showInViewport static method

Rect? showInViewport({
  1. RenderObject? descendant,
  2. Rect? rect,
  3. required RenderTwoDimensionalViewport viewport,
  4. Duration duration = Duration.zero,
  5. Curve curve = Curves.ease,
  6. AxisDirection? axisDirection,
})

Make (a portion of) the given descendant of the given viewport fully visible in one or both dimensions of the viewport by manipulating the ViewportOffsets.

The axisDirection determines from which axes the descendant will be revealed. When the axisDirection is null, both axes will be updated to reveal the descendant.

The optional rect parameter describes which area of the descendant should be shown in the viewport. If rect is null, the entire descendant will be revealed. The rect parameter is interpreted relative to the coordinate system of descendant.

The returned Rect describes the new location of descendant or rect in the viewport after it has been revealed. See RevealedOffset.rect for a full definition of this Rect.

The parameter viewport is required and cannot be null. If descendant is null, this is a no-op and rect is returned.

If both descendant and rect are null, null is returned because there is nothing to be shown in the viewport.

The duration parameter can be set to a non-zero value to animate the target object into the viewport with an animation defined by curve.

See also:

Implementation

static Rect? showInViewport({
  RenderObject? descendant,
  Rect? rect,
  required RenderTwoDimensionalViewport viewport,
  Duration duration = Duration.zero,
  Curve curve = Curves.ease,
  AxisDirection? axisDirection,
}) {
  if (descendant == null) {
    return rect;
  }

  Rect? showVertical(Rect? rect) {
    return RenderTwoDimensionalViewport._showInViewportForAxisDirection(
      descendant: descendant,
      viewport: viewport,
      axis: Axis.vertical,
      rect: rect,
      duration: duration,
      curve: curve,
    );
  }

  Rect? showHorizontal(Rect? rect) {
    return RenderTwoDimensionalViewport._showInViewportForAxisDirection(
      descendant: descendant,
      viewport: viewport,
      axis: Axis.horizontal,
      rect: rect,
      duration: duration,
      curve: curve,
    );
  }

  switch (axisDirection) {
    case AxisDirection.left:
    case AxisDirection.right:
      return showHorizontal(rect);
    case AxisDirection.up:
    case AxisDirection.down:
      return showVertical(rect);
    case null:
      // Update rect after revealing in one axis before revealing in the next.
      rect = showHorizontal(rect) ?? rect;
      // We only return the final rect after both have been revealed.
      rect = showVertical(rect);
      if (rect == null) {
        // `descendant` is between leading and trailing edge and hence already
        //  fully shown on screen.
        assert(viewport.parent != null);
        final Matrix4 transform = descendant.getTransformTo(viewport.parent);
        return MatrixUtils.transformRect(transform, rect ?? descendant.paintBounds);
      }
      return rect;
  }
}