#Z-Index Builder

Z-Index Builder is used to set z_index for views. It only affects sibling node ordering under same parent view, not global stacking context.

#Basic Writing

After importing ZIndexBuilder, all views implementing View can call .z_index(...).

use flor::view::builder::ZIndexBuilder;
use flor::views;
use flor_lys::div::div;
use flor_lys::label::label;

let panel = div(views![
    label("Normal Content").z_index(|| 0),
    label("Floating Content").z_index(|| 10),
]);

Current signature is:

pub trait ZIndexBuilder {
    fn z_index(self, z_index: impl Fn() -> i32 + 'static) -> Self;
}

So fixed value also needs to write as closure returning i32, for example .z_index(|| 10). If layer level depends on signal, read signal in closure:

use flor::signal::{create_signal, Read};
use flor::view::builder::ZIndexBuilder;
use flor_lys::label::label;

let popup_open = create_signal(false);

let popup = label("Menu")
    .z_index(move || if popup_open.get() { 100 } else { 0 });

#Relationship with class

After enabling class feature, z-* in layout class will be parsed into same set of runtime layer level values.

use flor::view::builder::ClassBuilder;
use flor_lys::label::label;

let popup = label("Menu").class("z-100");

z-auto will write 0, z-10 will write 10. z-* is special item in layout class: it won't enter Taffy layout style, but directly update ViewId's layer level value.

If you already use .z_index(...) to dynamically control layer level, don't use z-* on same view to express another fixed layer level, to avoid subsequent updates overriding each other.

#Suitable Scenarios

Common use is separating temporary content and normal content in same container:

Layer level only compares between sibling nodes. Two views with different parent views cannot achieve global covering solely through z_index; you need to put them into the same sortable parent container, or adjust the view tree structure.

#Mechanism Explanation

.z_index(...) will create a reactive updater. During initialization will immediately calculate closure result once, and call current view's ViewId::set_z_index(value); afterwards when signal depended by closure updates, will write new layer level value again.

ViewId::set_z_index will:

1. Write value to VIEW_STORAGE.view_z_index.
2. Find current view's parent view.
3. Re-sort parent view's child list according to sibling views' respective z_index().

Views that haven't set layer level, ViewId::z_index() returns 0.