render method

@override void render(Buffer buffer, Rect area)

Renders the underlying widget to the provided buffer within the area.

Implementation

@override
void render(Buffer buffer, Rect area) {
  final stack = widget as Stack;
  if (area.width <= 0 || area.height <= 0) return;

  final newElements = <Element>[];
  for (var i = 0; i < stack.children.length; i++) {
    final childWidget = stack.children[i];
    if (i < childElements.length &&
        childElements[i].widget.runtimeType == childWidget.runtimeType) {
      childElements[i].update(childWidget);
      newElements.add(childElements[i]);
    } else {
      final newEl = childWidget.createElement();
      newEl.mount(this);
      newElements.add(newEl);
    }
  }
  childElements = newElements;

  for (var i = 0; i < childElements.length; i++) {
    final childEl = childElements[i];
    final childWidget = childEl.widget;

    if (childWidget is Positioned) {
      int childX = area.x;
      int childY = area.y;
      int childWidth = area.width;
      int childHeight = area.height;

      if (childWidget.left != null) {
        childX = area.x + childWidget.left!;
        if (childWidget.right != null) {
          childWidth = area.width - childWidget.left! - childWidget.right!;
        } else if (childWidget.width != null) {
          childWidth = childWidget.width!;
        } else {
          childWidth = area.width - childWidget.left!;
        }
      } else if (childWidget.right != null) {
        if (childWidget.width != null) {
          childWidth = childWidget.width!;
          childX = area.x + area.width - childWidget.right! - childWidth;
        } else {
          childWidth = area.width - childWidget.right!;
        }
      } else if (childWidget.width != null) {
        childWidth = childWidget.width!;
      }

      if (childWidget.top != null) {
        childY = area.y + childWidget.top!;
        if (childWidget.bottom != null) {
          childHeight = area.height - childWidget.top! - childWidget.bottom!;
        } else if (childWidget.height != null) {
          childHeight = childWidget.height!;
        } else {
          childHeight = area.height - childWidget.top!;
        }
      } else if (childWidget.bottom != null) {
        if (childWidget.height != null) {
          childHeight = childWidget.height!;
          childY = area.y + area.height - childWidget.bottom! - childHeight;
        } else {
          childHeight = area.height - childWidget.bottom!;
        }
      } else if (childWidget.height != null) {
        childHeight = childWidget.height!;
      }

      if (childWidth <= 0 || childHeight <= 0) continue;

      final childArea = Rect(childX, childY, childWidth, childHeight);
      final viewport = Viewport(buffer, childArea);
      childEl.render(viewport, Rect(0, 0, childWidth, childHeight));
    } else {
      final viewport = Viewport(buffer, area);
      childEl.render(viewport, Rect(0, 0, area.width, area.height));
    }
  }
}