flutter判断是否超出可视范围

方法1:
visibility_detector | Flutter Package (pub.dev)

方法2:
获得目标RenderOject

context.findRenderObject();

获取 renderObject 跟Viewport的距离:

RenderAbstractViewport viewport = RenderAbstractViewport.of(renderObject);

然后使用 viewport 的 getOffsetToReveal API，可以判断出Widget与父Widget可视区域的相对位置。

然后通下面的方法，可以判断出是否可视：

Matrix4 getTransformTo(RenderObject ancestor) {
    assert(attached);
    if (ancestor == null) {
      final AbstractNode rootNode = owner.rootNode;
      if (rootNode is RenderObject)
        ancestor = rootNode;
    }
    final List<RenderObject> renderers = <RenderObject>[];
    for (RenderObject renderer = this; renderer != ancestor; renderer = renderer.parent) {
      assert(renderer != null); // Failed to find ancestor in parent chain.
      renderers.add(renderer);
    }
    final Matrix4 transform = Matrix4.identity();
    for (int index = renderers.length - 1; index > 0; index -= 1)
      renderers[index].applyPaintTransform(renderers[index - 1], transform);
    return transform;
  }

Offset localToGlobal(Offset point, { RenderObject ancestor }) {
    return MatrixUtils.transformPoint(getTransformTo(ancestor), point);
  }


final Offset position = child.localToGlobal(Offset.zero, ancestor: parent);
 
bool childIsActivedInViewport = ((position.dx - size.dx).abs() < 1 &&
					(position.dy - size.dy).abs() < 1);