DmabufTextureBuilder

Added in version 4.14.

class DmabufTextureBuilder(**properties: Any)

Superclasses: Object

GdkDmabufTextureBuilder is a builder used to construct Texture objects from DMA buffers.

DMA buffers are commonly called *dma-bufs*.

DMA buffers are a feature of the Linux kernel to enable efficient buffer and memory sharing between hardware such as codecs, GPUs, displays, cameras and the kernel drivers controlling them. For example, a decoder may want its output to be directly shared with the display server for rendering without a copy.

Any device driver which participates in DMA buffer sharing, can do so as either the exporter or importer of buffers (or both).

The memory that is shared via DMA buffers is usually stored in non-system memory (maybe in device’s local memory or something else not directly accessible by the CPU), and accessing this memory from the CPU may have higher-than-usual overhead.

In particular for graphics data, it is not uncommon that data consists of multiple separate blocks of memory, for example one block for each of the red, green and blue channels. These blocks are called *planes*. DMA buffers can have up to four planes. Even if the memory is a single block, the data can be organized in multiple planes, by specifying offsets from the beginning of the data.

DMA buffers are exposed to user-space as file descriptors allowing to pass them between processes. If a DMA buffer has multiple planes, there is one file descriptor per plane.

The format of the data (for graphics data, essentially its colorspace) is described by a 32-bit integer. These format identifiers are defined in the header file drm_fourcc.h and commonly referred to as *fourcc* values, since they are identified by 4 ASCII characters. Additionally, each DMA buffer has a *modifier*, which is a 64-bit integer that describes driver-specific details of the memory layout, such as tiling or compression.

For historical reasons, some producers of dma-bufs don’t provide an explicit modifier, but instead return DMA_FORMAT_MOD_INVALID to indicate that their modifier is *implicit*. GTK tries to accommodate this situation by accepting DMA_FORMAT_MOD_INVALID as modifier.

The operation of GdkDmabufTextureBuilder is quite simple: Create a texture builder, set all the necessary properties, and then call build to create the new texture.

The required properties for a dma-buf texture are

  • The width and height in pixels

  • The fourcc code and modifier which identify the format and memory layout of the dma-buf

  • The file descriptor, offset and stride for each of the planes

GdkDmabufTextureBuilder can be used for quick one-shot construction of textures as well as kept around and reused to construct multiple textures.

For further information, see

Constructors

class DmabufTextureBuilder
classmethod new() → DmabufTextureBuilder

Creates a new texture builder.

Added in version 4.14.

Methods

class DmabufTextureBuilder
build(destroy: Callable[[None], None] | None, data: None) → Texture | None

Builds a new GdkTexture with the values set up in the builder.

It is a programming error to call this function if any mandatory property has not been set.

If the dmabuf is not supported by GTK, None will be returned and error will be set.

The destroy function gets called when the returned texture gets released.

It is possible to call this function multiple times to create multiple textures, possibly with changing properties in between.

It is the responsibility of the caller to keep the file descriptors for the planes open until the created texture is no longer used, and close them afterwards (possibly using the destroy notify).

Not all formats defined in the drm_fourcc.h header are supported. You can use get_dmabuf_formats to get a list of supported formats.

Added in version 4.14.

Parameters:

  • destroy – destroy function to be called when the texture is released

  • data – user data to pass to the destroy function

get_display() → Display

Returns the display that this texture builder is associated with.

Added in version 4.14.

get_fd(plane: int) → int

Gets the file descriptor for a plane.

Added in version 4.14.

Parameters:

plane – the plane to get the fd for

get_fourcc() → int

Gets the format previously set via set_fourcc() or 0 if the format wasn’t set.

The format is specified as a fourcc code.

Added in version 4.14.

get_height() → int

Gets the height previously set via set_height() or 0 if the height wasn’t set.

Added in version 4.14.

get_modifier() → int

Gets the modifier value.

Added in version 4.14.

get_n_planes() → int

Gets the number of planes.

Added in version 4.14.

get_offset(plane: int) → int

Gets the offset value for a plane.

Added in version 4.14.

Parameters:

plane – the plane to get the offset for

get_premultiplied() → bool

Whether the data is premultiplied.

Added in version 4.14.

get_stride(plane: int) → int

Gets the stride value for a plane.

Added in version 4.14.

Parameters:

plane – the plane to get the stride for

get_update_region() → Region | None

Gets the region previously set via set_update_region() or None if none was set.

Added in version 4.14.

get_update_texture() → Texture | None

Gets the texture previously set via set_update_texture() or None if none was set.

Added in version 4.14.

get_width() → int

Gets the width previously set via set_width() or 0 if the width wasn’t set.

Added in version 4.14.

set_display(display: Display) → None

Sets the display that this texture builder is associated with.

The display is used to determine the supported dma-buf formats.

Added in version 4.14.

Parameters:

display – the display

set_fd(plane: int, fd: int) → None

Sets the file descriptor for a plane.

Added in version 4.14.

Parameters:

  • plane – the plane to set the fd for

  • fd – the file descriptor

set_fourcc(fourcc: int) → None

Sets the format of the texture.

The format is specified as a fourcc code.

The format must be set before calling build.

Added in version 4.14.

Parameters:

fourcc – the texture’s format or 0 to unset

set_height(height: int) → None

Sets the height of the texture.

The height must be set before calling build.

Added in version 4.14.

Parameters:

height – the texture’s height or 0 to unset

set_modifier(modifier: int) → None

Sets the modifier.

Added in version 4.14.

Parameters:

modifier – the modifier value

set_n_planes(n_planes: int) → None

Sets the number of planes of the texture.

Added in version 4.14.

Parameters:

n_planes – the number of planes

set_offset(plane: int, offset: int) → None

Sets the offset for a plane.

Added in version 4.14.

Parameters:

  • plane – the plane to set the offset for

  • offset – the offset value

set_premultiplied(premultiplied: bool) → None

Sets whether the data is premultiplied.

Unless otherwise specified, all formats including alpha channels are assumed to be premultiplied.

Added in version 4.14.

Parameters:

premultiplied – whether the data is premultiplied

set_stride(plane: int, stride: int) → None

Sets the stride for a plane.

The stride must be set for all planes before calling build.

Added in version 4.14.

Parameters:

  • plane – the plane to set the stride for

  • stride – the stride value

set_update_region(region: Region | None = None) → None

Sets the region to be updated by this texture. Together with update_texture this describes an update of a previous texture.

When rendering animations of large textures, it is possible that consecutive textures are only updating contents in parts of the texture. It is then possible to describe this update via these two properties, so that GTK can avoid rerendering parts that did not change.

An example would be a screen recording where only the mouse pointer moves.

Added in version 4.14.

Parameters:

region – the region to update

set_update_texture(texture: Texture | None = None) → None

Sets the texture to be updated by this texture. See set_update_region for an explanation.

Added in version 4.14.

Parameters:

texture – the texture to update

set_width(width: int) → None

Sets the width of the texture.

The width must be set before calling build.

Added in version 4.14.

Parameters:

width – The texture’s width or 0 to unset

Properties

class DmabufTextureBuilder
props.display: Display

The display that this texture will be used on.

Added in version 4.14.

props.fourcc: int

The format of the texture, as a fourcc value.

Added in version 4.14.

props.height: int

The height of the texture.

Added in version 4.14.

props.modifier: int

The modifier.

Added in version 4.14.

props.n_planes: int

The number of planes of the texture.

Note that you can set properties for other planes, but they will be ignored when constructing the texture.

Added in version 4.14.

props.premultiplied: bool

Whether the alpha channel is premultiplied into the others.

Only relevant if the format has alpha.

Added in version 4.14.

props.update_region: Region

The update region for update_texture.

Added in version 4.14.

props.update_texture: Texture

The texture update_region is an update for.

Added in version 4.14.

props.width: int

The width of the texture.

Added in version 4.14.