pushClipRect method
- bool needsCompositing,
- Offset offset,
- Rect clipRect,
- PaintingContextCallback painter, {
- Clip clipBehavior = Clip.hardEdge,
- ClipRectLayer? oldLayer,
Clip further painting using a rectangle.
The needsCompositing
argument specifies whether the child needs
compositing. Typically this matches the value of
RenderObject.needsCompositing for the caller. If false, this method
returns null, indicating that a layer is no longer necessary. If a render
object calling this method stores the oldLayer
in its
RenderObject.layer field, it should set that field to null.
When needsCompositing
is false, this method will use a more efficient
way to apply the layer effect than actually creating a layer.
The offset
argument is the offset from the origin of the canvas'
coordinate system to the origin of the caller's coordinate system.
The clipRect
is the rectangle (in the caller's coordinate system) to use
to clip the painting done by painter
. It should not include the
offset
.
The painter
callback will be called while the clipRect
is applied. It
is called synchronously during the call to pushClipRect.
The clipBehavior
argument controls how the rectangle is clipped.
For the oldLayer
argument, specify the layer created in the previous
frame. This gives the engine more information for performance
optimizations. Typically this is the value of RenderObject.layer that a
render object creates once, then reuses for all subsequent frames until a
layer is no longer needed (e.g. the render object no longer needs
compositing) or until the render object changes the type of the layer
(e.g. from opacity layer to a clip rect layer).
Implementation
ClipRectLayer? pushClipRect(bool needsCompositing, Offset offset, Rect clipRect, PaintingContextCallback painter, { Clip clipBehavior = Clip.hardEdge, ClipRectLayer? oldLayer }) {
if (clipBehavior == Clip.none) {
painter(this, offset);
return null;
}
final Rect offsetClipRect = clipRect.shift(offset);
if (needsCompositing) {
final ClipRectLayer layer = oldLayer ?? ClipRectLayer();
layer
..clipRect = offsetClipRect
..clipBehavior = clipBehavior;
pushLayer(layer, painter, offset, childPaintBounds: offsetClipRect);
return layer;
} else {
clipRectAndPaint(offsetClipRect, clipBehavior, offsetClipRect, () => painter(this, offset));
return null;
}
}