pushLayer method
- ContainerLayer childLayer,
- PaintingContextCallback painter,
- Offset offset, {
- Rect? childPaintBounds,
Appends the given layer to the recording, and calls the painter
callback
with that layer, providing the childPaintBounds
as the estimated paint
bounds of the child. The childPaintBounds
can be used for debugging but
have no effect on painting.
The given layer must be an unattached orphan. (Providing a newly created object, rather than reusing an existing layer, satisfies that requirement.)
The offset
is the offset to pass to the painter
. In particular, it is
not an offset applied to the layer itself. Layers conceptually by default
have no position or size, though they can transform their contents. For
example, an OffsetLayer applies an offset to its children.
If the childPaintBounds
are not specified then the current layer's paint
bounds are used. This is appropriate if the child layer does not apply any
transformation or clipping to its contents. The childPaintBounds
, if
specified, must be in the coordinate system of the new layer (i.e. as seen
by its children after it applies whatever transform to its contents), and
should not go outside the current layer's paint bounds.
See also:
- addLayer, for pushing a layer without painting further contents within it.
Implementation
void pushLayer(ContainerLayer childLayer, PaintingContextCallback painter, Offset offset, { Rect? childPaintBounds }) {
// If a layer is being reused, it may already contain children. We remove
// them so that `painter` can add children that are relevant for this frame.
if (childLayer.hasChildren) {
childLayer.removeAllChildren();
}
stopRecordingIfNeeded();
appendLayer(childLayer);
final PaintingContext childContext = createChildContext(childLayer, childPaintBounds ?? estimatedBounds);
painter(childContext, offset);
childContext.stopRecordingIfNeeded();
}