independent code points for video signal type identification" shall be referred to as simply H.273 here.

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    Copyright 2022 Simon Ser
    Copyright 2022 Red Hat, Inc.
    Copyright 2022 Collabora, Ltd.
    Copyright 2022-2025 Red Hat, Inc.

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Interface wp_color_representation_manager_v1 — color representation manager singleton

A singleton global interface used for getting color representation extensions for wl_surface. The extension interfaces allow setting the color representation of surfaces.

Compositors should never remove this global.

Request wp_color_representation_manager_v1.destroy — destroy the manager

Destroy the wp_color_representation_manager_v1 object. This does not affect any other objects in any way.

Request wp_color_representation_manager_v1.get_surface — create a color representation interface for a wl_surface

If a wp_color_representation_surface_v1 object already exists for the given wl_surface, the protocol error surface_exists is raised.

This creates a new color wp_color_representation_surface_v1 object for the given wl_surface.

See the wp_color_representation_surface_v1 interface for more details.

Event wp_color_representation_manager_v1.supported_alpha_mode — supported alpha modes

When this object is created, it shall immediately send this event once for each alpha mode the compositor supports.

For the definition of the supported values, see the wp_color_representation_surface_v1::alpha_mode enum.

  • alpha_mode uint: supported alpha mode

Event wp_color_representation_manager_v1.supported_coefficients_and_ranges — supported matrix coefficients and ranges

When this object is created, it shall immediately send this event once for each matrix coefficient and color range combination the compositor supports.

For the definition of the supported values, see the wp_color_representation_surface_v1::coefficients and wp_color_representation_surface_v1::range enums.

  • coefficients uint: supported matrix coefficients
  • range uint: full range flag

Event wp_color_representation_manager_v1.done — all features have been sent

This event is sent when all supported features have been sent.

Enum wp_color_representation_manager_v1.error — protocol errors

  • surface_exists: color representation surface exists already

Interface wp_color_representation_surface_v1 — color representation extension to a surface

A wp_color_representation_surface_v1 allows the client to set the color representation metadata of a surface.

By default, a surface does not have any color representation metadata set. The reconstruction of R, G, B signals on such surfaces is compositor implementation defined. The alpha mode is assumed to be premultiplied_electrical when the alpha mode is unset.

If the wl_surface associated with the wp_color_representation_surface_v1 is destroyed, the wp_color_representation_surface_v1 object becomes inert.

Request wp_color_representation_surface_v1.destroy — destroy the color representation

Destroy the wp_color_representation_surface_v1 object.

Destroying this object unsets all the color representation metadata from the surface. See the wp_color_representation_surface_v1 interface description for how a compositor handles a surface without color representation metadata. Unsetting is double-buffered state, see wl_surface.commit.

Request wp_color_representation_surface_v1.set_alpha_mode — set the surface alpha mode

If this protocol object is inert, the protocol error inert is raised.

Assuming an alpha channel exists, it is always linear. The alpha mode determines whether and how the color channels include pre-multiplied alpha. Using straight alpha might have performance benefits.

Only alpha modes advertised by the compositor are allowed to be used as argument for this request. The "alpha_mode" protocol error is raised otherwise.

Alpha mode is double buffered, see wl_surface.commit.

  • alpha_mode uint: alpha mode

Request wp_color_representation_surface_v1.set_coefficients_and_range — set the matrix coefficients and range

If this protocol object is inert, the protocol error inert is raised.

Set the matrix coefficients and video range which defines the formula and the related constants used to derive red, green and blue signals. Usually coefficients correspond to MatrixCoefficients code points in H.273.

Only combinations advertised by the compositor are allowed to be used as argument for this request. The "coefficients" protocol error is raised otherwise.

A call to wl_surface.commit verifies that the pixel format and the coefficients-range combination in the committed surface contents are compatible, if contents exist. The "pixel_format" protocol error is raised otherwise.

A pixel format is compatible with the coefficients-range combination if the related equations and conventions as defined in H.273 can produce the color channels (RGB or YCbCr) of the pixel format.

For the definition of the supported combination, see the wp_color_representation_surface_v1::coefficients and wp_color_representation_surface_v1::range enums.

The coefficients-range combination is double-buffered, see wl_surface.commit.

  • coefficients uint: matrix coefficients
  • range uint: range

Request wp_color_representation_surface_v1.set_chroma_location — set the chroma location

If this protocol object is inert, the protocol error inert is raised.

Set the chroma location type which defines the position of downsampled chroma samples, corresponding to Chroma420SampleLocType code points in H.273.

A call to wl_surface.commit verifies that the pixel format and chroma location type in the committed surface contents are compatible, if contents exist. The "pixel_format" protocol error is raised otherwise.

For the definition of the supported chroma location types, see the wp_color_representation_surface_v1::chroma_location enum.

The chroma location type is double-buffered, see wl_surface.commit.

  • chroma_location uint: chroma sample location

Enum wp_color_representation_surface_v1.error — protocol errors

  • alpha_mode: unsupported alpha mode
  • coefficients: unsupported coefficients
  • pixel_format: the pixel format and a set value are incompatible
  • inert: forbidden request on inert object

Enum wp_color_representation_surface_v1.alpha_mode — alpha mode

Specifies how the alpha channel affects the color channels.

Enum wp_color_representation_surface_v1.coefficients — named coefficients

Named matrix coefficients used to encode well-known sets of coefficients. H.273 is the authority, when it comes to the exact values of coefficients and authoritative specifications, where an equivalent code point exists.

A value of 0 is invalid and will never be present in the list of enums.

Descriptions do list the specifications for convenience.

Enum wp_color_representation_surface_v1.range — Color range values

Possible color range values.

A value of 0 is invalid and will never be present in the list of enums.

Enum wp_color_representation_surface_v1.chroma_location — Chroma sample location for 4:2:0 YCbCr

Chroma sample location as defined by H.273 Chroma420SampleLocType.

A value of 0 is invalid and will never be present in the list of enums.

The descriptions list the matching Vulkan VkChromaLocation combinations for convenience.