LayerTree

This CDP domain is experimental.

Types

Generally, you do not need to instantiate CDP types yourself. Instead, the API creates objects for you as return values from commands, and then you can use those objects as arguments to other commands.

class cdp.layer_tree.LayerId

Unique Layer identifier.

class cdp.layer_tree.SnapshotId

Unique snapshot identifier.

class cdp.layer_tree.ScrollRect(rect, type_)

Rectangle where scrolling happens on the main thread.

rect = None

Rectangle itself.

type_ = None

Reason for rectangle to force scrolling on the main thread

class cdp.layer_tree.StickyPositionConstraint(sticky_box_rect, containing_block_rect, nearest_layer_shifting_sticky_box=None, nearest_layer_shifting_containing_block=None)

Sticky position constraints.

containing_block_rect = None

Layout rectangle of the containing block of the sticky element

nearest_layer_shifting_containing_block = None

The nearest sticky layer that shifts the containing block

nearest_layer_shifting_sticky_box = None

The nearest sticky layer that shifts the sticky box

sticky_box_rect = None

Layout rectangle of the sticky element before being shifted

class cdp.layer_tree.PictureTile(x, y, picture)

Serialized fragment of layer picture along with its offset within the layer.

picture = None

Base64-encoded snapshot data.

x = None

Offset from owning layer left boundary

y = None

Offset from owning layer top boundary

class cdp.layer_tree.Layer(layer_id, offset_x, offset_y, width, height, paint_count, draws_content, parent_layer_id=None, backend_node_id=None, transform=None, anchor_x=None, anchor_y=None, anchor_z=None, invisible=None, scroll_rects=None, sticky_position_constraint=None)

Information about a compositing layer.

anchor_x = None

Transform anchor point X, absent if no transform specified

anchor_y = None

Transform anchor point Y, absent if no transform specified

anchor_z = None

Transform anchor point Z, absent if no transform specified

backend_node_id = None

The backend id for the node associated with this layer.

draws_content = None

Indicates whether this layer hosts any content, rather than being used for transform/scrolling purposes only.

height = None

Layer height.

invisible = None

Set if layer is not visible.

layer_id = None

The unique id for this layer.

offset_x = None

Offset from parent layer, X coordinate.

offset_y = None

Offset from parent layer, Y coordinate.

paint_count = None

Indicates how many time this layer has painted.

parent_layer_id = None

The id of parent (not present for root).

scroll_rects = None

Rectangles scrolling on main thread only.

sticky_position_constraint = None

Sticky position constraint information

transform = None

Transformation matrix for layer, default is identity matrix

width = None

Layer width.

class cdp.layer_tree.PaintProfile

Array of timings, one per paint step.

Commands

Each command is a generator function. The return type Generator[x, y, z] indicates that the generator yields arguments of type x, it must be resumed with an argument of type y, and it returns type z. In this library, types x and y are the same for all commands, and z is the return type you should pay attention to. For more information, see Getting Started: Commands.

cdp.layer_tree.compositing_reasons(layer_id)

Provides the reasons why the given layer was composited.

Parameters:layer_id (LayerId) – The id of the layer for which we want to get the reasons it was composited.
Return type:Generator[Dict[str, Any], Dict[str, Any], List[str]]
Returns:A list of strings specifying reasons for the given layer to become composited.
cdp.layer_tree.disable()

Disables compositing tree inspection.

Return type:Generator[Dict[str, Any], Dict[str, Any], None]
cdp.layer_tree.enable()

Enables compositing tree inspection.

Return type:Generator[Dict[str, Any], Dict[str, Any], None]
cdp.layer_tree.load_snapshot(tiles)

Returns the snapshot identifier.

Parameters:tiles (List[PictureTile]) – An array of tiles composing the snapshot.
Return type:Generator[Dict[str, Any], Dict[str, Any], SnapshotId]
Returns:The id of the snapshot.
cdp.layer_tree.make_snapshot(layer_id)

Returns the layer snapshot identifier.

Parameters:layer_id (LayerId) – The id of the layer.
Return type:Generator[Dict[str, Any], Dict[str, Any], SnapshotId]
Returns:The id of the layer snapshot.
cdp.layer_tree.profile_snapshot(snapshot_id, min_repeat_count=None, min_duration=None, clip_rect=None)
Parameters:
  • snapshot_id (SnapshotId) – The id of the layer snapshot.
  • min_repeat_count (Optional[int]) – (Optional) The maximum number of times to replay the snapshot (1, if not specified).
  • min_duration (Optional[float]) – (Optional) The minimum duration (in seconds) to replay the snapshot.
  • clip_rect (Optional[Rect]) – (Optional) The clip rectangle to apply when replaying the snapshot.
Return type:

Generator[Dict[str, Any], Dict[str, Any], List[PaintProfile]]
Returns:

The array of paint profiles, one per run.
cdp.layer_tree.release_snapshot(snapshot_id)

Releases layer snapshot captured by the back-end.

Parameters:snapshot_id (SnapshotId) – The id of the layer snapshot.
Return type:Generator[Dict[str, Any], Dict[str, Any], None]
cdp.layer_tree.replay_snapshot(snapshot_id, from_step=None, to_step=None, scale=None)

Replays the layer snapshot and returns the resulting bitmap.

Parameters:
  • snapshot_id (SnapshotId) – The id of the layer snapshot.
  • from_step (Optional[int]) – (Optional) The first step to replay from (replay from the very start if not specified).
  • to_step (Optional[int]) – (Optional) The last step to replay to (replay till the end if not specified).
  • scale (Optional[float]) – (Optional) The scale to apply while replaying (defaults to 1).
Return type:

Generator[Dict[str, Any], Dict[str, Any], str]
Returns:

A data: URL for resulting image.
cdp.layer_tree.snapshot_command_log(snapshot_id)

Replays the layer snapshot and returns canvas log.

Parameters:snapshot_id (SnapshotId) – The id of the layer snapshot.
Return type:Generator[Dict[str, Any], Dict[str, Any], List[dict]]
Returns:The array of canvas function calls.

Events

Generally, you do not need to instantiate CDP events yourself. Instead, the API creates events for you and then you use the event’s attributes.

class cdp.layer_tree.LayerPainted(layer_id, clip)
clip = None

Clip rectangle.

layer_id = None

The id of the painted layer.

class cdp.layer_tree.LayerTreeDidChange(layers)
layers = None

Layer tree, absent if not in the comspositing mode.