main.dart

// In RenderCompositedClock (parent layout)
location.layout(constraints, parentUsesSize: true);

// In RenderLocation
_textPainter = TextPainter(...);
_textPainter.layout(maxWidth: constraints.biggest.width); // constraints here are what was given in location.layout
size = _textPainter.size; // size here is the size of the RenderLocation render object

// Back in RenderCompositedClock after laying out the location
locationData.offset = Offset( // Setting the offset positions the child
  size.width / 2 - location.size.width / 2, // size here is the size of the whole layout
  locationHeight, // Fixed height
);
date.layout(...);
dateData.offset = Offset( // date holds the render object and dateData holds the parent data
  size.width / 2 - date.size.width / 2, // Centers the text horizontally
  locationData.offset.dy + location.size.height, // Places the date right below the location
);

// Same that I did for date now also happens for the weather.
// Additionally, I supply the size and offset of the weather component to the background, 
// so the background curve can react to it.