performLayout method
Implementation
@override
void performLayout(BoxConstraints constraints) {
final w = targetW > 0
? constraints.constrain(Size(targetW, 0)).width
: constraints.maxWidth;
final h = targetH > 0
? constraints.constrain(Size(0, targetH)).height
: constraints.maxHeight;
final childW = w.clamp(0, 0x3FFFFFFF);
final childH = h.clamp(0, 0x3FFFFFFF);
child?.layout(BoxConstraints.tight(Size(childW, childH)));
child?.setOffset(0, 0);
setSize(w, h);
}