Method handleOnScroll

valdi/src/valdi/runtime/Context/ViewNode.cpp:998–1032

        }
        node = next;
        nodeTop = nextTop;
    }
    return anchor;
}

ViewNode* preserveFindDescendantById(ViewNode* node, RawViewNodeId id, int depth) {
    // id 0 is the unset/default rawId (e.g. synthetic placeholder nodes); never "match" it, or
    // we would anchor to the first id-less node (content top) and jump the viewport.
    if (depth <= 0 || id == 0)
        return nullptr;
    for (auto* child : *node) {
        if (child->getRawId() == id)
            return child;
        auto* found = preserveFindDescendantById(child, id, depth - 1);
        if (found)
            return found;
    }
    return nullptr;
}

// Re-pick the anchor (the node at the viewport center) and remember its id + screen position
// (absolute top relative to the viewport top) so a later content reflow can pin it back. Called
// from both layout (updateScrollState) and scroll (handleOnScroll) so the anchor never goes stale
// between layout passes.
void refreshPreserveAnchor(ViewNode* scrollNode, ViewNodeScrollState& scrollState, float offsetY, float viewportH) {
    float probeY = offsetY + viewportH * 0.5f;
    // Only anchor on a node with a real, trackable rawId. id 0 (unset/default) can't be re-found
    // across passes, so don't record it -- clear instead and re-pick next pass.
    if (auto* anchor = preserveDescendantAtY(scrollNode, probeY); anchor != nullptr && anchor->getRawId() != 0) {
        scrollState.setPreserveAnchor(anchor->getRawId(), preserveAnchorAbsoluteTop(scrollNode, anchor) - offsetY);
    } else {
        scrollState.clearPreserveAnchor();
    }
}

} // namespace

void ViewNode::handleOnScroll(const Point& directionDependentContentOffset,