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LayerTree Domain

Experimental

Methods

LayerTree.enable

Enables compositing tree inspection.

LayerTree.disable

Disables compositing tree inspection.

LayerTree.compositingReasons

Provides the reasons why the given layer was composited.

Parameters
layerId
LayerId The id of the layer for which we want to get the reasons it was composited.
Return object
compositingReasons
array [string] A list of strings specifying reasons for the given layer to become composited.

LayerTree.makeSnapshot

Returns the layer snapshot identifier.

Parameters
layerId
LayerId The id of the layer.
Return object
snapshotId
SnapshotId The id of the layer snapshot.

LayerTree.loadSnapshot

Returns the snapshot identifier.

Parameters
tiles
array [ PictureTile ] An array of tiles composing the snapshot.
Return object
snapshotId
SnapshotId The id of the snapshot.

LayerTree.releaseSnapshot

Releases layer snapshot captured by the back-end.

Parameters
snapshotId
SnapshotId The id of the layer snapshot.

LayerTree.profileSnapshot

Parameters
snapshotId
SnapshotId The id of the layer snapshot.
minRepeatCount
integer The maximum number of times to replay the snapshot (1, if not specified).
minDuration
number The minimum duration (in seconds) to replay the snapshot.
clipRect
DOM.Rect The clip rectangle to apply when replaying the snapshot.
Return object
timings
array [ PaintProfile ] The array of paint profiles, one per run.

LayerTree.replaySnapshot

Replays the layer snapshot and returns the resulting bitmap.

Parameters
snapshotId
SnapshotId The id of the layer snapshot.
fromStep
integer The first step to replay from (replay from the very start if not specified).
toStep
integer The last step to replay to (replay till the end if not specified).
scale
number The scale to apply while replaying (defaults to 1).
Return object
dataURL
string A data: URL for resulting image.

LayerTree.snapshotCommandLog

Replays the layer snapshot and returns canvas log.

Parameters
snapshotId
SnapshotId The id of the layer snapshot.
Return object
commandLog
array [object] The array of canvas function calls.

Events

LayerTree.layerTreeDidChange

Parameters
layers
array [ Layer ] Layer tree, absent if not in the comspositing mode.

LayerTree.layerPainted

Parameters
layerId
LayerId The id of the painted layer.
clip
DOM.Rect Clip rectangle.

Types

LayerId

Unique Layer identifier.

Type: string

SnapshotId

Unique snapshot identifier.

Type: string

ScrollRect

Rectangle where scrolling happens on the main thread.

Type: object

Properties
rect
DOM.Rect Rectangle itself.
type
string Reason for rectangle to force scrolling on the main thread Allowed values: RepaintsOnScroll, TouchEventHandler, WheelEventHandler.

StickyPositionConstraint

Sticky position constraints.

Type: object

Properties
stickyBoxRect
DOM.Rect Layout rectangle of the sticky element before being shifted
containingBlockRect
DOM.Rect Layout rectangle of the containing block of the sticky element
nearestLayerShiftingStickyBox
LayerId The nearest sticky layer that shifts the sticky box
nearestLayerShiftingContainingBlock
LayerId The nearest sticky layer that shifts the containing block

PictureTile

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

Type: object

Properties
x
number Offset from owning layer left boundary
y
number Offset from owning layer top boundary
picture
string Base64-encoded snapshot data.

Layer

Information about a compositing layer.

Type: object

Properties
layerId
LayerId The unique id for this layer.
parentLayerId
LayerId The id of parent (not present for root).
backendNodeId
DOM.BackendNodeId The backend id for the node associated with this layer.
offsetX
number Offset from parent layer, X coordinate.
offsetY
number Offset from parent layer, Y coordinate.
width
number Layer width.
height
number Layer height.
transform
array [number] Transformation matrix for layer, default is identity matrix
anchorX
number Transform anchor point X, absent if no transform specified
anchorY
number Transform anchor point Y, absent if no transform specified
anchorZ
number Transform anchor point Z, absent if no transform specified
paintCount
integer Indicates how many time this layer has painted.
drawsContent
boolean Indicates whether this layer hosts any content, rather than being used for transform/scrolling purposes only.
invisible
boolean Set if layer is not visible.
scrollRects
array [ ScrollRect ] Rectangles scrolling on main thread only.
stickyPositionConstraint
StickyPositionConstraint Sticky position constraint information

PaintProfile

Array of timings, one per paint step.

Type: array