pushOffset method Null safety

OffsetEngineLayer? pushOffset (
  1. double dx,
  2. double dy,
  3. {OffsetEngineLayer? oldLayer}
)

Pushes an offset operation onto the operation stack.

This is equivalent to pushTransform with a matrix with only translation.

If oldLayer is not null the engine will attempt to reuse the resources allocated for the old layer when rendering the new layer. This is purely an optimization. It has no effect on the correctness of rendering.

Passing a layer to addRetained or as oldLayer argument to a push method counts as usage. A layer can be used no more than once in a scene. For example, it may not be passed simultaneously to two push methods, or to a push method and to addRetained.

When a layer is passed to addRetained all descendant layers are also considered as used in this scene. The same single-usage restriction applies to descendants.

When a layer is passed as an oldLayer argument to a push method, it may no longer be used in subsequent frames. If you would like to continue reusing the resources associated with the layer, store the layer object returned by the push method and use that in the next frame instead of the original object.

See pop for details about the operation stack.

Implementation

OffsetEngineLayer? pushOffset(
  double dx,
  double dy, {
  OffsetEngineLayer? oldLayer,
}) {
  assert(_debugCheckCanBeUsedAsOldLayer(oldLayer, 'pushOffset'));
  final EngineLayer engineLayer = EngineLayer._();
  _pushOffset(engineLayer, dx, dy);
  final OffsetEngineLayer layer = OffsetEngineLayer._(engineLayer);
  assert(_debugPushLayer(layer));
  return layer;
}