场景图

本库提供了一个类似于Unity或Unreal引擎中使用的场景图结构。它速度快，性能好，易于操作。

快速入门

要安装，请将以下内容添加到您的Cargo.toml中

scene-graph = "0.1.0"

或运行

cargo add scene-graph

以下是一个基本的SceneGraph示例

use scene_graph::SceneGraph;

fn main() {
    let mut sg: SceneGraph<&'static str> = SceneGraph::new("root");

    sg.attach_at_root("first child");
    // note that insertion order is honored.
    let second_child_handle = sg.attach_at_root("second child");

    // collect the nodes
    let nodes = Vec::from_iter(sg.iter().map(|(_parent, node)| *node));

    // note that the "root" is not seen in an `iter` operation.
    assert_eq!(nodes, ["first child", "second child"]);

    sg.attach(second_child_handle, "first grand-child").unwrap();
    sg.attach(second_child_handle, "second grand-child").unwrap();

    sg.attach_at_root("weird third way younger child");

    let nodes = Vec::from_iter(sg.iter().map(|(_parent, node)| *node));

    // note the iteration order -- because we `iter` depth first, we'll get the youngest child last.
    assert_eq!(
        nodes,
        [
            "first child",
            "second child",
            "first grand-child",
            "second grand-child",
            "weird third way younger child"
        ]
    );
}

SceneGraph的iter函数在深度优先遍历中返回父节点值和当前节点值的一个元组。SceneGraph主要设计用于Transform树，其iter是遍历这些Transform以将局部变换的场景图转换为世界空间变换的最佳方式。

分离节点

可以通过调用detach来分离场景图中的节点，这将返回一个新的SceneGraph<T>，其根是提供的节点。可以通过SceneGraph::attach_graph将SceneGraph<T>附加到另一个SceneGraph<T>上。如果不需要此功能，用户可以使用remove简单地删除节点并完全丢弃它。

// in `scene-graph`
for (parent, child) in sg.iter() {
    todo!();
}

// in `petgraph`
petgraph::visit::depth_first_search(&petgraph_sg, Some(root_idx), |event| match event {
    petgraph::visit::DfsEvent::Discover(_, _) => todo!(),
    petgraph::visit::DfsEvent::TreeEdge(_, _) => todo!(),
    petgraph::visit::DfsEvent::BackEdge(_, _) => todo!(),
    petgraph::visit::DfsEvent::CrossForwardEdge(_, _) => todo!(),
    petgraph::visit::DfsEvent::Finish(_, _) => todo!(),
});