layout method

@override void layout(Context context, BoxConstraints constraints, { bool parentUsesSize = false, })

First widget pass to calculate the children layout and bounding box

Implementation

@override
void layout(
  Context context,
  BoxConstraints constraints, {
  bool parentUsesSize = false,
}) {
  final childCount = children.length;

  var hasNonPositionedChildren = false;

  if (childCount == 0) {
    box = PdfRect.fromPoints(PdfPoint.zero, constraints.biggest);
    return;
  }

  var width = constraints.minWidth;
  var height = constraints.minHeight;

  BoxConstraints? nonPositionedConstraints;

  switch (fit) {
    case StackFit.loose:
      nonPositionedConstraints = constraints.loosen();
      break;
    case StackFit.expand:
      nonPositionedConstraints = BoxConstraints.tight(constraints.biggest);
      break;
    case StackFit.passthrough:
      nonPositionedConstraints = constraints;
      break;
  }

  for (final child in children) {
    if (child is! Positioned) {
      hasNonPositionedChildren = true;
      child.layout(context, nonPositionedConstraints, parentUsesSize: true);
      assert(child.box != null);

      final childSize = child.box!;
      width = math.max(width, childSize.width);
      height = math.max(height, childSize.height);
    }
  }

  if (hasNonPositionedChildren) {
    box = PdfRect.fromPoints(PdfPoint.zero, PdfPoint(width, height));
    assert(box!.width == constraints.constrainWidth(width));
    assert(box!.height == constraints.constrainHeight(height));
  } else {
    box = PdfRect.fromPoints(PdfPoint.zero, constraints.biggest);
  }
  final resolvedAlignment = alignment.resolve(Directionality.of(context));
  for (final child in children) {
    if (child is! Positioned) {
      child.box = PdfRect.fromPoints(
        resolvedAlignment.inscribe(child.box!.size, box!).offset,
        child.box!.size,
      );
    } else {
      final positioned = child;

      var childConstraints = const BoxConstraints();

      if (positioned.left != null && positioned.right != null) {
        childConstraints = childConstraints.tighten(
          width: box!.width - positioned.right! - positioned.left!,
        );
      } else if (positioned.width != null) {
        childConstraints = childConstraints.tighten(width: positioned.width);
      }

      if (positioned.top != null && positioned.bottom != null) {
        childConstraints = childConstraints.tighten(
          height: box!.height - positioned.bottom! - positioned.top!,
        );
      } else if (positioned.height != null) {
        childConstraints = childConstraints.tighten(
          height: positioned.height,
        );
      }

      positioned.layout(context, childConstraints, parentUsesSize: true);
      assert(positioned.box != null);

      double? x;
      if (positioned.left != null) {
        x = positioned.left;
      } else if (positioned.right != null) {
        x = box!.width - positioned.right! - positioned.width!;
      } else {
        x = resolvedAlignment.inscribe(positioned.box!.size, box!).left;
      }

      double? y;
      if (positioned.bottom != null) {
        y = positioned.bottom;
      } else if (positioned.top != null) {
        y = box!.height - positioned.top! - positioned.height!;
      } else {
        y = resolvedAlignment.inscribe(positioned.box!.size, box!).bottom;
      }

      positioned.box = PdfRect.fromPoints(
        PdfPoint(x!, y!),
        positioned.box!.size,
      );
    }
  }
}