Function refreshPreserveAnchor

valdi/src/valdi/runtime/Context/ViewNode.cpp:985–994

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.

// 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();
    }
}